APPLICATIONS OF A RUTHENIUM CATALYST IN ACYCLIC DIENE
METATHESIS (ADMET) CHEMISTRY: DEPOLYMERIZATION AND
POLYOLEFIN MODELLING STUDIES
MARK D. WATSON
A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE
UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
UNIVERSITY OF FLORIDA
I have been told many times by Dr. Ken Wagener, my graduate advisor, that
graduate school can be the best time of one’s life. As a result of his guidance, the
stimulating environment provided by the University of Florida’s Department of
Chemistry and the people within it; and of course the arrival of my wife, Kim, I am
inclined to agree.
The polymer group is made up of a unique collage of people excited about their
work and life outside the lab. I am truly grateful to members, past and present, of the
polymer group for providing both a stimulating working environment discussing
chemistry on the chalkboards, written on paper towels, etc. and a great social life from
shooting pool to canoe trips. My time here was made rich by the acquaintances of
Fernando Gomez, Debby Tindall, Jason Smith, Jason Portmess (the group cheerleader,
his presence is sorely missed), Tammy Davidson, Dominique Valenti, Todd Younkin.
and Karen Dai. Special thanks go to Shane Wolfe my long time friend and roommate for
nearly the duration, BOO-YOW! BOTBOTH! I am very fortunate to have shared a lab
with Krystyna Brzezinska as she shared friendship, unique perspective, and an
incomparable professional example in the laboratory.
Thanks go to members of the faculty including Dr. Merle Battiste (for many late
afternoon discussions of chemistry and otherwise), Dr. William Dolbier, Dr. Lisa
McElwee-White, and Dr. Eric Enholm for sharing with one struggling to become a
successful chemist. Lorraine Williams remains a marvel to me. Her delightful persona,
which accompanies an endless capacity for helping in any situation, is the glue that holds
the polymer group together. In similar fashion, Donna Balkcom made my life here at UF
much smoother doing all the things which she does behind the scenes for all graduate
students. Thanks go to members of the faculty and staff who offered excellent technical
support in characterization including Dave Powell, Lidia Matveeva, Ion Ghiviriga, and
Dr. Ken Wagener truly fulfilled the designations of advisor and mentor not only
in professional but personal growth. He not only provided the where-with-all for
conducting research but also exuded the excitement of someone who sincerely pursues
the task of mentor.
Gratitude is also extended to the National Science Foundation for financial
support which made this work possible.
I am most grateful for having met my new and permanent roommate, my wife
Kim. If I had only known what I know now nine years ago when our paths first briefly
TABLE OF CONTENTS
1 INTRODUCTION 1
The Olefin Metathesis Reaction 2
Development of the Olefin Metathesis Reaction 6
Well-Defined Metathesis Catalysts 8
Ruthenium Metathesis Catalysts 1 1
Discrete Ruthenium Carbene Complexes 13
Acyclic Diene Metathesis (ADMET) Polymerization 16
Summary of Results Presented in this Dissertation 20
2 EXPERIMENTAL 24
Instrumentation and Analysis 24
Materials and Techniques 26
Synthesis and Characterization 27
ADMET Depolymerizations 27
Metathesis and in situ Hydrogenation 28
Synthesis ofFunctionalized Diene Monomers for Model Ethylene
Synthesis of extended chain co-alkenyl bromides and carboxylic acids 32
Synthesis of symmetrical alcohol-functionalized dienes 35
Synthesis of symmetrical dienes with pendant acetate groups 38
Synthesis of symmetrical dienes with pendant carboxylic and
alkoxycarbonyl groups 40
Synthesis of symmetrical dienes with pendant chloride and phenyl
Synthesis of ADMET Model Ethylene/Polar Monomer Copolymers 45
Synthesis of ADMET model ethylene/vinyl acetate copolymers 46
Synthesis of ADMET model ethylene/acrylate copolymers 47
Synthesis of ADMET model ethylene/vinyl chloride and styrene
3 ADMET DEPOLYMERIZATION OF 1 ,4-POLYBUTADIENE UTILIZING
A WELL-DEFINED RUTHENIUM METATHESIS CATALYST 50
Ethenolysis of 1,4-Polybutadiene 53
Ethenolysis of 1,4-Polybutadiene Catalysed by a Well-Defined Ruthenium
Bulk Depolymerization of Polybutadiene 62
Bulk Depolymerization of Polybutadiene to Produce Telechelics 67
4 TANDEM HOMOGENEOUS METATHESIS/HETEROGENEOUS
Immobilization of a Well-Defined Ruthenium Complex on the Surface of
Catalytic Activity of _L4 Adsorbed on Silica 74
Hydrogenation with the Residue of Catalyst L4 Adsorbed on Silica 78
Preparation of Saturated Polymers by Tandem Homogeneous
ADMET/Heterogeneous Hydrogenation 83
Preparation of End-Functionalized Polyethylene by
Synthesis of a Polyester with Long Aliphatic Segments 85
5 THE SYNTHESIS OF MODEL ETHYLENE/POLAR MONOMER
COPOLYMERS VIA ADMET AND HYDROGENATION 90
Ethylene/Polar Monomer Copolymers 93
Model Polymers 95
Preparation of Model Polymers via Metathesis 97
Model Polymers via Metathesis Polymerization and Hydrogenation 98
Design and Synthesis of Symmetrical Diene Monomers for Ethylene/Polar
Monomer Model Polymers 102
Synthesis of Acetoxy-Functional Monomers 105
Chloro- and Phenyl-Substituted Dienes 106
Monomers with Pendant Alkoxy-Carbonyl Moities 107
Preparation and Characterization of ADMET Ethylene/Polar Monomer
ADMET Ethylene/Vinyl Acetate Model Copolymers 1 1 1
Thermal Analysis of EVA Model Copolymers 1 15
ADMET Ethylene/Alkyl Acrylate Copolymers 122
ADMET Ethylene/Styrene Copolymer 126
ADMET Ethylen/Vinyl Chloride Copolymer 128
BIOGRAPHICAL SKETCH 139
Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy
APPLICATIONS OF A RUTHENIUM CATALYST IN ACYCLIC DIENE
METATHESIS (ADMET) CHEMISTRY: DEPOLYMERIZATION AND
POLYOLEFIN MODELLING STUDIES
Mark D. Watson
Chairman: Kenneth B. Wagener
Major Department: Chemistry
Investigation of the utility of Grubbs’ ruthenium carbene, Ru(CHPh)(PCy 3 ) 2 Cl 2 ,
as a catalyst for various operations of Acyclic Diene Metathesis (ADMET) chemistry is
presented. Applications include the metathesis depolymerization of cis- 1,4-
polybutadiene, ADMET polymerization of functionalized dienes, and tandem metathesis/
hydrogenation reactions in which the ruthenium complex serves to catalyze both
In Chapter 3, the unprecedented stability of the ruthenium complex in the
presence of ethylene is exploited for effective depolymerization of 1,4-polybutadiene by
cross-metathesis with ethylene. Vastly improved yields of hexadiene over those
previously reported utilizing well-defined early transition metal complexes were
realized. The first accounts of the remarkable ability of the ruthenium complex to effect
the solvent-free depolymerization of 1,4-polybutadiene and its application in the
synthesis of end-functionalized polymers are also disclosed.
In Chapter 4, the dual utility of the catalyst for both olefin metathesis and
hydrogenation is described. Adsorption of the catalyst residue on the surface of silica gel
converts it to a heterogeneous system, which is effective for catalytic olefin
hydrogenation at room temperature and moderate pressures. The two reactions may be
conducted in tandem to produce saturated polymers, including telechelic polyethylene.
Further application of the tandem process for C-C bond construction in small molecule
synthesis is described.
In Chapter 5, the metathesis/hydrogenation process disclosed in Chapter 4 is
exploited for the production of model periodic ethylene copolymers. A homologous
series of symmetrical dienes with varied central pendant functionality were synthesized
to this end. ADMET polymerization of these monomers and subsequent hydrogenation
yielded periodic models for copolymers of ethylene with vinyl acetate, vinyl chloride,
acrylates, and styrene. Thermal analysis of the resulting polymers revealed the predicted
relation of increasing melting point with increasing ethylene run length. Within a series
of polymers with identical ethylene run lengths, increasing steric bulk of the regular
pendant functionality resulted in greater melting point depression.
The now continuous stream of advances in polymer chemistry attending new
developments in catalytic organometallic chemistry 1 can generally be classified into two
categories: (1) original chemical transforms and (2) the betterment of known chemical
transforms. The latter class may be manifestations of improved catalyst efficiency,
chemoselectivity, broader scope to encompass substrates with diverse functionalities, and
resistance to ubiquitous trace poisons allowing more practical implementation.
The subject of this dissertation, which falls into the second category above,
involves the exploitation of unique properties of a well-defined ruthenium metathesis
catalyst to improve upon and expand the scope of various applications of Acyclic Diene
Metathesis (ADMET) chemistry. One aspect of the studies focussed on ADMET
depolymerization where the resilience of the catalyst was exploited for improved
conversions in reactions involving ethylene as a substrate. Also the first, to the best of
our knowledge, “solid state” depolymerizations of ultra-high molecular weight
polybutadiene catalyzed by a discrete metathesis catalyst were performed. Exciting
observations were made regarding the dual-purpose use of the catalyst for post-
metathesis hydrogenation chemistry, made possible by the nature of the late-transition
metal center. The timing of these observations coincided with the growing implication of
metathesis polymerization in tandem with hydrogenation as a powerful method for
macromolecular engineering. This prompted the development of a facile process for the
production of periodic model ethylene copolymers involving homogeneous metathesis in
tandem with heterogeneous hydrogenation.
To facilitate cohesive presentation, the somewhat disparate subjects of
depolymerization, hydrogenation, and model polymer engineering are apportioned into
chapters 3, 4, and 5, respectively. The remainder of this chapter will serve to briefly
introduce the metathesis reaction and advances in catalyst development pertinent to the
the establishment of the ADMET reaction as a viable synthetic scheme. The ADMET
reaction, which is the unifying concept common to all the studies reported herein,
deserves separate discussion for adequate understanding of the subject matter.
The Olefin Metathesis Reaction
The olefin metathesis reaction is a powerful organic transform, which formally
divides olefinic compounds at the carbon-carbon double bonds into carbene fragments
and then redistributes them, forming new olefins. 2 The process is catalyzed by a metal
carbene complex which may be preformed or formed in situ, and may be homogeneous,
heterogeneous, or supported on an insoluble substrate. The key steps in the mechanism
are shown in Figure 1-1. Coordination of a substrate olefin to the metal center leads to
the formation of a metallocyclobutane. Cleavage of this ring may occur either along the
vertical or horizontal leading to, respectively, starting materials or a new olefin and new
metal carbene. The olefin product may be cis, trans or a mixture as determined by the
steric demands of the substrate and the choice of catalyst. In the special case where R =
R”, termed degenerate metathesis, no new products are formed in the forward reaction.
The mechanism finds analogy in the Wittig reaction, shown for comparison in
Figure 1-1, where a carbene fragment is delivered to a carbon doubly bonded to oxygen
forming a new C=C bond. A major difference between the two mechanisms lies in the
reactivity of the other doubly bonded product liberated upon cleavage of the cyclic
intermediate. In contrast to the Wittig reaction, the new metal carbene formed in the
metathesis reaction can repeat the reaction with any other reactive C=C bond.
Wittig Reaction(Stoichiometric, irreversible)
l 3 p
Olefin Metathesis (Catalytic, reversible)
L n M-r
Figure 1-1. Key steps of the olefin metathesis reaction compared to the Wittig reaction.
2 i •
The olefin metathesis reaction may be divided into categories depending on the
structure of the starting materials and products as depicted in Figure 1-2. Regardless of
the particular pathway, it is now widely accepted that each of these processes has as
common intermediates the metal carbene and the metallocyclobutane. In the simplest
case of a single symmetrical olefin, the substrate will be isomerized to an equilibrium
mixture of cis/trans stereoisomers via repetitive degenerate metathesis. For an
unsymmetical olefin substrate or a mixture of different starting olefins of similar
reactivity, the result is a statistical redistribution of carbene fragments upon reaching
equilibrium. Following Le Chatelier’s Principle, removal or addition of any of the
reactants or products may shift the position of the equilibrium.
Ring Opening Metathesis Polymerization (ROMP)
Ring Opening Cross-Metathesis
Acyclic Diene Metathesis Polymerization (ADMET)
^"R^ - ^R^ + C 2 R 4
Figure 1-2. Classifications of olefin metathesis reactions.
By ring opening metathesis polymerization (ROMP), cyclic olefins may be
converted to high polymer via a chain process provided the energetics are favorable. The
process is thermodynamically favored for 3-, 4-, 8-, and larger membered rings but is
unfavorable for cyclcohexene due to stability of the six-membered ring. Cyclic olefins
may also be ring opened to monomeric compounds by cross-metathesis of cyclic and
acyclic olefins. This “arrested ROMP” reaction occurs when cross-metathesis of the
newly formed metal carbene from either the cyclic or acyclic olefin is favored over self-
Conversely, compounds with more than one double bond appropriately spatially
disposed may be cyclized by ring closing metathesis (RCM). This particular transform
has been extensively exploited for the preparation of fine chemicals and extended to
complicated natural product syntheses. Dienes may also be condensed intermolecularly
to polyenes and high polymers by acyclic diene metathesis polymerization (ADMET), to
be discussed in detail later. Competition between RCM and ADMET often exists, and its
outcome may be governed to varying degrees by altering reaction conditions. The most
significant variable is concentration, where dilute conditions favor intramolecular (RCM)
reaction and bulk conditions favor intermolecular (ADMET) reaction. Chemical
characteristics that hold the double bonds in close proximity, such as bulky groups
between the olefins (Thorpe-Ingold Effect) and intramolecular hydrogen bonding may
augment cyclization of dienes at the expense of linear products. 1
Recently, Grubbs reported 4 an elegant study in which ADMET, RCM, or ROMP
could be driven in high conversion from the same olefinic substructure depending on
reaction conditions as shown in Figure 1-3. Under bulk conditions, the oligoether diene
was condensed to high polymer by ADMET. Introduction of an appropiate metal cation
to a solution of either the polymer or the monomeric diene leads to hapto-coordination of
the ether oxygens to the cation, bringing sequential olefins into proximity favoring RCM.
The resulting crown ether could be obtained either from the diene or from high polymer
in high yields. Removal of the cation in the presence of active metathesis catalyst leads
to ROMP of the crown ether to high polymer.
Figure 1-3. Interplay of ADMET, RCM and ROMP utilizing a template. Metathesis
conversion >95% in all three cases by NMR.
Development of the Olefin Metathesis Reaction
The history of the reaction parallels other catalytic processes such as Ziegler-
Natta polymerization where obvious technical utility spurred almost immediate
commercial exploitation preceding a fundamental understanding. 2 The reaction found
application in the interconversion of hydrocarbon streams, diversifying olefin-
manufacturing processes. These processes typically used empirically developed
heterogeneous catalysts where a transition metal precatalyst was loaded onto an inorganic
support and pretreated to generate the active catalyst, the structure of which was
unknown. Two such processes 2 ' 5 that were developed by Phillips Petroleum Co. are
depicted in Figure 1-4. The Phillips triolefin process, implemented in 1966, utilized
metathesis to convert propene to ethylene and but-2-ene. In 1969, the Neohexene
process was initiated, where neohexene is generated from ethylene and 2,4,4-
In spite of these early commercial applications of the process, it was not until the
beginning of the 1970’s that fundamental research resulted in proposal of the now-
accepted mechanism 6 (cf Figure 1-1) involving the key intermediacy of metal carbenes
and metallocyclobutanes. The reaction became the subject of a number of research
programs, both academic and applied, where the reasons for fundamental investigation
were manifold. 7 The initial commercial catalyst systems required excessive temperatures
for practical activity, limiting the substrates to those with functionality that could
withstand the harsh conditions. Application was also limited by low tolerance of the
catalysts to Lewis basic functionality. 8 In addition, lack of insight into the mechanism
prohibited prudent catalyst engineering.
Phillips Triolefin Process
Figure 1-4. Early commercial applications of the olefin metathesis reaction.
Specific refinements were necessary to make the metathesis reaction a more
general tool: (a) The catalyst must promote only one reaction (metathesis) with olefins;
(b) the catalyst must tolerate and remain inert to other functionality (c) the catalyst should
be active under milder conditions. Refinement in these aspects continues today through
variation in the choice of the metal center, cocatalysts, and ligand environment.
Early catalysts were two part systems most commonly based on Mo, W, and Re
activated by a main-group metal alkyl cocatalyst 9 such as A1 and Zn alkyls. The
cocatalysts may serve more than one functions such as: A) provide alkyl ligands via
transmetallation which can rearrange to the alkylidene by elimination processes, B) act as
a ligand, modifying electron density of the transition metal through, for example,
coordination to oxo and halo ligands. Due to their high Lewis acidity, some cocatalysts
initiated side reactions via electrophilic reaction with C=C bonds. This shortcoming was
overcome with the realization of cocatalysts with diminished Lewis acidity such as those
based on Pb IOa,b and Sn IOc f . Byproducts of a given catalyst system might also induce
deleterious chemistry as in the case of WCl 6 /Me 4 Sn which generates HC1. 2
Greater functional group tolerance was realized with the development of catalysts
based on late transition metals. 8 The late transition metals are softer Lewis acids and as a
result, metathesis catalysts derived from these are more selective towards olefin groups in
the presence of polar functionality. Heterogeneous systems based on Re have been
studied extensively" and have proven to be more tolerant of functionality than early
transition metal species. Though the process has yet to achieve commercial success,
heterogeneous Re systems have been proven effective for the metathesis of unsaturated
Well-Defined Metathesis Catalysts
Research efforts aimed at delineating the mechanism of the olefin metathesis
reaction shifted towards the development of active preformed metal carbenes. Although
stable isolable metal carbenes were reported as early as 1964 by Fischer, these species
proved to be inactive for metathesis. The first isolable, metathetically active carbene
complex was reported in 1974 13 and shown to effect the ROMP of cyclooctene shortly
thereafter 14 . This complex, C 05 W=CPh 2 , required activation for metathesis through loss
of a CO ligand induced by heating or UV irradiation but still represented a significant
advance as the necessity for cocatalyst was eliminated.
Various researchers subsequently secured their place in the history of this drive to
obtain well-defined metathesis catalysts, but most were to be overshadowed by the names
Schrock and Grubbs. The former prepared the first class of highly active species based
on W and Mo systems which were soon complemented by the Ru systems of Grubbs, to
be discussed later.
M = W
M = Mo
_ _ N
CF 3 (CH 3 ) 2 C
CH 3 (CF 3 ) 2 C
CH3(CF 3 ) 2 COm..^ 0
Ch^CF^Cd^ ^ Ph
Figure 1-5. Well-defined, highly active W(VI) and Mo(VI) alkylidines.
Through systematic variation of ligand environment, Schrock eventually
developed a series of four-coordinate W(VI) and later Mo(VI) alkylidenes with tunable
reactivity, shown in Figure 1-5. The bulky imido and alkoxy ligands serve in one fashion
to diminish bimolecular catalyst decomposition while still allowing the approach and
coordination of olefinic substrates. Variation of the steric and electronic nature of the
alkoxide ligands allows the reactivity of the metal alkylidine to be engineered to differing
degrees, with highest reactivity observed for R = CH 3 (CF 3 ) 2 C, or hexafluoro-t-butoxy.
For example, catalyst 1.1a is effective for ROMP but not acyclic chemistry while 1.1c
not only catalyzes ROMP but is highly active for acyclic metathesis (TON = 1000 min' 1
for 2-pentene). While representing a landmark advance in catalyst development, the W
analogues still suffered from low tolerance to functionality. For example, although
catalyst 1.1c effected the metathesis of methyl oleate, catalyst lifetime was limited by
deactivation via Wittig-type reaction with the ester carbonyl group.
The less electrophilic molybdenum analogues proved to be more tolerant of
functionality and became the vehicle by which olefin metathesis was transformed into a
trustworthy synthetic tool. The Mo catalysts’ improved chemoselectivity has allowed the
ROMP, RCM and acyclic metathesis of substrates containing a broad range of
functionality including halo, ether, amine, amide, ester, thioether, and metal containing
groups. 15 The neophylidene complex 1.2d , although no more effective than the
neopentylidene analogue, is more easily prepared and therefore preferred.
Utilization of these catalyst systems for ROMP chemistry offers several
advantages in addition to greater mechanistic insight. They allowed the preparation of a
broad range of polymers in living fashion with predictable and narrow PDI's as well as
block copolymers with well-defined block lengths. 1:1 Also mild reaction conditions
together with well-delineated reactivity minimized defects in the polymer microstructure.
The Mo catalysts are still sufficiently oxophilic to react with aldehydes and ketones in a
Wittig fashion, and this particular reaction has been capitalized upon for stoichiometric
cyclizations of unsaturated carbonyl compounds 16 and for end-capping of living ROMP
reactions as shown in Figure 1-6. If functionalized benzaldehydes are used as end-
capping reagents in ROMP reactions, polymers with narrow polydispersity and useful
end-groups can be obtained.
Figure 1-6. Reaction of Mo alkylidenes with carbonyl-containing substrates: Ring-
closing olefination 16 and end-capping of living ROMP 17 .
As mentioned previously, these catalyst systems would soon be overshadowed by
well-defined ruthenium catalyst systems which are superior in many aspects. Schrock's
W and Mo alkylidines, like their ill-defined predecessors based on early transition metals,
still displayed moderate functional group tolerance. They are easily deactivated by
compounds containing active hydrogens (acids, alcohols, H 2 0, etc) and oxygen. Their
widespread usage is also limited by thermal instability during storage and expense of
Ruthenium Metathesis Catalysts
The promise of ruthenium systems as robust, functional group tolerant catalysts
was foreshadowed during the first stages of development of the metathesis reaction,
where R11CI3 was shown to be effective for the ROMP of cyclobutenes and norbornene in
aqueous and alcoholic environments. 2 Polynorbornene has been produced commercially
for over 15 years in a process utilizing RuCls in alcohol solvent and the reaction is even
promoted by the presence of oxygen. However, utility is limited to ROMP of high strain
In 1992, reports began to emerge of the in situ activation of ruthenium complexes
for ROMP by addition of diazo compounds. 18 ' 20 Activation occurred presumably via the
formation of ruthenium carbenes, the presence of which was supported by NMR studies.
Initial studies 19 with diruthenium (II) tetracarboxylates activated by ethyl diazoacetate
were limited to high strain olefins and suffered from competing cyclopropanation of the
olefin substrates. This observation finds precedent in extensive studies of transition
metal catalyzed cyclopropanation, which is most effective with diazocarbonyl
compounds. 21 Ethyl diazoacetate may be used to activate Ru(H 2 0) 6 (OTs) 2 for the ROMP
of cyclooctene, which also indicates that the difficulty in polymerizing the low strain
monomers with Ru(II) complexes lies not in propagation but in initiation. 20
Figure 1-7. Functionalized cyclooctenes polymerized via ROMP catalyzed by
[Ru(p-cymene) 2 Cl 2 ] 2 + PCy 3 + trimethylsilyldiazomethane.
A variety of ruthenium complexes have been studied, with relative success
reported 19 for the type [Ru(arene) 2 Cl 2 ] 2 activated by trimethylsilyldiazomethane (TMSD)
both with and without added trialkyl phosphines. These multicomponent systems have
been applied to the ROMP of various functionalized norbornenes, oxanorbornenes, and
cyclooctenes. Each of the functionalized cycloctenes shown in Figure 1-7 were
polymerized to high molecular weight (M n = 5-12 X 10 4 g/mol, PDI = 1.4 - 2.2) in
good to moderate yields.
While these multicomponent ruthenium systems enabled the metathesis of
substrates with a variety of functionality not previously possible with other transition
metals, concurrent developments in the synthesis of related preformed ruthenium
carbenes would come to virtually dominate the attention of the metathesis community. 8 ’ 22
The first preformed ruthenium species which were highly active for acyclic metathesis
were reported" 3 in 1993 and an improved version 24 , IA, followed shortly thereafter
(Figure 1-8). While other versions were prepared with differing phosphine and carbene
ligands, JL4 is preferred as its synthesis is extremely fascile, utilizing diazo compounds
similar to the process described earlier for in situ activation of ruthenium complexes. In
addition, L3 has been shown to be a slower initiator due to the greater stability of the
more highly conjugated vinylidene relative to the benzylidene.
Figure 1-8. Discrete ruthenium carbene olefin metathesis catalysts.
While it is certain that the continually growing knowledge base will lead to ever-
Discrete Ruthenium Carbene Complexes
increasingly effective catalysts, the explosion of applications made possible by this series
of Ru carbenes makes them seem the current zenith. Their technical and synthetic value
has sparked a flurry of research efforts aimed at more facile catalyst preparations, which
now approach the degree of difficulty of sophomore organic chemistry laboratory
Some of the outstanding features of the catalysts are as follows. They can be
employed in both aqueous' 3 " 6 and alcoholic solutions 23 . The unprecedented stability of
the catalysts to adventitious moisture and other typical poisons enables their practical use
without highly specialized equipment, and they may be stored for long periods of time in
air without decomposition. The practical organic chemist has only to sparge a simple
reaction vessel, the substrate and any solvents with nitrogen before reaction. The catalyst
1-3 has been used for RCM of dienes containing aggressive functionality such as OH,
C0 2 H, aldehyde and amide groups 27 (Figure 1-9). These transforms are impossible with
early transition metal catalysts due to intolerance of the catalysts to these functionalities.
Figure 1-9. RCM of dienes with aggressive functionality.
It should be noted however that the success of the reactions in Figure 1-9 does not
show that the complex is impervious to these functionalities, but rather the catalyst is
sufficiently tolerant to allow good yields of product when the kinetics of the desired
reaction (e.g. RCM) are sufficiently rapid to compete with any deleterious side reactions.
The success of a metathesis reaction in the presence of these functionalities therefore
depends on the substrate under study. For instance, while hydroxy-functionalized
substrates may be employed successfully in ROMP and RCM schemes, dimerization of
acyclic co-alkenol alcohols gives poor yields and some isomerization of the alcohol
substrates to aldehydes due to slower kinetics of acyclic chemistry. 28
While catalysts L3 and 1A are much more tolerant to oxygenated groups, they are
less effective than early transition metal complexes for the metathesis of sulfur 29 and
phosphorous 20 containing substrates. This can be explained in terms of hard-soft theory
where the softer S and P atoms more effectively complex the soft ruthenium center than
the harder earlier transition metal centers. Catalyst L4 has, however, been proven
effective for the first ever RCM reaction of phosphonate compounds as shown in Figure
1 - 10 .
3 mole % ±A
MeCI2, reflux, 30 min
3 mole % ±A
MeCI2, reflux, 30 min
Figure 1-10. RCM of dienes with phosphonate functionality catalyzed by L4.
Complexes JL3 and L4 have promoted the affirmation of the metathesis reaction
by the synthetic community, where growing confidence is indicated by the willingness to
incorporate the reaction as a transform in advanced stages of multi-step synthetic
sequences. 2 The most common application is ring closure, noteworthy examples 22 ' 34 of
which are shown in Figure 1-11.
Figure 1-11. Applications of RCM catalyzed by L4 in multistep synthesis.
Acyclic Diene Metathesis (ADMET) Polymerization
ADMET polymerization 35,36 is a step-condensation polymerization where dienes
are connected via metathesis in a stepwise fashion to produce polyenes as depicted in
Figure 1-12. Monomer is consumed in the early stages of the reaction to produce dimer,
trimer, tetramer, etc with the evolution of the condensate, a small monoene. Each species
in the system can react with any other species resulting in a distribution of homologous
products. As each step is reversible, the condensate may also react with homologues
splitting the chains to smaller species and in a closed system, this reverse reaction
restrains the equilibrium product mixture to relatively low molecular weight species. In
the typical case involving a,o>dienes, the ethylene liberated with each connection is
easily removed under reduced pressure to drive the equilibrium to the right yielding a
product distribution with progressively higher average molecular weight. The
equilibrium nature of the reaction permits the reaction of all species in the system, which
randomizes the product distribution to the most probable distribution described by the
polydispersity index, PDI = M w /m„ = 2.0.
+ C 2 H 4
C 2 H 4
^ r k
+ C 2 H 4
Figure 1-12. The ADMET step/condensation polymerization of an a, co-diene.
For typical step/condensation polymerizations, the relationship between the
number average degree of polymerization (DP„), the conversion (p), and the
stoichiometric imbalance (r) is described by Equations 1-1. In this relation, r is the molar
ratio of groups "A" to groups "B" which condense to form the polymer linkages. In the
limit of 100% conversion (p = 1.000), Equation 1-la reduces to 1-1 b. It can be seen from
Equation 1-lb that any decrease in “r” from unity results in a decrease in the maximum
obtainable average molecular weight.
1 + r
1 + r - 2 rp
Eqn (1-1 a)
DP„ = 1 + r Eqn ( 1 - lb)
Attainment of high molecular weight requires near perfect stoichiometric balance
of the reactive groups 37 , a concept that must be modified to apply to ADMET. The
ADMET polymerizations to date are somewhat unique amongst condensation
polymerizations in that the functional groups, which condense to form the linkages in the
polymer backbone, are not chemically different. They do not fit into the schemes of A-A
+ B-B or A-B type polymerizations where different functional groups “A” and “B” react,
common examples of which are polyesterifications schematically represented in Figure 1-
13. In the second case in which a hydroxy-functional carboxylic acid condenses to a
polyester, r = 1.000 due to the fact that both the “A” and “B” groups are in a single
monomer. An exception to these polycondensation schemes similar to ADMET is the
hydrolytic step-polymerization of dichlorosilanes 38 in which Si-Cl groups are converted
to silanol groups which then condense with each other to form siloxanes and the
condensate, water. Of course in this particular type of polymerization, the SiOH groups
may also react with any residual SiCl groups to form the same polymer.
HO R OH
^ R X
ho A r' oh
HotV 0 ^
Cl— Si-Cl + H 2 0
A TV monomer
— HO-j-Si-O-jH + H 2 0
Figure 1-13. Comparison of classical condensation polymerizations.
Therefore, perfect stoichiometric balance in the case of ADMET simply means
that vinyl groups terminate all linear molecules in the system at both ends throughout the
course of the reaction. In this light, the relationship between DP n and conversion is
more appropriately described by Equation l-2a, often referred to as the Carothers
equation, where / avg is the average functionality of all linear species. For perfectly
difunctional species ,/ avg = 2.0, and the more commonly presented Equation 1 -2b results.
DP = Eqn (l-2a) DP n = - Eqn(l-2b)
" 2-p/„„ 1-P
Any loss of vinyl groups due to competing chemistry decreases / avg and lowers the
maximum achievable molecular weight. This critical requirement tor successful
ADMET polymerization deferred its development until the arrival of the well-defined
Schrock W(VI) and Mo(VI) carbenes (cf Figure 1-5). Initial attempts to polymerize
dienes as early as 1970 were destined to failure as the classical catalyst systems of that
time period participated in side reactions which decreased f av g.~ The reaction was
revisited in 1987 by Wagener and coworkers with the realization that the key to success
was the utilization of single-site catalysts. 41 The a,o>-dienes 1,5-hexadiene and 1,9-
decadiene were condensed to high molecular weight linear polymers utilizing W catalyst
1.1c. 35 ’ 41 The reaction has since been demonstrated with other Schrock alkylidines, most
commonly catalyst 1.2d , with homogeneous W(VI) classical catalysts 4 " activated by alkyl
tin cocatalysts, and most recently with ruthenium catalyst L4. 43
Successful demonstration of the ADMET reaction was followed by systematic
studies designed to delineate monomer structure reactivity relationships, the bulk of
which has centered on Mo catalyst L2d. It became clear that the slower kinetics of the
ADMET reaction relative to faster processes such as ROMP and RCM placed greater
restraints on the type and placement of functionality in substrates. For dienes with Lewis
basic functionalities appropriately placed within the structure, reaction may be
prohibitively slow or even completely halted. This effect has been attributed to
intramolecular coordination of the Lewis basic functionality, schematically represented in
Figure 1-14, and finds precedent in similar ROMP systems. 44 The degree to which the
ADMET reaction is hindered may depend on the stability and persistence of this chelate.
This effect, termed the negative neighboring group effect, has been noted tor a variety of
functionality but can generally be overcome through monomer design by separating the
Lewis basic group "X" from the olefin groups by a suitable number of methylene spacers.
Figure 1-14. The proposed negative neighboring group effect.
With the knowledge of the keys for successful ADMET chemistry in hand,
polymers with a broad range of functionality have been prepared including ether, ketone,
ester, amine, thioether, conjugated olefins, silane, siloxane, and metal-containing
groups . 36 Just as for other catalyzed polymerizations, the scope of the ADMET reaction
continues to evolve as a result of new developments in catalyst design. Most recently,
the arrival of the extremely robust ruthenium catalyst L4 has allowed the direct
preparation of hydroxy-functional polymers. With the realization of classical systems
activated by main-group metals with diminished Lewis acidity, ADMET polymers can
now be prepared without the necessity for preformed metal carbenes . 42,44 A particularly
novel twist to this concept was reported where tin-containing dienes were prepared which
function both as monomer and as cocatalysts . 44
Summary of Results Presented in this Dissertation
The ADMET reaction and the polymers produced thereof share many
characteristics with other common step/condensation polymerization systems. High
molecular weight polymers can only be obtained when the equilibrium between terminal
and internal olefins can be driven to high conversion, a direct consequence of the relation
between DP n and conversion described by Equation 1 -2b. A further consequence is that
the reverse reaction may also be driven in high conversion, where high molecular weight
polyalkenamers may be depolymerized to low molecular weight species. The
relationship between / avg and DP„ (Equation 1 -2a) may also be capitalized upon to
control molecular weight through the incorporation of monoenes, or chain limiters, in the
forward ADMET reaction. End-functionalized oligomers and polymers may be prepared
by either the forward or reverse reaction if functionalized chain limiters are employed
Chapter 3 describes results obtained concerning the depolymerization of high
molecular weight polybutadiene to prepare low molecular weight species and end-
functionalized polymers utilizing complex E4. The unprecedented stability ot IA in the
presence of ethylene implicated it as a good candidate to catalyze the exact microscopic
reverse of the ADMET reaction, whereby polyalkenamers are depolymerized with
ethylene as chain limiter. This assumption was born out as much higher conversions in
this reaction were achieved than previously possible with well-defined W and Mo
alkylidenes. In addition, the unique ability of E4 to initiate depolymerization of
polybutadiene in the solid state was observed and exploited to prepare end-functionalized
Figure 1-15. ADMET depolymerization and polymerization with chain limiters.
With judicious choice of catalyst system with reactivity appropriate to a given
type of diene monomer, linear polymers with highly pure microstructure are obtained.
The only variation in structural homogeneity is the olefinic cis/trans ratio, which is
typically >70% trans. This backbone unsaturation provides sites for post-polymerization
reaction by which novel polymers may be prepared that are difficult or impossible to
obtain by direct means. One such reaction, which has generated both commercial' and
high academic interest is hydrogenation whereby the carbon-carbon double bonds are
converted to single bonds. It was discovered in our laboratories that addition of silica gel
to a completed metathesis reaction catalyzed by ruthenium complex E4 followed by
exposure to hydrogen gas constitutes an efficient method for catalytic heterogeneous
hydrogenation of the metathesis products. The development of this process and its
application to the indirect synthesis of saturated polymers, including telechelic
polyethylene, are described in Chapter 4.
The highly pure microstructure of ADMET polymers appoints this polymerization
route as a means to prepare well-defined models for polymers with less pure constitution.
ADMET polymerization coupled with quantitative olefin hydrogenation has been
shown 46 ' 51 to be particularly well suited for the preparation of models for polyethylene
and ethylene copolymers as shown in Figure 1-16. Any functionality (R), within the
restraints imposed by catalyst compatibility, may be incorporated at regular intervals
along a polymer which is in essence a perfectly linear terpolymer of ethylene, butadiene
and a monomer containing the functionality. The number of methylene spacers (“n” in
Figure 1-16) incorporated in the monomer synthesis precisely controls the frequency of
the desired functionality in the polymer backbone. Saturation of the backbone double
bonds produces model polymers for ethylene copolymers. In Chapter 5, the tandem
ADMET/ hydrogenation process described above is utilized to prepare a range of model
ethylene copolymers including copolymers with vinyl acetate, acrylates, styrene, and
vinyl chloride. The synthesis of the necessary dienes and the effect of the chemical
nature of the incorporated substituents on thermal properties of the polymers are also
n n J x
Figure 1-16. Indirect synthesis of model polymers via ADMET/hydrogenation.
Instrumentation and Analysis
'H NMR 300 MHz and l3 C NMR 75 MHz were recorded on a Gemini Series
NMR Superconducting Spectrometer System or a Varian VXR-300. NMR spectra were
recorded in chloroform-J (CDCR), benzene-ek (C6D 6 ), toluene-dg, and bromobenzene-ds.
Resonances are referenced to residual protio solvent and reported in § units downfield
from TMS at 0.0 ppm. Heteronuclear decoupled quantitative l3 C NMR spectra were
acquired over 8-12 hours with a pulse delay of 20s. Gas chromatographic measurement
of purity and product distributions were conducted with a Hewlett-Packard HP5880A gas
chromatograph with cross-linked methyl silicone gum capillary column and flame
ionization detector. Low and high-resolution mass spectrometry data were recorded on a
Finnigan MAT 95Q or Finnigan MAT GCQ Gas Chromatograph/Mass Spectrometer
utilizing either electron ionization or chemical ionization. Elemental analyses were
conducted by Atlantic Microlab, Inc., Norcross, GA, where each recorded value is the
average of duplicate analyses.
Differential Scanning Calorimetric (DSC) and Thermogravimetric Analysis
(TGA) data were obtained with a Perkin Elmer 7 Series Thermal Analysis System. DSC
samples (5-10mg) were analyzed with either liquid nitrogen or ice as coolant and under a
Helium flow rate of 25 ml/min. All samples were pre-dried at 40-50°C under reduced
pressure (<0. 1 mm Hg) for 8-12 hours. The instrument was calibrated in the appropriate
temperature ranges with cyclohexane and/or ultra-high purity water (subambient
measurements), or Indium. Samples were heated to at least 40°C above the melting point
to erase thermal history and then scanned at 5°C/min, cooling cycle first. TGA samples
(5-10 mg) were heated at 20°C/min under N 2 or air with a flow rate of 30 ml/min, until
Gel Permeation Chromatography (GPC) was performed using a Waters
Associates Liquid Chromatograph U6K equipped with tandem ABI Spectraflow 757 UV
absorbance detector and a Perkin-Elmer LC-25 RI detector. The GPC solvent delivery
system was configured for elution with either HPLC grade CDCI3 or THF through an
Ultrastyragel linear mixed bed column (CHC1 3 ) or through 5 x 10 3 A and 5 x 10 4 A
Phenogel columns in series (THF). Solvents were sonicated immediately prior to use and
delivered at a rate of 1.0 ml/min. Retention times were calibrated against narrow (PDI <
1.07) polystyrene standards (Scientific Polymer Products, Inc) with M p = 1900, 7700,
12000, 30000, 59000, 79000, and 139400 g/mol. Polymer samples were prepared in
HPLC grade THF or CHCL3 (-1% w/w) and slowly passed through a 50p syringe filter
prior to injection. Molecular weight measurements by vapor pressure osmometry (VPO)
were conducted utilizing a Jupiter Instruments Model 233 with toluene as solvent at
50°C. The instrument constant was determined by calibration (R 2 > 0.98) with
recrystallized sucrose octaacetate and verified against narrow PDI polystyrene GPC
standards (error in measured M n < 5%).
Materials and Techniques
The olefin metathesis catalysts Ru(=CHPh)(PR 3 ) 2 CI 2 , R = cyclohexyl or phenyl,
and Mo[=CHC(CH 3 ) 2 Ph](N- 2 , 6 -C 6 H 3 -/-Pr 2 )[OCCH 3 (CF 3) 2 ] 2 were prepared according to
published methods. These catalysts were graphically depicted in the appropriate sections
of Chapter One. Polybutadiene (MW = 2 x 10 ^, 98% cis- 1,4-repeat unit, Aldrich #
18,374-4) was purified by precipitation from methylene chloride into methanol, then
degassed and azeotropically dried by dissolution in dry toluene followed by removal of
toluene under reduced pressure. It was then stored in an amber bottle inside an argon-
purged dry box. Polymer grade ethylene (99.9% min.) was obtained from Matheson and
purified by passage through activated molecular sieves followed by two Alltech 8115
High Pressure Oxy-Traps in series. Silica gel-60 (Selecto Scientific cat # 162824,
particle size 32-63p) used in hydrogenation reactions was sonicated twice in reagent
grade CHCI 3 , dried under reduced pressure at 80°C for 24 hours, and stored in an argon-
purged dry box until use. 1-Octene, trans-7-tetradecene, 1 ,9-decadiene, HMPA,
diisopropyl amine, bromobenzene, iodomethane, ethyl iodide, and CDCI3 were dried over
CaH 2 and vacuum transferred. Olefin substrates were further degassed by three
consecutive freeze/pump/thaw cycles. Pyridine and acetyl chloride were stored over
CaH 2 and manipulated under argon. Carbon tetrachloride and methyl formate were
distilled under argon from P 2 Os, with the latter subsequently distilled from CaH 2 .
Acetone (reagent grade) was stirred over anhydrous CaS0 4 (lOOg/L) overnight, decanted
to fresh CaS0 4 (50g/L), and distilled immediately prior to use. Acetic anhydride was
distilled from anhydrous Na 2 C0 3 . Triphenylphosphine (Aldrich, 99%) was dried in the
molten state (85°C) with stirring under reduced pressure (5 mm Hg) for 8-12 hours then
stored in an argon purged dry box until use. Diethyl ether and tetrahydrofuran were
distilled under argon from Na/K alloy with the respective metal benzophenone ketyls and
stored over 5 A molecular sieves. Toluene was washed with cold cone. H2SO4, distilled
from Na/K alloy, and stored over 5 A molecular sieves. All other materials were used as
Synthesis and Characterization
Ethenolysis of cis-1 ,4-Polybutadiene . Depolymerizations were conducted in
either glass pressure tubes or glass-lined stainless steel bombs appropriate to the applied
pressure. Inside an argon purged dry box polybutadiene 2bl (500mg, 9.26mmol repeat
unit, 400 eq) cut in small chunks and catalyst L4 (19 mg, 1 eq) were combined inside the
appropriate pressure vessel together with 3 ml CDC1 3 . The vessel was sealed, removed to
a gas manifold, and opened to a constant dynamic pressure of C 2 H 4 with vigorous stirring
at room temperature for 48 hours. The reaction vessel was then chilled to avoid loss of
volatile products, and the ethylene pressure was slowly vented to the atmosphere. The
homogeneous solutions were then immediately exposed to air to decompose any
remaining active catalyst. See text for data analysis.
Synthesis of Ester-terminated Polybutadiene(3.5 and 3.6) , The chain limiter (3.4 )
was prepared immediately before use by dimerization of ethyl 10-undecenoate (3.3),
Inside an argon-purged dry box, 3 3 (0.788g, 3.71 mmol, 400 eq) and 1.4 (7.6 mg,
9.25pmol, 1 eq) were combined in a high vacuum flask. The flask was removed to a high
vacuum manifold and the contents stirred under reduced pressure at room temperature for
3 hours after which time the reaction was heated to 40°C for an additional 24 hours.
Inside the dry box, portions of this dimer/catalyst mixture were combined with
polybutadiene 3J_ (500 mg, 9.24 mmol repeat unit) cut in small chunks in glass vials, in
two different proportions to generate end-functionalized polymers with predicted DP =
20(3.5) and 40(3.6), Stoichiometry: Polymer .^5 (183 mg dimer 3A 46.2pmol),
Polymer 3.6(91 .7 mg dimer 3^4, 23.1pmol). Magnetic stir bars were inserted and the
vials were sealed and removed from the dry box. The mixtures were occasionally
agitated until viscosity was sufficiently reduced that they could be stirred with a magnetic
stir plate(12 hours). After stirring for 24 hours, reaction was quenched by placing under
reduced pressure then opening to air for 2 hours with stirring. Each polymer was
dissolved in toluene and stirred with alumina and filtered to remove catalyst residue, and
the toluene was evaporated under reduced pressure to yield clear colorless viscous oils.
Yield: X5, 592.8 mg, 86.7%; 3,6, 467.3 mg, 78.9%. *H- NMR 5 (ppm) 3^ 5.39(m,
42H); 4. 10(q, 4H); 2.26(t, 4H); 2.03(br, 94H); 1.59(t, 6H); 1.25(br)+1.23(t)=30H. I3 C-
NMR 5 173.82, 130.27, 130.07, 130.04, 129.95, 129.92, 129.53, 129.37, 60.07, 34.32,
32.65, 32.53, 29.55, 29.26, 29.18, 29.09, 29.03, 27.35, 24.92, 14.21. 'H- NMR 8 (ppm)
M 5.39(m, 80H); 4.10(q, 4H); 2.27(t, 4H); 2.03(br, 180H); 1.59(t, 6H);
Metathesis and in situ Hydrogenation
Model Study of Hydrogenation using frans-7-Tetradecene . Inside an argon-
purged dry box, trans- 7-Tetradecene (1.0 g, 5.09mmol) and 3 (5.2 mg, 0.13 mol%) were
combined in a pressure tube containing a magnetic stir bar and stirred 1 hour to allow
complete dissolution of catalyst and alkylidine exchange, during which time the purple
heterogeneous mixture became a clear maroon solution. 520 mg silica was added, the
tube was immediately sealed, removed to a hydrogen manifold and exposed to a constant
120 psig H 2 at room temperature. Adsorption of the catalyst residue onto the silica
surface was indicated by rapid decolorization of the substrate/catalyst solution. After 30
minutes, the reaction was quenched by releasing pressure to the atmosphere and filtration
to remove catalyst residue and silica, yielding a clear, colorless liquid. Extent of
reduction was estimated by ‘H NMR(CDC1 3 ) comparing the resonances at 5.4 ppm
(multiplet, internal olefin) to that at 0.88 ppm (triplet, CH 3 group). Experiments at each
pressure were conducted in triplicate and the average conversions calculated. See text for
Synthesis of 1,18-Bisacetoxyoctadecane (4.2) . 9-Decenyl acetate ( 4.1 ) (l.Og,
5.04mmol) and catalyst JL4 (5.2 mg, 52pmol) were combined in a high vacuum flask
containing a magnetic stir bar. The vessel was sealed, removed to a schlenk line, and
opened to a slight positive pressure of argon. It was heated to 60°C with vigorous stirring
for 4 hours, after which reaction was continued for an additional 2 hours at ~0.2 mm Hg.
The reaction mixture was taken up in 3 ml toluene, combined with 600 mg silica in a
pressure tube, and the whole was exposed to 120 psig H 2 at 90°C for 5 hours. Filtration
and evaporation of solvent yielded the product as a white powder (0.90 g, 96% yield).
LRMS: 372 (m+2). Elemental anal, calcd for C 22 H 42 0 4 : C, 71.31; H, 11.42. Found: C,
7 1 .37; H. 1 1 .50. 'H- NMR 8 (ppm) 4.02(t, 4H); 2.02(s, 6H); 1 ,59(m, 4H); 1 ,23(br, 28H).
13 C-NMR 5 171.24, 64.65, 29.65, 29.56, 29.52, 29.24, 28.59, 21.02.
Synthesis of Telechelic Polyethylene (4.6). Inside an argon-purged dry box, 1 ,9-
decadiene (3.0g, 21.7mmol, 1 eq), 9-decenyl acetate ( 4.1) (0.861g, 4.34 mmol, 0.2 eq)
and catalyst L4 (49mg, 0.06mmol) were combined for a total of 800: 1 olefin-to-catalyst
ratio. The reaction vessel was sealed, removed to a schlenk line, opened to slight positive
pressure of argon and heated to 45°C. Over a period of 6 hours, pressure was slowly
decreased (intermittant vacuum) then left open to dynamic vacuum of 10' 2 mmHg, while
slowly increasing temperature to 65°C. After 24 hours, the reaction vessel was sealed
and returned to the dry box. 1.5g crude polymer was initimately mixed with 2.5 g silica
in a pressure tube, the tube was sealed and removed to a hydrogen manifold. The
contents were exposed to 120 psig H 2 at 90°C for 30 minutes. 15 mL toluene was then
added via syringe under H 2 purge. The vessel was then exposed to 120 psig H 2 at 90°C
with vigorous stirring for 5 hours. Reaction was quenched by release of pressure and
filtered while still hot through a heated course glass frit to remove catalyst residue and
silica. Toluene was removed under reduced pressure to yield 1.45 g white solid.
Elemental anal, calcd for [Cio 2 H 202 0 4 ]: C, 82.07; H, 13.64. Found: C, 82.03; H, 13.70.
'H- NMR 6 (ppm) (90°C, toluene-d 8 ) 3.98(t, 4H); 1.73(s, 6H); 1.50(m, 4H); 1.30(br,
220H). M n = 1.5 x 10 3 (PDI = 1.9, high temp. GPC vs PE), 1.7 x 10 3 (‘H NMR end-
Synthesis of saturated polyester (4.9). Monomer 47 was dried by stirring at 50°C
for 8-12 hours under reduced pressure (< 0.1 mm Hg) in an appropriate storage flask
equipped with a high-vacuum valve. The atmosphere in the flask was deoxygenated by
three cycles of evacuation under reduced pressure and replacement with argon, and the
monomer was stored under argon. Inside an argon-purged dry box 47 (3.00 g, 9.31
mmol, 600 eq) and catalyst L4 ( 12.7 mg, 15.5 jimol, 1 eq) were combined in a small
glass tube with a 24/40 ground glass joint and a magnetic stir bar. The flask was fitted
with a Kontes® high vacumm valve, sealed, and attached to a high vacuum scklenk line
via ground glass joint sealed with silicone grease. Evolution of ethylene was observed
within 5 minutes as evidenced by formation of small bubbles which rapidly increased as
the stirrer was set in motion and a 45°C oil bath was raised. The pressure was slowly
decreased by applying intermittent vacuum eventually reaching a dynamic vacuum of 10'
2 - 10' 3 mm Hg while the temperature was slowly increased to 70°C. After 48 hours, the
vessel was sealed and returned to the dry box. Crude yield: 2.70g, 97.8%. A l.OOg
chunk of the crude polymer/catalyst residue mixture was combined with 500 mg silica
gel in a glass pressure tube containing a magnetic stir bar. 10 mL dry degassed toluene
was added and the tube was rapidly sealed with a brass valve fitted via a threaded
Teflon™ flange, removed to a gas manifold where it was charged with H 2 (120 psig,
dynamic pressure) and heated to 90°C with vigorous stirring. Note: Hydrogen pressure is
applied prior to dissolution of the polymer chunk. After 24 hours, pressure was released
to the atmosphere and the heterogeneous mixture was filtered while still hot through a
course glass frit. The reddish-brown silica was washed with hot toluene and the
washings were combined with the clear, colorless filtrate. The polymer precipitated on
cooling to below 60°C. The toluene was evaporated under reduced pressure to yield
as a white solid. Yield: 0.96g, 95% based on lg 4JI. Elem. Anal. Calcd. for [Q9H36O2]:
C, 76.97; H, 12.24. Found: C, 77.06; H, 12.22. . 'H- NMR 5 (ppm) (90°C toluene-d 8 )
4.02(t, 2H); 2. 1 7(t, 2H); 1.56(m,4H); 1 ,28(br, 28H). n C-NMR 5 177.01, 139.12, 114.06,
51.21, 45.67, 33.76, 32.47, 29.49, 29.35, 29.05, 28.86, 27.42. M n = 1.02 x 10 4 (PDI =
2.3, high temp. GPC vs PE).
Synthesis of Functionalized Diene Monomers for Model Ethylene Copolymers
Synthesis of extended chain oalkenyl bromides and carboxylic acids
Synthesis of 9-decenyl bromide(5.1), 9-Decenol (lOg, 64 mmol, 1 eq) and CBr 4
(25.47 g, 76.8 mmol, 1.2 eq) were dissolved in 100 ml anhydrous ether in an argon-filled
schlenk flask. A small amount of freshly ground CaH 2 was added and stirred for one
hour. Solid PPh^ (20.14 g, 76.8 mmol, 1.2 eq) was added under argon in ~4 g increments
over 20 minutes. After 20 hours the reaction mixture was diluted with 50 mL pentane,
filtered, and concentrated under reduced pressure. 1 1.2 g (80% yield) pure 5J_ (100%
GC) was obtained after distillation from CaPL (bp = 96-98°C/10 mmHg). 'H- NMR 8
(ppm) 5.78(m, 1H); 4.94(m, 2H); 3.38(t, 2H); 2.02(q, 2H); 1.83(m, 2H);
1.37(m)+1.28(br) = 10H. 13 C-NMR 5 139.06, 1 14.14, 33.95, 33.73, 32.78, 29.24, 28.97,
Synthesis of 10-undecenyl bromide(5.2). The alkenyl bromide was prepared in
two steps from the respective alcohol via the tosylate. 10-Undecenol (82. 5g, 0.484 mol,
1 eq) was dissolved in 500 mL CHCI3 in a 1 L schlenk flask. The solution was placed
under argon and chilled to 0°C. Pyridine (78 mL, 2 eq) was decanted into the flask from
CaPL. Solid TsCl (138.4 g, 0.726 mol, 1.5 eq) was added under argon in increments over
- 1.5 hours. After 8 hours the reaction mixture was washed with water, sat’d NaHCCL,
3N HC1, and brine. The organic layer was dried with Na 2 S 04 and concentrated to 154.7
g pale yellow oil which was converted to the bromide without further purification. The
crude tosylate was dissolved in 900 mL dry acetone under argon. LiBr anh (126 g, 3 eq)
was added in one portion, the flask was fitted with a water-cooled condenser and the
mixture was refluxed for 12 hours. The mixture was filtered, diluted with 300 mL
pentane, filtered a second time and concentrated. The crude product was taken up in 300
mL pentane and washed with water, sat’d NaHCCL, and brine. The organic layer was
dried with Na 2 S0 4 , concentrated, and the bromide (97% GC) was vacuum transferred
from CaH 2 . Yield: 100.8 g, 89 % for two steps. 'H- NMR 8 (ppm) 5.80(m, 1H); 4.95(m,
2H); 3.40(t, 2H); 2.04(q, 2H); 1.85(m, 2H); 1 ,38(m)+l ,29(br) = 12H. 13 C-NMR 8
139.12, 1 14.12, 33.96, 33.76, 32.81, 29.33, 29.04, 28.88, 28.71, 28.13.
Synthesis of 1 1-dodecenoic acid(5.3). 10-Undecenyl bromide ( 5 . 2 ) (10 g, 42.9
mmol, 1.0 eq) was added slowly via syringe to freshly scoured Mg turnings (1.053 g,
43.3 mmol, 1.01 eq) in 50 mL dry THF with rapid stirring under argon. After stirring 2
hours at 45°C, the resulting Grignard solution was rapidly poured into a large beaker
containing 19g (—10 eq) finely crushed C0 2 (s). The mixture was stirred with 50 mL 3N
HC1 and 80 mL pentane, after which the aqueous layer was discarded. The organic layer
was washed with 3N HC1 and water, dried over Na 2 S0 4 , and concentrated to 8. 1 6g pale
yellow oil. The oil was further purified by distillation under reduced pressure (bp = 1 10-
1 15°C/0<P<0. 1 mmHg) to yield 6.7 1 g colorless oil (79% yield). 'H-NMR 8 (ppm)
1 1.76(br, 1H); 5.80(m, 1H); 4.93(m, 2H); 2.32(t, 2H); 2.01(q, 2H); 1.60(m, 2H); 1.26(br,
12H). 13 C-NMR 8 180.62, 139.13, 114.09, 34.11, 33.78, 29.67, 29.38, 29.35, 29.20,
Synthesis of 1 3-tetradecenoic acid(5.5). 10-Undecenyl bromide (5;2) (22.25 g,
95.4 mmol, 1.0 eq) was added slowly via syringe to freshly scoured Mg turnings (2.34 g,
96.2 mmol, 1.01 eq) in 100 mL dry THF with rapid stirring under argon. After stirring 2
hours at 45°C, the resulting Grignard solution was cooled to RT and transferred via
cannula to LiCl (anh) (0.161 g, 1.6 mmol) in 100 ml dry THF at 0°C. (3-Propiolactone
(Acros, unopened bottle) (5 mL, 79.5 mmol, 0.83 eq) was added dropwise via syringe
maintaining the temperature below 5°C. After one hour, reaction was quenched with 50
mL 3N HC1 and then concentrated. The crude product was taken up in 200 ml pentane
and washed with 3N HC1, water, and brine. The organic layer was dried over Na 2 S0 4
and concentrated to 20.03g (over theory) pale yellow oil, which solidified on standing.
The product can be further purified by distillation under reduced pressure (bp s
1 26°C/0<P<0. 1 mmHg) or by flash chromatography (20%EtOAc/Pentane) rendering 85
and 91% isolated yields, respectively of a white waxy solid. 'H- NMR 5 (ppm) 1 1.22(br,
1H); 5.79(m, 1H); 4.92(m, 2H); 2.32(t, 2H); 2.02(q, 2H); 1.6 l(m, 2H); 1.24(br, 16H).
n C-NMR 8 180.64, 139.19, 114.07, 34.12, 33.80, 29.55, 29.47, 29.41, 29.22, 29.13,
29.03, 28.93, 24.64.
Synthesis of 11-dodecenyl bromide(5.4). Following the LAH reduction of 11-
dodecenoic acid ( 5.3 ) to the respective alcohol, fL4 was obtained in two steps via the
tosylate as described previously for preparation of 53 . Solid LAH pellets (7.34 g, 1 .5 eq)
were added in increments over 1 hour to 53 (25. 6g, 0.129 mol) in 300 mL anhydrous
ether under argon and stirred for 8 hours. The solution was chilled below 0°C, quenched
with 300 mL 3N HC1, then combined with 100 ml ether. The organic layer was washed
with 3N HC1, water, IN NaOH, and brine, then dried over Na 2 S0 4 and concentrated to
22. 8 g clear colorless liquid (>99% GC). The resulting 11-dodecenol was converted to
the tosylate as described previously. The crude tosylate was recrystallized from
MeOH/H 2 0, taken up in HCCI 3 and dried with Na 2 S0 4 , and finally concentrated to
38. 1 9g white solid. The toslylate was converted to 54 by the action LiBr in refluxing
acetone as described previously, and purified by fractional distillation. Yield: 22. 5g, 71%
overall for 3 steps. ‘H- NMR 8 (ppm) 5.78(m, 1H); 4.93(m, 2H); 3.36(t, 2H); 2.01(q,
2H); 1.83(m, 2H); 1.35(m)+1.28(br) = 14H. I 3 C-NMR 8 139.06, 114.15, 33.96, 33.73,
32.79, 29.30, 29.02, 28.80, 28.67, 28.10.
Synthesis of 13-tetradecenvl bromide(5.6). Prepared from 1 3-tetradecenoic acid
( 5 . 5 ) in three steps as previously described for the preparation of 54 , excluding
recrystallization of the intermediate tosylate. The bromide was purified by flash
chromatography (pentane). Yield: 56 % overall for 3 steps. 1 H- NMR 8 (ppm) 5.78(m,
1H); 4.94(m, 2H); 3.38(t, 2H); 2.02(q, 2H); 1.83(m, 2H); 1.36(m)+1.25(br) = 18H. 13 C-
NMR 8 139.16, 1 14.06, 33.93, 33.81, 32.82, 29.53, 29.42, 29.13, 28.92, 28.77, 28.16.
Synthesis of symmetrical alcohol-functionalized dienes
Synthesis of 1 l-oxo-l,20-heneicosadiene ( 5 . 7 ). The ketone diene 5/7 was
prepared in two steps via Claisen condensation of ethyl 10-undecenoate to form the (3-
keto ester diene , followed by dealkoxycarbonylation without isolation of the first step.
Claisen condensation: Ethyl 10-undecenoate (60mL, 52.44 g, 247 mmol, 1 eq) was
added dropwise to a stirring suspension of KH [34.97g (35%wt/wt in mineral oil), 296.4
mmol, 1.2 eq] in 300 ml dry THF at room temperature. After 12 hours, the reaction was
cooled to OC, quenched by addition of 30 ml acetic acid, and the solution was poured into
I L cold D.I. water. The layers were separated and the aqueous phase was extracted with
ether (2 x 100 ml). The combined organic solutions were washed with D.I. water (3 x
1L), dried over MgS04, and concentrated under reduced pressure to a yellow oil. Crude
yield can not be determined as it contains mineral oil from the KH dispersion.
Dealkoxycarbonylation: The crude oil was combined with 93.4 g LiCl, 450 ml DMSO,
and 20 ml D.I. water and the mixture was sparged with argon for 30 minutes. The
mixture was then vigorously stirred at 155°C under argon for 12 hours. Upon cooling to
room temperature, the mixture separated and the upper phase solidified. The solid was
taken up in 500 ml ether and washed with D.I. water(3 x 300 ml). The lesulting crude
product was reduced with LAH without further purification. An analytical sample was
obtained by recrystallization from methanol. %. 'H- NMR 8 (ppm) 5.78(m, 2H); 4.92(m,
4H); 2.35(tr, 4H); 2.0 l(q, 4H); 1.53(m, 4H); 1.32(br, 24). 13 C-NMR 5 21 1.59, 139.13,
1 14.1 1, 42.78, 33.75, 29.33, 29.27, 29.05, 28.88, 23.87.
Synthesis of 1 1 -hydroxy- 1.20-heneicosadiene ( 5 . 8 ). Prepared by LAH reduction
of crude ketone diene 577 . The crude ketone was dissolved in 300 ml dry THF under
argon in a 500 ml schlenck flask equipped with an addition funnel. LAH (62 mL 1M in
THF, 0.5 eq) was added dropwise via the addtion funnel at room temperature with
stirring. After 12 hours, the solution was cooled to 0°C and quenched by slow addition
of 100 ml 3M HC1. Transferred to separatory funnel with 300 ml ether and discarded the
aqueous phase. The ether solution was washed with sat'd NaHCCL (300 ml), D.I. water
(3 x 300 ml), dried over MgS0 4 , and concentrated to an oily off-white solid. The pure
diene 5.8 was obtained as a white solid after flash chromatography (10%
EtO Ac/hexanes). Yield 27.0 g, 70.7% overall for three steps. 'H- NMR 5 (ppm) 5.78(m,
2H); 4.94(m, 4H); 3.55(b, 1H); 2.01(q, 4H); 1.37(m)+1.25(br) = 28H. 13 C-NMR 8
139.16, 1 14.07, 71.94, 37.45, 33.77, 29.66, 29.54, 29.42, 29.10, 28.89, 25.63.
Synthesis of l,22-tricosadiene-12-ol ( 5 . 9 ). 10-Undecenyl Bromide ( 5 . 2 ) (5 g,
21.4 mmol, 1.0 eq) was added slowly via syringe to freshly scoured Mg turnings (0.525
g, 21.6 mmol, 1.01 eq) in 50 mL dry THF with rapid stirring under argon. After stirring
lhour at 45°C, the resulting Grignard solution was chilled to 0°C and methyl formate
(0.63 mL, 0.48 eq) was added dropwise, while maintaining the temperature below 5°C.
The contents were warmed to RT, stirred 30 minutes and then concentrated. The product
mixture was taken up in pentane and 3N HC1. The organic layer was washed with 3N
HC1 and water, dried over Na 2 S0 4 , and concentrated to 3.0 g white solid. The alcohol
was purified by flash chromatography (10%EtO Ac/Hexanes). Yield: 2.76g, 76.6%. 'H-
NMR 8 (ppm) 5.78(m, 2H); 4.92(m, 4H); 3.55(b, 1H); 2.01(q, 4H); 1.37(m)+1.25(br) =
32H. I3 C-NMR 8 139.16, 1 14.06, 71.94, 37.47, 33.77, 29.69, 29.59, 29.53, 29.46, 29.1 1,
Synthesis of l,24-pentacosadiene-13-ol ( 5 . 10 ). Diene 5.10 was prepared by
reaction of 11-dodecenyl magnesium bromide (from 54) with methyl formate utilizing
similar protocol described previously for preparation of diene 5 . 9 . Yield: 81.4%. NMR
spectra identical within experimental error with that of 5 . 9 .
Synthesis of l,28-nonacosadiene-15-ol ( 5 , 11 ). Diene 5.11 was prepared by
reaction of 13-tetradecenyl magnesium bromide (from 5 . 6 ) with methyl formate utilizing
similar protocol described previously for preparation of diene 5 ^ 9 . Yield: 39 %. NMR
spectra identical within experimental error with that of 5^9.
Synthesis of symmetrical dienes with pendant acetate groups
General procedure for acetvlating alcohol-functional dienes. The alcohol diene
was weighed into a schlenk flask and dried by either stirring in the molten state at 45-
70°C under reduced pressure (< 5 mmHg) for several hours or by dissolution in dry
toluene followed by evaporation under reduced pressure. Excess AcCl (4-10 eq) was
added dropwise to a solution of the alcohol in either dry toluene or anhydrous ether
containing pyridine (slight excess over that of AcCl). Both AcCl and pyridine were
transferred via syringe after storage over CaH 2 under argon. After aqueous workup, the
crude acetates were purified by flash chromatography (2-3%EtOAc/pentane or hexanes).
Products obtained in this manner were free of detectable impurities (GC. NMR) with the
exception of 15-acetoxy-l,28-nonacosadiene which required further purification by
HPLC (normal phase, 2%EtOAc/hexanes) to separate impurities with nearly identical R f
values, possibly caused by side reaction (see below).
Synthesis of 1 l-acetoxv-l,20-heneicosadiene ( 5 . 12 ). Prepared as described above
from x 8 . Yield: 82%, clear, colorless oil (100% GC). LRMS: 351 (m+). Elem. Anal.
Calcd. for C 23 H 42 O 2 : C, 78.80; H, 12.08. Found: C, 78.82; H, 12.21. 'H- NMR 8 (ppm)
5.77(m, 2H); 4.94(m)+4.83(p) = 5H; 2.02(q)+l .99(s) = 7H; 1.46(m, 4H);
1.34(m)+1.23(br) = 24H. 13 C-NMR 5 170.71, 139.02, 114.04,74.27,34.05,33.73,29.41,
29.33, 29.03, 28.85, 25.24, 21.15.
Synthesis of 12-acetoxy-l,22-tricosadiene (5.13). Prepared as described above
from 5^9. Yield: 86%, clear, colorless oil (100% GC). LRMS: 378 (m+). Elem. Anal.
Calcd. for C^RkA: C, 79.30; H, 12.25. Found: C, 79.25; H, 12.29. 'H- NMR 8 (ppm)
5.77(m, 2H); 4.94(m)+4.83(p) = 5H; 2.02(q)+1.99(s) = 7H; 1.46(m, 4H);
1.34(m)+1.23(br) = 28H. 13 C-NMR 8 170.82, 139.13, 114.06,74.36,34.10,33.76,29.47,
29.42, 29.09, 28.91, 25.28, 21.23.
Synthesis of 13-acetoxv-l,24-pentacosadiene (5.14). Prepared as described above
from 5Jj). Yield: 93%, clear, colorless oil (100% GC). LRMS: 406 (m+). Elem. Anal.
Calcd. for C 27 H 50 O 2 : C, 79.74; H, 12.39. Found: C, 79.81; H, 12.45. 'H- NMR 5 (ppm)
5.77(m, 2H); 4.94(m)+4.83(p) = 5H; 2.02(q)+1.99(s) = 7H; 1.46(m, 4H);
1.34(m)+1.23(br) = 32H. 13 C-NMR 8 170.86, 139.10, 114.07,74.36,34.15,33.70,29.49,
29.43, 29.03, 28.85, 25.24, 21.17.
Synthesis of 15-acetoxy-l,28-nonacosadiene (5.15). Prepared as described above
from 5.11 . Violent reaction occurred upon addition of AcCl (evolution of gas, exotherm,
and formation of black particulates) perhaps due to adventitious moisture. Yield: 62 %,
white solid (100% GC). LRMS: 463 (m+1). Elem. Anal. Calcd. for C 3 iH 58 0 2 : C, 80.45;
H, 12.63. Found: C, 80.39; H, 12.75. 'H- NMR 8 (ppm) 5.78(m, 2H); 4.93(m)+4.80(p) =
5H; 2.02(q)+2.00(s) = 7H; 1.47(m, 4H); 1.33(m)+1.23(br) = 40H. I3 C-NMR 8 170.89,
139.21, 114.06, 74.41, 34.10, 33.81, 29.62, 29.60, 29.56, 29.53, 29.50, 29.14, 28.93,
Synthesis of symmetrical dienes with pendant carboxylic acid and alkoxycarbonyl
Synthesis of 2-(9-decenvl)-l 1-dodecenoic acid(5.18). Diene 5.18 was prepared
by C-alkylation of the dianion (enolate) of 1 1-dodecenoic acid ( 5.3 ) with 9-decenyl
bromide (5.1) . The dianion of 5J was generated by reaction with 2 eq LDA prepared in
situ. All manipulations were conducted using standard schlenk techniques under argon
atmosphere. Butyl lithium (74.4 mL 2.5M in hexanes, 0.186 mol, 2.05 eq) was added
slowly via syringe to diisopropyl amine (26.2 mL, 0.186 mol, 2.05 eq) in 100 mL THF
while maintaining the temperature at -15°C>T>-30°C. The solution was stirred 5 min at
-20°C, then 15 minutes at RT. 5J (18 g, 90.8 mmol, 1.0 eq) was added slowly via
syringe while maintaining the temperature at -15°C>T>-30°C during which a milky
white suspension formed. The solution was cooled to 0°C and HMPA (15.8 mL, 90.8
mmol, 1.0 eq) was added via syringe followed by rapid addition of 5J[ (19.9 g, 90.8
mmol, 1.0 eq) via syringe at which time the solution temperature elevated to 15-20°C.
After stirring 12 hours the reaction was chilled to 0°C, quenched with 500 mL ice cold
3N HC1, and concentrated under reduced pressure. The heterogeneous aqueous mixture
was extracted with pentane and the organic layer washed with 3N HC1, water and brine,
then dried over Na 2 S0 4 and concentrated to ~38g pale yellow oil. The oil was further
purified by flash chromatography (15%EtOAc/pentane) to render pure 5.18 in 71%
isolated yield as a white solid. ‘H- NMR 5 (ppm) 5.7(m, 2H); 4.94(m, 4H); 2.33(m, 1H);
2.0 l(q, 4H); 1.63(m, 2H); 1.48(m)+1.27(br) = 26H. I3 C-NMR 5 183.26, 139.15, 1 14.1 1,
45.57, 33.79, 32.12, 29.51, 29.39, 29.09, 28.89, 27.34.
Synthesis of 2-( 1 l-dodecenyD-13-tetradecenoic acid(5.19). Diene 5.19 was
prepared by C-alkylation of the dianion (enolate) of 1 3-tetradecenoic acid ( 5.5) with 1 1-
dodecenyl bromide (5.4), following the same procedures for preparation and purification
described previously for diene 5.18 . The carboxylic acid was isolated as a white powder
in 82% yield. ‘H- NMR 5 (ppm) 5.7(m, 2H); 4.94(m, 4H); 2.33(m, 1H); 2.0 l(q, 4H);
1.63(m, 2H); 1.48(m)+1.27(br) = 34H. 13 C-NMR 5 183.34, 139.10, 114.105, 45.63,
33.82, 32. 1 1 , 29.49, 29.38, 29. 1 1 , 28.80, 27.32.
Synthesis of 2-(8-nonenvl)-12-tridecenoic acid(5.25). Diene 5^25 was prepared
by C-alkylation of the dianion (enolate) of 10-undecenoic acid (Acros) with 10-
undecenyl bromide (5.2), following the same procedures for preparation and purification
described previously for diene 5.18 . The carboxylic acid was isolated as a clear,
colorless oil in 85% yield.
Synthesis of methyl 2-(l l-dodecenyl)-13-tetradecenoate (5.22). Diene 5.22 was
prepared by base-catalyzed O-alkylation of carboxylic acid diene 5.19 with Mel.
Anhydrous K 2 C0 3 (1.32 g, 9.6 mmol, 2.5 eq) and 5,19 (1.5 g, 3.8 mmol, 1 eq) were
combined with 50 mL dry acetone in a scklenk flask fitted with a water-cooled condenser
under argon. Mel (1.9 mL, 30.5 mmol, 8 eq) was added via syringe. The mixture was
heated with a 60-70°C oil bath for 24 hours with vigorous stirring. To minimize loss of
Mel due to evaporation, the condenser temperature was maintained at 15°C and the argon
backpressure was slightly increased over atmospheric. Two additional aliquots of Mel (2
mL) were added at intervals via syringe. The acetone was evaporated under reduced
pressure and the concentrate was taken up in 50 mL pentane and water. The organic
layer was washed with sat’d NaHC0 3 , 3N HC1, and brine, dried over Na 2 S0 4 and
concentrated to 1.57g pale yellow oil. The oil was further purified by flash
chromatography (5%EtO Ac/hexanes) to 1.45g (93.5%) 5,22 as a clear colorless oil
(100% GC). LRMS(EI): 406 (m+). Elem. Anal. Calcd. for C27H50O2: C, 79.74; H,
12.39. Found: C, 79.79; H, 12.54. 'H- NMR 8 (ppm) 5.80(m, 2H); 4.94(m, 4H); 3.70(s,
3H) 2.35(m, 1H); 2.04(q, 4H); 1.61(m, 2H); 1.39(m)+1.23(br) = 34H. 13 C-NMR 5
177.06, 139.18, 1 14.06, 51.24, 45.70, 33.80, 32.49, 29.54, 29.46, 29.13, 28.91, 27.46.
Synthesis of methyl 2-(9-Decenvl)-ll-dodecenoate ( 5 . 20 ), Diene 5.20 was
prepared by base-catalyzed O-alkylation of carboxylic acid diene 5.18 with Mel, utilizing
similar procedures for synthesis and isolation described previously for 5.22 (100% GC).
Yield; 88%. LRMS(EI): 351 (m+). Elem. Anal. Calcd. for C23H42O2: C, 78.80; H, 12.08.
Found: C, 78.90; H, 12.26. 'H- NMR 8 (ppm) 5.77(m, 2H); 4.92(m, 4H); 3.63(s, 3H)
2.29(m, 1H); 2.00(q, 4H); 1.55(m, 2H); 1.33(m)+1.23(br) = 26H. I3 C-NMR 8 177.01,
139.12, 1 14.06, 51.21, 45.67, 33.76, 32.47, 29.49, 29.35, 29.05, 28.86, 27.42.
Synthesis of ethyl 2-(9-Decenvl)-l 1 -dodecenoate ( 5 . 21 ), Diene 5^21 was
prepared by base-catalyzed O-alkylation of carboxylic acid diene 5.18 with EtI, utilizing
similar procedures for synthesis and isolation described previously for 5.22 (100% GC).
Yield: 83%. LRMS(EI): 365 (m+). Elem. Anal. Calcd. for C24H44O2: C, 79.06; H, 12.16.
Found: C, 79.10; H, 12.26. 'H- NMR 8 (ppm) 5.77(m, 2H); 4.92(m, 4H); 4.13(q, 2H)
2.34(m, 1H); 2.04(q, 4H); 1.55(m, 2H); 1 .33(m)+l ,23(br) = 29H. I3 C-NMR 8 176.51,
139.13, 1 14.06, 59.85, 45.72, 33.76, 32.47, 29.50, 29.36, 29.06, 28.89, 27.39, 14.32.
Synthesis of 2-(methyl)-l 1-dodecenoic acid(5.25). 5.25 was prepared by C-
alkylation of the dianion (enolate) of propionic acid with 9-decenyl bromide ( 5 , 1 ),
following the same procedures for preparation and purification described previously for
diene 5 , 18 . The carboxylic acid was isolated as a clear colorless oil in 70.8% yield. 'H-
NMR 5 (ppm) 1 1.34(br, 1H); 5.78(m, 1H); 4.94(m, 2H); 2.43(m, 1H); 2.01(q, 2H);
1.62(m, 1H); 1.32(m)+1.27(br)+1.15(d,) = 16H. I3 C-NMR 5 183.69, 139.16, 114.09,
39.39, 33.78, 33.49, 29.45, 29.39, 29.07, 28.89, 27.10, 16.80.
Synthesis of 2-(9-decenyl)-2-methyl-l 1-dodecenoic acid(5,23). 5.23 was
prepared by C-alkylation of the dianion (enolate) of 2-(methyl)-l 1-dodecenoic acid
( 5.25 ) with 9-decenyl bromide ( 5 . 1 ) , following the same procedures for preparation and
purification described previously for diene 5 . 18 . The carboxylic acid was isolated as a
clear colorless oil in 76 % yield. *H- NMR 8 (ppm) 5.78(m, 2H); 4.93(m, 4H); 2.01 (q,
4H); 1.59(m, 2H); 1 ,35(m)+l ,25(br)+l . 1 l(s) = 33H. I3 C-NMR 8 184.73, 139.16, 114.11,
45.75, 39.06, 33.80, 30.12, 29.43, 29.1 1, 28.91, 24.43, 20.99.
Synthesis of methyl 2-(9-decenyl)-2-methyl-l 1-dodecenoic acid ( 5 . 24 ). Diene
5.24 was prepared by base-catalyzed O-alkylation of carboxylic acid diene 5.23 with
Mel, utilizing similar procedures for synthesis and isolation described previously for 5.22
(100% GC). Yield: 96%. LRMS(EI): 364 (in+). 'H- NMR 8 (ppm) 5.77(m, 2H);
4.92(m, 4H); 3.61(s, 3H); 2.00(q, 4H); 1.55(m, 2H); 1.34(m)+1.22(br) = 26H; 1.07(s,
3H). I3 C-NMR 8 178.09, 139.12, 114.07,51.38,45.92,39.44,33.77,30.07,29.40,29.08,
28.88, 24.51, 21.13.
Synthesis of symmetrical dienes with pendant chloride and phenyl groups
Synthesis of 1 l-chloro-l,20-heneicosadiene ( 5 . 16 ). 5.8 (2.0 g, 65 mmol, 1 eq) in
10 mL CC1 4 was added via cannula under argon to Ph^P (5.5 g, 21 mmol, 3.2 eq) in 20
mL CC1 4 . The vessel was heated in an 80°C oil bath for 16 hours, during which time a
white precipitate formed and the solution developed a yellow tinge. The mixture was
filtered and the solids washed with pentane. Addition of the pentane washings to the
filtrate caused additional precipitation, which was again filtered, and the resulting liquid
was concentrated under reduced pressure. Repeated dissolution in minimal pentane,
chilling, and filtration followed by concentration yielded 2. 1 7g slightly cloudy liquid.
Pure (100% GC) diene 5.16 was obtained after flash chromatography (pentane) as a clear,
colorless liquid. Note: Ph 3 P and 5^8 were dried in the molten state under reduced
pressure prior to use and CC1 4 was distilled from P 2 0 5 (A previous attempt with less
rigorous exclusion of moisture gave much lower yields). Yield: 1.8g, 85%. LRMS(EI):
326 (m+). Elem. Anal. Calcd. for C 21 H 39 CI: C, 77.14; H, 12.02. Found: C, 77.07; H,
12.13. . 'H- NMR 5 (ppm) 5.79(m, 2H); 4.94(m, 4H); 3.86(m, 1H); 2.02(q, 4H); 1.69(m,
4H); 1.50(m)+1.36(m)+1.27(br) = 24H. 13 C-NMR 5 139.13, 114.12,64.29,38.50,33.80,
29.45, 29.40, 29. 16, 29.09, 28.90, 26.48.
Synthesis of 1 1 -phenyl- 1,20-heneicosadiene ( 5 . 17 ), Diene 5.17 was prepared via
nucleophilic attack of phenyl lithium on ketone diene 577 , followed by in situ
deoxygenation of the resulting tertiary benzylic alkoxide. Bromobenzene (2.0 mL, 19.6
mmol, 2 eq) in 20 ml ether was added slowly to lithium foil (1.087g, 157 mmol, 16eq) in
40 mL ether under argon. After refluxing for 1 hour, ketone diene 577 (3g, 9.79 mmol, 1
eq) in 20 mL ether was added slowly and the mixture was stirred for 1 hour. The mixture
was chilled to -50°C and ~50 mL NH 3 was condensed into the flask from a tank at which
time the reaction turned blue. After 10 minutes, the reaction was quenched via addition
of 1 1 g NH 4 Cl(anh) in portions through a solids addition funnel. The ammonia was
evaporated, the mixture was filtered and the ether solution was washed with brine and
D.I. water. Pure (100% GC) diene 5.17 was obtained after flash chromatography
(pentane) as a clear, colorless liquid. 2.2 g, 61 % yield. LRMS(EI): 368 (m+). Elem.
Anal. Calcd. for C 27 H 4 4 : C, 87.97; H, 12.03. Found: C, 88.00; H, 12.06. . 'H- NMR 5
(ppm) 7.25(m, 2H); 7.20(m, 3H); 5.79(m, 2H); 4.95(m, 4H); 2.45(m, 1H); 2.01 (q, 4H);
1.54(m, 4H); 1.34(m)+1.21(br) = 24H. 13 C-NMR 5 146.37, 139.18, 128.10, 127.63,
125.66, 1 14.06, 46.06, 36.97, 33.79, 29.73, 29.47, 29.10, 28.91, 27.60.
Synthesis of ADMET Model Ethylene/Polar Monomer Copolymers
General Procedure for Preparation of Model Polymers . The pure diene monomers
may be adequately dried and degassed by replacing the atmosphere three times with
argon via three successive pump/purge cycles and then stirring under reduced pressure at
50°C for several hours. The ADMET polymerizations and subsequent hydrogenations
were all conducted utilizing the procedure described for polymers fL6 and 4/9. Inside an
argon-purged dry box, monomer and catalyst (400: 1 ) were combined in a small tube with
a single 24/40 neck and containing a magnetic stir bar. The tube was sealed with a
Kontes high vacuum valve, removed to a vacuum line and the pressure was reduced in
steps ultimately reaching 10 " 2 - 10 ‘ 3 mm Hg while increasing the temperature to 65°C.
Alternately, the reaction may be conducted in a pressure tube fitted with a vacuum valve
via teflon bushing thereby eliminating the need to transfer the ADMET polymer to
another vessel before hydrogenation. A homemade magnetic stirrer constructed from a
powerful magnet and a stir motor was utilized to maintain agitation as long as possible as
the viscosity increased during the polymerization. After 48 hours, the vessel was sealed
and returned to the dry box. In a glass pressure tube, the polymer/catalyst mixture was
combined with silica gel-60 (100 X the weight of catalyst) and sufficient toluene to aid
dispersion (generally 10-15 ml for 500 mg polymer). Hydrogen pressure was applied as
quickly as possible, within 2-3 minutes, to deactivate the catalyst residue toward
metathesis prior to dissolution of the polymer. The mixture was then heated to 90°C with
vigorous stirring while maintaining a constant pressure of 120 psig H 2 for 24 hours. The
mixture was filtered to remove the silica/catalyst residue composite and the toluene
evaporated to yield colorless viscous or water-white solid polymers. Number average
molecular weights for these polymers as measured by GPC(vs polystyrene) were
consistently in the range 2 - 5 x 10 4 g/mol (PDI = 2.0).
Synthesis of ADMET model ethylene/vinyl acetate copolymers
ADMET/Hydrogenation of 1 l-acetoxy-l,20-heneicosadiene (HP5.12). Elem.
Anal. Calcd. for [C 2 iH 4 o0 2 ]: C, 77.72; H, 12.42. Found: C, 77.63; H, 12.50. 'H- NMR 8
(ppm) 4.83(p, 1H); 2.02(s, 3H); 1.50(br, 4H); 1.23(br, 32H). 13 C-NMR 8 170.86, 74.45,
34.15, 29.71, 29.58, 25.33, 21.28.
ADMET/Hydrogenation of 12-acetoxy-l ,22-tricosadiene (HP5.13), Elem. Anal.
Calcd. for [C^H^Cb]: C, 78.35; H, 12.58. Found: C, 78.16; H, 12.63. ‘H- NMR 8 (ppm)
4.82(p, 1H); 2.03(s, 3H); 1.49(br)+1.25(br) = 40H . 13 C-NMR 5 170.88, 74.42, 34.13,
29.65, 29.53, 29.29, 29.17, 25.31, 21.26.
ADMET/Hydrogenation of 1 3-acetoxy- 1 ,24-pentacosadiene (HP5.14), Elem.
Anal. Calcd. for [C 2 5H 48 0 2 ]: C, 78.88; H. 12.71. Found: C, 78.83; H, 12.76. 'H- NMR 5
(ppm) 4.83(p, 1H); 2.0 1 (s, 3H); 1.47(br)+l ,22(br) = 44H. 13 C-NMR 5 170.93, 74.44,
34.1 1, 29.70, 29.58, 29.54, 25.31, 21.23.
ADMET/Hydrogenation of 15-acetoxv-l,28-nonacosadiene (HP5.15). Elem.
Anal. Calcd. for [C 29 H 56 0 2 ]: C, 79.75; H, 12.92. Found: C, 79.61; H, 12.94. 'H- NMR 5
(ppm) 4.83(p, 1H); 2.01(s, 3H); 1.47(br, 4H); 1.22(br, 48H). 13 C-NMR 5 170.80, 74.38,
34.10, 29.62, 29.564, 29.50, 29.09, 25.30, 21.29.
Synthesis of ADMET model ethylene/acrylate model copolymers
ADMET/Hydrogenation of methyl 2-(l l-dodecenyl)-13-tetradecenoate (HP5.22).
Elem. Anal. Calcd. for [C 25 H 48 0 2 ]: C, 78.88; H, 12.71. Found: C, 78.92; H, 12.78. *H-
NMR 8 (ppm) 3.7 l(s, 3H) 2.33(m, 1H); 1.61(m)+1.39(m)+1.23(br) = 44H. I3 C-NMR 5
1 77.06, 5 1 .24, 45.70, 32.49, 29.52, 29.37, 29. 1 0, 28.9 1 , 27.43.
ADMET/Hydrogenation of methyl 2-(9-Decenyl)-l 1 -dodecenoate (HP5.20).
Elem. Anal. Calcd. for [C 2 ,H 40 O 2 ]: C, 77.72; H, 12.42. Found: C, 77.44; H, 12.43. 'H-
NMR 5 (ppm) 3.63(s, 3H) 2.29(m, 1H); 1.54(m)+1.40(m)+1.21(br) = 36H. 13 C-NMR 5
177.06, 51.22, 45.71, 32.50, 29.67, 29.57, 29.47, 27.47.
ADMET/Hydrogenation of ethyl 2-(9-DecenyI)-l 1 -dodecenoate (HP5.21). Elem.
Anal. Calcd. for [C 22 H 42 O 2 ]: C, 78.05; H, 12.50. Found: C, 77.81; H, 12.49. 'H- NMR 8
(ppm) 4.05(q, 2H); 2.38(m, 1H); 1.61(m,)+1.39(m)+1.22(br) = 39H. I 3 C-NMR 8 176.43,
59.89, 45.67, 32.47, 29.50, 29.36, 29.06, 28.92, 27.43. 14.32.
Synthesis of ADMET model ethylene/vinyl chloride and styrene copolymers
ADMET/Hydrogenation of 1 l-chloro-l,20-heneicosadiene (HP5.16), Although
the ADMET polymerization proceeded in similar fashion to all others, analysis of the
polymer after attempted hydrogenation showed very little conversion/virtually unchanged
olefin signals in *H and 13 C NMR. The resulting polymer was fully saturated using Pd/C.
Unsaturated polymer P5.16 was dried and degassed by placing under vacuum at 80°C for
several hours. Polymer P5.16 (483 mg) was combined with Pd/C (10% wt/wt, 500 mg)
and 15 ml dry, degassed toluene under argon in a pressure tube. The mixture was
exposed to a constant 80 psig H 2 at room temperature with vigorous stirring. After 8
hours, the polymer was seen to precipitate as evidenced by gelatinous particles and the
Pd/C was no longer freely dispersing. The mixture was heated to 40°C at which time
stirring resumed and the gelatinous particles disappeared. After 24 hours, the mixture
was filtered through a medium glass frit (while heated) and then passed through a 0 . 2 |im
syringe filter to insure complete removal of fine Pd/C particles. The water-white solid
polymer was obtained in quantitative yield after precipitation into methanol. Elem. Anal.
Calcd. for [C, 9 H 37 C1]: C, 75.83; H, 12.39; Cl, 11.78. Found: C, 75.74; H, 12.51; Cl,
11.68. 'H- NMR 8 (ppm) 3.86(m, 1H); 2.02(q, 4H); 1.68(m, 4H);
1.47(m)+1.38(m)+1.23(br) = 32H. 13 C-NMR 5 64.39, 38.53, 33.80, 29.70, 29.59, 29.53,
ADMET/Hydrogenation of 1 1 -phenyl- 1 ,20-heneicosadiene (HP5.17) , Elem.
Anal. Calcd. for [C 25 H 42 ]: C, 87.64; H, 12.36. Found: C, 87.39; H, 12.46. . *H- NMR 8
(ppm) 7.25(m, 2H); 7.20(m, 3H); 2.43(m, 1H); 1.60(m, 4H); 1.21(br, 32H). ,3 C-NMR 8
146.43, 128.10, 127.64, 125.64, 46.07, 37.00, 29.79, 29.71, 29.67, 29.57, 27.63.
ADMET DEPOLYMERIZATION OF 1 ,4 -POLYBUTADIENE
UTILIZING A WELL-DEFINED RUTHENIUM CATALYST
Extensive study has been made of the use of olefin metathesis to produce small
molecules from unsaturated elastomers where the bulk of the work has focused on
reaction of 1,4-polybutadiene (1,4-PB) with substituted olefins as chain transfer agents
(CTA). 52 As discussed in Chapter One, initial studies in this field, just as in all areas of
metathesis, utilized ill-defined catalyst systems consisting of some species with
sufficient lewis aciditiy to invoke side reactions such as vinyl addition via cationic
pathways. Thus these reactions were termed metathesis degradation rather than
depolymerization. With the advent of well-defined catalysts, and more recently classical
systems with cocatalysts of diminished Lewis acidity, clean metathesis depolymerizaiton
could be achieved.
The reaction is depicted in Figure 3-1, where cross-metathesis of the CTA with
the unsaturated linkages of the polymer backbone results in chain-scission and end-
fuctionalization. As in other normal cross-metathesis reactions, the product distribution
is governed by statistics. In the event of complete depolymerization, the only products
would be diene and excess CTA. In most studies, this has only been achieved with a
large excess of CTA. For example, when using the catalyst WCl 6 /Et 4 Sn/Et20, 200
equivalents of hex-3-ene were required to achieve above 90% conversion of 1,4-PB to
the monomer, deca-3,7-decadiene (Figure 3-1, R = Et, n = l). 2
Figure 3-1. Inter- and intramolecular depolymerization of 1 ,4-polybutadiene.
Unsaturated elastomers may also be depolymerized via intramolecular metathesis
to produce macrocycles or oligomeric cyclics. This ring-chain equilibrium, familiar in
step/equilibrium polymerizations is affected by temperature, repeat structure, and of
course concentration. At sufficient dilution, high molecular weight 1,4-PB may be
completely depolymerized to small cyclics (Figure 3-1, m = 2-8). In depolymerizations
employing CTA’s, these cyclics are present in neglible amounts at equilibrium provided
CTA/PB repeat unit > 10. Thus careful control of reaction conditions can determine the
position of the equilibrium which is established between the monomeric species, linear
and cyclic oligomers, and higher molecular weight species.
Recently, Wagener and coworkers reported the first example of a complete, non-
statistical depolymerization of 1,4-PB to monomeric diene using a silane-functional
CTA (Figure 3-1, R = CIUSiMeaCl, n = 1) catalyzed by 1.2b , 20 Approximately 3
equivalents of the CTA were sufficient to achieve this unprecendented observation.
Crowe and coworkers later reported 53 that allyl silanes function as selective olefin
metathesis substrates. Cross metathesis is much more favored between allyl silanes and
alkyl olefins than self-metathesis of either class of olefin due to electronic and steric
factors. It may be assumed that this phenomenon is responsible for the above-mentioned
Metathesis depolymerization with appropriately functionalized CTA’s results in
elastomers with reactive end-groups. Hydroxy-telechelic polybutadienes (HTPB) are
highly desired due in no small part to their technical utility in polyurethane formulations.
Due to the intolerance of most metathesis catalysts for hydroxyl functionality, HTPB s
have been prepared by indirect routes where the hydroxyl group is masked during the
metathesis reaction. Borane functional CTA’s were used in combination with
WCl 6 /Me 4 Sn in one such example (Figure 3-2), where the borane functional telechelics
could then be converted under mild conditions to HTPB’s. 52r
Figure 3-2. Indirect synthesis of HTBP via metathesis depolymerization.
Reports of the broad utility of the ruthenium metathesis catalysts (Figure 3-3)
described in part in Chapter One prompted their investigation in metathesis
depolymerization chemistry. Of particular significance are their tolerance to functional
groups and stability in the presence of ethylene. In this chapter the depolymerization of
cis- 1,4-polybutadiene with ethylene and with ester-functionalized CTA’s catalyzed by
1.4 is described. Observations of the remarkable ability of catalyst IA to effect
metathesis depolymerization of ultra-high molecular weight polybutadiene in the bulk
state are also disclosed.
Figure 3-3. Well-defined ruthenium metathesis catalysts.
Ethenolysis of 1,4-Poly butadiene
The cross-metathesis between internal olefins and ethylene was first dubbed as
ethenolysis in 1967. 54 This specific reaction has been the subject of a number of studies
and has been exploited commercially. 55 Applications include the production of o>
unsaturated carboxylic esters from esters of naturally occurring fatty acids and a,o
dienes from cyclic olefins, shown in Figure 3-4.
C 2 H 4
Commercial applications of ethenolysis.
The depolymerization of 1,4-polybutadiene, as well as other unsaturated
elastomers, via cross metathesis with ethylene catalyzed by the well-defined metathesis
catalyst, [(CF3)2CH 3 CO]2(NAr)W=CHC(CH3) 2 Ph has been reported. 56 This reaction
is essentially the reverse of the ADMET polymerization of 1,5-hexadiene, and if the only
reaction occurring is ethenolysis, then the principal products would be a, co-vinyl
terminated polybutadiene oligomers (Figure 3-1, R = H). Should conversion be
complete, only the monomer 1,5-hexadiene would be produced. Conversions were far
from complete, but instead this cross metathesis reaction produced clean oligomers with
M n = 1,000 along with trace amounts of 1,5-hexadiene. It was assumed that the low
conversions of polymer to pure ADMET monomer were due to inactivation of the
catalyst through a previously described competing reaction of the catalyst with ethylene.
Ethenolysis of 1,4-Polybutadiene Catalyzed by a
Well-Defined Ruthenium Complex
A polymeric substrate with highly pure microstructure was chosen for these
studies (cis- 1,4-polybutadiene: 98% minimum cis 1,4-microstructure) (3J_) to simplify
analysis of product mixtures. A systematic study was performed to determine the effect
of ethylene pressure on conversion with all other variables held constant, including
[ 3.11 / 11.41 , polymer concentration, solvent and temperature. Solutions of polymer and
catalyst in CDCI 3 ([3.11 = 2.5M, [3.1 1/[ 1 .41 = 400) were exposed to a constant pressure
of C 2 H 4 with vigorous stirring for 48 hours at room temperature, at which time reactions
were quenched by slowly bubbling air through the solution. To minimize loss of volatile
products, the reaction mixtures were chilled to T < -50°C and the C 2 H 4 was slowly
released prior to quenching. The catalyst was removed by briefly stirring with silica gel
followed by filtration.
Figure 3-5. Ethenolysis of 1,4-polybutadiene.
Analysis of the product mixtures by GC showed each to be consistently
composed of a complex mixture of products, schematically represented in Figure 3-5.
GC/MS analysis indicated that major products of these reactions were low molecular
weight a, co-vinyl terminated butadiene oligomers with mass spectral peaks consistently
found at FW = 82 + n(54), where n has the values between 0 and 5. Oligomers with
n>5 were not detected. Of course the product with n=0 is the monomer 1 ,5-hexadiene.
Trace peaks were identified with mass = m(54) which may be due to cyclic butadiene
Due to the complex nature of the product mixtures, individual products were not
isolated. A simple alternative is to simply to calculate a relative moment of the product
distribution from each experiment to determine the trend in conversion. Therefore,
product mixtures were analyzed as a whole by gas chromatography/mass spectrometry
(GC/MS) in concert with 'H and 13 C NMR to determine the trend in conversion vs
The concept of average molecular weight ' 7 is familiar to the polymer chemist as
most polymerizations produce not one discrete species with a single molecular weight
but instead a homologous series of products characterized by an average molecular
weight. One such average, the number average molecular weight ( M „ ), is directly
related to conversion for step/condensation polymerizations. Since ethenolysis is the
microscopic reverse of the forward ADMET reaction, a step polymerization, it seems
that the most straightforward measure of conversion is to determine M „ . M n values
were calculated from 'H NMR end-group analysis and from GC plots and the two values
were in good agreement.
7 6 5 4 3 2 1 PPm
Figure 3-6. 'H NMR of 1,4-Polybutadiene (3.1). Insets are partial spectra of product
mixtures from ethenolysis at A: 30 and B: 400 psig C 2 H 4 .
NMR spectra of all product mixtures were consistent with a,co vinyl-terminated
butadiene oligomers. Figure 3-6 demonstrates the extent of ethylene depolymerization
chemistry. It shows the 'H NMR spectrum of the reactant, cis- 1,4-polybutadiene with
peaks near 5.4 and 2.1 ppm corresponding to the olefinic and allylic protons
respectively. The insets "A" and "B" are partial spectra obtained from the product
mixtures resulting from ethenolysis at 30psig (lowest conversion) and 400psig (highest
conversion) C 2 H 4 , where the signals centered near 5 and 5.8 ppm represent the terminal
and penultimate protons, respectively, of terminal vinyl groups. For mixtures consisting
entirely of linear a,co vinyl-terminated species, number average molecular weights can
be calculated using equation 3-1:
M n = 108
where Ij 0 and Ie 0 are the areas under the peaks for the internal olefinic protons and
terminal vinylic protons, respectively. This method of end-group analysis has been
applied successfully to moderately high-molecular weight polymers with well-defined
vinyl end groups prepared by the forward ADMET reaction. Since the concentration of
other products (cyclics) was low in all cases as determined by GC, this may be
considered a reasonably reliable method to follow conversion.
The M n also was estimated from the peak areas of GC plots of each reaction
mixture. A representative GC plot for reaction at 400 psig is shown in Figure 3-7 with
peaks labeled by their masses determined from GC/MS. No species larger than the
tetramer were detected in this case. The trace peaks immediately preceding oligomers
have masses, m(54), corresponding to cyclic butadiene oligomers. The trace peaks
immediately following major peaks have identical masses as the preceding major peak
and are assumed to be linear cis/trans isomers. The relative mass percents of each
species (GC) were converted to mole percents then normalized neglecting contribution
from solvent and trace peaks due to cyclics. From these values, M ,, can be calculated
using the well-known equation 3-2:
where M x and N x equal the molar mass and number of moles, respectively of species x.
Figure 3-7. Representative GC trace with mass labels (GC/MS). Reaction mixture
from ethenolysis at 400 psig C 2 H 4 .
The results calculated from ‘H NMR and GC are compiled in Table 3-1 along
with the relative mole percents 1,5-hexadiene produced as calculated from GC
measurements. These results show a general trend in conversion with ethylene pressure
with highest conversion of polybutadiene to 1,5-hexadiene being observed at 400 psig
C 2 H 4 . This may be expected as an increase in ethylene pressure results in an increase in
ethylene concentration relative to polybutadiene. That is, CTA/PB repeat unit is
increased, making ethenolysis progressively more favored over self metathesis of
Surprisingly, beyond 400 psig conversions decrease which could be a
consequence of catalyst mortality. Grubbs has reported 57 that various versions of the
complexes L4 (L n Ru=-R, R = alkyl) slowly decompose in solution. He proposed
bimolecular decomposition pathways as evidenced by the formation of structures
"R-=-R" in solutions consisting of only catalyst and solvent. The methylidene,
L n Ru=CH2 , which is most definitely the catalytic species in ethenolysis, was reported
to decompose more quickly in solution; within a matter of hours.
At higher concentrations of ethylene, it may be that non-productive self-
metathesis of ethylene begins to offer substantial competition to ethenolysis of the
polymer. Further, the probable bimolecular decomposition of the methylidene could be
depleting the system of active catalyst, and these events could lead to the lower
conversions observed at higher ethylene pressures. The overall result is an asymptotic
upper limit to increasing conversion with increasing ethylene pressure. Similar limiting
conversions have been observed in our laboratories in the ethenolysis of low molecular
weight 1 ,2-disubstituted olefins catalyzed by 1A.
The identity of trace products with mass = m(54) could not be assigned
unequivocally to cyclic cyclic oligomers. Although a trace peak assigned the mass of
108 could be 1,5-cyclooctadiene, the cyclic dimer, an authentic sample of 1,5-
cyclooctadiene gave a different retention time from GC.
c 2 H 4
Mole % (a)
Table 3-1. Results of ethenolysis at varied C 2 H 4 pressure (a: GC, b: 'H NMR).
Abendroth 58 and Thorn-Csannyr 4 investigated the metathesis degradation of
polybutadiene containing substantial amounts of 1,2 linkages. Figure 3-8 shows the
cleavage of a 1,4- 1,2- 1,4 triad from the polymer backbone with hex-3-ene as CTA
(R=Et) to form a triene. Subsequent ring closing metathesis yields either of the cyclic
products shown. Polymer 3J_, like all 1,4-polybutadiene produced by chain
polymerization of butadiene contains 1,2-linkages. The presence of these irregularities
is indicated by a small unresolved multiplet in the 'H NMR of 3J_ (cf Figure 3-6) at
approximately 5 ppm, signifying the terminal CFF of pendant vinyl groups. RCM and
ethenolysis of these groups, in either order, as depicted in Figure 3-8 (R = H) renders
allyl cyclopentene and/or vinyl cyclohexene, both with FW = 108 making them likely
candidates for the unknown product. Reexamination of the insets in the 'H NMR
spectra in Figure 3-6 reveals a new small unresolved multiplet at 5.64 ppm which
corresponds well with the olefinic protons of cyclohexene and cyclopentene (both at 5.7
ppm). This small multiplet was observed in the 'H NMR spectra of all depolymerized
3.1 in this study, and will be discussed further later in this chapter.
Figure 3-8. Products from extrusion of 1 ,4- 1 ,2- 1 ,4 triad of PB .
To determine the extent to which 3J_ is intramolecularly depolymerized in the
absence of ethylene, a solution of 3J_ and catalyst in CDCI 3 was prepared in the same
proportions and concentrations as in the ethenolysis experiments. The PB chunks
visibly dissolved much faster (within 30 minutes) than in the absence of catalyst,
indicating rapid reaction. The solution was stirred 48 hours then quenched by exposure
to air. Silica was used to remove catalyst residue as previously described and the solvent
was removed under reduced pressure to yield a viscous liquid. H and C NMR were
consistent with 1,4-PB but with trans content increased to 81% (quant l3 C NMR). The
number average molecular weight determined by VPO was 2 x 10 1 g/mol. This value is
not a true measure of the molecular weight produced as any small cyclics would have
been removed under vacuum during isolation.
Bulk Depolymerization of Polybutadiene
A remarkable observation was made regarding the solid-state reaction of catalyst
1.4 with polymer 3J_ when the two are placed in intimate contact; in the absence of any
other reagents or solvent, the solid polymer begins to liquefy over a period of a few
hours! To determine the outcome 3J_ was cut into small chunks and its surface was
coated with catalyst (1 3.11 / |T.41 =400), and a magnetic stir bar inserted. During the first
few hours of reaction, the mixture was occasionally agitated with a large magnet, until
viscosity was sufficiently diminished that slow stirring could be accomplished with a
magnetic stir plate. After 24 hours, the reaction was quenched by exposure to air, and
■ I n
the polymer was dissolved in benzene and isolated as described above. H and C
NMR were consistent with 1,4-PB but with 72% trans microstructure(quant l3 C).
Characterization of the polymer by GPC indicated a decrease in M„ to 9.7 x 10 3 g/mol
(PDI=1.76, monomodal)! Again, any small cyclics, which may have been produced,
would have been removed during isolation.
Before discussing the possible route to achieve this depolymerization, the
uniqueness of its initiation must first be noted. Evidence suggests during reaction of
catalyst L4 with olefinic substrates, phosphine must dissociate to free the active site. For
metathesis to occur, the catalyst and the polymer must come in contact on a microscopic
scale, i.e. the catalyst must dissolve in the polymer. At room temperature, the polymer is
above its crystalline melting temperature, T m of -6"C, and well above its glass transition
temperature, T, of -102"C. 37 Under these conditions adequate translational, rotational, and
vibrational energies exist to allow molecular motion. This molecular motion together
with the solubility of the catalyst in a range of organic media perhaps is sufficient to
allow the polymer to imbibe the catalyst and form a "solid solution" at the interface. The
well known molybdenum metathesis catalyst, 1.2b did not display this reactivity under
the same conditions, perhaps due to lower solubility in the polymer.
Assuming the M n value obtained from GPC for the bulk depolymerized PB is
correct within an order of magnitude, the molecular weight of the polymer was reduced
by two orders of magnitude (2-3xl0 6 — » 9.7x10' g/mol). In the absence of added
sources of end-groups, this depolymerization could be considered to have occurred by
one or a combination of three metathetical routes: a:) conversion to lower molecular
weight macrocycles via intramolecular metathesis, b:) incorporation of the catalyst
residues as end groups, and c:) conversion of 1 ,2-linkages to end groups.
x X = CHPh, RuL n
Figure 3-9. Incorporation of residues from F4 as end-groups in depolymerization.
The catalyst itself can be converted to end-groups, as depicted in Figure 3-9.
Any productive metathesis reaction of the catalyst with the backbone of the polymer
causes chain scission. The products are a styril -terminated PB chain and a ruthenium
alkylidene terminated chain. Facile chain transfer of the ruthenium chain end with high
molecular weight chains begins the equilibration toward lower molecular weight species.
The total number of linear chains should be equal to the total number of catalyst
molecules and therefore the average degree of polymerization equals the repeat unit to
catalyst ratio. For this experiment this gives DP=400 which corresponds to M „ s 2.2 x
10 4 . Given the inherent error in GPC measurements using dissimilar polymers as
standards, this calculated M „ agrees within experimental error with that obtained from
GPC (9.7 x 10 3 g/mol).
If conversion of the catalyst to end-groups is the major contributor to this
depolymerization, then the outcome should be sensitive to the catalyst loading. The
experiment was repeated but with the 13.1 1/11.41=4000, an increase of an order of
magnitude. For formation of linear chains terminated by catalyst residues alone, the M n
should be over 2x1 0 5 . Upon quenching by exposure to air, the reaction mixture was
characterized without purification to retain any volatile products. The molecular weight
distribution in this case was found to be bimodal with the bulk of the sample having
essentially the same retention time and profile as the oligomerized PB prepared at higher
catalyst loading (M, = 9.0 x 10 3 , PDI = 1.72). An additional small peak was detected
with retention time indicative of very low M „ oligomers, which were probably removed
from the first reaction mixture during purification. Because the M n of the
depolymerized product was insensitive to the change in catalyst loading, it may be
assumed that incorporation of catalyst as end-groups is not the major determinant of the
decrease in molecular weight.
As discussed previously, the spacial placement of double bonds in 1,4- 1,2- 1,4
triads favors formation of cyclopentene and cyclohexene derivatives via ring closing
metathesis (RCM). It is proposed here that these imperfections are the major determinant
of the product's molecular weight via the route illustrated in Figure 3-10. RCM of the
backbone olefins (bonds a and b) of a 1,4- 1,2- 1,4 triad extrudes vinyl cyclohexene with
relatively infinitesimal decrease in chain size. This molecule however can then act as
CTA via cross-metathesis of the vinyl group with the polymer backbone, cleaving the
chain. Likewise, RCM of the vinyl group of the triad with an adjacent backbone olefin
(bonds a and c) results in direct chain scission.
Figure 3-10. Conversion of 1,4- 1,2- 1,4-triads to end-groups.
Equilibration of the termini toward the most probable distribution should produce
polybutadienes terminated by vinyl, cyclohexenyl and cyclopentenyl groups with average
molecular weight proportional to the mole percent 1,2 linkages. For example, the
production of entirely linear chains via the proposed route from polybutadiene initially
containing 0.5% 1,2 linkages would result in DP = 200, Mn =1.1 x 10 4 g/mol. The
presence of the proposed endgroups is supported by the occurrence of the same small
unresolved multiplet(5.64 ppm) in the ‘H NMR spectra of all depolymerized samples.
Corroborating evidence could be obtained via bulk depolymerization of a series of 1,4-
polybutadienes with varying levels of 1,2-linkages.
There is no doubt the increase in entropy associated with conversion of UHMW
PB to lower molecular weight macrocycles contributes to this depolymerization.
Synthetic ultra high molecular weight polymers may currently only be produced
kinetically by capitalizing on the release of energy via events such as alleviation of ring
strain or reduction of bond order. This -AH must be sufficiently large to overcome the
obvious major -AS inherent in the process of connecting a large number of small
molecules by covalent bonds.' It is essential that no mechanisms exist for reversing the
polymerization under the conditions employed. An example of such a mechanism is the
thermal depolymerization of polystyrene at or above the ceiling temperature.
ROMP of cycloctadiene results in an equilibrium mixture consisting of high
molecular weight polybutadiene, cyclic oligomers, and monomer. The same equilibrium
mixture may be reached whether starting with pure high polymer, pure monomer, or a
mixture of all species. Intramolecular metathesis depolymerization of ultra high
molecular weight polybutadiene by conversion to macrocycles provides a thermoneutral
route to increase entropy. Once metathesis is initiated in the system reported here, the
system should move towards the appropriate equilibrium for this catalyst/polymer
combination in the bulk state. Contributions from these processes cannot be excluded.
Bulk Depolymerization of PB to Produce Telechelics
Marmo reported the preparation of moderate molecular weight end-functonalized
polybutadienes by metathesis depolymerization utilizing molybdenum catalyst 1.2b . 60
Due to the inability of the catalyst to effect cross-metathesis between the CTA and the
polymer in the bulk state, a two step process was employed. The polybutadiene was
depolymerized by intramolecular metathesis in toluene prior to addition of the CTA,
after which the toluene was evaporated to favor the formation of higher molecular
weight oligomers at the expense of the cylics generated during solution
depolymerization. In this manner, end-functionalized polybutadienes with M„ = 1.1 x
10 3 and 2.6 x 10 3 g/mol were generated.
The unique reactivity of the ruthenium catalyst with polybutadiene in the bulk
state may be exploited to accomplish depolymerizations without the need for solvent. In
order to demonstrate the possibilities, polybutadiene was depolymerized by ethenolysis
in the bulk state. The polymer was cut into small chunks, intimately mixed with catalyst
(f 3.il /r i.41 = 400) and agitated until it could be magnetically stirred. Exposure to 100
psig C 2 H 4 (48 hours reaction time) resulted in a rapid decrease in viscosity. Analysis by
GC and NMR were consistent with the results obtained from ethenolysis in solution.
The M n calculated from GC was 147 g/mol, indicating lower conversion than obtained
in solution at the same pressure. This is justifiable in terms of relative concentrations,
where dilution of PB while maintaining constant ethylene pressure increases CTA/PB
repeat unit, favoring higher conversion.
It is highly desired to produce telechelic products consisting entirely of linear
chains with each and every chain end containing useful functionality, which may be
incorporated via the CTA. This corresponds to a number average functionality ( F „ )
equal 2.0. While competing processes prevent the realization of this ideal case,
optimization of reaction conditions can greatly reduce the adverse effect on F n - 2 ’ 41
Polymer chain back-biting producing cyclic species devoid of the desired end-groups
may be diminished by using the most concentrated conditions possible. Ill-defined end
groups resulting from termination due to catalyst decomposition may be avoided by
choosing a robust catalyst, such as L4. The catalyst loading should be kept as low as
possible as each catalyst molecule introduces two unwanted end-groups (cf Figure 3-9).
Bulk depolymerization of PB in the presence of CTA should give essentially the
same results as the ROMP of COD with CTA. It must however be noted that if the
ubiquitous 1,2-linkages are indeed converted to end groups the F n will be adversely
affected. Nonetheless, two ester-terminated PB’s (ETPB) of differing molecular weights
were prepared (Figure 3-11). Ethyl 10-undecenoate ( 3.3 ) and catalyst ([3.31/11.41 = 400)
were combined and placed under vacuum for 24 hours to prepare the dimer (3.4). This
dimer/catalyst mixture was then added to chunks of PB (/[L4] > 4000, r3.il/f3.31 =
20 and 40) and the heterogeneous mixtures were agitated occasionally until stirrable.
After 24 hours, the reactions were quenched by exposure to air and the products were
dissolved in toluene, stirred with silica and filtered to remove catalyst residue, and the
solvent removed under reduced pressure. The molecular weights of the products were
characterized by GPC and 'll NMR, the results of which are summarized in Table 3-2.
The values obtained by GPC are higher than the predicted values as expected due to
calibration of the instrument with polystyrene standards. However, the ratio of the
measured molecular weights for the two products is approximately the same as the ratio
of the predicted values.
(lO 3 )m„ (g/mol)
Table 3-2. Characterization of ester-telechelic PB’s.
The *H NMR spectrum of 3^ is shown in Figure 3-1 1 along with the reaction
scheme. The inset is a magnification of the diminutive signal attributed to the proposed
cyclohexenyl and/or cyclopentenyl end-groups created from 1,4- 1,2- 1,4 triads (cf Figure
Catalyst L4 has been shown to be highly effective in various types of metathesis
depolymerization schemes. Its unprecedented stability in the presence of ethylene
qualifies it as a suitable homogeneous catalyst for ethenolysis. The remarkable reactivity
of the catalyst with solid polybutadiene allows for the first solvent free depolymerizations
of ultra high molecular weight polybutadiene and this method can successively be
incorporated into schemes for preparing end-functionalized oligomers.
Figure 3-11. 1 H NMR of ester-terminated polybutadiene 3.5 .
TANDEM HOMOGENEOUS METATHESIS/ HETEROGENEOUS
Much research has been dedicated to the heterogenization of homogeneous
catalysts. 62 Theoretically, the advantages of homogeneous and heterogeneous catalysis
can be combined. Advantages of heterogeneous catalysts include long-lived activity,
facile mechanical separation from substrates and products, and recyclability. These
attributes have made them highly effective in batch processes common in industry.
Homogeneous catalysts often offer greater sight selectivity, greater activity, and operate
under milder conditions. Binding a homogeneous catalyst to insoluble substrates may
combine the positive aspects of both types of systems. Immobilization produces hybrid
heterogeneous catalysts, which are analogous to homogeneous complexes on the
microscopic scale. However, industrial research on this topic has decreased dramatically
as the desired benefits are seldom realized. Applications are limited by difficulty in
preparation, characterization, slower rates, failure to achieve site isolation, and catalyst
leaching. Regardless, as the knowledge base in this area increases, this class of catalysts
may bear useful systems.
In this chapter, some observations of the reactivity of catalyst L4 supported on
silica are reported. Preliminary attempts to prepare a well-defined hybrid of L4 tethered
to silica resulted in the formation ill-defined ruthenium species which are efficient
catalysts for olefin migration. This serendipitous observation lead to the realization of a
new system for one-pot homogeneous metathesis/heterogeneous
hydrogenation. It has been proven effective as a synthetic transform for constructing C-
C bonds and in the preparation of saturated aliphatic polymers.
Immobilization of a Well-defined Ruthenium Complex on the Surface of Silica
Catalyst 1A is effective in the solution and bulk depolymerization of
polybutadiene(PB) to produce functional telechelics. Its robust nature allows good
yields of hexadiene through the ethenolysis of PB. However, in the presence of excess
C 2 H 4 , L4 decomposes in solution most likely via bimolecular pathways. If the limiting
conversions for ethenolysis, described in Chapter 3, are a direct result then
immobilization of the catalyst on a bulky substrate might increase conversions by
extending catalyst lifetime. The immobilization of catalysts similar to L3 by attachment
to crosslinked polystyrene beads via phosphine tethers has been reported 6 ’ as shown in
Figure 4-1. This hybrid catalyst proved active for the metathesis of 2-pentene and could
be recycled. However, turnover numbers were substantially lower than for the
homogeneous analogue, which may be attributed to slow diffusion of the substrate and
product through the cavities of the tortuous beads.
The adverse effect on rate, due to slower diffusion, might be diminished by
attaching the catalyst to the exterior of particles rather inside pores. The method used by
Grubbs was modified to tether the catalyst to silica gel particles rather than cross-linked
polymer beads (Figure 4-2). Simple chromatographic silica gel was oxidized with
piranha wash to increase the surface hydroxyl content and alkyl-bromide tethers were
attached by a well known method 64 for preparing hydrophobic silica. A fraction of the
bromide groups were converted to phosphine groups via Sn 2 attack by LiPCy 2 . Reaction
with Cl 2 (Ph 3 P) 2 RuCHPh should give the immobilized, well-defined ruthenium complex
by displacement of one aryl phosphine ligand by a tethered trialkyl phosphine. The
insoluble product was washed repeatedly with toluene to remove any homogeneous
species. Grubbs has reported that mixed phosphine versions of ruthenium metathesis
catalysts like that proposed here are less active. 6 ’ The accepted mechanism for olefin
metathesis using L4 involves dissociation of one phosphine ligand to provide an open
active site. Should the trialkyl phosphine dissociate in this system, catalyst loading
would be lowered (catalyst leaching). It has been shown that trialkyl phosphines have a
stronger affinity for the ruthenium center than triaryl phosphines. It was hoped that this
tendency could be exploited to decrease catalyst leaching.
Figure 4-1. Immobilization of L3 on cross-linked polystyrene.
To qualitatively assess the metathesis activity of this system, 1-octene was added
and the heterogeneous mixture was stirred for 24 hours after which an aliquot was taken
for GC analysis. A peak was seen with the same retention time as an authentic sample
of fran.s-7-tetradecene, indicating that metathesis had occurred. In addition several other
peaks were seen including one with essentially the same retention time as unreacted 1-
octene. However, 'H NMR showed the complete disappearance of resonances from
external olefins. Given the low apparent yield of 7-tetradecene and the appearance of
various side products, the complete conversion of external olefin to internal olefins must
have occurred by competing chemistry other than metathesis.
°, Cl- R
u — ^
CI 2 (PPh 3 ) 2 RuCHPh
/'^> PCy *
O ' J 3
Figure 4-2. Immobilization of ruthenium complex on silica via phosphine tethers.
Catalytic Activity of L4 Adsorbed on Silica
Attempts to obtain well-defined, single-site catalysts by tethering sometimes
meet with failure due to incomplete coverage of the silica surface with the tethers. 65
Highly reactive species may then result from deposition of metal complexes and metal
particles on the silica surface itself. It was proposed that the side products obtained
above might be the result of such competing chemistry.
1-Octene and catalyst JL4 (0.25mole%) were combined with chromatographic
silica gel inside an argon-purged dry box and stirred vigorously 24 hours. The silica gel
became reddish-brown and the liquid became colorless signifying that the complex was
adsorbed onto the silica surface. 'H and l5 C NMR spectra of the liquid were consistent
with linear alkenes with double bonds in internal positions. Analysis of the product
mixture by GC/MS showed the presence of a distribution of products with masses
corresponding to a homologous series of straight chain aliphatic alkenes from C 6 to Ci 6 .
Removal of the product mixture and addition of fresh 1-octene to the heterogeneous
catalyst residue gave similar results.
It is proposed that the process for forming this product mixture consists of at
least two steps, one of which is olefin migration. Contributing processes may be olefin
dimerization. 66 ' 69 Figure 4-3 shows dimerization via olefin insertion followed by 13-
hydride elimination to give dimers, steps that are common to Ziegler-Natta
polymerization. With certain catalyst systems, the rate of (3-hydride elimination may be
fast enough to favor formation of dimers as the major or even exclusive products. Paths
A and B differ in the initial regioisomer formed from two different modes of insertion.
Olefin insertion into the resulting metal carbon bond may also occur with regioselective
competition. The product distribution may be further broadened due to competing
regioselective elimination. Only linear products V and VI are consistent with the
products obtained using L4 adsorbed on silica. The presence of odd carbon species and
the absence of branching in the product mixture for L4 on silica suggest an alternate
mechanism(s). Another possibility is a dimerization mechanism, which proceeds
through metallocyclopentanes, but this also gives branched alkenes.
A more likely combination of events is olefin migration in tandem with
metathesis as depicted in Figure 4-4. As an example, 1-octene may be isomerized to 2,
3, and 4-octenes through olefin migration. Metathesis of this mixture would result in
olefin products ranging from C 2 to C !4 with the olefins placed from the 1 to the 7
position. Further, the products larger than C[ 4 could be formed by olefin migration to
the 8 position in any given alkene followed by metathesis. The combination of these
two mechanisms results in alkenes with both odd and even number of carbons.
1 ' R
Figure 4-3. Example mechanism for olefin dimerization.
The precatalyst ChCPhrPERuCHPh used in the attempted preparation of the
tethered catalyst above was evaluated under the same conditions, i.e., adsorbed directly
on silica. The unmodified catalyst is not active for the metathesis of acyclic olefins. In
concord with the proposed mechanism here, 1-octene was isomerized to a mixture of
octenes but no other products were detected. The obligatory metal hydride likely
originates from reaction of the ruthenium complexes with silanol groups of the silica. In
a related process, co-unsaturated alcohols are isomerized to aldehydes due to proposed
Ru-H species formed in situ from reaction of L3 with hydroxyl functionality. 28 Given
the inability of 2 to metathesis acyclic olefins, higher olefins in the tethered system must
have been produced by the desired well-defined hybrid version of 1A. Metathesis with
1.4 directly adsorbed on the silica is perhaps due to intact metal carbene, which has been
C 3 - Cg a-olefins
C 4 - C ]4 Alkenes
n, m, y = 0 - 5
C 15 Alkene
Figure 4-4. Proposed olefin metathesis/migration to produce C 4 - C| 6 internal alkenes.
The result of this process may be compared to the overall result of the latter
stages of the Shell Higher Olefin Process (SHOP), Figure 4-5. 2 In the first step, ethylene
is oligomerized to a-olefins. These alk-l-enes are isomerized to an equilibrium mixture
of internal alkenes. These are then passed over a metathesis catalyst to produce a
statistical distribution of linear alkenes. The C 11 -Q 4 fraction is separated and the
remaining fractions are recycled through the process. The Ch-Ch alkenes may be
converted to detergent alcohols via hydroformylation. The olefin metathesis and
isomerization steps might be conducted in one vessel using 1A adsorbed on silica. If
this system should be proven robust, this could also be a batch process.
> C14 Alkenes
< Cl 1 Alkenes ■
Cl 3- 14 Alkenes
Cl 1-12 Alkenes ■
Figure 4-5. Block diagram of later stages of Shell Higher Olefins Process . 2
Hydrogenation with the Residue of Catalyst L4 Adsorbed on Silica
Catalytic olefin migration and hydrogenation mechanisms have as common
intermediates metal hydrides. Ruthenium hydride complexes have been shown to be
highly effective hydrogenation catalysts . 70 ' 71 If this system indeed forms Ru-H species,
then it should prove an effective catalyst for olefin hydrogenation. In two separate
pressure vessels, tran^-7-tetradecene and catalyst L4 (0.25 mole %) were combined. To
one vessel was added 1 g chromatographic silica gel. The two mixtures were stirred for
1 hour and then exposed to 120 psig H 2 for 14 hours with vigorous stirring. *H NMR
showed the complete disappearance of olefin in the reaction containing silica. The
product mixture prepared without silica was less than 30% reduced.
Concurrent with these observations was a report utilizing the residue of a
ruthenium metathesis catalyst for hydrogenation. McLain 72 et al. reported a one-pot
procedure for producing an ethylene/methyl acrylate copolymer by the ROMP of an
ester-functionalized cyclooctene catalyzed by L3, and then hydrogenating by simply
applying hydrogen pressure to the completed ROMP reaction system as shown in Figure
4-6. It was assumed that the catalyst residue was converted to HRuCl(PCy 3 ) 2 . H 2
pressures of at least 400 psi were required to achieve >99% reduction. Lower
conversions in the absence of large excess H 2 were contributed to decomposition of the
suspected highly unsaturated hydrogenating species. One possible route is the cleavage
of solubilizing phosphine ligands via the ubiquitous P-C oxidative addtion often seen in
transition metal phosphine adducts. ' The result may be species that are not active in
hydrogenation and/or precipitation of ruthenium species from solution. Precipitation
may result in aggregates with diminished surface area and therefore fewer available
reactive sites. Addition of silica may produce ruthenium complexes that are not
susceptible to this decomposition pathway. Adsorption of the catalyst residue from a
homogeneous solution not only provides for high surface area (more available reactive
sites) and diminishes formation of aggregates but also perhaps initiates the reduction by
forming the obligatory Ru-H species.
Figure 4-6. One-pot ROMP/hydrogenation to produce model ethylene/acrylate
copolymer. Ethylene run length varies (n = 6,7,8) due to unsymmetrical
nature of monomer.
A brief model study demonstrates the effect of varied H 2 pressure on the
effectiveness of the heterogeneized catalyst L4 for olefin hydrogenation, trans-1-
Tetradecene and 1A were combined as above and stirred one hour to allow complete
dissolution of catalyst. A change from purple heterogenous mixture to reddish-brown
homogeneous solution indicated dissolution and carbene exchange. Silica was added
and the system was exposed to a constant H 2 pressure at room temperature with vigorous
stirring for thirty minutes. Conversions were estimated from 'H NMR, comparing the
resonances due to the olefinic protons (~5.4 ppm) to those of the terminal methyl
groups(~0.8 ppm). As can be seen from Figure 4-7, reaction can be driven to
completion within 30 minutes at low to moderate pressures.
Ru, silica \ / \ ^
M ' V/
H 2 12
Pressure H 2 (psig)
Figure 4-7. Hydrogenation of rrans-7-tetradecene. Conversion estimated from ! H NMR.
This hydrogenation may be incorporated into a two-step, one pot procedure for
forming C-C bonds at pressures that are convenient in a laboratory environment without
the need for specialized equipment. In the first step, carbon skeletons are constructed via
metathesis. In the second step, silica is added to the reaction mixture and the system is
exposed to hydrogen to reduce the olefinic product(s), forming the desired C-C single
bond. For this procedure to be successful, it is necessary that hydrogen is applied
immediately after addition of silica to preclude homologation via olefin migration and
further metathesis catalyzed by the ruthenium residue as it is adsorbed on silica.
To confirm the utility of this process, the olefinic ester 41 was dimerized
quantitatively by U4 (Figure 4-8). Upon completion of the reaction, silica was added and
the system was exposed to 120 psig FU. After mechanical separation of the catalyst
residue/silica composite, the long chain a,co-diacetate 42 was obtained in >95% isolated
-C 2 H 4
v / \ ^ -u / \/OAc Add silica AcCU / \^OAc
8 8 n 2 18
Figure 4-8. Tandem homogeneous metathesis/heterogeneous hydrogenation to produce a
It has been found desirable by coworkers in our laboratory to prepare bipolar
surfactants of the type 45 (Figure 4-9) as they can be polymerized using Langmuir trough
techniques to produce a 2-dimensional cross-linked network polyaniline. The
methodology reported herein was exploited in constructing the long aliphatic segment of
4.5 . The diene 43 might be expected to give a mixture of products due to reaction of the
styrenic double bond (bond b) in addition to the a-olefin (bond a). As predicted based on
recent reports of selectivity in the metathesis of substrates with varied electronic and
steric modifications, bond b is unreactive under the conditions employed for metathesis
catalyzed by L4. Crowe 5 ’ investigated the reactivity of olefins with varied steric and
electronic modifications including allyl silanes, acrylonitrile, and styrenes, where cross-
metathesis of these substrates with alkyl olefins proved to be selective. [3-Alkyl styrenes
were also shown to be of lower reactivity. Perfluoroalkyl and some fluoroalkyl
substituted olefins have also been shown to be inert towards catalyst 44 due to lowered
electron density of the double bonds. Bond b of substrate 43 also proved to be
unreactive at room temperature in the presence of L4. Not only is it sterically crowded,
but the electron density of bond b is diminished by the nitro-substituted benzene ring. As
a result, triene 44 can be obtained in 95% isolated yield after flash chromatography.
80 % cis
C 2 H 4
o 2 n
nh 2 22 nh 2
Figure 4-9. Attempted synthesis of bipolar aniline surfactant.
In situ hydrogenation of 44 revealed some aspects of relative selectivity of the
system reported here. Hydrogenations were conducted at room temperature (24 hrs) and
conversions were estimated from 'H NMR. At 120 psig H 2 , bond a is quantitatively
hydrogenated. However, bond b(cis) is only converted by approximately 90% while
b(trans) is virtually unreacted. At 800 psig, conversions are near quantitative and
approximately 80% for b(cis) and b(trans), respectively. This is in keeping with the
selectivity typically observed in the hydrogenation of sterically hindered cis/trans isomers.
In both cases, trace peaks were detected ('H NMR) which might be assigned to the aniline
moiety resulting from reduction of the nitro group. Reports of hydrogenation with
various homogeneous catalysts of general formula Cl n (R 3 P) m RuL n indicate pressures in
excess of 80 atm are required to obtain good to excellent conversion of aromatic nitro
compounds to aniline derivatives in practical reaction times. 74 Optimization of reaction
conditions might allow higher conversion in hydrogenation of nitro-functionalized
substrates providing an indirect route to primary amines without the need for
Preparation of Saturated Polymers by Tandem Homogeneous
ADMET/ Heterogeneous Hydrogenation
Olefin metathesis polymerization has proven to be quite broad in scope for the
preparation of well-defined polymers and hydrogenation of these provides additional
polymers with unique microstuctures. 46-51 Hydrogenation also produces new polymers
with differing physical and chemical properties, including greater oxidative stability.
These syntheses typically involve first the synthesis and separation of unsaturated
polymers from the metathesis catalyst followed by a second hydrogenation step.
Hydrogenated polymers from norbenene and derivatives of norbornene have been
produced commercially as Zeonex™ since 1991 .
Preparation of End-Functionalized Polyethylene by ADMET/Hydrogenation
A useful application of metathesis/hydrogenation is the production of
commercially valuable telechelic polyethylenes. This has been demonstrated in the
production of hydroxy-telechelic polyethylene via diimide reduction of intermediate
telechelic polyalkenamers. 61 The polyalkenamers were produced through ROMP of
cyclooctadiene in the presence of 1,2-disubstituted olefins, as described in Chapter Three.
Similar polyalkenamers may be produced by ADMET polymerization in the presence of
The new tandem homogeneous metathesis/heterogenous hydrogenation technique
utilizing catalyst L4 proved effective for preparing end-functionalized polyethylene (4.6)
(Figure 4-10). 1 ,9-Decadiene was polymerized using E4 under typical ADMET
conditions in the presence of 0.2 equivalents 9-decenyl acetate (4.1) as a chain transfer
agent. Subsequent heterogeneous hydrogenation requires the addition solvent to aid
dispersion, but dilution in the presence of active metathesis catalyst would favor
formation of lower molecular weight cyclics at the expense of linear species. Therefore,
the polymer was intimately mixed with silica and the system was exposed to 120 psig H 2
for 30 minutes prior to addition of toluene. Extensive hydrogenation had already occurred
at this point to yield a product with sufficient polyethylene character to render it poorly
soluble in toluene. Hydrogen pressure (120 psig) was reapplied for five hours while
heating in a 90°C oil bath to prevent precipitation of the product. Simple hot filtration
and removal of the solvent under reduced pressure yielded a water-white solid in near
Molecular weight measurements agree well with the value predicted Mn = 1 .5 x
10 3 g/mol based on the ratio of chain limiter to diene in the ADMET reaction. End-group
analysis ( 1 H NMR) and high temperature GPC (vs PE) gave 1.5 x 10 3 and 1.7 x 10 3
g/mol, respectively. The polydispersity ( 1 .9) approaches that expected for equilibrium
condensation polymerization. Examination of the ‘H NMR spectrum (Figure 4-10) in
the region from 4.8 - 6.0 ppm reveals good conversion in the hydrogenation step, as
indicated by complete disappearance of signals rising from olefinic protons. Acetate
content of the product as calculated from * H NMR did not decrease from that expected
from initial stoichiometry indicating that these groups remain intact throughout the olefin
hydrogenation. This reaction was repeated, with aliquots periodically removed to
qualitatively assess the time required for complete reduction. By ‘H NMR, signals due to
olefinic protons completely disappear within 4 hours.
Synthesis of a Polyester with Long Aliphatic Segments
Pennelle 7 ^ and coworkers reported the synthesis of a polyester with regular long
alkyl segments within the polymer backbone by classical condensation of a long chain
aliphatic diol with a diacid (Figure 4-11). Their interests lie in the control of lamellar
crystal structure by introducing regular defects in a polymer with high polyethylene
Similar polymers may be constructed by the ADMET/hydrogenation method
reported here as illustrated in Figure 4-12. The ester diene ( 4 . 7 ) was condensed by
ADMET and the polymer was hydrogenated as described previously in this chapter for
hydrogenation of end-functionalized polyoctenamer. The higher molecular weight and
crystallinity of the unsaturated polyester (fL8) slows its dissolution in toluene, allowing
the addition of solvent just prior to exposure to hydrogenation without fear of rapid
metathesis depolymerization. The saturated polyester ( 4 . 9 ) was obtained as a white solid
in near quantitative yield. The structure shown is not entirely correct as the ester groups
may by incorporated in head-head, head-tail, and tail-tail distribution, a consequence of
the unsymmetrical nature of the ester moiety.
- C 2 H 4 AcO v
" i " — r- — i " " i " " i " i " ' i '
6.0 5.8 5.6 5.4 5.2 5.0
6 5 4 3 2 1 PPm
Figure 4-10. 'H NMR of telechelic polyethylene from ADMET/hydrogenation.
E = 0 2 C(CH 2 ) 3 C0 2
Figure 4-11. Preparation of a polyester with long ethylene run lengths by classic
The 'll NMR spectra for polyesters and fF9 are shown in Figure 4-13. Due to
its highly crystalline nature (AHf = 122 J/g, T,,, = 97°C, DSC) and long ethylene run
lengths, polymer 4J9 displays very limited solubility in typical organic solvents at room
temperature, but is freely soluble above 60°C. Thus NMR measurements for this polymer
were acquired at 90°C in toluene-dg which apparently also increases resolution of the
overlapping signals corresponding to the protons (3 to the ester group ("a" and "d"). Note
the signals ("g", upper and "e", lower) indicating conversion of vinyl ends groups of
polymer 4.8 to methyl end groups upon hydrogenation. High temperature GPC (vs
polyethylene standards) gave M» = 1.0 xlO 4 g/mol (PDI = 1.7) for polymer 4d) and these
values agree within experimental error with those obtained for 4J5 under the same
4/7 4J5 4j}
Figure 4-12. Preparation of saturated aliphatic polyester by ADMET/hydrogenation.
6 5 4 3 2 1 PPm
a O c
b d e
Figure 4-13. 'H NMR spectra of 4JS (upper, CDCI 3 ) and 43) (lower, toluene-dg, 90°C).
The method reported herein is a facile one-pot route for forming carbon-carbon
bonds in the synthesis of polymers and small molecules. No additional catalysts or
reagents are needed for hydrogenation other than inexpensive silica gel and hydrogen
gas. Addition of silica as a support for the ruthenium complex not only facilitates
hydrogenation at low to moderate pressures but also simplifies purification of products.
No purification step is required prior to hydrogenation and the catalyst may be removed
by simple mechanical filtration. It shows promise both commercially in the preparation
of telechelic polyethylenes and in the preparation of model polymers.
The ester moieties of the polymers in Figures 4-11 and 4-12 can be easily
incorporated into polymer backbones with long ethylene run lengths by classical ester
condensation chemistry. However, other functional groups that may provide deeper
insight into the engineering of crystal structures may prove difficult or even impossible
to incorporate into a high molecular weight polymer. The method of
ADMET/hydrogenation is very well suited to producing model polymers of this type, as
symmetrical dienes with a wide variety of functional groups at their center may be
constructed by typical organic transforms. The method for incorporating the functional
group into the polymer is the same mild procedure regardless of constitution.
Applications of this process to the preparation of such model “functionalized
polyethylenes” will be described in the following chapter.
THE SYNTHESIS OF MODEL ETHYLENE/POLAR MONOMER
COPOLYMERS VIA ADMET AND HYDROGENATION
Since macromolecular compounds are, almost without exception, polymolecular
mixtures, one does not deal with uniform materials, as is the case for low
molecular compounds. In the most favorable case, such a material is
polymeruniform, that is, a mixture of macromolecules of the same structure, but
different chain lengths.
Hermann Staudinger 76
Flawless control in the construction of discrete molecules of high molar mass has
been exhibited only in nature, where the macromolecular engineer and the legislator of
laws governing the implication of chemical transforms are one and the same. The
indispensability of this level of control is demonstrated by the horrendous outcome of
rare mistakes in these biological polymerizations. DNA, one of the many forms of
natural polymers, stores coded information in its perfect sequences of nucleic acid repeat
units and these codes are read and used to replicate the perfect polymers as well as to
produce others. 77 Numerous cancers, birth defects, and diseases are now linked to what
are errant polymerizations induced by mutated DNA or misreading of its codes.
Man’s clear mediocrity in this arena is demonstrated by current practices to
combat the polymerizations gone awry. These include “shotgun” approaches such as
chemotherapy and radiation treatments, with their well-known grim physiological side
effects due to the indiscriminate statistical termination of both properly and improperly
functioning polymerizations. All modern synthetic schemes are governed to some extent
by statistical elements, limiting the control which chemists may exert over the outcome of
their chemical products, including polymers. Man’s subjugation to statistics has even
prompted some to ascribe the development of nature’s perfect polymerizing machines to
a statistical process termed evolution.
With regard to chemical homogeneity, the aesthetic simple structures assigned to
synthetic polymers are rarely accurate depictions. For example, even in the absence of
side reactions such as chain transfer and termination, butadiene may be incorporated into
a polymer backbone via chain polymerization in numerous regiochemical and
steriochemical modes of propagation 37 which are certainly not adequately represented by
the single generic structure depicted in Figure 5-1. The monomer may be incorporated
into the chain in 1,4 (both cis and trans) and 1,2 fashion and sequences of 1 ,2 repeats may
also display varying degrees of tacticity. An example of a highly efficient near perfect
polymerization is Zeigler-type polymerization of butadiene with Neodymium catalysts by
which ultra-high molecular weight polybutadiene, i.e., on the order of 10 6 g/mol may be
prepared with 1,4 content as high as 99.5% (> 98% cis). 78 This is truly an amazingly well
controlled reaction as any organic chemist would be thrilled to conduct transforms
yielding crude product mixtures that are 99.5% pure. However, in this case, the 0.5% 1,2
units cannot be removed from the product mixture as they are covalently bound to the
pure portion of the product. By comparison with small molecule chemistry, while the
bromination of butadiene may afford a mixture of products where 1,2 and 1,4 addition
compete, distillation, chromatography, or a combination may separate the desired
While pure polymer microstructure is not a prerequisite for technical utility, the
availability of polymers with progressively greater chemical homogeneity has allowed
deeper insight into structure/property relationships. With judicious choice of catalyst and
monomer, ADMET polymerization has been shown to produce polymers with pure
microstructure within spectroscopic detection limits. The combination of the clean
ADMET polymerization with mild chemoselective olefin hydrogenation has been shown
to be an effective method for preparing model polymers that are polymer uniform. The
realization of the facile one-pot procedure for ADMET/hydrogenation reported in
Chapter 4 served to streamline this process for producing model polymers. The
remainder of this chapter describes the use of this process to prepare models for
copolymers of ethylene with vinyl monomers including vinyl acetate, vinyl chloride,
styrene, and acrylates and subsequent preliminary thermal analysis of these polymers. A
brief description of the commercial polymers for which these polymers serve as models is
first given in order that the reader may grasp the significance of the results reported here.
Polymerization: Products from different modes of addition inseparable
Bromination: Products from different modes of addition easily separable
Figure 5-1. Macromolecular versus small molecule chemistry of butadiene.
Ethylene/Polar Monomer Copolymers
Polyethylene has been produced commercially since 1942 79 and has grown to be
the world’s largest volume commercial polymer. 80 A multitude of grades exist,
depending on the method of manufacture, with varying molecular weights and levels and
types of branching granting a broad scope of properties. Variation of the polymer
constitution via copolymerization of ethylene with various substituted ethylenes
dramatically increases the range of new materials.
Commercial products in the class of ethylene/polar monomer copolymers include
as comonomers vinyl acetate, acrylates, acrylic acid, etc. Inclusion of vinyl acetate or
acrylates, for example, yields products with decreased crystallinity and increased room
temperature flexibility, impact resistance, and optical clarity relative to ethylene
homopolymer. Variation of the comonomer content also greatly effects properties
allowing application of EVA in such diverse end uses as packaging films, gloves,
squeeze toys, and hot-melt adhesive formulations. 37
Ethylene/polar monomer copolymers are produced commercially by the same
high-pressure free radical processes utilized for low density polyethylene. As a result of
the nature of the free radical polymerization, the polymer microstructures are ill-defined
with uncontrolled branching and broad polydispersities due to chain transfer reactions.
Branching can occur via hydrogen-atom extraction (chain transfer) by the propagating
chain end both intra- and intermolecularly. The former leads to short chain branching
(SCB) while the latter leads to long chain branching (LCB) as shown schematically in
Intramolecular: Short Chain Branching
Intermodular: LongChain Branching
2 n 4
Figure 5.2. Origin of SCB and LCB in free radical polymerization.
Some polar monomers contain hydrogen atoms which are more easily abstracted
and therefore copolymers containing these have a higher degree of branching. For
example, both the methine proton of the vinyl acetate repeat unit and the methyl protons
of the acetoxy group in either the monomer or the repeat unit provide sites for additional
The microstructures of these copolymers are further complicated by statistical
incorporation of the comonomers into the polymer backbone. The comonomers may be
incorporated in different amounts according to their relative concentrations and
reactivities. The sequence distributions may also vary between alternating, blocky, and
random as governed by the product of the monomer reactivity ratios ri and r 2 as defined
below. For a system consisting of two monomers, Mi and M 2 , kn is the rate constant for
a chain ending in M| adding to monomer M|, k) 2 is the rate constant for a chain ending in
Mi adding to monomer M 2 , and so on.
k\ | k 2 2
' ~ k 2 ~ k
For ri = r 2 s 0, the monomers tend to be incoiporated in an alternating fashion
where each Mj is followed by M 2 and vice versa. When ri>l, r 2 > 1, the chain end has a
higher tendency to add to the monomer from which it was derived resulting in blocks, or
extended sequences, of each monomer. In the case of i'i r 2 = 1, the polymerization is
termed an ideal polymerization and the two monomers are incorporated in a random
fashion. This is generally the case for ethylene vinyl acetate, ethylene/acrylate and some
other commercial ethylene polar monomer pairs in the typical temperature/pressure
regimes used in commercial free radical copolymerizations.
Among commercial polar monomer copolymers with differing comonomers there
is broad variability in the molecular weights, PDI's, branch content and identity, and
sequence distributions. Model copolymers with less variable microstructure should
greatly ease the evaluation of structure/property relationships. The preparation of such
models will be described in this chapter.
“The term ‘model polymers’ in its modern meaning now refers to samples with
often complex architectures in which fluctuations in size, structure, composition, or
functionalization are minimal.” 83 A polymer chemist, mindful of the limitations of
modern synthetic chemistry, penned this definition including the key word “minimal”.
The production of model polymers requires 1) a mechanistic route that is free of
competing chemistry and is long lived, 2) each and every monomer unit must be
incorporated in precisely the same fashion, and 3) reaction must be site-specific in that
intended spectator functionality in the monomer remains as such. In short, only one
mechanistic event may occur.
Typical routes used to prepare model polymers include living chain
polymerizations utilizing ionic, radical, and group transfer chain techniques which have
been optimized to limit chain transfer, termination, and other side reactions to maximize
control of the primary structure. These modifications have allowed the construction of
polymers with narrow polydispersity and of block copolymers with relatively uniform
block lengths. However, it must be noted that even for polymers with perfect
microstructure and extremely narrow polydispersity, PDI < 1.03, one has but to observe a
MALDI spectrum to recognize that the products are still chemical mixtures of
The synthesis of discrete macromolecules has only been achieved by stepwise
synthesis where the building blocks are connected one at a time and the resulting product
is isolated and purified after each connection. 88 Now prolific examples of this repetitive
approach to macromolecular engineering are the three dimensional dendrimers. 86 This
repetitive approach has been utilized to prepare discrete polyalkenamers (Figure 5.3)
identical in repeat structure to polydisperse samples which might be prepared through the
ADMET or ROMP of 1 , 1 3-tetradecadiene and cyclododecene, respectively. The “dimer”
is prepared by Wittig reaction after which the product is isolated and divided into two
portions. One portion is hydrolyzed to the aldehyde and the other is converted to the
Wittig salt. These may be reacted together and the sequence of events is repeated, each
time doubling the degree of polymerization.
Figure 5-3. Repetitive approach to synthesis of polyalkenamers.
Preparation of Model Polymers via Metathesis
For the purposes here, the definition for model polymers provided at the
beginning of the previous section shall be modified. These shall include polymers
synthesized by alternate methods to obtain a primary structure similar to existing
polymers but greater chemical homogeneity than is obtainable by traditional means.
Vinyl Acetate/butadiene/ethylene terpolymer
Figure 5-4. Synthesis of model polybutadiene and butadiene copolymers.
A few examples, illustrated in Figure 5-4, serve to demonstrate the utility of
metathesis polymerizations in preparing models for polybutadiene and its copolymers.
Purely linear, branch-free polybutadiene with 100% 1,4 microstructure may be prepared
by the ADMET of 1 ,5-hexadiene or the ROMP of cyclobutene, 1,5-cyclooctadiene, 1,5,9-
cyclododecatriene, etc. Polymerization of monomers with a greater number of methylene
spacers between the double bonds produces models for sequence-ordered copolymers of
ethylene and butadiene where the exact frequency of unsaturated sites (butadiene repeat
unit) is governed by the number of methylene spacers in the monomer. A strictly
alternating butadiene isoprene copolymer has also been prepared in this manner as
shown in Figure 5-4. It must be noted that due to the unsymmetrical nature of the
monomer, the isoprene units may be incorporated in 1,4 or 4,1 fashion; the methyl
substituent may be in the 2 or 3 position of the isoprene unit. In an analogous example
utilizing ROMP, Hillmyer 61 prepared a model butadiene, ethylene, vinyl acetate
terpolymer by the ROMP of 5-acetoxy cyclooctene. In both of the last two examples, the
number of carbons separating the carbon with a pendant substituent varies between 6, 7,
and 8. This introduces the important caveat that the production of polymers by these
methods with perfect repeating sequences requires the use of symmetric monomers.
Model Polymers via Metathesis Polymerization and Hydrogenation
The only variable in the repeat structure of ADMET homopolymers is the
cis/trans ratio of the backbone olefinic bonds. Coupling of ADMET polymerization with
a clean, quantitative olefin hydrogenation technique constitutes a viable synthetic method
to produce polymers with perfect repeating sequences. This was first demonstrated 89
whereby polyoctenamer was fully saturated utilizing stoichiometric diimide reduction to
a perfectly linear, branch-free model for the largest volume industrial polymer,
polyethylene (Figure 5-5). The key to this successful, clean hydrogenation was the
addition of a bulky amine base, tripropyl amine, to prevent side reactions induced by a
known side product, p-toluene sulfonic acid. A polyethylene with narrow polydispersity
was later produced 90 by hydrogenation of a polybutadiene obtained via the ROMP of
TsNHNH 2 , Pr 3 N
Figure 5-5. Production of perfectly linear polyethylene via ADMET/hydrogenation.
This method was later extended to prepare models to study branching in
polyethylene. 51 Symmetrical dienes like that shown in Figure 5-6 were condensed by
ADMET and then hydrogenated by the diimide reduction. The microstructure of the
resulting polymers is essentially the same as polyethylene with regularly spaced methyl
branches, where precision in the sequence distribution of methyl substituents is granted
by the nature of the ADMET reaction. The frequency of the methyl branches is
prescribed by the value of “n” which may easily be varied during monomer synthesis.
These polymers and others like them may serve as useful models to study polymer
crystallization, as more in depth studies follow.
Figure 5-6. The synthesis of model “polyethylene” with regular methyl branches.
Similar polymers have been prepared via hydrogenation of alternating
butadiene/a-olefin copolymers obtained by Ziegler-type polymerization. 91 While the
frequency and chemical identity of branching is highly controlled, the only possible
frequency of branching is one branch on every 5 lh carbon. Attempts to prepare models
with lower counit frequency by chain techniques results in random placement. This
introduces a second important caveat in these modeling studies: Model polymers with
“long ” linear aliphatic segments of precise lengths are most conveniently prepared by
condensation chemisty. Further, ADMET condensation chemistry is perhaps currently
the most general method, allowing the macromolecular engineer to dictate the precise
length of the hydrocarbon segment as well as the incorporation of a broad range of
functionality into the backbone or as pendant groups.
A simple retrosynthetic analysis (Figure 5-7) of the generic model polymer
teaches this point. The target polymers have repeat units with precisely defined aliphatic
segments separated by functional groups “Z”. Utilizing classical polycondensation
chemistry the polymer can be prepared from the bifunctional monomers shown where
“X” and “Y” are reactive functional groups which condense to form the desired
functionality “Z”. This approach will be sufficient for polymers such as polyesters (Z =
C0 2 ; X, Y = C0 2 H, OH) where the associated chemistry has been well delineated and
applied commercially for many years. Due to the relation between conversion and M n
in condensation chemistry, the types of functionality “Z” that may be substituted for ester
is limited to only those groups that may be constructed in very high yield.
To illustrate the value of the ADMET/hydrogenation approach in preparing these
type models, we need only to attempt to design a synthetic route for the same type
polymer but substitute any functional group “Z” for which polycondensation chemistry
has not been proven so effective. For example, should it be desired to prepare a polyether
(Z = oxygen), low molecular weight oligomers might be produced by reaction of a long
chain dialkoxide (X = OLi) with a dihalide(Y = Br), but the limiting yields of this
reaction would not allow production of high molecular weight polymers.
m = (n/2) -1
Figure 5-7. Classic condensation chemistry versus ADMET/hydrogenation to prepare
model polymers with long, defined aliphatic segments.
Instead, the ether moiety could be incorporated into a long chain diene by the
Williamson ether synthesis and then this monomer condensed to high molecular weight
by ADMET; hydrogenation then provides the desired polyether. Regardless of the
identity of Z, the polymerization proceeds to high conversion, provided that Z is
compatible with the metathesis catalyst. This approach should be quite general as
ADMET chemistry has been proven effective for the polymerization of dienes containing
a wide variety of functionality. 36 Some examples of polymers prepared by
ADMET/hydrogenation are shown in Figure 5-8.
Poly( p-phenylene octylenef 6 Ethylene/ethylene oxide blocks 41 ' 49 Polyalcohol 50
Figure 5-8. Examples of model polymers produced by ADMET/hydrogenation.
Design and Synthesis of Symmetrical Diene Monomers
for Ethylene/Polar Monomer Model Polymers
The preparation of ADMET model ethylene/polar monomer copolymers hinges
on the availability of highly pure dienes with relevant functionality. A series of
symmetrical dienes with central pendant functionality were prepared with varied
functionality and number of methylene spacers separating the functionality from the
olefin groups. These were obtained in sufficient purity that contaminants could not be
detected by NMR, GC, and HPLC.
Central starting materials in nearly all synthetic schemes used to prepare ADMET
monomers have been co-alkenyl bromides. They are versatile reagents in that they can
serve as alkylating agents (electrophiles) and as nucleophiles when converted to Grignard
reagents allowing for the synthesis of a broad range of dienes. These starting materials
are commercially available with varied number of spacers between the terminal alkene
and bromo functionality. In all previous ADMET studies, it was not the focus to prepare
polymers with “very long” aliphatic segments. However, as the target polymers reported
here are to have long aliphatic segments it was necessary to prepare longer dienes,
through chain extension of commercially available co-alkenyl materials. Decenyl and
undecenyl bromide are the longest commercially available starting materials but were
found to be contaminated by regioisomers (internal olefin) which could not be removed
in a practical manner. The consequence of using these starting materials would be
unsymmetrical placement of the double bonds about the central pendant group of the
diene monomers and consequently irregularity in the periodicity of the polymer.
Commercially available synthons for these starting materials are decenol,
undecenol, and undecenoic acid, which are free of detectable regioisomeric impurities.
Many means are available in the literature for the conversion of alcohols to bromides
however a mild method must be chosen here to avoid reaction with the terminal olefin.
The least expensive and simplest techniques, utilizing PL n /Br 2 , PBr n , or HBr as the Br
source can result in the unwanted side reactions of hydrobromination and bromination of
the terminal olefin. The co-unsaturated alcohols may easily be converted to the bromide
by either of two very mild methods, both in good to excellent yields, as shown in Figure
5-9. In the first method, the alcohol is tosylated and then converted to the bromide after
only simple aqueous workup without the need for further purification. The second
method utilizing PPh 3 /CBr 4 achieves the conversion in comparable yields in one step.
Both reactions are highly atom-inefficient but are facile and typically afford the bromides
in high isolated yield and purity after distillation.
Figure 5-9. Syntheses of co-unsaturated carboxylic acids and bromides, a: Ph 2 P,CBr 4 . b:
LAH. c: TsCl, pyr. d: LiBr, acetone, e: ®Mg, ®C0 2 .f : ®Mg, ® CuCl, (3-
These alkenyl bromides were chain-extended by reaction of their Grignard salts
with C0 2 or (3-propiolactone. In the second case, the addition of catalytic Cu(I) favors
nucleophilic attack at the methylene adjacent to the ring oxygen over attack at the
carbonyl carbon. These synthetic fatty acids may not be purified on a large scale by the
classical method of extraction into basic aqueous solution as they are of sufficient length
to act as surfactants producing intractable emulsions under typical isolation conditions.
They instead are purified by distillation or flash chromatography. These acids were
reduced to the alcohols with excess LAH and then converted to the corresponding chain-
extended bromides via the tosylate as above. Conversion of the bromides to the chain
extended alcohols, transforms e + b or f+ b in Figure 5-8, could also each be achieved in
one step by substituting formaldehyde and oxirane, respectively, for C0 2 and (3-
propiolactone. However, the co-unsaturated acids are useful starting materials for
preparing additional dienes as will be discussed later.
Synthesis of Acetoxy-Functional Monomers
A series of symmetrical dienes with central pendant acetoxy groups (Figure 5-10)
was synthesized with the goal of preparing model ethylene/vinyl acetate copolymers.
The shortest acetate-functional diene ( 5.12 , n=8) was prepared by a four-step procedure,
due to the very low cost of starting material, and the ease of the steps. The first three
steps were conducted with aqueous extraction as the only workup. The secondary
alcohol was purified by flash chromatography as acetylation without prior purification
produced a mixture with impurities that could not be practically separated from the target
acetate monomer. The remaining secondary alcohols (n = 9, 10 and 12) were prepared in
good yields in one step via reaction of in situ formed alkenyl Grignard reagents with
methyl formate, after which acetylation provided the desired monomers.
5Ji 8 = n
Figure 5-10. Syntheses of diene monomers with central pendant acetoxy groups, a: 0.5
eq KH. b : LiCl, DMSO, H 2 0, A. c: LAH. d: ®Mg, ©0.5 eq HC0 2 Me. e:
AcCl or Ac 2 0, pyr.
5.12 8 = n
Chloro- and Phenyl-Substituted Dienes
Intermediates shown in Figure 5-10 were also converted to symmetrical dienes
with central pendant chloro and phenyl substituents (Figure 5-11) from which
ethylene/vinyl chloride and ethylene/styrene model copolymers may be prepared. The
reported mildest method for converting alcohols to chlorides is a variation of the
Mitsunobu reaction, utilizing PPh 3 , DEAD and ZnCE where the nucleophile is chloride
ion supplied by the zinc salt. Multiple attempts to prepare the chloride monomer 5.16
by this route proved to be low-yielding (< 40% crude yield). Combination of the
products from each of the reactions yielded a practical quantity of crude monomer (~lg).
However, an impurity was present in detectable (GC, NMR) amount which proved
difficult to separate even by HPLC. The combination of excess Ph 3 P in refluxing CCI4
did however prove effective in converting the secondary alcohol to the chloride in good
yield. Some elimination was apparent in the ’H NMR spectrum (small broad multiplet
near 5.4 ppm) of the crude product but, surprisingly, the eliminated product could be
separated and the pure chloride (100% GC) was obtained after simple flash
Dienes substituted by a phenyl ring can be used to prepare model ethylene/styrene
copolymers. To this end a phenyl-substituted monomer was easily obtained from the
ketone diene ( 5 . 7 ) also shown in Figure 5-11. The phenyl ring is attached via
nucleophilic attack by phenyl lithium on the carbonyl carbon and the resulting benzylic
alkoxide is deoxygenated in situ under Birch reduction-like conditions. 93
Ph 3 P,CCI 4
2) NH 3 , XSLi
3) NH 4 CI
Figure 5-11. Preparation of chloro- and phenyl-substituted dienes.
Monomers with Pendant Alkoxy-Carbonyl Moieties
Dienes with central pendant alkoxy-carbonyl groups (Figure 5-12) were
synthesized as monomers for model ethylene/acrylate copolymers. One of the most
useful organic transforms for constructing carbon skeletons of this type is the dialkylation
of enolate ions with alkyl halides. This method has previously been shown to be
effective in the synthesis of symmetrical diene intermediates for use as ADMET
monomers. 51 This route, was exploited to prepare the methyl substituted dienes (Figure
5-5) discussed earlier in this chapter. The diene skeleton is constructed by twice
alkylating the enolate of ethyl acetoacetate, generated in situ by deprotonation with t-
butoxide base. Deacylation by simple retro-Claisen reaction yields the desired ester-
functionalized dienes like the target monomers shown in Figure 5-12. To convert to
other esters (different R), would simply require trans-esterification or the use of a
different starting acetoacetate ester.
Review of the literature indicated that this process for constructing the diene
skeleton would not be effective for producing the desired larger dienes as dialkylation of
[3-keto esters with very long alkyl halides has been shown 94 to be a very low yielding
reaction. As an alternative, previous researchers turned to the dianions of carboxylic
acids as carbon nucleophiles. These may be generated by reaction of a carboxylic acid.
with a-hydrogens, with two equivalents of LDA at 0° > T > -15°C and are stable in THF
solution even at 50°C for several hours. 95 Their use is not complicated by Claisen
condensation type reactions, multiple sites for C-alkylation, and very low temperatures
are not required for their generation or alkylation.
1 ) 2 LDA, -1 5°C
n+1 2 )
Methyl methacrylate-like functionality
1) 2 LDA, -15°C
C0 2 H
C0 2 H
K 2 C0 3 , Rl
2) XS Mel
K 2 C0 3i Mel
1) 2 LDA, -15°C
0 1) 2 LDA, -15°C
C0 2 H
C0 2 R
5^20 n=8, R=Me
L21 n=8, R=Et
5^22 n=10, R=Me
Figure 5-12. Synthesis of dienes with pendant alkoxycarbonyl functionality.
The needed long chain co-unsaturated carboxylic acids were available in our
laboratories, as they are intermediates in the synthesis of alkenyl bromides described
earlier in this chapter (Figure 5-9). The synthetic scheme for preparing ester-
functionalized dienes is outlined in Figure 5-12. Construction of the diene skeleton
proved to be high yielding and the products are easily purified by simple flash
chromatography. The acid groups of these dienes were O-alkylated in near quantitative
yields by base promoted esterification with excess methyl or ethyl iodide, which has been
shown in the literature to be a particularly effective method for sterically hindered
esters. 96 Classic Fischer esterification with sulfuric acid catalysis was not utilized due to
the susceptibility of the olefinic groups to acid-catalyzed hydration or isomerization.
The acid dienes may also be alkylated at the a-position, via the same enolate
chemistry, producing monomers with methacrylic acid-like functionality. It was
reported 96 that trisubstituted acids, produced by alkylation of the enolates of disubstituted
acids, could be easily purified by simple aqueous extraction. That is, the starting material
could be separated from the product by simple preferential extraction of the disubstituted
acid into basic aqueous solution. Hoping to capitalize on this presumed facile method,
the acid diene 5.18 was methylated in the a-position. However, the starting material and
the product, 5.23 , could not be separated as described by aqueous extraction. As
expected due to the very small structural difference between the starting material and the
product, 5.23 could not be adequately purified by practical techniques. Only after
repeated small-scale HPLC purification could a satisfactory sample be obtained. A more
fascile approach to 5.23 involves twice alkylating the enolate of propionic acid with 9-
decenyl bromide. The much larger disparity in molar mass and polarity of the starting
materials and product greatly eased purification. Base-promoted O-alkylation of 5.23
then affords the desired precursor with methyl methacrylate-like functionality. The
polymer which results from this monomer is yet to be prepared.
An unsymmetrical acid-functional diene, 5.26 , was constructed by this method
and then deoxygenated to the corresponding methyl-substituted monomer, 5.27 , for
comparison with its symmetrical counterpart prepared previously and to be published
Propylene-like functionality (unsymmetrical)
1) 2 LDA, -15°C
2) > Br
'7 ' '9
Figure 5-13. Synthesis of unsymmetrical methyl substituted monomer.
Preparation and Characterization of ADMET
Ethylene/Polar Monomer Copolymers
Each of the model polymers was prepared by the one-pot homogeneous
ADMET/heterogeneous hydrogenation process described in Chapter 4. The only
exception, a model ethylene/vinyl chloride copolymer, required the use of a different
hydrogenation system to be discussed later. Monomer and catalyst (400: 1 ) were
combined inside an argon-purged dry box and the reaction was then conducted at 45-
65°C (48hrs) under reduced pressure utilizing schlenk line techniques. The resulting
unsaturated polymers were combined with silica (100 times the weight of ruthenium
catalyst) and olefin hydrogenation was conducted in toluene at 90°C under 120 psig H 2
for 24 hours to insure maximum reduction. The catalyst residue/silica composite was
filtered from solution and the solvent evaporated under reduced pressure to yield the
colorless, viscous or white solid polymers in virtually quantitative yield. The samples
were not reprecipitated except where noted. Molecular weights as measured by GPC
versus polystyrene standards consistently fell within the range 2 - 5 x 10 4 g/mol with
PDI's - 2.
ADMET Ethylene/Vinyl Acetate Model Copolymers
Ethylene/vinyl acetate (EVA) copolymers constitute the world’s largest volume
ethylene copolymer, due in no small part to the technical significance of the post-
polymerization hydrolysis to ethylene vinyl alcohol copolymers.' They are prepared by
the traditional free-radical techniques employed for low-density polyethylene. This is a
special case of an ideal copolymerization, termed Bernoullian, where the reactivity ratio
product rir 2 = 1.0 and ri = r 2 = 1.0. Monomer incorporation is truly random and the
copolymer constitution is the same as the feed ratio, allowing the preparation of EVA’s
with a broad range of compositions. The ready availability of EVA's with varying VA
content has made this copolymer system the most ideal available one for studying
copolymer composition/property and morphology relationships and as a result much
physical data has accumulated for these copolymers. 97 The abundance of physical data
concerning random EVA's should prove most useful for later comparison with the model
periodic ADMET EVA's reported here.
A series of ADMET EVA's was prepared with pendant acetate groups separated
by 18, 20, 22, and 26 backbone carbons. The latter 3 polymers yield tough films and
fibers from solution and from the melt and optically transparent or translucent articles
may be obtained from the melt.
Figure 5-14. 'H NMR spectra for P5.12 and HP5.12 ,
220 200 180 160 140 120 100 80 60 40 20 0 ppm
Figure 5-15. I3 C NMR spectra for P5.12 and HP5.12 .
The ‘H and l3 C NMR spectra for P5.12 and HP5.12 are shown in Figures 5-14
and 5-15. Examination of the olefin regions indicates that the method for hydrogenation
is exhaustive as indicated by complete disappearance of signals at -5.3-5. 4 ppm ('H) and
at -130 ppm ( I3 C). The diminutive 'H signals at 4.9 and 5.8 ppm (terminal vinyl groups
of unsaturated polymer) and at 0.8 ppm (corresponding methyl end groups of saturated
polymer) indicate high molecular weight. Hydrogenation greatly simpliflies the 13 C
spectrum as a result of the degeneration of chemical environments distal to the acetate
group. All spectra for the remaining EVA models are identical, regardless of ethylene
run length, aside from changes in the ‘H integrals corresponding to decreasing acetate
The pattern of peaks in the 13 C spectra of the model EVA is characteristic of all
the model polymers regardless of the pendant functionality. In addition to peaks
attributed to the pendant group and the methine carbon, the only other peaks are a
partially resolved cluster of peaks at - 30 ppm ("f" in Figure 5-15) and signals slightly
downfield and upfield relative to "f" for the carbons a and (3, respectively, to the methine
carbon. The cluster of peaks "f" may be partially resolved to 3-5 peaks and corresponds
to backbone carbons (polyethylene segments) more than twice removed from the methine
carbon. The GPC traces of P5.12 and HP5.12 are overlaid in Figure 5-16 to illustrate
constancy in retention time and polydispersity. The unchanged PDI suggests the absence
of any reactions such as chain scission or other means of molecular weight reduction
during hydrogenation. The fact that the retention time remains the same is not conclusive
evidence that DP is unaffected, only that hydrodynamic volume is similar. It might
however be expected that the conversion of isolated double bonds, separated by long
flexible segments to single bonds would not drastically affect hydrodynamic properties.
Should this assumption hold, then it can also be assumed that identical M p from GPC
truly indicates unchanged DP. Also of note, PDI for all of these polymers will remain ~2
as opposed to much broader and variable PDI's (3 - 7) for commercial EVA’s.
Figure 5-16. GPC traces for P5.12 and HP5.12 . M n = 4 x 10 4 g/mol, PDI = 1.8.
Thermal Analysis of EVA Model Copolymers
The physical properties of EVA copolymers can be tailored by varying the VA
content to fit applications as diverse as hot melt adhesives, packaging films, and rubbery
toys. Melting point depression upon inclusion of a noncrystallizable repeat unit into a
crystallizable backbone is a general phenomenon and EVA copolymers are no exception,
where the degree of depression is proportional to the comonomer content.
This phenomenon was treated theoretically by Flory 98 and described by the well-
known Equation 5-2. The equation describes the observed melting point ( T m ) as a
function of the mole fraction of noncrystallizable groups (Xb) where T° is the theoretical
maximum melting point of the crystalline homopolymer and A H° is the heat of fusion
per crystallizable repeat unit. While this equation adequately describes the generally
observed trends in melting point depression, it underestimates the magnitude of
depression due to oversimplifying assumptions." Among other things, the theory
assumes crystals of infinite dimensions, ignores the chemical identity of the non-
crystallizable unit, and assumes crystallization of very short segments. Subsequent
revisions of the theory provide closer fit to experimental data but these versions still fall
A Hi h
Not surprisingly, the same trend in T m (DSC) with increasing VA content was
observed with these model EVA polymers. As expected, each of the polymers displayed
narrow melting transitions relative to commercial EVA’s due to greater chemical
homogeneity. Typical DSC heating traces, with varying thermal pretreatment are shown
in Figure 5-17 along with a trace reported elsewhere for a commercial EVA (28% VA
wt/wt, not to scale); overlaid to demonstrate the stark contrast in melting behavior. The
melting transition for this polymer spans 50°C, typical of semicrystalline random
copolymers indicating a broad range of crystalline morphologies ascribed to chemical
/ Commercial EVA (28 wt % VA) \
Figure 5-17. Annealing studies for HP5.13 (24.4 wt % VA). Annealing conditions are
indicated above each trace.
The samples were heated to 100°C to erase thermal history and then scanned at
5°C/min, cooling cycle first, to locate thermal transitions. On the cooling cycle, all
polymers displayed a first order, sharp exotherm, generally spanning <15°C. On the
heating cycle, a broader endotherm with a shoulder on the high temperature side was
observed (bottom curve, Figure 5-17). The difference between the peak temperatures for
the two major transitions, assigned as T c and T m respectively, was < 20°C. The onset of
the T m is unclear due to observed premelting indicated by the slope of the baseline
leading up to the peak, which may induce error in the measured values for AH m .
Annealing was found to affect the positions and shapes of the melting endotherms
in typical fashion 101 (Figure 5-17). Samples were isothermally crystallized from the melt
at various temperatures (T a ) below T m , cooled to 15°C and then scanned at 5°C/min.
Some observations regarding the effect of annealing are:
• Peak T m and AH,„ increase with increasing T a and the peak sharpens.
• Baseline preceding T m changes (dotted lines included to aid visualization).
• For T a = 34°C, AFI„,decreases and broad endotherm below T a appears.
While interpretation of thermal analyses such as these in relation to polymer
morphology without corroboration with other techniques (e.g., X-ray, microscopy, etc.)
can be perilous, some general statements are in order. Annealing between T m and T c
provides energy to allow amorphous polymer to organize into crystals, allows crystals to
organize into larger crystals, and allows defective crystals to become more perfect. The
outcome is generally an increase in T m and/or AH m as seen in the results above. The
slope of the baseline preceding T m for the unannealed sample may be the result of
melting (possibly with simultaneous recrystallization) of a population of smaller or less
perfect crystals formed during the thermal scan. In the annealed samples, a greater
percentage of this population has most likely been more highly organized and melts at the
higher temperature. Annealing at T a =34°C shifts the T m to a still higher value but
provides enough thermal energy to maintain more of the polymer in the liquid state.
Poorly formed crystals can then arise during the cooling prior to scanning and these
crystals may give rise to the broad exotherm preceding the higher temperature, narrow
Figure 5-18. DSC trace of HP5.15 with endotherm prior to T m on heating indicating
cold-crystallization, a: Annealed from the melt (49°C, 5 hrs)
The DSC trace for HP5.15 reveals thermal behavior not observed with any other
polymer reported in this dissertation (Figure 5-18). The endothermic peak on the heating
cycle just prior to the T m indicates cold crystallization. This phenomenon, first
theoretically treated by Wunderlich. 102 is most effectively observed after a crystalline
polymer is quenched from above T m to below T g , minimizing crystallization. On heating
to a given temperature between T m and T g , crystallization ensues. The rate of
crystallization for HP5.15 may be significantly slower than for the other EVA's,
diminishing the effective crystallization which occurs during the cooling scan. On the
subsequent heating cycle, more of the amorphous material then crystallizes rapidly just
below T ra . Annealing just below T m as before for the other polymers all but eliminates
the sharp endotherm in the subsequent heating scan.
The melting points (unannealed) of the polymers are plotted versus weight % VA
together with the values reported 103 for the commercially available Elvax® series (Figure
5-19). Like the commercial resins, the relationship is linear (R 2 = 0.99) in the region
studied. The values are consistently lower for the model polymers and the absolute value
for the slope is approximately 3 times that of the commercial resins. It is interesting to
note the relationship between the values of the y-intercepts, corresponding to 0%VA.
The intercept for the commercial resins is 1 14°C which is very close to the reported T m =
110°C for the parent low density polyethylene prepared under the same conditions.
Although it may be purely coincidental, the intercept for the model EVA’s (145.6°C) is
almost exactly the same as the theoretical value for perfectly linear
polyethylene( 145. 5°C).
Figure 5-19. Plot of T m vs. weight % VA. ▲ ADMET EVA copolymers (5°C/min).
OElvax® series commercial EVA (10°C/min) 103 .
Upon heating to approximately 300°C, acetic acid is thermally eliminated from
the polymer backbone and this is the source of the upper limit for processing and end use
temperatures of commercial EVA's. Measurement of weight loss due to this reaction by
TGA has been shown to be a useful technique for measuring the acetate content of EVA
copolymers. 104 A representative TGA plot (HP5.12 ) is shown in Figure 5-20 together
with the tabulated predicted and measured % weight loss due to thermal elimination of
acetic acid for each polymer. The transition between the weight loss due to thermal
elimination of AcOH and the onset of further decomposition was not seen as a distinct
plateau nor did it occur at the exactly same temperature for each run. The end of the first
step was taken as the inflection point “A” (Figure 5-20) digitally calculated for each plot.
Average values for each of the model EVA's are tabulated showing good correlation
between the measured acetate content and that calculated from the known repeat unit.
Wt % AcOH
18.7 +/- 0.3
17.1 +/- 0.5
15.7 +/- 1.0
14.1 +/- 0.3
Figure 5-20. TGA trace for HP5.12 showing typical two-stage weight loss. Values
reported for AY are average of 3 runs.
ADMET Ethylene/Alkyl Acrylate Copolymers
Commercial ethylene/methyl acrylate (EMA) copolymers generally contain
approximately 20 weight % methyl acrylate. 37 The monomer reactivity ratios for methyl
acrylate and ethylene differ substantially (ri=ll, r 2 = 0.2, Mi = methyl acrylate)
compared to the EVA system(ri=l .02, r 2 =0.97, M, = vinyl acetate) at 60°C. A plot of
copolymer composition (Fi) vs feed composition (fj) using these values for both systems
is shown in Figure 5-21. The high initial slope of the line for EMA indicates that very
small changes in feed ratio have a significant effect on copolymer composition in the
range of copolymer composition (10-40 weight % comonomer) typical for useful
properties in EVA. In this range, a change of 1% in f) results in approximately 5%
change in F(.
EMA’s exhibit similar physical properties to EVA’s which is not surprising
considering that the pendant groups in the polar repeat units are merely isomers, differing
only in the orientation of the ester group. Technical bulletins put forth by Chevron make
numerous comparisons between their EMAC® series of ethylene/methyl acrylate
copolymers with commercial EVA copolymers. Reported melting points for the
EMAC® resins are within 10°C of the analogous EVA (Elvax®, DuPont) resins with
approximately the same weight percent comonomer.
The DSC heating curves for HP5.20 are HP5.22 are shown in Figure 5-22 along
with the analogous ADMET EVA’s for comparison. In agreement with the commercial
relatives, DSC thermal data for the ADMET EVA’s and EMA’s do not show drastic
differences in peak melting temperatures. However, distinction is seen in the shape of the
endotherms where the EMA peaks appear narrower and do not exhibit a high temperature
shoulder as seen in the latter.
Figure 5-21. Dependence of copolymer composition (F|) on comonomer feed
composition (fi) for EMA and EVA.
Without corroborative evidence, we can only speculate at this point as to the
cause of this difference. While no attempts were made to measure second order
transitions here, it has been shown that commercial EVA’s and EMA’s exhibit
significantly different second order transitions attributed to flexible side-group
reorientation. Numerous studies, empirical 101 and theoretical , 106 reach the general
consensus that the cause is greater hindrance of rotation of the pendant ester group of MA
relative to VA repeat units about the bond by which each is attached to the main chain.
0 10 20 30 40 50 60
Temperature ( °C)
Figure 5-22. DSC heating curves for ADMET EMA’s and EVA’s (2 nd scan 5°C/min)
Comparison of representative partial 'H NMR spectra (Figure 5-23) of the EVA
and EMA models in the region of the methine protons reveals the differing chemical
environments exerted by the two groups on the proximal backbone atoms. The methine
proton of the EVA gives rise to the expected pentet due to splitting by four equivalent
geminal protons. However, in the case of the EMA, these four protons are not equivalent
due to anisotropy induced by the attached carbonyl, supporting theoretical calculations
indicating greater hindrance to rotation. Perhaps the differing mobilities of these two
pendant groups affects crystal packing in these periodic polymers giving rise to the
observed differences in melting behavior.
4.80 4.70 PPm 2.50 2.40
2.20 2.10 PPm
Figure 5-23. Partial 'H NMR spectra of ADMET EVA and EMA showing differing
multiplicities of methine proton signals.
A significant difference exists between the thermal stabilities of commercial
EVA’s and EMA’s, with important technical implications, where the lower thermal
stability of the former limit their maximum processing temperatures to 232°C, nearly
100°C lower than for the latter. TGA measurements bear out the expected higher thermal
stability of the ADMET EMA’s with Tj (10% Wt loss) = 445°C, and with an onset
approximately 100°C greater than for the EVA’s.
The larger ethoxycarbonyl group of HP5.21 (ethylene/ethyl acrylate, EEA) causes
a significant change in the profile of the DSC melting endotherm (Figure 5-24) relative to
the analogous EMA. Two maxima are seen and the position of the higher temperature
maxima is within 1°C of the peak seen for the analogous EMA model. Annealing at
3°C(lhour) shifts the lower temperature maxima by nearly 4°C toward the higher
temperature peak, creating greater overlap and eliminating visible premelting as
evidenced by flattening of the slope of the baseline prior to the endotherm. It might be
assumed that incorporation of the larger ethoxy carbonyl group into some type of ordered
array is more difficult than the smaller methoxy carbonyl. Although based solely on
speculation, the observed melting behavior of the EEA and EMA might suggest that
similar morphologies are formed in both with more of a less perfect phase in the EEA
giving rise to the lower temperature peak. Annealing just below this lower temperature
peak shifts it to higher temperature possibly indicating crystal perfection toward that
giving rise to the higher temperature peak.
Figure 5-24. DSC heating traces for ADMET EMA( HP5.20 ) and EEA( HP5,21) .
A: EEA, B: EEA annealed 3°C(1 hr), C: EMA.
ADMET Ethylene/Styrene Model Copolymer
Due to the extremely high reactivity of styrene relative to ethylene, copolymers
with even moderate levels of ethylene incorporation are unattainable by free-radical
copolymerization. Alternately, traditional Ziegler-Natta copolymerization of ethylene
and styrene typically produced polymers which contain less than 1% styrene. 107 Recent
reports disclose the use of homogeneous half-sandwich and metallocene catalysts,
activated by MAO, to successfully prepare ethylene/styrene copolymers with varied
levels of styrene content. 108
In order to compare the effect of a regularly spaced phenyl group on
crystallization, an ADMET ethylene/styrene copolymer ( HP5.17 ) was prepared. Much
larger melting point depression is seen relative to the analogous EVA copolymer with 18
carbons between pendant groups. Figure 5-25 shows the DSC heating trace with two
broad but apparently separate endotherms with low AH relative to other polymers.
Annealing for 5 hours between the two peaks resulted in a relatively broad peak at
approximately -6°C with several maxima following the peak temperature. The obvious
assumption in this case is that the greater steric bulk of the phenyl ring has a drastic effect
on the packing behavior of the polymer chains.
Figure 5-25. DSC traces for ADMET E/STY ( HP5.17)
ADMET Ethylene/Vinyl Chloride Copolymer
Chlorinated polyethylene (CPE) may be prepared from polyethylene via various
chlorination techniques resulting in polymers with are formally ethylene/vinyl chloride
(EVC) copolymers. 109 These materials have significant technical possibilities and have
proven convenient subjects for microstructure/morphology studies. 110 In particular,
morphological studies have been aimed at determining whether the chloride groups are
included into crystal lattices as defects or excluded in amorphous regions. In an elegant
study by Wegner, 1 ll)J EVC's were prepared by several chlorination techniques from PE
and partially hydrogenated polyoctenamers. The different methods produced polymers
with varying incorporation of isolated and vicinal chloro substituents. X-ray studies in
concert with DSC measurements indicated that the chloro groups were incorporated as
defects in the crystals. As the chloride content of the polymers increased, the lateral
dimensions of the unit cell were shown to increase relative to the unit cell of pure
polyethylene. Polymers with vicinal chloro groups showed greater melting point
depression as a result of the larger defects. Alternately, EVC's with a broad range of
chlorine content have also been prepared by partial reduction of PVC with trialkyl tin
hydrides and similar results were obtained from X-Ray and DSC measurements. 1 IOc
The DSC melting points of random EVC's were compared to analogous
ethylene/propylene (EP) copolymers as a function of counit content and the two data sets
fell on the same line. ll0b The researchers concluded that the melting behavior was the
same due to the similar size of the chloro and methyl groups. The smaller van der Waals
radius 111 of chloride(1.75 A) relative to methyl (2.0 A) may be offset somewhat by the
longer C-Cl bond length (1.78 A) relative to C-C(1.54 A).
In order to compare the effect of a periodic chloro group to the other pendant
groups in this study, an ADMET ethylene/vinyl chloride (EVC) copolymer was prepared.
The EVC could not be prepared by the one-pot method used for all the other polymers in
this study. While the ADMET reaction proceeded in high conversion utilizing the
ruthenium catalyst, the heterogeneous hydrogenation step never proceeded to greater
than 70% ('H NMR). It is postulated that the chloride acts in some fashion to poison the
heterogeneous hydrogenating species. However, hydrogenation over Pd/C at 5 atm H 2 in
toluene proved quantitative within spectroscopic detection limits. The reduction was
conducted at 40°C as the polymer begins to precipitate from room temperature toluene
during the course of the reaction as evidenced by the formation of gelatinous particles in
the mixture. Subsequent observations showed the final product to be poorly soluble in
toluene, benzene, methylene chloride, and 1,2-dichloroethane but freely soluble in
chloroform and THF at room temperature.
Based purely on steric arguments, a model ethylene/vinyl choride copolymer with
pendant chloride every 19 th carbon would be expected to have a higher melt than any of
the analogues reported here with the same ethylene run length. This was indeed found to
be the case as HP5.16 shows a T m = 77°C (AH m = 78 J/g). In stark contrast to the studies
involving random EVC and EP, llob the analogous ADMET EP polymer with a pendant
methyl every 19th carbon melts 21°C lower (Tm = 56°C) 51c than this ADMET EVC.
TGA shows stepwise weight loss due to thermal elimination of HC1 prior to
catastrophic decomposition. The elimination of HC1 occurs at a lower temperature than
for loss of AcOH from EVA, consistent with the relative stabilities of secondary alkyl
chorides and acetates. The measured weight loss due to elimination of HC1 (1 1.54 %) is
in reasonable agreement with that predicted from the known structure (12. 1 1 %).
100 200 300 400 500 600
Temperature ( °C )
Figure 5-26. TGA trace of HP5.16 , Onset for catastrophe decomposition = 445°C.
The method of homogeneous ADMET/heterogeneous hydrogenation has been
demonstrated as an effective and facile alternative to two step procedures for the
generation of models for ethylene polar monomer copolymers. The necessary dienes are
easily prepared by typical organic transforms whereby the type of substituent in the
polymers and their frequency in the backbone is regulated during the monomer synthesis.
Access to periodic polymers with much longer ethylene run lengths than previously
reported was made possible through the synthesis of homologated co-alkenyl bromides
and carboxylic acids used in the diene synthesis.
Comparison of polymer melting behavior of a series of polymers with identical
ethylene run lengths but differing pendant groups R, found correlation between the
degree of melting point depression and the steric bulk of R with the highest degree of
depression for R = phenyl and the lowest for R = Cl. The trend is graphically depicted in
Figure 5-27. In addition to precisely defined run lengths, all the model ethylene polar
monomer copolymers regardless of comonomer, have approximately the same molecular
weights and PDI's, decreasing the number of variables which must be considered for
adequate analysis of physical data. Enormous potential for obtaining deeper insight into
structure property relationships of commercial ethylene/polar mononomer copolymers via
more applied property studies of these models is at hand.
Figure 5-27. Peak melting temperatures of ADMET ethylene/polar monomer
copolymers as a function of chemical identity of the regular pendant
group. Value for R = Ph is the average of two observed peaks.
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Mark Deas Watson was born on February 23, 1969 in Pascagoula, Mississippi.
Shortly thereafter, he moved with his parents and five older siblings as they reestablished
residence in their hometown, Hattiesburg, MS. Upon graduation from Oak Grove High
School in 1987, he entered the University of Southern Mississippi enrolling in the
Department of Polymer Science. He conducted undergraduate research in various facets
of solution phase properties of surfactants and polymeric viscosity modifiers under the
guidance of Prof. Robert Y. Lochhead. He also participated in a cooperative education
program with Schering-Plough in Memphis, Tennessee where he spent three alternating
semesters in the Dr. Scholl’s Materials and Devices R & D. After receiving his B.S.
degree in August 1992, he remained at USM for one year conducting research in the
Shelby F. Thames group in the area of formulation and physical testing of adhesives and
coatings. He began his graduate studies in organic/polymer chemistry at the University
of Florida in August 1993 under the guidance of Professor Kenneth B. Wagener. During
a brief visit home in March 1996, he met his wife-to-be, Kim, whom he married in
August of the following year. Mark received his Ph.D. in May 1999, and began post-
doctoral research at the Max-Planck-Institut fur Polymerforschung in Mainz, Germany in
the research group of Prof. Dr. Klaus Mullen.
I certify that I have read this study and that in my opinion it conforms to acceptable
standards of scholarly presentation and is fully adequate, in scope and quality, as a
dissertation for the degree of Doctor of Philosophy.
1 /^C 0 IS)- ) —
Kenneth B. Wagener, Chairman '
Professor of Chemistry
I certify that I have read this study and that in my opinion it conforms to acceptable
standards of scholarly presentation and is fully adequate, in scope and quality, as a
I certify that I have read this study and that in my opinion it conforms to acceptable
standards of scholarly presentation and is fully adequate, in scope and quality, as a
dissertation for the degree of Doctor of Philosor
Randolph S. Dut&n
Associate Professor of Chemistry
I certify that I have read this study and that in my opinion it conforms to acceptable
standards of scholarly presentation and is fully adequate, in scope and quality, as a
dissertation for the degree of Doctor of Philosophy.
Kirk S. Schanze
Professor of Chemistry
I certify that I have read this study and that in my opinion it conforms to acceptable
standards of scholarly presentation and is fully adequate, in scope and quality, as a
dissertation for the degree of Doctor of Philosopf
Anthony B. btenrtan
Associate Professor of Materials
Science and Engineering
This dissertation was submitted to the Graduate Faculty of the Department of
Chemistry in the College of Liberal Arts and Sciences and to the Graduate School and
was accepted as partial fulfillment of the requirements for the degree of Doctor of
Dean, Graduate School