Acyclic diene metathesis, a new equilibrium step propagation, condensation polymerization

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Acyclic diene metathesis, a new equilibrium step propagation, condensation polymerization
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viii, 154 leaves : ill. ; 28 cm.
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Nel, Jan Geldenhuys, 1960-
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Metathesis   ( lcsh )
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Diolefins   ( lcsh )
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Thesis:
Thesis (Ph. D.)--University of Florida, 1989.
Bibliography:
Includes bibliographical references (leaves 146-153).
Statement of Responsibility:
by Jan Geldenhuys Nel.
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Typescript.
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Vita.

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Full Text










ACYCLIC DIENE METATHESIS, A NEW EQUILIBRIUM STEP PROPAGATION,
CONDENSATION POLYMERIZATION












By

JAN GELDENHUYS EL


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


1989


























Opgedra aan my huisgesin,
Pa-Jan, Ma-Beatrice,
Hanli, Basson en Clarissa Nel.










ACKNOWLEDGEMENTS


I wish to thank all the members of my supervisory committee:
Dr. K.B. Wagener, Dr. J.M. Boncella, Dr. R.C. Stoufer, Dr. W.R. Dolbier
and Dr. C.D. Batich.
Thanks go to all my past and present colleagues for their
support and friendship. The friendly, yet serious atmosphere of the
polymer floor has been wonderful; I'll remember it all my life.
Thanks also go to Mark Hillmyer and Joe Morelli for washing glass
and assisting me. Special thanks go to Lorraine Williams and Pat
Hargraves, our beloved secretaries, who were cheerful even on
deadline days. A word of acknowledgement goes to Dr. R. King for
NMR assistance and to Dr. D Powell for mass spectroscopy analysis.
I also thank Dr. R.P. Duttweiler and Dr. J.M. Boncella for preparing the
catalyst.
Special thanks are given to Rudy Strohschein and Dick Moshier
in the glass shop. Many an hour was spent mentally recovering by
sharing laughs and fishing. Thanks for teaching me the art and
beauty of glassblowing; I'll always love "gloo-blasting".
Words cannot express my gratitude to Lucy Kuykendall for her
patience and encouragement in preparing this manuscript. Thank you
very much for all the hours of typing over the weekends; it is deeply
appreciated.
Words fail me in expressing my gratitude towards Dr. Ken
Wagener. Thank you for your unselfish support and encouragement
throughout my studies. "Don't give up" will always be my motto.













TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS............................................................................... iii

A BST RA C T ..................................................................................................... vii

CHAPTER

1. INTRODUCTION

The Nature of Step Polymerization Chemistry................. 1
The Olefin Metathesis Reaction............................................ 5
Brief History of Olefin Metathesis.................................. 8
The Mechanism for Metathesis Chemistry........................ 11
Catalysts Used in Olefin Metathesis................................... 12
Ring Opening Metathesis Polymerization (ROMP)............ 13
Acyclic Diene Metathesis Polymerization (ADMET)........ 15


2. EXPERIMENTAL

General Inform ation.......................... ..... ............................. 18
High Vacuum and Schlenk Line Techniques...................... 1 9
Schlenk Vacuum Line Techniques................................. 1 9
High Vacuum Line Techniques............................................ 21
Purification of Monomers, Reagents and Solvents....... 24
Attempted Metathesis of Styrene Using a
Lewis Acid Containing Catalyst........................................ 26
Attempted Metathesis of Fluorinated Styrenes Using
a Lewis Acid Containing Catalyst System.................. 30
Preparation of Fluorinated Polystyrene Via
Anionic Polymerization Techniques............................. 31
Metathesis of Styrene Using a Lewis
Acid Free Catalyst.................................................. ........ 34
Metathesis of Fluorinated Styrenes
Using a Lewis Acid Free Catalyst.................................. 38








Metathesis of Substituted Styrenes
Using a Lewis Acid Free Catalyst................................... 40
Acyclic Diene Metathesis (ADMET)
Polymerization of 1,9-Decadiene.............................. 41
General Polymerization Procedure.............................. 41
Reaction Conditions for 1,9-Decadiene
Polym erizations................... ........................................... 4 7
Acyclic Diene Metathesis (ADMET)
Polymerization of 1,5-Hexadiene............................... 53
General Polymerization Procedure............................... 53
Reaction Conditions for 1,5-Hexadiene
Polym erizations.................................................................... 5 3


3. THE KEY TO SUCCESSFUL ACYCLIC DIENE METATHESIS
(ADMET) POLYMERIZATION CHEMISTRY

Styrene as a Model Compound............................. ........... 57
Preventing the Cationic Polymerization of Styrene...... 60
Investigation of a Lewis Acid Free Catalyst System
with Styrene as Model Compound................................... 64
Investigation of a Lewis Acid Free Catalyst System
with Substituted Styrenes as Model Compounds....... 68


4. ACYCLIC DIENE METATHESIS POLYMERIZATION (ADMET).
SYNTHESIS OF POLYOCTENAMER USING 1,9-DECADIENE
AS A MONOMER

Acyclic Diene Metathesis as a Polymerization
Reaction................................ .................. .......................... 8 1
Bulk Polymerization Conditions......................... ........ 84
Tailoring of Acyclic Diene Metathesis Formed
Polym ers...................................................... .................. 8 6
Determining the Stereochemistry of the Olefin
Units in Polyoctenamer......................................................... 87
Effects of Percentage Trans Stereochemistry on the
Melting and Recrystallization Temperatures of
Polyoctenam er................................................ ..................... 9 3
Determination of the Molecular Weights of the
Polyoctenamer Samples Produced by Acyclic
Diene Metathesis Polymerization................................ 100
Determination of the Mark-Howink-Sakurada








Constants, "K" and "a", for Polyoctenamer
at 25C in Toluene ........................................................ 1 08
Testing calculated Mark-Howink-Sakurada constants 117
An Investigation of the Possible Formation of
Macrocycles During Acyclic Diene Metathesis
Polym erization....................................................................... 1 1 7


5. THE STEP PROPAGATION, CONDENSATION NATURE OF
ACYCLIC DIENE METATHESIS POLYMERIZATION

Determining the Linearity of Acyclic Diene
Metathesis Produced Polybutadiene................................ 1 24
Determining Optimal Reaction Conditions for
Acyclic Diene Metathesis Polymerizations................. 134
Large Volume of Solvent............................... ........... 1 36
Bulk polymerization conditions................................. 1 38
An Evaluation of the Equilibrium Step Propagation
Condensation Nature of Acyclic Diene Metathesis
Polym erization ............................................... ............. 1 40


REFERENC ES ................................................................................................ 14 6


BIOGRAPHICAL SKETCH................................................................................. 1 54














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

ACYCLIC DIENE METATHESIS, A NEW EQUILIBRIUM STEP PROPAGATION,
CONDENSATION POLYMERIZATION

By

Jan Geldenhuys Nel

December 1989

Chairman: Dr. Kenneth B. Wagener
Major Department: Chemistry


The first high molecular weight polymers synthesized by
acyclic diene metathesis (ADMET) polymerization are reported
herein. Prior to the research discussed in this dissertation, the
catalyst requirements and the reaction conditions required to
produce high molecular weight polymers by acyclic diene metathesis
polymerization techniques were unknown. Thus, this reaction
becomes one of only three room temperature step polymerizations
known today.
Model compound studies were investigated to eliminate all
competing side reactions. The metathesis of styrene, catalyzed by a
Lewis acid free catalyst under bulk and high vacuum reaction
conditions, yielded stilbene quantitatively, without any traces of








side reactions. Substituted styrenes also metathesized cleanly and
quantitatively.
A series of 1,9-decadiene polymerizations facilitated the
direct comparison of products formed by acyclic diene metathesis
polymerization with ring opening metathesis polymerization
samples. High molecular weight polyoctenamer samples were
produced which had a high percentage trans stereochemistry that
resulted in high melting points. A prediction of the melting and
recrystallization temperatures of 100% trans polyoctenamer was
made. The Mark-Houwink-Sakurada constants for polyoctenamer
were calculated for the molecular weight range 103-105.
Since acyclic diene metathesis produces exclusively linear
polymers with no branching, ADMET was applied to 1,5-hexadiene
and exclusively linear poly-1,4-butadiene resulted, as indicated by
the absence of 1,2-vinyl linkage.
The possibility of acyclic diene metathesis (ADMET)
cyclization side reactions and the subsequent ring opening
metathesis polymerization were studied by mass spectroscopy and
size exclusion chromatography. Parent ion peaks corresponding to
linear polymer were observed in both the 1,5-hexadiene and 1,9-
decadiene polymerizations. The continued presence of ethylene
throughout the course of the reaction indicated the condensation
nature of ADMET. A polydispersity approaching 2 was obtained for
high molecular weight polyoctenamer and polybutadiene samples.
Thus, acyclic diene metathesis polymers are formed by a step
propagation mechanism.


viii














CHAPTER 1
INTRODUCTION


During the past 20 years, the olefin metathesis reaction has
been explored extensively for its ability to create polymers.
Principally, the method investigated has been the ring opening
metathesis polymerization (ROMP) of strained cycloalkenes, and as a
result several polymers presently are produced commercially using
ROMP chemistry [1]. Ring opening metathesis polymerizations are
driven by the release of ring strain, and thus ring opening
metathesis is limited to the polymerization of strained alkene rings
[2].
The polymerization of acyclic dienes has been attempted as
well, but with little success prior to the research reported herein
[3]. This dissertation reports the first successful metathesis
reactions in the equilibrium step propagation condensation
polymerization of acyclic dienes, thereby broadening the scope of
metathesis polymerization. A variety of acyclic dienes exist that
could become monomers for acyclic diene metathesis
polymerizations, producing new and unique polymers.





2


The Nature of Step Polymerization Chemistry
As the name implies, step polymerization proceed in a step-
wise manner [4]. Initially, monomer reacts with monomer to produce
a dimer, and the dimer can react, in turn, with monomer or another
dimer to form either a trimer or tetramer. The step-wise
mechanism by which a polymer is progressively formed is
illustrated in Figure 1-1.

monomer + monomer dimer
dimer + monomer trimer
dimer + dimer tetramer
trimer + monomer tetramer
trimer + dimer pentamer
trimer + trimer hexamer
etc.


Figure 1-1. Equilibrium step polymerization growth


Monomer disappears early in step propagation reactions, and a
range of molecular weight oligomers and polymer chains result. The
step-wise growth of monomer to oligomers, eventually reaching high
molecular weight polymers, imparts stringent requirements for any
chemical reaction to be used in an equilibrium step polymerization

[5].
In general, for a small-molecule reaction to be useful in a step
polymerization reaction, a favorable equilibrium is necessary. The
formation of unstrained rings, as opposed to linear polymer, is an
example of an unfavorable equilibrium reaction that can prevent
acyclic diene metathesis polymerization.








High conversion (i.e., extent of reaction) is one of the more
important criteria required for the synthesis of high molecular
weight polymer by step polymerization chemistry. In small
molecule synthesis, the reaction is considered to be a success if
90% conversion is achieved. In contrast, a conversion greater than
99% is needed for any step polymerization to produce high molecular
weight polymer.
W.H. Carothers [6], derived equation (1) which correlates
molecular weight and percentage conversion.

Xn = 1/(1-p) (1)

According to Carothers, Xn is the number average degree of
polymerization, and p is the extent or fraction of conversion of
functional group to polymer, illustrating the importance of a high
extent of conversion. A perfect balance of stoichiometry is assumed
in this relationship, and it can be seen that when p equals 0.9
(corresponding to 90% conversion), the "polymer" which results
possesses only 10 repeating units, which is an oligomer, not a
polymer. A conversion of 99.5% produces a polymer consisting of
200 repeating units and, depending on the molecular weight of the
repeating unit, a moderate molecular weight. A step condensation
reaction only produces high molecular weight polymer when a high
extent of conversion is achieved. Figure 1-2 portrays the
relationship between the extent of conversion and the molecular
weight of polymer. Chemical reactions that are useful for step
polymerizations include esterification, amidation, the formation of
urethanes, aromatic substitution and only a few others [4].











200


P Xn

0.8 5
0.9 10 Xn
0.95 20
0.99 100
0.995 200
0
0.00 1.00

Figure 1-2. Variation of molecular weight with conversion
for equilibrium step polymerizations


Two general types of monomers can be employed in step
polymerizations. The first type of monomer has two different
bifunctional and/or polyfunctional groups with each monomer

possessing only one type of functional group. The second type has a
single bifunctional monomer containing two different functional

groups.or the same monomer. The two groups of reactions can be

represented by the following equations, where A and B are the two
different types of functional groups.



n A-A + n B-B -[-A-AB-B -,n (2)


n A-B


-- A--B--


L





5


Metathesis represents another reaction in addition to those
already mentioned that can be employed as a equilibrium step
polymerization mechanism. The monomers that would be suitable
for this mechanism have double bonds (i.e., enes) as functional
groups, represented schematically as A-A. An equilibrium step
propagation condensation type polymerization (4) will produce a
repeat unit contain an internal olefin (-B-) and a small molecule (C):


catalyst
n A-A t -B--- + nC (4)
n



The removal of the by-product (a small molecule) provides the
driving force for a productive polymerization reaction.


The Olefin Metathesis Reaction
The word metathesis is derived from the Greek words meta
(change) and tithemi (place), and as a grammatical term, it means
the transposition of sounds or letters in a word [7]. For chemistry,
metathesis corresponds to the interchange of atoms between two
molecules. Olefin metathesis refers to the interchange of carbon
atoms between a pair of double bonds (olefins).
Olefin metathesis reactions (Figure 1-3) fall into three broad
categories: exchange (5), ring opening polymerization (ROMP) (6),
and cyclization reactions (7).








RCH=CHR
+
CH2= CH2


catalyst


catalyst


= =CHCH2-R-CH2CH=





30


catalyst


Figure 1-3. Olefin metathesis reactions.


Acyclic diene metathesis (ADMET) polymerization (Figure 1-4)
provides the possibility of extending exchange olefin metathesis
reactions into a polymerization scheme. Demonstrating the
feasibility of employing exchange olefin metathesis as an
equilibrium step condensation type polymerization has been the goal
of this investigative effort.


1 R1 catalyst
n (s(( R2x)x C .)-n + n


R1


Figure 1-4. The acyclic diene metathesis polymerization reaction.


RCH
CH2


Cw
+ II
CH2


(5)








Metathesis reactions generally are reversible, and with an
effective catalyst system, an equilibrium can be obtained in a
relatively short time. The reversibility of the olefin metathesis
reaction results in either a productive or degenerate metathesis
product. A productive metathesis reaction produces two chemically
different molecules, and a specific example of such a reaction is
shown in Figure 1-5, where propene produces 2-butene and ethylene.


CH3CH=CH2
+C 2
CH3CH=CH2


catalyst


CHCH CH2
113CH + H2
CH3OH CH2


Figure 1-5. The productive metathesis of propylene.


On the other hand, no new chemical compound results when a
degenerate metathesis reaction occurs. Degenerate metathesis is
illustrated with a specific example in Figure 1-6: propene is the
reagent, and propene is also the resultant product.


CH3CH=CH2
+
CH2= CHCH3


catalyst


CH3CH CH2
CH+ HCH
Cd- CHCH3


Figure 1-6. The degenerate metathesis of propene.


Isotopic labeling studies have shown that degenerate
metathesis is much faster than productive metathesis for terminal


L








olefins [8]. By carefully controlling the reaction conditions and
catalyst system, the possibility exists that productive metathesis
can become the dominant reaction. Productive metathesis must
produce yields of better than 99% for olefin metathesis to become a
viable reaction in a polymerization scheme. Obtaining the optimum
reaction conditions that lead to productive metathesis is one of the
criteria to be met before acyclic diene metathesis reactions can
produce a step condensation type polymer.
The principal side reactions that can occur during olefin
metathesis are; alkylation, isomerization, cyclization, and addition
across the double bond. The following precautions have been found
to minimize side reactions [9, 10]:
(i) The proper choice of solvent to suppress alkylation
reactions; halogenated solvents such as chlorobenzene
are preferred.
(ii) The use of a base to suppress cationic side reactions;
alkali metal hydroxides can be added to supported
catalysts, and tertiary amines or other polar additives
can be added to catalyst systems in solution.
(iii) The careful selection of the order of addition of catalyst,
cocatalyst, and substrate; and,
(iv) The use of as low a temperature as possible during the
reaction.


Brief History of Olefin Metathesis
A patent disclosure by Eleuterio in 1957 on reaction 5 (Figure
1-3), and the norbornene reaction shown in Figure 1-7 were the first








metathesis reactions reported. The first literature published on
metathesis polymerizations, in 1960 by Truett, concerned the ring
opening polymerization of norbornene to polynorbornene (Figure 1-7)
[11].




7n catalyst --CHH-



Figure 1-7. The polymerization of norbornene.


Exchange metathesis reactions such as those shown in Figure 1-8
were first published in 1964 by Banks [12].
Calderon, in 1967, coined the expression olefinn metathesis"
[13]. Prior to 1967, the chemistry of exchange reactions and of ring
opening metathesis polymerization reactions had developed
independently. The connection between the two types of reactions
was not immediately apparent because different catalysts and
conditions were involved.
Calderon's discovery that the catalyst system
WCI6/EtAICI2/EtOH would bring about not only the very rapid
polymerization of cyclooctene and 1,5-cyclooctadiene [14], but also
the disproportionation of 2-pentene [15] at room temperature
provided the bridge leading to the realization that olefin
disproportionation and ring opening metathesis polymerization were
the same chemical reaction. Calderon [16] demonstrated that the








double bonds are completely broken in the reaction (Figure 1-8) and
lead to the exchange of alkyldiene moieties.


CH3CH=CHCH3 WCI6/EtAICI2/EtOH CH3CH CHCH3
+ 11 + I
CD3CD=CDCD3 CD3CD CDCD3

Figure 1-8. Metathesis reaction illustrating the exchange
of alkyldiene moieties.


Consequently, transalkylidenation reactions became known as olefin
metathesis reactions. Mol [17], Levisalles [18] and K. Tanaka [19]
separately confirmed Calderon's findings, but used isotopically
labelled samples with different catalyst systems. Dall'Asta [20]
proved that the double bond is completely broken during ring opening
metathesis polymerizations of cycloalkenes.
Chemists were quite impressed by the beauty and elegance of
the olefin metathesis reaction. Earlier authors frequently used the
words, "fascinating, intriguing, exciting and even doubly exciting
(commercially and academically)" to describe these reactions. K. J.
Ivin [21] wrote about olefin metathesis, "We now know quite a lot
about this beautiful woman metathesiss) but she still has a few
secrets locked away".
One of those hidden secrets, Acyclic Diene Metathesis
Polymerization (ADMET polymerization), has been uncovered by the
research reported herein. The beauty and elegance of ADMET
polymerizations will be discussed in subsequent chapters.








The Mechanism of Metathesis Chemistry
Originally, metathesis was [22] thought to occur when two
double bonds approached one another in the vicinity of the transition
metal catalyst site. Transition metal orbitals were proposed to
overlap with olefin double bonds to allow exchange to occur via a
weakly held cyclobutane type complex. This "pairwise mechanism"
(Figure 1-9) has been discarded in favor of the metal carbene chain
mechanism [23].



S C C-------C C=C
[M] [M] [M]
C C -------C =C


Figure 1-9. The pairwise mechanism.


Herisson and Chauvin first proposed that a metal carbene
species might be involved in olefin metathesis [24]. The research
describing the initial products of cross metathesis of cyclo- and
acyclic olefins, and the identification of both initiating and
propagating metal carbenes by 1 H and 13C NMR spectroscopy [25, 26,
27, 28] (between 1979 and 1982), is regarded as unequivocal proof
of the metal carbene mechanism. Numerous experiments have
confirmed the metal carbene mechanism, and it is generally
accepted for olefin metathesis reactions. In the metal carbene chain
mechanism, the propagating compound is a metal carbene formed in
some way from the catalyst/substrate system. Generalized
propagating steps are shown in Figure 1-10, where











C C C-C C C
[M] C J IM]- C_ [M]=C


Figure 1-10. The metal carbene mechanism.


propagation proceeds via a metallacyclobutane species. During the
process a metal carbene is regenerated at every stage.


Catalysts Used In Olefin Metathesis
Numerous catalyst systems exist that will initiate olefin
metathesis reactions. Currently, several researchers [28, 29, 30]
are actively pursuing catalytic reactions in search of yet more
reactive and better defined organometallic complexes. Metathesis
catalyst systems can be divided into three types:
(a) those consisting of an actual metal carbene;
(b) those containing an alkyl or allyl group in one of the
components, e.g. EtAICI2, from which a carbene ligand

can readily be generated; and,
(c) those having neither a preformed carbene nor an alkyl
group in any component. In this case, a metal carbene
can only formed by interaction of the substrate olefin
with the transition metal center.
Eleven transition metals are the most commonly used as
catalysts: Ti, Zr, Hf, Nb, Ta, Mo, W, Re, Ru, Os and Ir. Compounds








containing non-transition metals are not commonly used as a
catalyst, with A1203 [31] and EtAICI2 [32] being two rare examples.
The metathesis of acyclic olefins is usually thermoneutral.
Therefore, if an equilibrium is to be obtained quickly, only the most
active Mo-, W-, Re- and Ta- based systems should be used.
A cocatalyst normally consists of an organometallic compound
of a non-transition metal from groups I-IV, and the function of the
cocatalyst may be severalfold. The cocatalyst may provide an alkyl
ligand to the transition metal that can be converted into an
alkyldiene ligand. Alternately, the cocatalyst itself may act as a
ligand and thereby modify the electron density of the transition
metal atom. Presently, much emphasis has been placed on catalyst
systems which consist of an actual metal carbene and do not require
cocatalysts or activators [28, 29].


Ring Opening Metathesis Polymerization (ROMP).
Eleuterio's (1957) and Truett's (1960) norbornene
polymerization disclosures were the first ring opening metathesis
reactions performed. These were followed by Natta and Dall'Asta
(1964), who reported the metathesis polymerization of
cyclopentene using a transition metal catalyst system [33]. Since
that time there have been numerous reports of successful
polymerizations of cyclic olefins [34-46], and as stated previously,
the ring opening metathesis polymerizations (Figure 1-11) are
driven by the release of ring strain.









-C catalyst
n R I "- ICH = CH R--R
CH


Figure 1-11. Ring opening metathesis polymerization (ROMP).


Schrock, Grubbs, and Osborn investigations have resulted in
new metathesis catalysts that are broadening the scope of ring
opening metathesis polymerization [28, 29, 30]. The ring opening
metathesis polymerization (ROMP) of strained cycloolefins has been
the only metathesis reaction leading to the formation of useful
polymers. Polyoctenamer [47] (formed from cyclooctene, marketed
in 1980) and polynorbornene [48, 49] (formed from norbornene,
marketed in 1976) are examples of ring opened polymers that are
commercially available.
Extensive research has been done on ring opening metathesis
polymerization reactions, and researchers are actively pursuing
ROMP chemistry [1]. The effects of ring size, substituents on rings,
formation of cyclic oligomers and several other aspects of ROMP
reactions have been investigated thoroughly. The use of monocyclic,
bicyclic, and tricyclic alkenes as monomers have also been studied
[50], and copolymers of cycloalkenes and cross metathesis telomers,
formed between cyclic and acyclic olefins were also investigated
[51].
Recent studies have revealed, in certain cases at least, that
ring opening metathesis polymerization is a living polymerization








reaction, and polyuniformities approaching the ideal value of 1.0
have been found [34, 42]. A uniformities of 1.0 demonstrates that
the catalyst does not dissociate from the living-chain end and can
lead to the formation of block copolymers. However, ring opening
metathesis polymerization chemistry is hampered by the fact that
monomers are restricted to strained cyclic olefins.


Acyclic Diene Metathesis Polymerization (ADMET)
Acyclic diene metathesis polymerization (ADMET) (Figure 1-4)
presents another opportunity to exploit the metathesis reaction to
create polymers. Acyclic diene metathesis polymerization is
completely different from ring opening metathesis polymerization
and offers possibilities not available when one is constrained to
cyclic monomers.




R1 )x R1 catalyst +
-n -(--(R2)x + n
R,

Figure 1-4. Acyclic diene metathesis polymerization (ADMET).


The metathesis reaction of acyclic dienes is an equilibrium
reaction that generally has an overall change in free energy close to
zero. Reactions do not proceed to high molecular weight polymer,
and only oligomers are formed if the equilibrium is not shifted in
favor of the forward reaction. Removing the byproduct (small








molecule) provides an opportunity to shift the equilibrium and drive
the polymerization to high molecular weight.
Side reactions (e.g. the formation of cyclic compounds as
opposed to linear products) also limit equilibrium step condensation
polymerization reactions [52]. It is especially true for step
condensation reactions in which the cyclic product formed is more
stable than the linear product and thus becomes the principal
product of the reaction. The percentage conversion of monomer to
polymer is reduced by cyclization reactions, and according to the
Carothers equation (1), only low molecular weight oligomers can be
expected [5, 6].
Early studies show that six membered rings are preferentially
formed from acyclic dienes where double bonds are separated by
four carbon atoms [53]. For example, cis,cis-2,8-decadiene produces
cyclohexene in 90% yields.



-_ catalyst



Figure 1-13. The formation of cyclic compounds
via acyclic diene metathesis chemistry.


Researchers studied the metathesis reaction of 1,7-octadiene [49]
to gain insight into the mechanism of metathesis. Several catalyst
systems were used, and without exception the products are
cyclohexene and small quantities of oligomers.








Reactions with isotopically labeled terminal olefins revealed
that degenerate metathesis is much faster than productive
metathesis [8]. Subsequently, degenerate metathesis explains the
fact that for acyclic dienes, without exception, only oligomers are
formed under the reaction conditions employed. One reaction that
received significant attention was the attempted acyclic diene
metathesis polymerization of 1,5-hexadiene to polybutadiene [54,
55]. It was eventually concluded that ADMET polymerization of 1,5-
hexadiene was impossible because degenerate metathesis is
strongly favoured [56].
By the late 1970s it was generally accepted that acyclic
dienes would not produce linear polymers by acyclic diene
metathesis. What would have been the first new step condensation
type polymerization reaction in 20 years was abandoned, and
polymerization efforts were focused on ring opening metathesis
polymerization reactions.
This dissertation demonstrates unequivocally that acyclic
diene metathesis (ADMET) polymerization is possible. It elaborates
on the requirements necessary for acyclic diene metathesis to
become a feasible polymerization reaction. Specific model
compound studies were performed to gain insight regarding the
requirements necessary for acyclic diene metathesis to be used as a
polymerization reaction. Two important polymers were prepared by
acyclic diene metathesis polymerizations and reaction conditions
and the properties of the formed polymers were delineated.














CHAPTER 2
EXPERIMENTAL


General Information
A Varian XL-Series NMR Superconducting Spectrometer system
was used to obtain IH NMR 200 MHz and 13C NMR 50 MHz spectra.
Chemical shifts are reported in parts per million downfield from the
internal reference tetramethylsilane. Infrared spectral analysis
was performed on a Perkin-Elmer 281 Infrared Spectrophotometer
with KBr pellets and percent transmission being recorded relative to
wavenumber. Ulraviolet spectroscopy was done with a Perkin-Elmer
Lambda 9 UV/Vis/NIR spectrometer using THF as solvent. Elemental
analyses were done by Atlantic Microlab inc. in Norcross, Georgia.
Mass Spectroscopic data were obtained from a Finnigan 4600 Gas
Chromatographic Mass Spectrometer. Differential scanning
calorimetry data were obtained with the Perkin-Elmer 7 Series
Therm Analysis system, equipped with a data station. The
instrument was calibrated by a two point method using cyclohexane
and indium. Dry argon was used as purge gas, and a scan rate of 100C
per minute was used.
Size exclusion chromatograph data was obtained using a
Waters Associates Liquid Chromatograph apparatus equipped with an
RI detector. Tetrahydrofuran or toluene were used as solvent and g-








styragel columns covering the region of interest were employed. A
constant flow rate of 1.04 ml/min was maintained and the
instrument calibrated by using polybutadiene or polystyrene
standards (Polysciences, Inc.) that covered the region of interest.
Intrinsic viscosities were determined using an Oswaltd dilution
viscometer at 25 C with toluene as the solvent. A Wescan Vapor
Pressure Osmometer model 233 was used for osmometry. Toluene
was the solvent of choice at an operating temperature of 51C.


High Vacuum and Schlenk Line Techniques
The catalysts used for metathesis reactions vary in their
sensitivity toward impurities, such as moisture and oxygen[57].
Since little is known about the exact conditions required for
metathesis to occur when vinyl bonds are used, a variety of reaction
conditions were employed to optimize the synthesis of model
compounds, and polymers.


Schlenk Vacuum Line Techniques
The first polymerizations of 1,9-decadiene and 1,5-hexadiene
were carried out with a Lewis acid containing catalyst system
(WCL6/ETAICI2) using Schlenk line techniques [58]. Schlenk
techniques also were used initially in the model compound studies.
A specially designed flask (Figure 2-1) equipped with a porthole
having a Suba SealT rubber septum and a ground glass joint (14/20)
was designed, and the ground glass joint was connected to a gas trap
in the system. All condensed gases were analyzed with a gas
chromatography equipped with a flame ionization detector, or a










To Vacuum

.


Septum -,


Gas Trap


Figure 2-1. Schlenk vacuum line apparatus








mass spectrometer.
In a typical experiment, freshly sublimed tungsten
hexachloride (WCI6) was added into the flask described above, which
was placed in a dry box free of oxygen and moisture. When
chlorobenzene was used as solvent, a 1.0 M solution of WCI6 in
chlorobenzene was used instead of powderous WCI6. The flask was
sealed using a septum and a RotafloTM stopcock. This apparatus was
connected to a Schlenk vacuum line via a ground glass joint and then
evacuated. The gastrap of the apparatus was closed off from the
vacuum line using an in-line RotafloT stopcock, and the system was
filled with dry argon. The reagent and the co-catalyst were added
via a syringe.
Schlenk methods allowed for the addition of reagents in
varying order and quantities. The gas trap was cooled in liquid
nitrogen while the reaction mixture was chilled in an ice bath. A
moderate vacuum was applied to the system by opening the RotafloT
joint of the gas trap, and the condensed gases were removed for
further analysis.


High Vacuum Line Techniques
Due to the high oxygen and moisture sensitivity of the Lewis
acid free catalyst system (Catalyst 2; W(CH-t-Bu)(N-2,6-C6H3-i-
Pr2)[OCMe(CF3)2]2, Figure 2-2), high vacuum line techniques had to
be employed when this catalyst was used. A vacuum system,
custom-made in the University of Florida glass shop [59], was
constructed entirely of PyrexTM glass and consisted of a rotary oil
pump in conjunction with an oil diffusion pump. High vacuum PyrexT











C(CH3)3
I
CH
(CH3),(CH3)CO I
(CH3)2(CH3)CO N





Catalyst 1






C(CH3)3
CH

(CF3)2(CH3)CO



(CF Catalyst 2


Catalyst 2


Figure 2-2. Lewis acid free catalysts used in metathesis reactions.








ground glass joints were used at various junctions in the line to
permit evacuation of reaction vessels and to transfer solvents and
reagents from one vessel to another. A mercury McCleod gauge,
attached to the manifold, was used to monitor the pressure in the
system.
The PyrexT glass vessels used in the reactions were self
designed and built with the use of a hand-held gas and oxygen torch
(Figures 2-4, 2-7, 2-8, 2-9 and 2-10). The manipulations required
for various reactions, such as catalyst addition and transfer of
reagents, were performed in vacua using breakseal techniques [60,
61]. All glassware used was cleaned in the following order:
KOH/isopropanol (15% W/V), water and acetone. The apparatus was
oven dried before attaching it to the vacuum line. The entire system
was evacuated and dried thoroughly with a torch to remove traces of
adsorbed water vapor and oxygen from the surface of the glass. The
system then was checked for the presence of pinholes using a Tesla
high voltage discharge coil. Reactions were carried out only after
confirming that a "sticking vacuum" (10-6 mm Hg) existed, as
registered on the McCleod gauge.
The reactions were terminated by disconnecting the apparatus
from the vacuum line and then opening the Rotaflow joints, which
allowed air into the system to destroy the catalyst. Following these
operations, the apparatus had to be cut into smaller sections to
remove the products.








Purification of Monomers. Reagents and Solvents
All chemicals were of high grade purity (>98%). Due to the
sensitive nature of catalysts 1 and 2 (Figure 2-2), all monomers,
reagents and solvents used in conjunction with these catalysts were
of greater than 99% purity. In order to ensure absolute dryness and
an oxygen free atmosphere, all chemicals used were dried over
calcium hydride for 24 hours, degassed several times using freeze-
pump-thawing cycles, and then vacuum transferred into a potassium
mirrored flask. The reagents were stirred for a half hour and then
vacuum transferred into a divider. Break-seals filled with the
desired amounts of reagent were frozen in liquid nitrogen and sealed
under a 10-6 mm Hg vacuum (Figure 2-3).
In cases where a reagent had impurities not removed by drying
techniques, the reagent was allowed to react with a single aliquot
(20 mg) of catalyst 2 for 15 minutes, then the purified reagent was
vacuum transferred into a new breakseal and sealed under high
vacuum. Allowing any impurities to react with catalyst (in effect
destroying the catalyst) and then removing the remainder of the pure
reagent from the reaction vessel, proved effective for removing
impurities that would otherwise poison the catalyst and prevent
metathesis. Without exception, reagents purified by exposure to
catalyst metathesized and produced only the expected products in
high yields.
The reagents used with the classical catalyst system,
WCl6/EtAICI2, were purified in an identical fashion up to the point
that they were sealed in breakseal ampules. The reagents were
vacuum transferred from the potassium mirrored reaction vessel







High Vacuum Line Manifold


Potassium Mirrored
Flask


Breakseals


Figure 2-3. High vacuum line purification setup.








into a 50 ml round bottom flask by cooling the flask in a liquid
nitrogen bath. After the reagents were allowed to thaw, the flask
was filled with argon and sealed with a rubber septum. Storing the
reagent under argon in a round bottom flask facilitated the use of
Schlenk vacuum line techniques (i.e., transfer through double ended
needles under argon).

Attempted Metathesis of Styrene Using a Lewis Acid
Containing Catalyst
An attempted model metathesis reaction of styrene to stilbene
was conducted repeatedly to determine the reaction conditions and
catalyst system which would lead to the expansion of the
metathesis reaction into a equilibrium step propagation,
condensation type polymerization. The order in which the catalyst,
co-catalyst, and styrene were added was varied, as was the time
that the catalyst and co-catalyst were allowed to react,
particularly when the reagent was added last. The variations were
done to investigate the possibility of eliminating side reactions.
Styrene generally was added while the apparatus was cooled in an
ice bath, after which the reaction was allowed to warm to room
temperature. The first reaction was started at -780C, and once all
reagents were added, the reaction was allowed to slowly warm to
room temperature. Also, several reactions were started at room
temperature. The above variations in reaction conditions were
employed using both Schlenk and high vacuum techniques.
Tungsten hexachloride (Aldrich) was stored in a dry box and
periodically sublimed in order to ensure purity. Tungsten








hexachloride (0.9929g) was dissolved in 25 ml of chlorobenzene to
produce a 0.1M solution which was stored in a Schlenk flask under
argon. A variety of co-catalysts (i.e., EtAICl2, Et2AICI and Et3AI)
were used as 1.0 M solutions in hexane in separate reactions. The
co-catalyst was added to the reaction vessel via a syringe. The
ratio of the cocatalyst to WC16 was 4:1. Hexane was removed from
the reaction vessel and replaced with argon. The apparatus was
cooled in an ice-bath, and the reagent was added to the vessel via a
syringe through the septum. Typically, 0.82 ml of a 0.1 M WC16
(0.082 mmol) in chlorobenzene was used with 1 ml of styrene (9.6
mmol) and 0.33 ml of a 1.0 M EtAICI2 (0.33 mmol) in hexane. The
reactions performed, utilizing the above variations in reaction
conditions, were allowed to continue for varying lengths of time and
were terminated with an excess of methanol. 1H and 13C NMR
spectra of the products indicated that only polystyrene was
produced. The gases produced in these reactions were analyzed at 5-
minute intervals by removal of a 50 p~l aliquot with a gastight
syringe. A mixture of ethane and ethylene, as analyzed by GC/MS,
was observed with ethane as the major product. Varying the solvent
and the addition sequence of reagents did not produce stilbene.
It was concluded that different reaction conditions had to be
utilized to eliminate the side reaction that produced polystyrene and
inhibited metathesis. High vacuum techniques were employed.
Tungsten hexachloride (0.82 ml of a 0.1 M in chlorobenzene) and
EtAICl2 (0.33 ml of a 1.0 M in hexane), at a ratio of 1:4, were added,
in a dry box, into break-seal ampules via a syringe. The break-seal
ampules were sealed with rubber septa and then removed from the








dry box. After freezing them in liquid nitrogen, a vacuum was
applied using a needle pierced through the septum. The break-seal
ampules were then sealed under vacuum using a hand held gas and
oxygen torch. Styrene (8.6 ml) was purified as described previously
and sealed in a break-seal ampule to give a 100:1 mol ratio with
respect to WCl6. The ratio of catalyst: co-catalyst: reagent,
typically were 1:4:100.
The break-seal ampules containing the catalyst, co-catalyst
and reagent were joined to a reaction vessel (Figure 2-4) and the
reaction vessel was connected to the high vacuum line via a ground
glass 14/35 joint and evacuated. After closing the gas trap by
closing the RotafloT stopcock, the reagents were added in varying
order by breaking the break-seal ampules. Hexane (solvent for the
co-catalysts) was evacuated after the breakseal containing the co-
catalyst was broken. At this point the reaction vessel was sealed
off from the vacuum line to prevent any impurities from entering the
reaction. By opening the RotafloT stopcock of the gas trap and
cooling the trap in liquid nitrogen, a steady vacuum was applied, and
any gases produced in the reaction could be removed and condensed.
Thus, a constant vacuum used to drive the reactions could be
maintained. No gases were produced, and the only product was
polystyrene, which was corroborated by the following analysis.
13C NMR (CDCl3, 50 MHz, 8 in PPM): 41 (methine carbons), 43-

46 (methylene carbons), 145-146 (aromatic carbons).
CHN : %C= 92.31, %H = 7.69 (Theory)
%C = 92.29, %H = 7.72 (Found)















To Vacuum


WCI + Solvent


Gas Trap


Figure 2-4. High vacuum breakseal apparatus.







Attempted Metathesis of Fluorinated Styrenes Using a Lewis Acid
Containing Catalyst System
In order to investigate the possibility of metathesizing
fluorinated styrenes, four different fluorinated styrenes were used:
2-fluorostyrene, 3-fluorostyrene, 4-fluorostyrene and 2,3,4,5,6-
pentafluorostyrene. The experimental procedures for these
reactions were identical to those adopted for the metathesis of
styrene. The results also were identical: monofluorinated styrenes
produced fluorinated polystyrenes. Authentic fluorinated
polystyrenes samples were not available and were subsequently
prepared by means of anionic polymerization techniques discussed in
the next section of this chapter. Spectral data of fluorinated
polystyrenes formed when a Lewis acid cocatalyst is used are:
Polv-2-fluorostyrene
13C NMR (CDCl3, 50 MHz, 6 in PPM): 35 (methine carbons),40-41

(methylene carbons), 114-129 (aromatic carbons), 131 (substituted
aromatic quarternary carbons), 160,5d, JC-F = 246 Hz (fluorinated
aromatic carbons).
Poly-3-fluorostyrene
13C NMR (CDC13, 50 MHz, 6 in PPM): 40 (methine carbons), 41-46

(methylene carbons), 113-130 (aromatic carbons), 147 (substituted
aromatic quarternary carbons), 162,5d, JC-F = 243 Hz (fluorinated
aromatic carbons).
2,3,4,5,6-Pentafluorostyrene did not react under the reaction
conditions described. In order to determine if the catalyst was
active, experiments were run in which 1,9-decadiene (shown in this
work to metathesize) was added to the reaction of 2,3,4,5,6-








pentafluorostyrene after approximately 24 hours. 1,9-Decadiene
(0.5 ml) was syringed into the reaction vessel through the septum
after the vessel was filled with argon while using Schlenk vacuum
line techniques. 1,9-Decadiene oligomerized, indicating that the
catalyst was active.
When high vacuum line techniques were used, 1,9-decadiene
again was employed to test for catalyst activity. Under high vacuum
conditions, breakseal ampules containing purified 1,9-decadiene (0.5
ml) were incorporated into the reaction vessel prior to the start of
the reaction to allow for the addition of 1,9-decadiene at any stage
of the reaction. The breakseal ampules were used as a precaution
against contamination of the reaction with oxygen or moisture. NMR
analysis indicated that 1,9-decadiene oligomerized to
polyoctenamer, whereas 2,3,4,5,6-pentafluorostyrene did not
metathesize or polymerize. Thus, the catalyst was active but did
not cause 2,3,4,5,6-pentafluorostyrene to react.

Preparation of Fluorinated Polystyrene by Anionic Polymerization
Techniques
Authentic fluorinated polystyrenes were unavailable for
comparison with the products formed when a Lewis acid containing
catalyst is reacted with fluorinated styrenes, and so high vacuum
line techniques were used to make authentic fluorinated
polystyrenes. The apparatus illustrated in Figure 2-5 was used in
the preparation of these polymers.
All fluorinated styrene reagents were dried over calcium
hydride and then distilled on a vacuum line into a round bottom
















Monomer


To Vacuum
t


Septum


Dry-ice/CCI i-
Dry-ice/lsopropanol


Figure 2-5. Anionic polymerization apparatus.


Methanol








flask, which was coated with potassium metal. After stirring for
30 minutes the monomer was transferred into a breakseal ampule
and sealed under vacuum. Approximately 2 ml of the monomer was
sealed in each breakseal ampule and vacuum sealed
The apparatus was connected to the vacuum line, evacuated,
flame dried to ensure absolute dryness and then filled with dry
argon. One milliliter of a 1.6 molar solution of t-butyllithium, used
as the initiator, was syringed into the vessel through the septum.
The reaction section of the apparatus was cooled in liquid nitrogen.
The whole apparatus was evacuated, after which the sidearm with
the septum was sealed off using a gas/oxygen flame. Dry
tetrahydrofuran, approximately 50 ml, was distilled into the vessel,
and the apparatus was sealed from the vacuum line.
Tetrahydrofuran and t-butyllithium (0.1 ml) were allowed to
warm to -78C and were kept at this temperature in a dry-
ice/isopropanol bath. The breakseal ampule containing the
fluorinated styrene (5 ml) under study was broken, and the reagent
was allowed to flow into the round bottom flask that had been
cooled to -200C using a dry-ice/carbon tetrachloride bath. Addition
occurred over a one hour period to facilitate the slow and controlled
transfer of the monomer into the reaction section of the apparatus.
The reaction was allowed to continue for 2 hours at -780C and was
slowly warmed to room temperature; then stirred for an additional 2
hours. In each case, dry methanol was used to terminate the
reaction.
These anionically prepared reference polymers were
precipitated using an excess of methanol and further purified by








dissolving them in benzene, followed by precipitation in methanol.
The NMR spectra of all of these polymers were identical to those of
the products formed when a Lewis acid was used as co-catalyst in
the metathesis reactions, described previously. These results
confirm that fluorinated polystyrenes result when a Lewis acid
containing catalyst is reacted with fluorinated styrenes as reagents.
Typical data for the polymers are as follows:
Polv-2-fluorostyrene
13C NMR (CDCI3, 50 MHz, 8 in PPM): 35 (methine carbons), 40-41

(methylene carbons), 114-129 (aromatic carbons), 131 (substituted
aromatic quarternary carbons), 160,5d, JC-F = 246 Hz (fluorinated
aromatic carbons).
Poly-3-fluorostyrene
13C NMR (CDCI3, 50 MHz, 8 in PPM): 40 (methine carbons), 41-46

(methylene carbons), 113-130 (aromatic carbons), 147 (substituted
aromatic quarternary carbons), 162,5d, JC-F = 243Hz (fluorinated
aromatic carbons).
Polv-2.3.4.5.6-Dentafluorostyrene
13C NMR (CDCI3, 50 MHz, 8 in PPM): 33 (methine carbons), 37-39

(methylene carbons), 115 (substituted aromatic quarternary
carbons), 135.5m, 138m, 140.5m, 143m, 148m (fluorinated aromatic
carbons)


Metathesis of Styrene Using a Lewis Acid Free Catalyst
The catalytic ability of a Lewis acid free catalyst was
examined using styrene as a model reaction. Styrene (Fisher) was
purified by stirring over calcium hydride for 24 hours, followed by








fractional distillation under vacuum (750C/95 mmHg). The middle
fraction was collected in a breakseal ampule, and the ampule was
attached to the apparatus (Figure 2-6), then evacuated. A side arm
containing freshly cut potassium metal was heated gently with a
torch to form a shiny mirror in the main flask. The break-seal
ampule containing styrene was broken and the styrene was stirred
for 30 minutes over the potassium mirror to ensure absolute purity.
After degassing, the liquid was distilled into a divider, and the
break-seals of each ampule were carefully sealed off and stored in a
freezer.
Catalyst 2 W(CH-t-Bu)(N-2,6-C6H3-i-Pr2)[OCMe(CF3)2]2,
(Figure 2-2, page 22), stored in a dry-box because of its oxygen and
moisture sensitivity, was dissolved in pentane (20 mg/2 ml) and
transferred to a break-seal ampule via a syringe. The break-seal
was then removed from the dry box and sealed under vacuum.
Break-seals containing styrene (1.5 ml) and the catalyst (ratio of
500:1) were connected to the apparatus illustrated in Figure 2-7.
The apparatus then was connected to the high vacuum line via a
14/35 ground glass joint and evacuated. The entire apparatus was
flame dried and the gas trap was closed. The catalyst was
introduced into the reaction flask and the solvent (pentane)
removed by evacuation, after which the apparatus was sealed off
and removed from the line. As soon as styrene was introduced, the
vacuum trap was opened and the gasses that were produced were
condensed with a liquid nitrogen bath. After approximately 2 hours,
the reaction mixture had turned into a light yellow solid, which was
determined to be trans stilbene. The product was dissolved in a











To Vacuum


Styrene


Side Arm


Divider


Potassium Metal


Breakseals


Figure 2-6. Styrene purification over a potassium mirror.










To Vacuum


Condenser


Reagent Catalyst


Gas Trap


Figure 2-7. Reaction flask for metathesis of various
styrene reagents.








minimum amount of hot ether and allowed to precipitate in the
freezer. Typical data obtained from these reactions are as follows:
Trans stilbene
1H NMR (CDC13, 200 MHz, 8 in PPM): 7.05 (vinyl methine protons),
7.15-7.5 (aromatic protons).
13C NMR (CDCL3, 50 MHz, 5 in PPM): 126.4, 127.5 and 128.6

(aromatic carbons), 128.7 (methine carbons), 137.3 (substituted
aromatic quarternary carbons).
CHN: %C = 93.3, %H = 6.67 (Theory)
%C = 93.2, %H = 6.62 (Found)

Metathesis of Fluorinated Styrenes Using a Lewis
Acid Free Catalyst
The ability of the Lewis acid free catalyst to initiate
metathesis on electron deficient vinyl bonds was tested by
employing fluorinated styrenes as reagents. 2-Fluorostyrene
(Lancaster Synthesis Ltd), 3-fluorostyrene (Lancaster Synthesis Ltd)
and 4-fluorostyrene (Lancaster Synthesis Ltd) were all purified and
reacted with catalyst 2. The reactions were all conducted in the
exact manner as described for styrene i.e., approximately 1.5 ml of
reagent was reacted with 20 mg of catalyst 2.
All products were dissolved in hot ether and allowed to
precipitate in a freezer. The products of the reaction of
4-fluorostyrene formed long white needle like crystals was
determined to be pure 4,4'-difluorostilbene. The data for the
product, corroborated by the literature data for 4,4'-fluorostilbene,
follows:








1H NMR (CDCl3, 200 MHz, 8 in PPM): 6.94 (vinyl methine protons),

6.97-7.46 (aromatic protons)
13C NMR (CDCI3, 50 MHz, 8 in PPM): 115,6d, JC-F = 20 Hz, 128,8d,

JC-F = 5 Hz (aromatic), 127,2 (vinyl), 133,3d, JC-F =3 Hz
(substituted aromatic), 162,3d, JC-F = 245 Hz (fluorinated
aromatic).
CHN: %C = 77.77, %H = 4.66 (Theory)
%C = 77.82, %H = 4.72 (Found)
The products of the 2-fluorostyrene reaction and
3-fluorostyrene reaction did not crystallize as well as those from
the 4-fluorostyrene reaction. However, the NMR and CHN data, listed
below confirm them to be 2,2'-difluorostilbene and
3,3'-difluorostilbene, respectively.
2,2'-Difluorostilbene
1H NMR (CDCI3, 200 MHz, 8 in PPM): 7.33 (vinyl methine protons),
7.0-7.3 and 7.58-7.68 (aromatic protons).
13C NMR (CDCI3, 50 MHz, 8 in PPM): 115,8d, JC-F = 25 Hz, 122,9,

124,3, 129,1d, JC-F = 8 Hz (aromatic), 127,1 (vinyl), 125,1d, JC-F
=10 Hz (substituted aromatic), 160,5d, JC-F = 246 Hz (fluorinated
aromatic).
CHN: %C = 77.77, %H = 4.66 (Theory)
%C = 75.51, %H = 5.00 (Found)
3.3'-Difluorostilbene
1H NMR (CDC13, 200 MHz, 8 in PPM): 7.1 (vinyl methine protons),
6.89-7.0 and 7.3-7.34 (aromatic protons)
13C NMR (CDCI3, 50 MHz, 8 in PPM): 112,9d, JC-F = 21 Hz, 114,6d,

JC-F = 18 Hz, 122,6, 130,0d, JC-F = 10 Hz (aromatic), 128,8 (vinyl),








139,1d, JC-F =10 Hz (substituted aromatic), 163,2d, JC-F = 243 Hz
(fluorinated aromatic).
CHN: %C = 77.77, %H = 4.66 (Theory)
%C = 77.75, %H = 4.68 (Found)

Metathesis of Substituted Styrenes Using a Lewis
Acid Free Catalyst
4-Bromostyrene and 3-methylstyrene were metathesized in
the exact manner as for styrene and produced, exclusively, their
substituted stilbene analogues. The data obtained were:
4.4'-Dibromostilbene
1H NMR (CDCI3, 200 MHz, 8 in PPM): 7.01 (vinyl methine protons),

7.26-7.5 (aromatic protons).
13C NMR (CDCI3, 50 MHz, 8 in PPM): 121.6 (aromatic substituted

quarternary carbons), 127 and 128 (aromatic carbons), 131.9
(vinyl methine carbons), 135.8 brominatedd aromatic carbons).
CHN: %C = 49.73, %H = 2.96 (Theory)
%C = 49.12, %H = 2.55 (Found)
3.3'-dimethylstilbene
1H NMR (CDC13, 200 MHz, 8 in PPM): 2.34 (methyl protons), 7.05

(vinyl methine protons), 7.1-7.35 (aromatic protons).
13C NMR (CDC13, 50 MHz, 8 in PPM): 21.4 (methyl carbons), 123,

127 and 128 (aromatic carbons), 137.3 (substituted aromatic
quarternary carbons), 138.0 (methylated aromatic carbons)
CHN: %C = 92.31, %H = 7.69 (Theory)
%C = 86.89, %H = 7.78 (Found)







Acyclic Diene Metathesis (ADMET) Polymerization
of 1.9-Decadiene
General Polymerization Procedure.
Several acyclic diene metathesis (ADMET) polymerizations
were investigated using a Lewis acid free catalyst and 1,9-
decadiene as the monomer. The monomer was dried over calcium
hydride, then subjected to four freeze thaw vacuum cycles to remove
dissolved gases. To insure absolute dryness, the monomer was
transferred in a vacuum line to a flask containing a potassium
mirror, where it was stirred for approximately one hour. The
purified monomer was transferred under vacuum to breakseal
ampules and were sealed under high vacuum.
1,9-Decadiene (Aldrich) was 98% pure (as determined by
GC/MS), and the impurities that were not eliminated by the drying
techniques just described, were removed by allowing the monomer
to react with a single aliquot (20 mg) of catalyst 2 for 15 minutes.
The purified monomer was vacuum transferred into new breakseal
ampules, then sealed under high vacuum. Allowing impurities to
react with the catalyst, in effect destroying a portion of the
catalyst, proved to be an effective method to eliminate impurities.
Monomers purified by this method, without exception, exclusively
metathesized and produced only the expected products in
quantitative yields.
Catalyst 2, W(CH-t-Bu)(N-2,6-C6H3-i-Pr2)[OCMe(C F3)2]2,
was prepared according to published procedures [62, 63]. Twenty
mg of catalyst 2 were dissolved in 2 ml pentane and transferred
into a breakseal ampule. The transfer was performed in a dry box,








in an argon atmosphere, and the breakseal ampule containing the
catalyst solution was sealed with a rubber septum and removed
from the dry box. After freezing the catalyst solution in liquid
nitrogen and applying a high vacuum via a needle pierced through
the septum, the breakseal ampule was sealed using a gas/oxygen
flame.
Breakseal ampules containing aliquots of the catalyst solution
and the purified monomer were connected to a single reaction
vessel, which itself was designed specifically to perform these
polymerizations. Prior to all polymerizations, the entire apparatus
was connected to a high vacuum line and flame dried to remove all
traces of oxygen and moisture adsorbed onto the glass.
The first reaction was performed using the apparatus
illustrated in Figure 2-7. Solvent (i.e., toluene) could not be added
once the reaction was started; thus, the apparatus had to be
modified.
A new apparatus (Figure 2-8) subsequently was designed which
allowed for the removal of ethylene by opening RotafloTM
stopcock A. However, this apparatus produced only oligomers due
to the precipitation of the reaction product in the breakseal
connection arms and was not used further.
This precipitation in the breakseals was eliminated by placing
the breakseals above the condenser (Figure 2-9). The apparatus
allowed higher molecular weight polymers to be produced, but
reaction times were lengthy. Even so, some monomer and solvent
condensed in the gas trap, due to ineffective refluxing. Monomer
and solvent were removed from the apparatus when the












To Vacuum


RotafloT Stopcock A


Gas Trap


Dry-ice/Isopropanol
Condenser


Monomer


Liquid Nitrogen
Condenser




Catalyst


Figure 2-8. Acyclic diene metathesis polymerization apparatus





44
Monomer


To Vacuum


Gas Trap


Dry-ice/Isopropanol
Condenser


Catalyst


Liquid Nitrogen
Condenser


Figure 2-9. Acyclic diene metathesis polymerization apparatus with
monomer and catalyst breakseals above reaction section.








ethylene was pumped out, resulting in lower yields, and the use of
this apparatus was discontinued.
A major problem in conducting the polymerizations proved to be
the premature precipitation of the product. In order to decrease
reaction times by more effective refluxing of solvent and
monomer, modifications were made to the apparatus (Figure 2-10).
Modifications allowed for the controlled removal of ethylene
without loss of monomer. The polymer could be heated
continuously while kept in solution, thereby, remaining in contact
with the catalyst.
All polymerizations were conducted by first transferring the
catalyst solution from a breakseal ampule to the reaction vessel,
then removing the solvent (pentane, in this case). A solid deposit
of catalyst residue remained, and the monomer was introduced
from its breakseal ampule directly into the reaction vessel
containing this catalyst. Upon addition of the monomer, a gas was
released instantly, which was determined to be pure ethylene by GC
mass spectrometry. Ethylene was continuously removed from the
vessel and solidified in a liquid nitrogen trap built into the
reaction vessel. The monomer also distilled in the process, but
was trapped with a partial condenser and returned to the reaction
vessel.
All polymerizations either were performed using carefully dried
toluene as the solvent, or under bulk conditions (no solvent at all).
The temperature of the reaction was varied between 20-750C. All
polymerizations were terminated by exposure to the atmosphere.
The products were purified by dissolving in benzene and






Catalyst


Liquid Nitrogen
Condenser


Dry-ice/Isopropanol
Condenser


Figure 2-10. Acyclic diene metathesis polymerization apparatus with
capillary return line, spiral gas trap and bubble condenser.


46
Monomer








precipitation with methanol. White solids for the high molecular
weight samples and soft elastomers for the oligomers were found.


Reaction Conditions for 1.9-Decadiene Polymerizations
To optimize the reaction conditions for the acyclic diene
metathesis polymerization of 1,9-decadiene several different
reactions were performed with the goal of obtaining high
molecular weight polymer samples in the shortest possible
reaction times. The effect of a large volume of solvent on the
molecular weight of the resulting polymer was examined in this
reaction.


Reaction 1. Approximately 2 ml of purified 1,9-decadiene and 40
ml of toluene were used. Four successive additions of catalyst 2, 8
hours apart, were made. The reaction temperature was kept at
250C for a total reaction time of 32 hours. The reaction time was
not optimal, since the experimental conditions were unknown and
had to be refined. The results of the reaction were:
1H NMR (CDCI3, 200 MHz, 8 in PPM): 5.35 ppm (internal olefinic

protons), 1.95 and 1.25 ppm (methylene protons).
13C NMR (CDCI3, 50 MHz, 8 in PPM): 139.1 ppm (terminal vinyl

methylene carbons),130.4 and 129.8 ppm (trans and cis internal
olefinic carbons), 114.1 ppm (terminal vinyl methine carbons), 32.7
and 27.3 ppm (trans and cis methylene carbons adjacent to internal
olefinic carbons), 29.8 and 29.1 ppm (methylene carbons).


Molecular Weight (Mn): 1700 (end-group analysis).










Reaction 2. In order to evaluate bulk polymerization
conditions,1,9-decadiene (25 ml) and 3 additions of catalyst 2
were added 12 hours apart. The temperature was raised by 5C
increments in order to keep the polymer in the liquid state, up to
500C. No solvent was used. The total reaction time was 40 hours.
A long reaction time was used due to the ineffective refluxing of
the monomer that prevented it from being in constant contact with
catalyst. The following results revealed that polyoctenamer was
produced:
1H NMR (CDC13, 200 MHz, 8 in PPM): 5.35 ppm (internal olefinic

protons), 1.95 and 1.25 ppm (methylene protons).
13C NMR (CDCI3, 50 MHz, 8 in PPM): 139.1 ppm (terminal vinyl

methylene carbons),130.4 and 129.8 ppm (trans and cis internal
olefinic carbons), 114.1 ppm (terminal vinyl methine carbons), 32.7
and 27.3 ppm (trans and cis methylene carbons adjacent to internal
olefinic carbons), 29.8 and 29.1 ppm (methylene carbons).

CHN: %C = 87.27, %H = 12.73 (Theory)

%C = 87.16, %H = 12.68 (Found)

Molecular Weight (Mn): 11 000 (end-group analysis); 12 000 (VPO).
Viscosity [n]: 0.26 dL/g


Reaction 3. Approximately 2 ml of monomer was run under bulk
conditions at 25C for I 1/2 hours during which the polymer
completely solidified. A large volume of toluene, approximately








100 ml, was vacuum transferred into the reaction vessel, and the
reaction temperature was increased from 25C to 50C. Two more
additions of catalyst 2 were made fifteen hours apart, and the
reaction was exposed to continuous vacuum for 40 hours. In order
to compare Reaction 3 with previous reactions, a long reaction
time was employed. Oligomeric polyoctenamer was produced as
indicated by the following results:
1H NMR (CDCI3, 200 MHz, 8 in PPM): 5.35 ppm (internal olefinic

protons), 1.95 and 1.25 ppm (methylene protons).
13C NMR (CDC13, 50 MHz, 8 in PPM): 139.1 ppm (terminal vinyl
methylene carbons), 130.4 and 129.8 ppm (trans and cis internal
olefinic carbons), 114.1 ppm (terminal vinyl methine carbons), 32.7
and 27.3 ppm (trans and cis methylene carbons adjacent to internal
olefinic carbons), 29.8 and 29.1 ppm (methylene carbons).

Molecular Weight (Mn): 1600 (end-group analysis).


Reaction 4. The minimum amount of solvent that would facilitate
magnetic agitation, and its effect on the reaction was tested.
Approximately 2 ml of monomer was used and 3 additions of
catalyst 2 were made; one at the start of the reaction and the rest
as described below. The temperature was slowly raised to 50C
and when the polymer solidified, 10 ml of toluene were added
together with another aliquot of catalyst at 250C. The reaction
temperature was raised slowly to 500C over a period of six hours.
A third addition of catalyst 2 was made after which the reaction








allowed to continue for an additional 24 hours. The following
results were obtained:
1H NMR (CDCI3, 200 MHz, 6 in PPM): 5.35 ppm (internal olefinic
protons), 1.95 and 1.25 ppm (methylene protons).
13C NMR (CDCl3, 50 MHz, 8 in PPM): 130.4 and 129.8 ppm (trans

and cis internal olefinic carbons), 32.7 and 27.3 ppm (trans and cis
methylene carbons adjacent to internal olefinic carbons), 29.8 and
29.1 ppm (methylene carbons).
CHN: %C = 87.27, %H = 12.73 (Theory)
%C = 87.11, %H = 12.68 (Found)

Molecular Weight (Mn): 57 000 (SEC); (Mw): 108 000 (SEC)
Viscosity [n]: 0.89 dL/g


Reaction 5. The effect of increased reaction temperature on the
activity of the catalyst was investigated. Approximately 2 ml of
monomer was polymerized using a double addition of catalyst 2.
The second addition of catalyst 2 was made after one week, and no
solvent was used throughout the reaction. A temperature of
approximately 75C was maintained while a high vacuum was
applied for 2 weeks. Results of the benzene soluble portion were:
1H NMR (CDC13, 200 MHz, 6 in PPM): 5.35 ppm (internal olefinic
protons), 1.95 and 1.25 ppm (methylene protons).
13C NMR (CDCl3, 50 MHz, 8 in PPM): 139.1 ppm (terminal vinyl

methylene carbons),130.4 and 129.8 ppm (trans and cis internal
olefinic carbons), 114.1 ppm (terminal vinyl methine carbons), 32.7








and 27.3 ppm (trans and cis methylene carbons adjacent to internal
olefinic carbons), 29.8 and 29.1 ppm (methylene carbons).

Molecular Weight (Mn): 3000 (end-group analysis).



Reaction 6. The possible formation of cyclic compounds at short
reaction times was investigated. Monomer (0.5 ml of 1,9-
decadiene) was added to 20 mg of catalyst 2 after removal of
pentane from the catalyst, and bulk polymerization conditions were
employed. The reaction temperature was kept at 25C and after 20
minutes the monomer had polymerized sufficiently to solidify,
after which the reaction was terminated by exposure to the
atmosphere. The obtained results were:
1H NMR (CDC13, 200 MHz, 6 in PPM): 5.35 ppm (internal olefinic

protons), 1.95 and 1.25 ppm (methylene protons).
13C NMR (CDC13, 50 MHz, 6 in PPM): 139.1 ppm (terminal vinyl

methylene carbons), 130.4 and 129.8 ppm (trans and cis internal
olefinic carbons), 114.1 ppm (terminal vinyl methine carbons), 32.7
and 27.3 ppm (trans and cis methylene carbons adjacent to internal
olefinic carbons), 29.8 and 29.1 ppm (methylene carbons).

Molecular Weight (Mn): 2500 (end-group analysis).

Reaction 7. Bulk reaction conditions over a shortened reaction
time were investigated. A bulk polymerization was carried out on
1 ml of 1,9-decadiene, using a single addition of catalyst 2. The
polymer solidified after 30 minutes and the temperature was
raised to between 50 and 55C. A high vacuum was applied for 10








hours after which the reaction was terminated. The following
results were obtained:
1H NMR (CDC13, 200 MHz, 8 in PPM): 5.35 ppm (internal olefinic

protons), 1.95 and 1.25 ppm (methylene protons).
13C NMR (CDCI3, 50 MHz, 8 in PPM): 130.4 and 129.8 ppm (trans

and cis internal olefinic carbons), 32.7 and 27.3 ppm (trans and cis
methylene carbons adjacent to internal olefinic carbons), 29.8 and
29.1 ppm (methylene carbons).
CHN: %C = 87.27, %H = 12.73 (Theory)
%C = 87.18, %H = 12.69 (Found)

Molecular Weight (Mn): 25 000 (VPO).
Viscosity [n]: 0.39 dL/g


Reaction 8. The possibility of further polymerizing an existing
polymer was investigated. A portion of the polyoctenamer sample
(1 g) formed in reaction 2 was dissolved in 20 ml of toluene,
syringed into the reaction vessel and then subjected to four
freeze-thaw-vacuum cycles. A single addition of catalyst 2 was
made, and the reaction temperature was slowly raised to 650C.
The reaction was allowed to proceed for 36 hours after which it
was terminated by exposure to the atmosphere, obtaining the
following results:
1H NMR (CDCI3, 200 MHz, 8 in PPM): 5.35 ppm (internal olefinic

protons), 1.95 and 1.25 ppm (methylene protons).
13C NMR (CDC13, 50 MHz, 8 in PPM): 130.4 and 129.8 ppm (trans

and cis internal olefinic carbons), 32.7 and 27.3 ppm (trans and cis








methylene carbons adjacent to internal olefinic carbons), 29.8 and
29.1 ppm (methylene carbons).
CHN: %C = 87.27, %H = 12.73 (Theory)
%C = 87.20, %H = 12.71 (Found)

Molecular Weight (Mv): 83 000 (viscosity).
Viscosity [n]: 0.76 dL/g

The Acyclic Diene Metathesis (ADMET) Polymerization
of 1.5-Hexadiene.
General polymerization Procedure.
The metathesis of 1,5-hexadiene to linear poly-1,4-butadiene
was investigated, using a Lewis acid free catalyst. The monomer,
1,5-hexadiene, was purified in the same manner as for 1,9-
decadiene. The catalyst solution and apparatus were unchanged from
that used in producing polyoctenamer (ie., 20 mg of catalyst 2,
W(CH-t-Bu)(N-2,6-C6H3-i-Pr2)[OCMe(CF3)2]2, and the apparatus
shown in Figure 2-10).


Reaction Conditions for 1.5-Hexadiene polymerizations
Two polymerizations were conducted. In the first
polymerization, 50 ml toluene (2.53 x 10-5 mol) were used as the
solvent. Three additions of catalyst, 20 mg per addition, were made
to approximately 5 ml (6.0 x 10-2 mol) of 1,5-hexadiene. The three
additions of catalyst were made approximately 24 hours apart. The
reaction temperature was kept at 25C, while the reaction was
continuously stirred for a period of two months. Since the reaction
had been reported to be impossible [56], an excessively long reaction








time was used in the first reaction. The lifetime of the catalyst is
also unknown and an extensive reaction time was used to give some
indication of the activity of the catalyst over a long period of time.
A slight vacuum was occasionally applied to remove the ethylene
produced.
The product was purified by dissolving in benzene and
precipitating the polymer with methanol. The resulting elastomeric
polymer, obtained in a quantitative yield, was light yellow in color.
The following results were obtained:
1H NMR (CDC13, 200 MHz, 8 in PPM): 5.42 ppm (internal olefinic
protons) and 2.05 ppm (methylene protons)
13C NMR (CDCI3, 50 MHz, 8 in PPM): 130.0 and 129.4 ppm (trans and

cis internal olefinic carbons) and 32.7 and 27.5 ppm (trans and cis
methylene carbons)
CHN: %C = 88.82, %H = 11.18 (Theory)
%C = 88.61, %H = 11.16 (Found)

Molecular Weight (Mn): 8300 (SEC); (Mw): 16 400 (SEC)
The second reaction was done in order to compare the ability
of the catalyst to polymerize 1,5-hexadiene under bulk reaction
conditions. The reaction was modeled after reaction 7 of the 1,9-
decadiene series, where bulk reaction conditions were employed. A
single aliquot (20 mg.; 2.5 x 10-5 mol) of catalyst and 2 ml (0.024
mol) of 1,5-hexadiene was used. The reaction temperature was
maintained at 250C until the polymer could no longer be stirred by
magnetic agitation. The reaction temperature was then increased to
520C and a continuous high vacuum (10-6 mmHg) applied. The








polymer's viscosity increased over the next 5 hours, after which it
could no longer be agitated and the reaction was terminated. The
total reaction time of the second reaction was 10 hours.
The product was purified by dissolving it in benzene and
precipitating with methanol. The resulting elastomeric polymer,
obtained in near quantitative yields, was light yellow in color. The
following results were obtained:
1H NMR (CDCI3, 200 MHz, 8 in PPM): 5.42 ppm (internal olefinic
protons) and 2.05 ppm (methylene protons)
13C NMR (CDC13, 50 MHz, 8 in PPM): 130.0 and 129.4 ppm (trans and

cis internal olefinic carbons) and 32.7 and 27.5 ppm (trans and cis
methylene carbons)
CHN: %C = 88.82, %H = 11.18 (Theory)
%C = 88.54, %H = 11.22 (Found)

Molecular Weight (Mn): 14 000 (SEC); (Mw): 28 000 (SEC)















CHAPTER 3
THE KEY TO SUCCESSFUL ACYCLIC DIENE METATHESIS (ADMET)
POLYMERIZATION CHEMISTRY.


Competing side reactions are one of the major factors that
determine if a given reaction is suitable for equilibrium step
propagation, condensation type polymerization. Even a very small
percentage of side reactions will prevent the principal reaction
from producing high molecular weight polymer, leading instead to
the formation of low molecular weight oligomers, and perhaps other
undesirable by-products.
Previous polymerization studies on acyclic dienes revealed
that more than olefin metathesis polymerization was taking place
[58]. While metathesis chemistry appears to be the dominant
reaction, vinyl addition chemistry does compete with acyclic olefin
metathesis. Thus, vinyl addition reactions must be eliminated
completely in order for acyclic diene metathesis polymerization to
be useful chemistry.









(CH2)x
Acyclic Diene



WC16 /
EtAIC2 / EtOH
R
I
-[--CH-CH-(CH2)n--
I -+ (CH2)x' + n C2H4
-+-CH-CH-(CH2)n-
I Acyclic Diene Metathesis
Polymerization
A Vinyl Addition Reaction

Figure 3-1. The possible reactions that can occur when a
Lewis acid is used as cocatalyst.



Styrene as a Model Compound
A model compound study was undertaken to investigate the
elimination of side reactions. Vinyl addition chemistry was
expected to be the principal side reaction that was occurring, and a
model compound system that would allow a simultaneous
investigation of vinyl addition and metathesis chemistry was
selected. The reaction of styrene was chosen, since benzyl
carbocations can be formed quite easily, which would permit the
vinyl addition reaction to compete directly with metathesis. In order
to study the competition between metathesis and vinyl addition
chemistry (Figure 3-1), bulk reactions of styrene were examined








with WCI6/EtAICI2 as the catalyst. The styrene reaction is an

excellent model system, since vinyl addition would lead to
polystyrene [64], whereas metathesis would lead to stilbene. Both
styrene and stilbene can be readily identified by spectroscopic
methods [65] even when a mixture of products is produced. In fact,
vinyl addition chemistry proved to be the only reaction occurring,
presumably because of the cationic polymerization of styrene
(Figure 3-2) with no stilbene being observed.




Metathesis does
not occur
Vinyl addition 6

WC16
EtAlC12/ EtOH H 2
nCH2
CH2
-(- CH2-CH--H2



Polystyrene Stilbene


Figure 3-2. Attempted metathesis of styrene using a
Lewis acid catalyst system.
The main competing side reaction is believed to be the cationic
polymerization of styrene. Cationic polymerization can be initiated
by the Lewis acid used as cocatalyst in the classical reaction
scheme (Figure 3-2), and consequently, model reactions were
conducted to eliminate these vinyl addition reactions.








The minimization of vinyl addition reaction (polymerization)
was investigated by varying the sequence of addition of reactants
into the reaction vessel (Table 3-1).


Table 3-1. Order of addition of reactants in the
styrene model reaction.
First Second Last
Catalyst Co-catalyst Styrene
Catalyst Reagent Cocatalyst
Cocatalyst Reagent Catalyst
Cocatalyst Catalyst Reagent
Reagent Catalyst Cocatalyst
Reagent Cocatalyst Catalyst


The catalyst and cocatalyst were allowed to react for varying
amounts of time at various temperatures prior to the addition of
reagent. No change in the products was observed, and only
polystyrene was identified as the product of the reaction.
The cocatalyst solvent, hexane, was removed either
immediately after the catalyst and cocatalyst were combined, or
after the catalyst and cocatalyst were allowed to react for some
time. No change in the chemistry was observed.
Three solvents were examined, including chlorobenzene, which
is the most widely used solvent with this specific catalyst system
[66]. Because cationic polymerization of styrene occurs instead of
metathesis, solvents of lower dielectric constants were used.
Solvents of low dielectric constant are known to eliminate the








formation of ions [67], thus possibly preventing cationic
polymerization. Carbon tetrachloride (2.0) and hexane (5.7) were
tried, but no change in the chemistry was observed.
When Schlenk vacuum line techniques were used, the analysis
of the gases produced frequently indicated the presence of ethane.
Evidently, trace amounts of moisture were present that reacted with
the EtAICI2 to produce ethane. In order to assure absolute purity and
dryness of the reagents, and the apparatus, high vacuum techniques
were employed. Under these conditions no ethylene was observed in
the styrene reactions, indicating that metathesis did not occur, and
only cationic polymerization was observed.
Since the Lewis acid (EtAICI2) initiated vinyl addition,
different cocatalysts (Et2AICI and Et3AI) were tried. No stilbene
was produced, and as before, only polystyrene resulted.
The use of different reaction conditions, addition sequences,
solvents, and Lewis acid cocatalysts proved to be unsuccessful, and
it can be concluded that the metathesis of styrene does not occur
when WCI6 and an alkyl-aluminum containing Lewis acid is used as
the catalyst system.


Preventing the Cationic Polymerization of Styrene
In an effort to destabilize styrene toward cationic
polymerization, four fluorinated styrenes (2-fluorostyrene, 3-
fluorostyrene, 4-fluorostyrene and 2,3,4,5,6-pentafluorostyrene)
were investigated with the WCI6/ETAICL2 catalyst system. By
reducing the electron density in the vinyl bond of styrene the
likelihood of forming styrene carbocations might be eliminated,








thereby reducing styrene's propensity to undergo vinyl addition
polymerizations. In each case, however, vinyl addition predominated.
Although the reaction proceeded at a slower rate, the only products
observed were fluorinated polystyrenes. A comparison of the NMR
spectra of the products formed with NMR spectra of authentic
fluorinated polystyrenes (Spectra 3-1, 3-2), prepared by anionic
polymerization, indicates that only fluorinated polystyrenes were
produced. 2,3,4,5,6-Pentafluorostyrene polymerized the slowest of
all the fluorinated styrenes that were used, and when high vacuum
techniques were employed, 2,3,4,5,6-pentafluorostyrene did not
react at all, indicating that destabilization of the carbocation does
indeed prevent carbocation formation.
In order to test for catalyst activity in the fluorinated
systems, an acyclic diene known to undergo metathesis
oligomerization (i.e., 1,9-decadiene), was added to the reaction after
24 hours, which metathesized to give polyoctenamer of low
molecular weight and some intractable material [58]. A metathesis
active catalyst system obviously was present, and apparently, the
electron withdrawing nature and the bulkiness of the fluorine groups
on the 2,3,4,5,6-pentafluorostyrene prevent this reagent from either
polymerizing or metathesizing









i



j


UC


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-8




















































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-7e







Investigation of a Lewis Acid Free Catalyst System with
Styrene as the Model Compound
The use of Lewis acid free catalysts could obviate the
formation of carbocations, thereby eliminating vinyl addition
reactions. Efforts were focused on choosing an appropriate catalyst
system which would be less acidic and would not induce vinyl
addition polymerization. The homogeneous metathesis catalyst
prepared by Schrock [62, 63] was chosen because it is free of Lewis
acids. Schrock reported that the catalyst was extremely active for
the metathesis of internal olefins, yet, under the reaction conditions
reported, styrene, 1-octene, and allyltrimethylsilane metathesized
slowly [62].
While these results were encouraging, it was not apparent if
these catalysts would be suitable for acyclic diene metathesis
polymerization. Two derivatives of the catalyst, types 1 and 2
(Figure 2-2, page 22), were chosen since they are reported to be the
least active (catalyst 1) and most (catalyst 2) active metathesis
catalysts for internal olefins. Catalyst 1 produced stilbene from
styrene. However, under similar reaction conditions, the reaction
rates were much slower compared to catalyst 2. Preliminary
styrene metathesis results and the metathesis of cis-2-pentene [63]
led to the exclusive use of catalyst 2 in subsequent studies.
Reaction conditions were chosen that were appropriate for
modeling bulk polymerization reactions. Specifically, no solvent
was used as is appropriate for equilibrium step propagation,
condensation polymerization chemistry [68], and when using








catalyst 2 (page 22), the mechanism for the styrene reaction
changed completely from vinyl addition to metathesis chemistry
(Figure 3-3).



Vinyl addition does th
not occur Metathesis

C(CH3)3
CH
(R)2(CH3)CO, I CH
(R)2(CH3)CO + C,
-CH2-CH CH2

I Catalyst_2 R = CF3

Polystyrene Stilbene

Figure 3-3. Styrene metathesis using a
Lewis acid free catalyst.


Metathesis occurs quantitatively, a result which represents a
spectacular change from the previous result shown in Figure 3-2.
The reaction was permitted to continue over a two hour period, and
no side reactions (i.e., vinyl addition reactions) were observed. The
NMR spectrum 3-3 of the unpurified product only shows resonances
that are indicative of trans stilbene. No other products were
present.
The gas formed during the reaction was analyzed by mass
spectroscopy (Spectrum 3-4), which shows that only ethylene was
produced by the reaction (expected if only metathesis occurred).






66























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Investigation of a Lewis Acid Free Catalyst System with Substituted
Stvrenes as Model Compounds
In order to demonstrate the potential of this olefin metathesis
reaction, a variety of substituted styrenes were investigated, and
the reactions in Figure 3-4 indicate the versatility of the Lewis acid
free catalyzed metathesis reaction. Using a Lewis acid free
catalyst system, 2-fluorostyrene (Reaction A), 3-fluorostyrene
(Reaction B) and 4-fluorostyrene (Reaction C) all metathesize
cleanly and produce the analogous substituted stilbenes in a manner
much the same as for styrene.
The reactions were carried out over a 24 hour period in the
reaction vessel (Figure 2-5) designed for styrene reactions.
Powderous, substituted stilbenes in essentially quantitative yields
were obtained. Reaction times were not optimal, nor were they
indicative of the rate of the reactions, and it is expected that under
optimal reaction conditions, reaction times will be considerably
shortened. The products were pure as is shown by the NMR spectra
3-5, 3-6 and 3-7. Elemental analysis substantiated the exclusive
formation of substituted stilbenes without a trace of any vinyl
addition products.














Metathesis
Catalyst 2
Catalyst_2


Reaction A


Reaction B


Reaction C


Reaction D


Reaction E


R,=R3=R4=H ;R2=F


R,=R2=R4=H ;R3=F


R,=R2=R3=L1 ;R4=F


R1=R2=R4=H ;R3=Br


R,=R2=R3=H ;R4=CH3


Figure 3-4. The Metathesis of substituted styrenes.



Producing substituted stilbenes in high yields and purity is

in sharp contrast to the previous methods used to prepare these

products [69 70, 71 72]. The preparation of 4,4-difluorostilbene by

Ager [73] in 1972, using the synthetic route shown in Figure 3-5, is

a prime example of the lengthy, low yield reactions previously used


RI



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in the synthesis of substituted stilbene compounds. Obviously,
metathesis provides a much more efficient, single step synthetic
method. Yields of previous synthetic methods ranged from 10-30 %,
and mixtures of products were always observed which made
purification difficult.

CHO

F- CH2CI g F- CH2MgC +
Et20
F

(1) 2 hours, heat
(2) NH4C (aq.)


F-\CH2-CHOH -- F

P205
benzene
heat

\/ CH\=CH F


Column
Chromatography


trans 4,4'-difluorostilbene (10% yield)


Figure 3-5. Synthesis of 4,4'-difluorostilbene








2,3,4,5,6-Pentafluorostyrene did not react at all under these
reaction conditions. If the reaction is heated to 700C, poly-
2,3,4,5,6-pentafluorostyrene is formed (Spectrum 3-8). A second
addition of catalyst also proved to be ineffective. No
decafluorostilbene was produced. Two possible reasons why
2,3,4,5,6-pentafluorostyrene does not metathesize are:
(1) The five fluorine atoms have such a strong electron
withdrawing effect on the molecule that the electron density of the
vinyl bond is diminished to the extent that it cannot coordinate with
the already electron deficient catalyst metal center. The tungsten
carbon double bond in the analogous benzylidene metal complex was
found to be shorter when fluorinated alkoxide ligands were present
than in the presence of non-fluorinated ligands [63]. Shortening of
the tungsten carbon double bond was attributed to the electron
withdrawing nature of the hexa-fluoro alkoxide ligand. A
combination of the electron withdrawing effect of the hexafluoro
alkoxide ligands and the diminished electron density of the
pentafluorostyrene vinyl bond provide a plausible explanation for the
unreactivity of 2,3,4,5,6-pentafluorostyrene.
(2) Fluorine atoms are relatively small. Due to a high
electron density, repulsion are experienced over long ranges, thus
making fluorine bulky in terms of stereochemistry [63]. This
"bulkiness" could be a factor in preventing the vinyl bond of
2,3,4,5,6-pentafluorostyrene from coming into close proximity with
the catalyst to produce the metallocyclobutane ring intermediate,
essential for metathesis to occur [25, 26, 27]. X-ray structural
analysis of W(CHPh)(NAr)[OCMe(CF3)2]2 indicates that the two


























(3
(D0
r L>
U-)
0 4
ca






a ) c
~Cl
E-

0
aca

EO









-u



0a)
.4-U


4.-'



0

0

0
N LV
a)V
LO'








alkoxide ligands are turned away from each other and also that the
two tryfluoromethyl groups, in each alkoxide, are turned away from
the benzylidene and imido ligands [62]. The presence of fluorine
atoms at the two ortho positions of 2,3,4,5,6-pentafluorostyrene
result in bigger steric repulsion between the alkoxide ligands and
the pentafluoro benzylidene ligand. Van der Waals interactions
between trifluoromethyl and hydrocarbon groups, as well as any
interaction between triflouromethyl and the ortho fluorines on the
pentaflourobenzylidene ligand must be diminished for a
metallocyclobutane ring to be formed. Stereochemical overcrowding
at the metal center may prevent a second 2,3,4,5,6-
pentafluorostyrene molecule from approaching, thereby preventing
the formation of a metallocyclobutane intermediate and
subsequently metathesis.
4-Bromostyrene (Reaction D; Figure 3-4, page 69) and 3-
methylstyrene (Reaction E Figure 3-4, page 69) metathesize cleanly
and form the respective substituted stilbenes in quantitative yields,
as confirmed by elemental analysis and NMR spectroscopy (Spectra
3-9,10). Cadogan and Inward [74] investigated the three possible
methods [75, 76, 77] for the preparation of trans-4,4'-
dibromostilbene and found that a modified version of the Bance,
Barber and Woolman method [77], was the most satisfactory with
yields slightly higher than 40%. The other two methods gave
stilbene yields ranging from 3%-40%. All three methods involved
multistep reactions and rigorous purification of the starting
materials. It is evident that the single step metathesis reaction























U)
C)
ca
r0
a)
E
0a


-c














08
o
-0



(3 -


















0.
Coa
ocu













a)

2

In








E



a-





Qd


cu











-vu









cu



--m


















to


C
13


E


CL
aO








procedure with its essentially quantitative yield is the preferred
route to produce stilbenes..
These model reactions demonstrate the versatility of the
metathesis reaction system, and show that vinyl addition side
reactions can been eliminated completely. The essentially
quantitative yields fulfill the prerequisite of high percentage
conversion (>99%) of monomer to polymer, required by step
condensation type polymerization.
Expanding small molecule metathesis chemistry into a
polymerization reaction is the next challenge. Acyclic diene
metathesis polymerization would be the first new equilibrium step
propagation condensation type polymerization in 20 years.
Subsequent chapters elaborate on the feasibility and implementation
of the acyclic diene metathesis polymerization technique.














CHAPTER 4
ACYCLIC DIENE METATHESIS POLYMERIZATION (ADMET).
THE SYNTHESIS OF POLYOCTENAMER USING 1,9-DECADIENE AS
A MONOMER.



The first high molecular weight polymer synthesized by
acyclic diene metathesis polymerization is reported herein. Prior to
the research discussed below, the catalyst requirements and the
reaction conditions required to produce high molecular weight
polymers by acyclic diene metathesis polymerization techniques
were unknown. Following the successful metathesis of styrene and
its derivatives, the focus of the research turned toward the
polymerization of 1,9-decadiene to demonstrate that acyclic diene
metathesis (ADMET) could produce high molecular weight
polyoctenamer.
Polyoctenamer was chosen as a target model polymer since it
is well characterized [78]. The physical properties of polyoctenamer
prepared by ring opening metathesis polymerization are known [78];
thus it was possible to compare the properties of acyclic diene
metathesis polymerization samples directly with polymers formed
by ring opening metathesis polymerization.
Eight polymerizations were performed to establish the most
suitable conditions to yield high molecular weight polymers, and to








investigate the different properties of the polyoctenamer samples
produced. A discussion of the molecular weights obtained under
different experimental conditions, as well as the physical
properties of the polymers formed, follows.


Acyclic Diene Metathesis as a Polymerization Reaction
The polymerization chemistry under investigation (Figure 4-1)
yields only two products, polyoctenamer and ethylene, and by

ZC2=CH-(CH2)6-C=CH2
1,9-decadiene

Catalyst : Monomer
1 :5000
Vacuum (10-6mmHg)
Heat (25-65oC)


--CH=CH-(CH2)6-)- + CH2=CH2
polyoctenamer
Figure 4-1. Acyclic Diene Metathesis Polymerization
of 1,9-decadiene.


removing ethylene the polymerization could be driven to produce
high molecular weight polyoctenamer. No accompanying reactions
were observed. The first four reactions specifically were done to
show that high molecular weight polyoctenamer can be produced by
ADMET polymerization (Table 4-1).









Table 4-1. Molecular weights of first four polyoctenamer samples
prepared by acyclic diene metathesis polymerization


Polyoctenamer Viscositya Molecular Weight
Reaction (d/g) ((Mn)
1 1 700b


2 0.26 11 000b
12 000C


3 1 600b


4 0.89 57 000d


(a) 250C in toluene; (b) Endgroup analysis by 3C NMR;
(c) Mn by VPO analysis; (d) Mw (108000) and Mn were
measured assuming the polymer to be polystyrene, the
calibration standard, and multiplied by 0.45. This
factor is the estimated ratio of the unperturbed
dimensions, , for polystyrene and polyoctenamer.



Three additions of catalyst were made, and a large volume of
solvent was used in the first reaction. While a low molecular
weight (1700) pure polyoctenamer sample with a trans content of
65% was produced in the first reaction, it was encouraging that no
intractable material was observed. The low molecular weight of the
polymer is attributed to the oligomers solidifying in the breakseal
ampules (Figure 2-7, page 37) that contained the catalyst and








monomer, which prevented metathesis. Thus, oligomers were
prevented from constant contact with the catalyst thereby reducing
polymerization rates and allowing only the formation of oligomeric
material.
Placing the monomer and catalyst ampules above the reflux
condenser prevented the precipitation of polymer in the breakseal
ampules. An increase in both the molecular weight and trans
stereochemistry percentage of the product produced in the second
polymerization reaction was achieved. More efficient refluxing and
return of the unreacted monomer and solvent to the reaction vessel
could increase the molecular weight and simultaneously decrease
the reaction time.
When large volumes of solvent are used, it becomes evident
from reaction 3 that only low molecular weight oligomers with a
low stereochemical trans content are formed. In light of Reaction 3
results, it seems as if higher temperatures and a minimal amount of
solvent could produce the desired high molecular weight polymers.
A minimal amount of solvent and reaction temperature of
55C produced a polymer of high molecular weight and high
percentage trans stereochemistry. Based on the results of Reaction
4, acyclic diene metathesis (ADMET) polymerization can produce high
molecular weight polyoctenamer. Experiments followed in which
different reaction conditions were examined.









Table 4-2. Molecular weights of polyoctenamer samples produced
under bulk acyclic diene metathesis polymerization conditions.


Reaction % transa Molecular weight
(Mn)


5 85 3000b


6 90 2000b


7 91 25000c


(a) As determined by quantitative 1C NMR; (b)
Endgroup analysis utilizing "C NMR; (c) Mn
determined by VPO.


Bulk Polymerization Conditions
Bulk polymerizations are the most common method used for
step polymerization since they yield fast reactions which can easily
be controlled.
Bulk polymerizations [68]. are performed generally above the
melting point of the polymer to facilitate agitation. Calderon [79]
reported that 100% trans polyoctenamer melts at 73C, and so a
polymerization temperature of 75C was chosen for the first bulk
polymerization (Reaction 5, Table 4-2). A fraction of the product
formed at 750C was soluble in boiling benzene and had a low number
average molecular weight.








Two additional reactions were performed under bulk
polymerization conditions. Reaction 6 was allowed to proceed for
20 minutes at 25C under bulk reaction conditions and a low
molecular weight, 91% trans polyoctenamer resulted. No intractable
material was produced indicating that no side reactions occurred at
the lower temperature.
Effective agitation of polyoctenamer samples formed under
bulk conditions at 25C becomes impossible after approximately one
half hour due to the increased viscosity of the reaction product. By
raising the reaction temperature to 55C, it was possible to reduce
the viscosity of the sample and magnetic agitation again became
possible. However, after an additional four hours, the polymer's
viscosity increased to the point where magnetic agitation ceased.
These manipulations increased the molecular weight to a value of
25000. The increased molecular weight observed in reaction 7
indicates that polyoctenamer can successfully be prepared by
acyclic diene metathesis polymerization under bulk reaction
conditions at 55 OC.
Higher molecular weights can be achieved in shorter times
with agitation from high torque mechanical stirring. Results from
bulk polymerizations indicated that the catalyst does not decompose
at 55 oC. A polymer of high trans stereochemistry (approximately
90%) with moderate molecular weight can be produced in a
relatively short time under bulk conditions. Better agitation
undoubtedly will produce even higher molecular weights.







Tailoring of Acyclic Diene Metathesis Formed Polymers
The ability to tailor acyclic diene metathesis polymerization
reaction conditions to produce a wide variety of polymers with
varying molecular weights and physical properties (e.g., melting and
crystallization points) was investigated in this experiment.
Termination of acyclic diene metathesis polymerization is achieved
by exposing the polymerization to oxygen and moisture, which
decomposes the catalyst. Because the catalyst is not permanently
fixed to the chain ends, both chain ends of the polymer retain vinyl
bonds that can be further polymerized by acyclic diene metathesis
techniques if the polymer is to be reacted with active catalyst
(Figure 4-2).

/f-C6 -=C-\

I ADMET


C6 -= y- C6

where Y >>> X


Figure 4-2. Continued telechelomer ADMET polymerization to
high molecular weight polyoctenamer.
A polyoctenamer sample that had a reduced viscosity of 0.26
dL/g was converted to a higher molecular weight polymer, as
indicated by an increased reduced viscosity number of 0.76 dL/g.
The trans olefin content increased from 78% to 88% which resulted








in higher melting and crystallization points for the produced
polymer.
Acyclic diene metathesis polymerization eliminates the
possibility of producing a polymer with undesirable physical
properties, provided these properties can be altered by an increase
in molecular weight. The ability to increase the molecular weight of
a sample and tailor its physical properties indicates the advantage
that acyclic diene metathesis polymerization has over other
polymerization techniques.

Determining the Stereochemistry of the Olefin Units in
Polyoctenamer
The stereochemistry of the internal olefin units of
polyoctenamer varies [78], depending on the method and reaction
conditions used to produce the polymer sample. Because the
physical properties of a specific polyoctenamer sample depend on
the stereochemistry of the internal olefin units, it is important that
the cis/trans ratio of the internal olefin units be determined
accurately. Three spectroscopic techniques can used to determine
the cis and trans stereochemistry, 1H NMR, 13C NMR and infrared
spectroscopy. All three methods were employed to characterize the
polymer samples that are described in this dissertation and the
accuracy of the cis/trans ratios assigned by these methods was
individually accessed.
The proton NMR spectra for all of the polymer.samples
prepared by acyclic diene metathesis essentially were identical
(Spectrum 4-1), with the exception of cis/trans ratios. Hatada [80,





























H










co
0a
-a


L.


E



CLU
Maa



0
~a-c

LC.)
ca,v



CI
=0



Z
0C


N
N

E

00
C~l -








81] used spin decoupling to distinguish between the cis and trans
proton signals of 1,4-polybutadiene, a technique which can be
applied to polyoctenamer. Spin decoupling was applied to
polyoctenamer by Sato [82], whereby the olefinic protons of
polyoctenamer can be separated into cis and trans peaks. However,
the use of quantitative 13C NMR would lead to much more accurate
assignment of cis/trans ratios for polyoctenamer, because the
separation between the two decoupled proton NMR peaks, is minimal
(only 0.5 ppm without baseline separation). A comparison of the 13C
NMR resonances for polyoctenamer reported by Katz [83] and those
found for the polyoctenamer samples prepared by acyclic diene
metathesis polymerization indicates that only linear polyoctenamer
is produced (Spectrum 4-2).
Prior to performing any quantitative 13C NMR experiments, the
Ti relaxation times of all the carbon atoms present in a repeat unit
of polyoctenamer were determined with a Varian XL 200
spectrometer [84]. Reliable carbon integration can only be obtained
from fully relaxed 13C NMR spectra [85], and relaxation times were
measured for 3 different polyoctenamer samples in order to
determine the longest T1 present in a repeating unit. Spectrum 4-3
indicates the 8 different relaxation times used and the effect of the
relaxation times on the signals of the different carbon atoms in a
repeat unit. The Ti relaxation times found for the 8 carbon atoms in
a repeat unit are listed in Table 4-3.







































; i


vi


q.

I a
IA'


LU



70
n


(1)
C.)
Q
0

0c
CL
a)
E
c

0cU

cXa)

a)V
CZ


0
Co,


coc




c~J
N
N (D
E

0 0






4-'
C.,
E


a)
a
U)

























C
0

ca















IF-




O'4-C3






E cn
ZC
00

,- M
o >
>% (D
ca c



a),

C:l'
z C:
0 C

cn CZ
N C :

N %




LO a- *r







Table 4-3. Relaxation times of carbon atoms in a
repeat unit of polyoctenamer.


Peak(ppm) T1 (sec.) Error(sec.)

139.1 10.42 2.73
130.3 1.99 0.03
129.9 1.49 0.15
114.1 4.89 0.95
32.7 0.99 0.02
29.6 1.15 0.02
29.2 1.27 0.14
29.0 1.13 0.02
27.2 1.21 0.11



Based on this information, a single pulse delay mode and delay
times more than four times that of the longest T1 were used for
quantitative carbon experiments.
Using 13C NMR spectroscopy, it is possible to distinguish
between both the cis and trans internal olefin carbons and the
allylic carbon adjacent to the internal olefin carbon. The internal
cis olefin carbon appears at 129.8 ppm and the trans internal olefinic
appears at 130.4 ppm. Several researchers [86, 87, 88, 89, 90, 91]
have demonstrated that the carbon atom adjacent to the internal
olefinic carbon has two different resonances, (i.e., the cis carbon at
27.3 ppm and the trans carbon at 32.7 ppm). The resonances at 32.7
ppm were reported to be weak or unobserved for the predominantly
cis-polyoctenamers produced by ring opening metathesis. A one to
one correlation between the peak intensities of these allylic carbon
resonances and those of the internal olefin carbons corroborates the