Acyclic diene metathesis (ADMET) polymerization

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Acyclic diene metathesis (ADMET) polymerization the synthesis of well-defined model polymers for polyolefin materials
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Valenti, Dominick J., 1969-
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Thesis (Ph. D.)--University of Florida, 1997.
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Includes bibliographical references (leaves 161-172).
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by Dominick J. Valenti.
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Typescript.
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Vita.

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ACYCLIC DIENE METATHESIS (ADMET) POLYMERIZATION:
THE SYNTHESIS OF WELL-DEFINED MODEL POLYMERS FOR
POLYOLEFIN MATERIALS











By
DOMINICK J. VALENTI


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



























This dissertation is dedicated to my family: Anthony, Patricia, and Julia
Valenti, all of whom have provided me with unlimited support, confidence,
love and strength to achieve any goal or challenge in the known universe.













ACKNOWLEDGMENTS


I would like to first acknowledge Dr. Guy Mattson for introducing me

to the world of polymer chemistry and for his faith in my abilities from the

beginning.

Special thanks are extended to Dr. Chris Marmo and Dr. Jason Portmess

who instigated my interest in ADMET chemistry. Sincere thanks are

extended to all the members of the Wagener group, past and present: Dr. K.
Brzezsinka, Dr. J. Anderson, Dr. J. O'Gara, Dr. D. Tao, Dr. H. Tamura, Dr. J.

Konzelman, J. Reichwein, F. Gomez, S. Cummings, T. Davidson, D. Tindall,

M. Watson, S. Wolfe and L. Williams.

I would also like to recognize the cooperation of Drs. R. Duran, J.

Reynolds, K. Wagener and G. Butler that has created an institute of vast

resources, knowledge and funding for this and other scientific pursuits.

Sincere thanks are also extended to the past and present members of
the Duran and Reynolds groups for their contributions and support of my

research goals. Specific recognition is extended to J. Batten, Dr. A. Kumar, D.

Cameron, Dr. P. Balanda, and Dr. M. Diverti for significant contributions of

scientific knowledge and philosophical ideas.

Grateful acknowledgment for funding is given to the National Science
Foundation and The Dow Chemical Company. Special recognition is

extended to Steve Hahn from Dow for his contributions, ideas, and faith in
this project from start to finish.








Respects go to D. Panosian, T. Nguyen, J. Miller, L. Wolert, and N.
Morales for boundless friendship, support and thoughtfulness.
Finally I would like to thank Dr. Wagener for believing in my abilities
and providing nearly unlimited resources, freedom and knowledge that have
made this research and my graduate education possible.














TABLE OF CONTENTS




ACKNOWLEDGMENTS.............................................. iii

A BST R A C T ........................................................................ ..................................viii

CHAPTERS

1 INTRODUCTION......................................................... 1

History of Polyethylene and Related Polymers............................... ......3
Discovery and Synthesis of "Polymethylene".................... .............. 3
Synthesis of Polyethylene via Radical Chemistry..................................... 6
Synthesis of "Polyethylene" (Heterogeneous Ziegler Catalysts).............9
Synthesis of "Polyethylene" (Homogeneous Ziegler Catalysts)........... 12
Copolymerization of a-olefins............................ .............. ...........15

Structure-Property Relationships of Polyolefins...................... ............ 18
Crystallinity, Morphology, and Melting of Flexible Chain
M acrom olecules................................... ..... .......................... 20
Thermal Behavior and Chain Structure.............................................. 23

M etathesis Polym erization......................................................................... 27
Ring Opening Metathesis Polymerization (ROMP)
and Well Defined Alkylidenes...........................................................27
Acyclic Diene Metathesis Polymerization (ADMET)..............................30
ADMET: Step Condensation Method to Producing a-Olefin
Precursor Polym ers................................... ....................................34


2 EXPERIM EN TA L.............................. ........................................................ 36

Instrumentation and Analysis......................... .............................36

M materials and Techniques..................................... ..................................... 38

Synthesis and Characterization.............................. ......... ........................ 39
Synthesis of Symmetrical Alkyl-Substituted Terminal Dienes............39








Alternative Enolate Displacement Reactions for the
Synthesis of Compounds la, and lb................................................45
Alternative Methods for the Synthesis of Compounds (5a)-(5c)..........52
W ittig M ethod............................................. .... .........................53
Tertiary alcohol synthesis and Reduction............................................54

ADMET Polymerizations of Monomers (5a) and (5b)................................ 57
General Metathesis Conditions............................. ........................ 57

Hydrogenation of Polymers (P5a) and (P5b)...................................................60

Alcohol Monomer Synthesis.................................................61

ADMET Polymerizations of Alcohol Monomers (Al), (A2), (A3).............64
General M etathesis Conditions................................................................64
Hydrogenation of Poly [1,10-Undecadiene-6-ol] (HPA2).......................66

Preliminary Alcohol Dimerization Experiments..................................68


3 DESIGN AND SYNTHESIS OF SYMMETRICAL ALKYL-
SUBSTITUTED TERMINAL DIENES...................................................71

Designing the Target Monomers........................................ .........................72

Synthesizing the Target Monomer.......... ............. ...........................75
3-Keto Ester Substitution Method....................... ............ ............... 75
Enolate Alkylation of Ethyl Acetoacetate and the
Retro-Claisen Condensation.................................................... 80
Reduction, Tosylation, and Hydride Displacement.............................. 87
Dealkoxycarbonylation of the Keto Ester.................................. .....88
W ittig M ethod............................................................. .........................91
Malonic Ester, Di-Grignard and Lactone Methods.................................93
Organometallic/Tert-Alcohol Method................. ......... ........... .. 95

C onclusions........................................... ................................................... 100


4 ADMET MODELING OF BRANCHING IN POLYETHYLENE:
THE SYNTHESIS OF MACROMOLECULES WITH
PERFECTLY SPACED METHYL BRANCHES...................................... 101

Modeling Polyethylene............................................ .........................101
ADMET Modeling of Branching in Polyethylene............................... 104
Polymer synthesis via ADMET......................... ..... ........... 106
Hydrogenation of the unsaturated polymer...................................113
Thermal Analysis of Methyl Substituted Polyethylene..................... 120








Thermal Analysis of ADMET Methyl Substituted Polyethylene.......122

C onclusions........................................ ...................................................... 128


5 THE DIRECT SYNTHESIS OF WELL-DEFINED ALCOHOL
FUNCTIONALIZED POLYMERS VIA ACYCLIC DIENE
METATHESIS (ADMET) POLYMERIZATION................................... 130

Alcohol Functionalized Polymers via Metathesis.................................... 132
The Direct Synthesis of Alcohol Functionalized Polymers
via A D M ET................................................ ............. 135
Monomer Design and Synthesis......................................... .......... 136

ADMET Polymerization of Hydroxy Functionalized Dienes..................140
General ADM ET Polym erizations.......................................................... 140
Polymerization of 6-(4-Pentene)-l-Heptene-7-ol (Al)...........................141
Polymerization of 6-Methyl-l,10-Undecadiene-6-ol (A3).....................145
Polymerization of 1,10-Undecadiene-6-ol (A2).......................................146
Hydrogenation of Poly(6-Hydroxynonenylene) PA2...........................150
Thermal Analysis of the Alcohol Containing Polymers................... 152
Preliminary Dimerization Experiments.....................................156

Conclusions................. .................................................................. 160

R EFE R E N C ES........................................................................ ............ ............ 161

BIOGRAPHICAL SKETCH......................... ...... .........................173













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 (ADMET) POLYMERIZATION:
THE SYNTHESIS OF WELL-DEFINED MODEL POLYMERS FOR
POLYOLEFIN MATERIALS

By

Dominick J. Valenti

August 1997


Chairman: Professor Kenneth B. Wagener
Major Department: Chemistry

A synthetic method has been designed to facilitate the synthesis of
target monomers required for the preparation of perfectly branched

polyethylene model polymers. These polymers can be used to better
understand the relationships between branching in polyethylene and its
ultimate behavior. Symmetrical alkyl-substituted alpha omega dienes were
synthesized using a six-step procedure involving two enolate displacement

reactions, a retro-Claisen condensation, an ester reduction followed by a
tosylation, and a hydride displacement reaction. Purity of the resulting
monomers was greater than 99%.

The alkyl substituted monomers were condensed using Schrock's
molybdenum alkylidene (CF3)2CH3CO]2(N-2,6-C6H3-i-Pr2)Mo=CHC(CH3)2Ph
forming well-defined alkyl-substituted polyethylene prepolymers.
Quantitative hydrogenation (by NMR analysis) of the resulting unsaturated
polymers was achieved using a modification of typical diimide reduction


viii








procedures. The resulting polyethylene polymers' contain branch points
occurring at every 9 or 15 carbons, respectively. These samples are ideal with
regard to well-defined chain branching and precise branch distribution.
Presently, this high order of regularity in polyethylene copolymers cannot be

obtained by any other method. Thermal analysis of these polymers
demonstrates the unique behavior of these materials. The presence of

perfectly spaced methyl branches results in a significant drop in the polymers'

melting point within a very narrow range.

The synthesis of well-defined primary, secondary, and tertiary alcohol
functionalized ADMET polymers was also accomplished using a similar

methodology. Unsaturated polymers of this type can be hydrogenated in a
similar manner producing a new series of ethylene-vinyl alcohol copolymers
exhibiting precise chemical regularity.














CHAPTER 1

INTRODUCTION


Research in polymer chemistry during the past five decades has

resulted in the significant advancement of macromolecules as materials in

technical and nontechnical applications. We all have become everyday

consumers of the product of this research, from the clothes we wear to the

materials used to print this document. Advancements such as these do not

occur rapidly, but rather are derived from patient work leading to the

fundamental understanding needed to create polymers and tailor their

physical properties.

The dissertation represents a contribution to this fundamental
research. The work presented herein describes the creation of new techniques

that offer unique control over a polymer's microstructure, which in turn can

have an important effect on ensuing physical properties. This control of

microstructure is demonstrated by the synthesis of model polymers with well

defined structures that can be used to elucidate the effect of molecular changes

on the behavior of the polymer. Also demonstrated herein is the ability to

use Lewis basic/protic groups toward the synthesis of unsaturated,
functionalized polymers via acyclic diene metathesis (ADMET)
polymerization. These polymers then can be further hydrogenated, resulting
in the direct synthesis of saturated polyalcohols.






2



The model polymers are structurally similar to the industrially
significant a-olefin polymers; polyethylene and polyethylene-polyvinyl

alcohol copolymers. This work models the chemical/structural imperfections

or branch points that result from uncontrollable events which are present in

typical polymerization reactions. Branch points often are purposely
incorporated into polymer chains so that desired physical properties are

achieved and are typically incorporated by random copolymerization with

higher order a-olefins.

a-Olefin copolymerization (as well as uncontrollable chain transfer
events) causes random branch placement, thus producing materials with

variable physical properties. The resulting randomness makes it difficult to

study structure-property relationships of industrially important materials.

This dissertation presents a methodology that controls polymer structure

therefore producing analogous materials that can be used to investigate the

effect of structure on the physical properties of polyethylene and related

materials.

It is appropriate to describe polyethylene (PE) and related a-olefin
polymers as the main focus of this introduction. This will be accomplished
with a brief historical overview and a discussion of the important

polymerization mechanisms of PE. The concept of branching, related PE

studies and the crystallinity of flexible chain polymers are also presented.
Since ADMET is the chosen polymerization route, a discussion of metathesis

chemistry is also warranted for a complete understanding of the chemistry
within.








History of Polyethylene and Related Polymers


Discovery and Synthesis of "Polymethylene"


The repetitive joining of molecules of ethylene forming linear
macromolecules with the general formula -(CH2-CH2)n is known today as the
polymerization of polyethylene. The first samples of polyethylene were made

in 1898 by von Pechmann.1 He observed that small amounts of a white,
flocculent substance separated from an etheral solution of diazomethane on

standing, and while he was able to crystallize the substance from chloroform
there was not enough product for further study. Two years later, Bamberger
and Tschirner2 were able to precipitate a large quantity of this solid, which
was described as a white powder with a melting point of 128 'C and had a
corresponding chemical analysis consistent with the structure (CH2). This

compound was termed polymethylene and was the product of the reaction of
diazomethane with itself (Figure 1.1).3


n(CH2N2) -- (CH)n + n(N2)


Figure 1.1. The polymerization of diazomethane: the synthesis of
polymethylene.


Further investigations of this polymerization showed that the addition
of boron4 or copper5 catalysts resulted in the production of straight-chain,
high molecular weight, highly crystalline polymethylene. Further, the first
investigation of branching and polymethylene was done via the
homopolymerization of diazoethane or 1-diazopropane to produce
polyethylidene (methyl branched) and polypropylidene (ethyl branched). The










fH -H H2 H H H,

CH3 CH3 CH3 CH2CH3 CH2CH CH2CH3
n n
A B

Figure 1.2. A: Polyethylidene B: Polypropylidene



materials were described as rigid, amorphous, brittle glasses similar to

polystyrene (Figure 1.2).3 At this time, the structure-property relationship of
branching was investigated by the copolymerization (decomposition) of

diazomethane with varying amounts of diazoethane and
1-diazopropane.3 These samples demonstrated the influence of chain

branching on the crystallinity and therefore the physical properties of the
polymers. These copolymers would later be used as models to clarify the
structures of polyethylenes made by the more involved processes of high-
pressure, high-temperature polymerizations.3

In 1953 Kantor and Osthoff6 reported the synthesis of polymethylene
with a molecular weight greater than 3 million, chemistry which was

achieved by treating diazomethane in diethyl ether with a diethyl ether-boron
trifluoride complex at 0 "C.7 The polymer had a crystal melting point of 132
"C, which is close to what is expected for linear PE, while X-ray examination

showed a high degree of crystallinity. These results indicated a high
molecular weight and a low degree of branching. This assumption was
confirmed by comparison of these samples with those produced by high
pressure, high temperature radical polymerization.








Similar to the decomposition of diazomethane, this dissertation

presents the synthesis of polyethylene and its branching by an alternate

mechanism, and so it is appropriate to briefly discuss some of the details of

the mechanism to form polymethylene from diazo-decomposition. The first

such discussion was provided by Kantor and Osthoff6 who believed that the

polymerization took place through an ionic mechanism, a conclusion

derived from the fact that the catalyst and solvent were ionic reaction

promoters. Bawn and Rhodes8 also produced high molecular weight

polymethylene in a toluene solution with copper wire, copper stearate, and

boron trifluoride as catalysts. They derived the second order rate equation by

following the reaction via titration and measuring the evolving nitrogen,

and their results also indicated an ionic mechanism. Further investigations9

proposed two mechanisms for this catalytic conversion using boron

compounds, and in both cases the first step was the formation of an
intermediate by the nucleophilic attack of diazomethane on boron. The

difference in these mechanisms was that one was cationic in nature and the

other anionic. The accepted mechanism of today is anionic in nature.3

Alternate, yet historically less significant, routes to polyethylene have
also been described. In order to synthesize straight chain hydrocarbons,

Carothers et al.10 used Wurtz coupling to polymerize decamethylene
bromide. This method proved to be messy and did not successfully produce

polymers with more than 100 carbon atoms. The Fisher-Tropsch reduction
was also successful at producing polymethylene type paraffins. These

products had average molecular weights of 7,000-9,000 g/mole, and melting

points ranging from 117 to 132 'C.1,12 Other synthetic methods were derived
from the desire to study similar polymer structures. Hahn and Miiller,13 in
order to better understand the structure of poly(vinyl chloride), converted








PVC to PE by total reduction using excess lithium aluminum hydride under

high pressure and temperature. It was later determined that the total

reduction of poly(vinyl bromide) was much easier to accomplish.


Synthesis of Polyethylene via Radical Chemistry


The direct polymerization of ethylene to polyethylene was first
achieved in March of 1933 by Imperial Chemical Industries, Ltd. (I.C.I.),14

where a trace of white powder was discovered during the systematic study of
high-pressure chemistry of organic compounds. Soon after this discovery,
I.C.I. developed a commercial process to produce this polymer, and a fully

operational plant was erected in 1942 with the first applications being that of a

wire insulator for radar systems. The process I.C.I. developed was termed the

high-pressure free-radical process, for it involved the use of pressures greater
than 124 MPa, temperatures between 100-300 "C and a free radical catalyst.15

This method of polyethylene production is still used today and
produces a wide range of polymers called low density polyethylene (LDPE).
Further, this process has been modified in order to produce medium and
high density polyethylene. The first synthesis of "linear" polyethylene using
this method was accomplished by Dupont using temperatures between 50-80
"C and ethylene pressures of 707 MPa.16 The resulting polymer had a density
of 0.955 g/cm3, with less than 0.80 alkyl substituents per 1000 carbon atoms.17
However, the polymers that are industrially produced using this method are
low density (0.912-0.935 g/cm3) and usually contain 15-30 variable length alkyl
substituents per 1000 carbon atoms.








The radical polymerization of ethylene consists of a chain addition

mechanism and follows the classical description for free radical

polymerization (Figure 1.3).



I* + CH,=CH- k I-CH2-CH2'


I-CH2-CH2* + n CH2=CH2 k RCH2CH2'

Figure 1.3. Radical polymerization of ethylene. Initiation and Propagation.


As with other typical radical reactions, termination consists of radical

coupling and disproportionation (Figure 1.4 a ). Chain transfer events are

also evident with transfer to ethylene to form a vinyl end group, or the

transfer to solvent to form a terminated chain (Figure 1.4 b, c ).



2 RCH2CH2- k- RCH2CH2CH2CH2R or RCH=CH2 + RC2CH3 (a)



RCH2CH2- + CH2=CH, kt --, RCH=CH2 + CH3CH2* (b)



RCH2CH2* + SH kt -- RCH2CH3 + S* (c)

Figure 1.4. (1) Termination of radical chain growth.
(2) Chain transfer to ethylene. (3) Chain transfer to solvent.




In radical systems branching can occur as a result of chain transfer
events: intermolecular and intramolecular. Intermolecular transfer causes
the formation of long chain branches (> 6 carbons) and is the result of normal








chain transfer to polymer18,19 via transfer of a radical to a completed polymer
chain causing the growth of a grafted chain. The formation of long chains
causes changes in the melt flow viscosity of the polymer.
Intramolecular chain transfer, which is about 40 times more prevalent
than intermolecular chain transfer, causes the formation of short chain
branches. The number, size, and distribution of these branches have a
significant effect on the polymer's crystallinity. A methodology to study this
effect is the primary focus of this dissertation.


.
SCH,2CH2CH2CH2 CH2
CH2 /CH2
CH2
b


^'CH2CH2CH2 H CH3
CH2 /CH2
CH2
n-Butyl branch


-.CH2CHCH2ZH2 CH3
CH2 CH2
CH2
n-Hexyl branch




"CH2CH2CHCIH2 CH3
CH2 CH2
CHz

n-Amyl branch


maximum crystallinity 60-70%

Figure 1.5. Intramolecular chain transfer during the radical
polymerization of polyethylene.








The intramolecular chain transfer event of interest is caused by the
transfer of the propagating radical on the end of the chain to a more stable
secondary radical on the same chain which occurs by the extraction of a

hydrogen atom via a cyclization or "backbiting" mechanism (Figure 1.5). The
resulting species can continue to undergo radical propagation with ethylene,
which leads to the formation of an alkyl branch. This uncontrollable

backbiting results in the formation of ethyl, n-butyl, n-amyl, and n-hexyl

branches, where the relative abundance of these different branches depends

on the synthetic conditions.20 The formation of the n-butyl branch is the
most prevalent and is attributed to the favorable formation of a six-
membered transition state shown in Figure 1.5.

There is evidence that the polymerization of vinyl acetate follows the
same radical reactions and side reactions as those for ethylene.21,22 The
resulting polymer (polyvinyl acetate) is a precurser to alcohol functionalized
a-olefin polymers which will be discussed further in chapter 5 of this
dissertation.


Synthesis of "Polyethylene" (Heterogeneous Ziegler Catalysts)


In the fall of 1953, Ziegler and co-workers observed the polymerization
of ethylene at atmospheric pressure using titanium halides and alkyl
aluminum compounds,23,24,25 a landmark discovery which has had a
dramatic effect on the world of chemistry and is still the basis of extensive
organometallic research. These catalysts are formed by the reaction between a
metal alkyl or a metal hydride of the main group metals and a reducible
compound of the transition elements of groups 4 to 7.3 The most preferred
combination is an aluminum alkyl or hydride with a titanium-IV compound.








Natta and co-workers termed these new catalysts, Ziegler catalysts.26,27 These

systems are commonly referred to as classical or heterogeneous Ziegler
catalysts.

Ziegler's discovery made it possible to produce polyethylene,
previously only obtainable by extreme conditions of pressure and
temperature, in a simple flask or test tube.28 This was first demonstrated by
Ziegler in a Weck-glass vessel under atmospheric pressure and room
temperature using gasoline as the solvent.25 The polymer produced was more
rigid, stronger, and more heat resistant than those made by the radical
process. This was attributed to the fact that the polymers were made up of
nearly linear molecules which resulted in a material that was more dense
(0.95 g/cm3) and more crystalline. The branches that did occur were identified
as being mostly ethyl groups. The contributions that Ziegler made in this area
of organometallic/polymer chemistry resulted in his receipt of the Nobel
Prize for chemistry in 1963, along with Natta.

About the same time as Ziegler's discovery, two medium-pressure
polymerization methods using transition metal oxide catalysts were
discovered by the Phillips Petroleum Co. and the Standard Oil Co. of Indiana.3
The polyethylenes produced by these methods were more linear in nature
and therefore had a higher density of 0.96 g/cm3.

Ziegler polymers, as well as the medium pressure polymers, are
generally accepted to occur through an insertion mechanism. A
representation of this chain addition coordination polymerization is outlined
in Figure 1.6.29 This reaction initiates with the transfer of an alkyl group
from the alkyl aluminum to the titanium chloride, followed by the t-
complexation of the monomer to the transition metal's vacant d-orbital
(Figure 1.6 A-B). A four-centered anionic coordination insertion process that








inserts the monomer into the metal-carbon bond (C) then occurs. The result
of this process produces a vacant orbital with the opposite configuration of
the original complex (D). This mechanism is referred to as the monometallic
mechanism for the stereo specific polymerization of polypropylene and was
proposed by Cossee and Arlman.30,31



FPropagation


C ,,, I Cl

Cl


CH=CH2


C i/,,.. ,,\c i

Cl T
B


c i,,,. I Cl c Ci/,, ..,,\ -I .
Cl i O Cl L
Cl Cl '
D C

Figure 1.6. The insertion of ethylene as the propagation step of the
coordination polymerization of Polyethylene. The monometallic
mechanism.


The Ziegler and Phillips (chromium oxide-based) catalysts are used to
manufacture virtually all of the linear polyethylene made today. These








systems, as mentioned earlier, produce nearly linear high molecular weight

paraffins. These linear flexible chains are able to arrange in such a fashion

that they can acquire long range three dimensional order (crystalline regions)

which allows the polymer to pack better. This resulting order produces a

material that is termed high density polyethylene (HDPE). A density of 0.95

g/cm3 is the result of having 1 to 3 alkyl groups (branches) per 1000 backbone
carbon atoms (Figure 1.7), while a density of 0.97 g/cm3 results from, on

average of 1.5 alkyl groups per 1000 atoms.32



TiC14 + RA1CI2 RTiCI3 + AIC13

RTiC3 --- TiCl3 + R-


*^C^H^-C CF- I H2- CH H-- CHr- CH2-Vn
R v498R

0.5 3 R's per 1000 Carbons R = CH3
-CH2CH3
-CH2CH2CH3
etc.
Figure 1.7. High density polyethylene (HDPE) via Ziegler catalysts.



Synthesis of "Polyethylene" (Homogeneous Ziegler Catalysts)


The latest step in polyethylene research has been the introduction of a

family of transition metal complexes called metallocenes. These catalysts

have been extensively used to investigate the long debated mechanism of

Ziegler catalysts. Elucidating the elementary steps of a polymerization is

simplified by studying soluble well characterized systems;33 therefore,

metallocenes have contributed the most definitive results toward this








cause.32 Much of the drive to understand the details of the mechanism

originated from the special demands on understanding the structure-property

relationship of c-olefin systems.


x = C2H4, Me2Si


M = Zr, Hf
x = C2H4, Me2Si


x = C2H4, Me2Si M = Ti, Zr, Hf
RI= Me, Ph, Naph RI = H, 5*Me, neomenthyl
R2= H, Me R2 = Cl, Me

Figure 1.8. Examples of metallocene catalysts.33



The first structure of a metallocene was described in 1952 by Wilkinson

et al.34 and Fischer35 with the introduction of ferrocene. These molecules

(metallocenes) were commonly referred to as sandwich compounds due to

their unique spatial arrangement (Figure 1.8).33 This new class of compounds

showed considerable promise in the way of advancing organometallic








chemistry, but at the time failed to have an industrial impact. They were

frequently used as a transition metal catalyst in combination with either

triethyl or diethylaluminum chloride for the polymerization of olefins.27,36

The poor catalytic activity that they exhibited limited there use to mechanistic

studies.


This was the case until 1975 when water was accidentally added to a
NMR tube which contained biscyclopentadienyltitaniumdemethyl,

trimethylaluminum and ethylene.33 Upon this addition, the fast

polymerization of ethylene was observed in a system that was thought to be

inactive toward this process.37 It was soon determined that the best cocatalyst
for these systems was methylaluminoxane (MAO) (Figure 1.9). Today,

zirconocenes (zirconium transition metal metallocenes) that are combined

with MAO result in olefin catalysts that are 10-100 times more active than

classical Ziegler catalysts.38



H3K 3CH3 CH3
Al-O-41-O-Al-O-A,
H3C CH3 CH3

Figure 1.9. A proposed oligimer of methylaluminoxane (MAO). Cocatalyst
for homogeneous Ziegler-Natta polymerizations.33




Kaminsky states that the polymerization of ethylene with
bis(cyclopentadienyl)zirconium dichloride (Cp2ZrC12) and MAO can result in
the production of up to 40,000,000 g PE/g Zr h.33 The resulting polymers
have typical molecular weight distributions of M,/M. = 2 (a much higher








distribution is obtained with heterogeneous systems)39 with 0.9 to 1.2 pendent

methyl groups per 1000 backbone carbons atoms.

Arguably, the most important contribution that metallocenes have
brought to polymer chemistry is the opportunity to develop plastics with

variable control over their structure/property relationships. Metallocenes

grant structural control by defining a single site at which the building blocks

of the polymer monomerss) are joined together linearly. Single site

polymerization is in contrast to the nonuniform catalytic action that takes

place in heterogeneous systems which follow a similar mechanism. Due to
their solubility, the active sites of homogeneous systems are more accessible

for analytical examination, therefore provide the ability to make rational

catalyst modifications.33 The impact that this type of control can provide is

demonstrated by the design and synthesis of chiral zirconocenes, which are

used for the synthesis of stereoregular polypropylenes.40


Copolymerization of (c-olefins


For the past fifty years the majority of low density polyethylene has
been produced by the high pressure, free radical polymerization of ethylene.

This process inherently produces side chains (Figure 1.5), both long and short,

hence producing a large distribution of chains that pack poorly (low %

crystallinity) or have no semblance of order (amorphous).

The homopolymerization of ethylene using Ziegler catalysts results in
a very marketable plastic termed high density polyethylene (HDPE). These

polymers do contain some degree of short chain branching but are essentially
considered linear. In contrast, when ethylene and higher order olefins are
copolymerized in the presence of Ziegler catalysts, a new class of material is





16

obtained that is termed linear low density polyethylene (LLDPE) (Figure 1.10).

The copolymerization of ethylene with a-olefins like 1-butene, 1-hexene or 1-

octene has opened up a new chapter in polyethylene based materials and

currently shows a higher growth rate than the homopolymer. These new

products offer an advantage over those made via radical chemistry in that

there is no significant uncontrollable branching. This inherent linearity

produces molecules in which the only significant branch points are from the

incorporation of the a-olefins (Figure 1.11).



R R
CH,- CH, + = Ca\ C CH
R



R CH3










Figure 1.10. The copolymerization of higher order a-olefins with ethylene.
The polymerization of linear low density polyethylene (LLDPE).



LLDPE was introduced in 1977 with Union Carbide's implementation
of a low pressure, gas-phase, fluidized-bed process.7 This process was later
termed UnipolTM and was soon followed by Dow Chemical with a new line of

LLDPE polymers termed DowlexTM. Today these and other companies have





17

shifted gears toward the development and production of large amounts of

LLDPE.

The use of heterogeneous catalyst systems for these copolymerizations,

results in LLDPE products with large polydispersities and little to no control



HDPE Polymerized by Zeigler Natta or Metallocene chemistry


CH2 CH ca- CH2 CH2 CH- HH

n>>>m R
t

R= infrequent short
chain branches
LDPE --- Polymerized by radical addition mechanism


ICH2CH, + n CH, CH2 --- 4CH,--CH2 -CHf--jH- -

n>m

R= frequent short and
long chain branches
LLDPE Copolymerized by Zeigler type catalysts


nCH2== CH2 + m CH =CH t CH-- CH2 CH2--
R R


R= the identity of R
from monomer feed
Figure 1.11. The induced or non-induced branching in polyethylene.


over comonomer sequence distributions.41,42,43,44 Contrary to this, the

development and use of homogeneous catalysts have produced LLDPE
samples with narrow molecular-weight and more uniform comonomer








possible to design new materials that are driven by special demands on

properties. The resulting short branches on these polymers produce materials
with lower melting points, lower crystallinities, and lower densities as
compared to HDPE.33


Structure-Property Relationships of Polyolefins


The ability to design systems from a molecular standpoint
(comonomer identity and ratio) in order to tailor physical properties has
benefited tremendously from homogeneous systems. By adjusting
comonomer composition or catalytic activity/affinity, a macromolecule can
be designed and produced with known but irregular molecular composition.
The use of homogeneous systems provides a method to assemble these
mixtures of comonomers while eliminating nearly all the undesirable side
reactions and producing narrower molecular weight distributions.

This lack of "regular" order is due to the variable reactivities of
different monomers towards the polymerizing catalyst. The affinity for any

given olefin to insert depends on the last inserted monomer and is defined by
a parameter termed the monomer reactivity ratio. For a two monomer

system these ratios are represented by rl and r2 and defined in equation (1).
The term ri is expressed as the ratio of the rate constant


r,= r2 = (1)



of inserting an ethylene unit into the growing chain versus the rate constant
of inserting an a-olefin, when the last monomer inserted was an ethylene.
Parameter r2, in this case, would be the analogous ratio for the a-olefin.








Equation (2) defines the copolymer composition and is related to the
concentrations of the two monomers in the feed [ml] and [m2] and their

reactivity ratios.


d[m,] [m,](r,[m,]+[m,])
d[mz] -[mr ]([, + r2[lm 2])


The tendency for a comonomer to homopolymerize, randomly
copolymerize, or alternatively copolymerize can be inferred by reactivity
ratios. The product of the two reactivity ratios rl r2 represents the
distribution of the comonomers. When this product equals one it represents
a randomly distributed copolymer.33 A product value considerably less than



Table 1. Examples of copolymerization parameters of metallocene/MAO
catalysts in combination with ethylene and a-olefins.


Metallocene Temp. a-Olefin rl r2 ri r2
in C

Cp2ZrMe2 20 propene 31 0.005 0.25
[En(Ind)2]ZrCl2 50 propene 7 0.06 0.40

Cp2ZrCl2 40 butene 55 0.017 0.93

Cp2ZrCl2 80 butene 85 0.010 0.85
[En(Ind)2]ZrC12 30 butene 8 0.07 0.59

Cp2ZrMe2 60 hexene 69 0.02 1.38
Data taken from Kaminsky, W. Macromol. Chem. Phys. 1996, 197, 3907.


one represents a somewhat alternating structure.48 The use and modification
of metallocene catalysts have provided limited control over these reactivity








ratios, by modifying the symmetry and steric crowding of the active center as

well as the temperature of the polymerization. Some examples of this are

shown in Table 1.33


The modification of catalyst and conditions does afford some control of

comonomer distribution but the placement of monomers is still irregular.

These systems do, though, provide samples with better control over the

intermolecular distribution of branches than previously possible. This

inherent variability limits the usefulness of these systems toward the

fundamental understanding of structure, morphology and property

relationships.


Crystallinity, Morphology, and Melting of Flexible Chain Macromolecules


The ability of flexible chain polymers to orient in such a fashion as to
display long range three dimensional order is referred to as their ability to

crystallize. This is similar to the crystallization process in low molecular

weight molecules but differs in that the crystallizing molecule is larger than

the unit cell. The increased size of polymers enables a single chain to

crystallize in multiple unit cells. Multi-participation and its corresponding

thermodynamics are due to the connectivity of a vast number of chain atoms

which result in the unique yet complex crystallization properties of polymer

systems.

Polyethylene and its copolymers are considered semicrystalline
because they contain both crystalline regions and viscous glassy regions.49,50
The viscous glassy regions are termed amorphous and are composed of
unordered molecules or repeat units.







The ir.rrl',h..l of the crystalline regions of polymers has long been
debated. The fr'..'., d-'...ii.' theory, developed in the 1930s, proposed that a
polymer's crystallinity came from the occasional alignment of chains in an
extended fashion creating order. This theory was supported by the belief that
the most thermodynamically stable crystal was one involving extended
chains.51 Twenty years later, upon the isolation of a polymer single crystal, a
new theory on chain morphology arose called folded-chain lamella.52,53,54,55
This conformation consists of the chains folding back on themselves
lamellaee) creating ordered crystalline regions. The lamellae nucleate from a
central point making up a crystal region within the polymer termed a
spherulite. (Figure 1.12).


*


onPsL


****** *i *** 1

1*** ***

PE Spherulite Lamellae
Figure 1.12. Representation of PE Spherulite and Lamellae.


Mandelkern,56 in 1986, acknowledged that the crystallite morphology is
clearly lamella but that the molecular morphology and chain structure cannot
be determined by the analytical techniques currently available. The theory of
folded chain lamella is widely accepted today, but is still the subject of
extensive investigation.57,58,59,60,61


II


'""' ~"""""-'~""' "~^








The molecular requirement for crystallinity in macromolecules is that

the chain atoms or repeat units must be capable of adopting an ordered
configuration in which the adjacent units can lie parallel to one another

creating well defined lattice sites.62 This ability to conform is directly related

to the repeat unit's degree of regularity. The three forms of regularity are 1)

chemical, 2) geometrical, and 3) spatial.

Chemical regularity is defined by the frequency of the repeat units. For

example, in linear polyethylene the repeat unity is -(CH2-CH2)- and its degree

of chemical regularity is defined by how often this repeat unit exists without

the appearance of branches. When branching occurs, the degree of

crystallinity is noticeably changed. Linear polyethylene contains 2 to 3 side

branches per 1000 carbon atoms and is -90% crystalline,63 at 30 branches per

1000 carbons the crystallinity decreases to 50%.64 The decrease in crystallinity
due to an increase in branching is thought to be a result of the exclusion of

branched units from the crystalline regions.65

Geometrical regularity is defined as the regular placement of an
unsymmetrical repeat unit. If an unsymmetrical repeat unit is incorporated

into a chain in both directions, it results in what is termed head to tail (HT),

tail to tail (TT), head to head (HH), and tail to head (TH) placement. These

different connectivities result in a geometrical irregularity which disrupts a

chain's conformational abilities.

Spatial regularity results from the systematic placement of substituents

that can attain different spatial arrangements (stereo isomerism). This occurs
during the polymerization of monosubstituted alkenes such as higher order

a-olefins. This can be seen by examining samples of spatially regular (tactic)
and non-regular (atactic) oriented polypropylenes. The ordered (tactic)








polypropylene results in a highly crystalline polymer while the atactic version
is a completely amorphous material.

These three molecular -cguaij. r. requirements--chemical, geometrical,
and spatial--are determining factors for the ability of a material to crystallize

based solely on the makeup of the chain itself. However, there are many

other variables that affect the crystallinity of the material as a whole. These

include molecular weight, molecular distribution, end groups, diluents

(impurities), and thermal history.


Thermal Behavior and Chain Structure


Much of the research on polymer crystallinity concerns the resulting
thermal behavior. Thermal behavior relates to order because the chain

structure influences the melting point of crystalline regions (Tm) through

conformational properties and thus the entropy of fusion.66 The melting-

crystallization process of long chain polyethylenes is a first-order phase

transition and can be related to the same transition in small molecules.57

Small molecules, though, lack the conformational constraints of a large

polymer therefore resulting in sharp transitions when its equilibrium
temperature is attained. The longer chains introduce structural or

morphological "impurities" causing the broadening of this fusion process

(Figure 1.13).62 This broadening effect can also be observed by comparing the

melts of fractionated and polydisperse samples67 thus demonstrating that the
fusion process is interrupted by varying molecular constitution while the

peak of the fusion curve remains relatively the same.

Examination of linear, low molecular weight PE samples shows that
comparable fusion curves can be obtained that are similar to those of








hydrocarbons62 having a limited critical length of only 150 carbons.68

Therefore, relating folding and/or fusion effects from low molecular weight

samples to those of larger PE samples of similar molecular makeup is a viable

methodology. This is possible because the molecular weight (length) at which


















400 380 360 340 320
Sr(KI

Figure 1.13. Differential Scanning Calorimetric endotherms:62 (a) low MW
PE Mn= 725 g/mole; (b) n-hydrocarbon C44H90 MW= 618 g/mole



chain folding can occur is the same for n-alkanes and PE polymer

fractions.68'69,70,71 A detailed study comparing the melting temperatures of n-

alkanes with those of linear polyethylenes was done by Mandelkern et al.,72

demonstrating that identical melting points could be obtained for most

samples but a lack of correlation for infinitely large samples. Mandelkern et

al. explain this as being a result of a large increase in the interfacial free energy

with a large increase in size.72

The research in this dissertation is concerned with the effect of a

regularly distributed structural irregularity (branches). Therefore, it is








appropriate to briefly discuss how copolymerization affects the crystallization
and melting points of these types of materials.

It can be generally stated for random copolymers that the concentration
of crystallizable units decreases via the addition of a copolymer impurity, the
melting range becomes progressively broader and the level of crystallinity
decreases. The amount of theoretical temperature depression for random
copolymers was predicted by the Flory equation which is shown as equation
373 here where Tm and Tm are the melting temperatures of the unbranched




(/T.)-(TO )= -(R/AH,)lnX (3)


and branched polymers, R is the gas constant, Hu is the heat of fusion per
repeating unit, and XA is the mole fraction of crystallizable units. Results,
using this equation, have shown that the identity of the alkyl pendent groups
does not affect the amount of depression as related to the temperature
composition relationship.74,75 Alamo and Mandelkern point out that this
result is an example of the fundamental principle that the melting
temperature of a copolymer does not depend on the composition but on the
details of their sequence distribution.75

There have been numerous studies describing the physical effects of
these randomly copolymerized units.75,76,77,78 As described earlier, chain
copolymerization results in an inhomogeneous distribution of alkyl
branching. Compared to heterogeneous Ziegler catalysts, the metallocenes
grant some control over the intermolecular distribution of side chains.
Therefore, they produce polymers in which each individual molecule
possesses the same distribution of branches as another, but the distribution of








the branches is not uniform along the individual polymer backbones. The

lack of order in both cases has recently been termed intra and intermolecular

heterogeneity, respectively.79






CH3

Hydrogenated
butadiene/propene
co-polymer



CH3 CH3

Hydrogenated
butadiene/ethene/propene
terpolymer

Figure 1.14. Methyl branched model polymers for PE.80,81


Both types of distributions influence the superstructure and the

crystallization behavior of these materials; therefore, model systems that can

control both of these variables would be suitable for detailed investigations.

Gerum et al. 80,81 modeled this control by studying the short branching

achieved by strictly alternating hydrogenated poly[butadiene-alt-(1-olefin)]

copolymers and butadiene/ethene/1-olefin terpolymers (Figure 1.14). For the
copolymers, a limit of 167 short chain branches per 1000 back bone carbons

could be achieved with a intrahomogeneity of a branch point appearing every

6 backbone carbons, and a strictly alternating content greater than 97%. The

copolymers related to this dissertation are produced when propene (methyl

branch) is used as the copolymer. The copolymers with propene from Gerum








et al. show by X-ray scattering and thermal analysis that a completely

amorphous material is produced. It is important to note that a glass

transition was detected for these samples at -66 C.

Terpolymers subsequently were produced in order to increase the
number of methylene units between branch points by the incorporation of

ethene as a spacer. This type of ter-unit addition is able to dilute the number

of branch points per chain resulting in spacers between branches being on

average 5, 11, 17, 23 etc. The resulting terpolymers, using propene as the 1-

olefin, had as many as three thermal transitions with the first two being very

broad. Even though these models proved to be interesting to study, the

samples still contain a significant degree of intra- and intermolecular

heterogeneity. Until complete control of the copolymerization can be

achieved, the use of Ziegler chain addition reactions will not provide the

necessary control over the microstructure in these polymers. Therefore, the

design of well defined models for the fundamental study of structure property

relationships will not be possible using these means.


Metathesis Polymerization



Ring Opening Metathesis Polymerization (ROMP) and Well Defined
Alkylidenes


Olefin metathesis, over the last 25 years, has become a well established
means of cleanly producing linear unsaturated polymers. The majority of
this research lies in the area of a chain growth mechanism termed ring

opening metathesis polymerization (ROMP).82 ROMP is represented by the
polymerization of a strained cyclic olefin to its corresponding linear








unsaturated polymer (Figure 1.15). The resulting polymers (Figure 1.15) are
similar in structure to those produced by the Ziegler polymerization of
dienes (butadiene, isoprene) in that both types of products contain a site of
unsaturation and are linear carbon backbone chains.




O ROMP initiator _CH CH= CHf.



Figure 1.15. The ROMP of Cyclooctene.


The metathesis polymerization is made possible by a transition metal catalyst
(initiator) in the form of a metal carbene. This reaction, as are all metathesis
reactions, is governed by a competing ring chain equilibrium.82c The
feasibility of shifting the equilibrium toward chain production is usually
driven by enthalpy; therefore, strained cyclics, such as 3, 4, and 8 membered
rings and norbornenes provide the necessary energetic for polymerization.
Similar to the use of classical Ziegler-Natta catalysts, the synthesis of
ROMP polymers was first achieved by polymerization using heterogeneous
catalyst systems. These systems were typically composed of various transition
metal halides and oxohalides accompanied by a wide range of metal alkyl and
organohalide Lewis acid cocatalysts. Again, due to the unknown nature of
the true catalytic species, the mechanism of polymerization could not be
directly studied and therefore no rational changes in the system could be
made. The heterogeneous catalysts required the addition of a Lewis acid
cocatalyst giving these systems poor functional group tolerance. Some
examples of short term living systems were observed but upon longer








reaction times would undergo secondary metathesis reactions, therefore

broadening their molecular weight distribution.82c,83

In 1986, Shaverien, Dewan, and Schrock developed a well defined

alkylidene complex with a highly active four coordinate dO tungsten center.84

This complex did not require a Lewis acid cocatalyst and was capable of olefin

metathesis. Due to the homogeneous nature, these systems provided the

arena for structure elucidation and mechanistic pathway discovery.85s86

Following this discovery by Schrock and co-workers, similar alkylidene

systems were able to perform ROMP in a living manner as well as resist
"poisoning" functionalities. This enabled the design and synthesis of new

block copolymers and new functionalized polymers via a metathesis
mechanisms.




X Ru]




X = CO2H, CH2OH, CHO

Figure 1.16. Functionalized ring closing metathesis (RCM) using Grubbs'
ruthenium alkylidene.


Taking the design of homogeneous alkylidines one step further
Nguyen et al., in 1992, presented the synthesis of a well defined ruthenium
alkylidene which initiated ROMP in both organic and protic/aqueous
solvents.87 This design also showed living characteristics as well as multiple

functional group tolerances, therefore opening up new doors for olefin

metathesis chemistry. Unique to this system was its ability to undergo








metathesis in the presence of aldehydes, alcohols, carboxyclic acids and

quarternary amines.88 This was demonstrated by Fu, Nguyen, and Grubbs

using ring closing metathesis for the formation of six membered

functionalized rings (Figure 1.16).88 Further investigations of the ruthenium

systems have developed new structural reactivity relationships and isolatable

intermediates which have provided a tremendous impact from a mechanistic

standpoint.89 Chapter 5 in this dissertation examines a ruthenium alkylidene

as a catalyst for the direct synthesis of alcohol functionalized polymers.


Acyclic Diene Metathesis Polymerization (ADMET)


The inherent control over polymer structure that Schrock and Grubbs'

well-defined alkylidene catalysts provide has significantly broadened the

scope and applications of ROMP chemistry, but it has had an explosive effect
on the evolution of a rather new polymerization method called Acyclic Diene

Metathesis (ADMET) polymerization.90 ADMET has been under

investigation for 25 years, but upon the advent of Schrock's alkylidenes the

viability and understanding of these systems have become a reality. Prior to

their introduction the metathesis reaction was plagued with problematic side

reactions and an undefined mechanism. Based on theoretical and

experimental observations of Schrock's well defined tungsten alkylidene,

Wagener, Boncella, and Nel proposed the accepted mechanism of ADMET.90

The ADMET and ROMP mechanisms both proceed through the
equilibrium polymerization of olefins via metathesis. However, ADMET
differs by involving the polymerization of acyclic dienes, with its equilibrium

shifted to polymer by the removal of a small alkene (entropically) (Figure
1.17). ROMP is typically shifted to high polymers via a favorable enthalpy








change via ring strain release. The major mechanistic difference is that

ROMP follows a chain growth process where the active alkylidene acts as a

catalytic initiator. In contrast, ADMET follows a step condensation

mechanism and the alkylidene behaves as a true catalyst.



Catalyst _
%' _R + H2C:=CH2

Figure 1.17. ADMET polymerization: General reaction scheme.


The accepted mechanism for ADMET is outlined below in Figure 1.18.
Upon addition of the catalyst to a neat solution of dienes, the olefin will first

coordinate in a it complex with the transition metal center followed by an

insertion reaction forming either a productive (d) and nonproductive (c)

metallacyclobutane intermediate. The nonproductive cyclic (d) can collapse

to form the original it complex, whereas (c) undergoes a productive

rearrangement eliminating the precatalyst fragment (e) while forming the

monomer as part of the new alkylidene (f). Another monomer can then

coordinate and insert in the same fashion as before, producing the

metallacyclobutane (g). On the first trip around this cycle, collapse of this

metallacyclobutane forms the dimer, with ensuing trips forming powers
thereof. The collapse of (g) leaves the catalyst as a methylidene (h) which is

considered to be the true active catalysts species.89 This methylidene then
coordinates with another monomer, or appropriate chain end, forming the

metallocycle (i), which upon its collapse produces the small molecule









a

LnM=CR2


4-"?s


coordination LnM=CR, /

of olefin (CH, non-productive
insertion

productive (CH2)6
insention C

R R c


Ln. d

R R
formation of
new alkylidene


R,C=CH2

HC=CH2 /CH 2
HLnM=C second monomer
release or polymer olefin insertion
release of
ethylene
(driving force)

( /,2,, i Ln


Ln ,'/-- (CH2)6



generation of /
active methylidene
insertion onef eand free polymer
or polymer
LnM=CH,

(CH CH
^^(ru^\ ^^ru 'a


Figure 1.18. ADMET polymerization cycle.








ethylene while returning back to the top of the cycle with the alkylidene

having the identity of the stepwise growing chain.

The clockwise movement of this cycle is caused by the removal of the

small molecule, in this case ethylene, producing (depending on the number

of cycles) a high molecular weight polymer. The movement of this cycle in a

counter clockwise manner has also been demonstrated by the

depolymerization of high molecular weight polymer in solution via the

addition of excess ethylene91,92 or various functionalized monoenes.93,94,95

Unlike ROMP polymerizations, ADMET condensations are performed under

neat conditions so that competing equilibria are avoided and the release of

ethylene is favored.

The step condensation process of ADMET requires stringent conditions
to achieve high molecular weight polymer. Under step conditions, high

polymer can only be achieved if the system obtains an overall conversion

greater than 98%. This kinetic behavior is in contrast to the chain methods

used to make PE and the corresponding copolymers were a conversion of 90%

is considered excellent.51 In these chain growth systems, monomers add to a

highly energized chain end, which results in high molecular weight polymer

almost instantly. Step condensations proceed by monomers first coming

together to form dimers, which then condense to form the tetramer and so

on. Carothers defines the stepwise growth in an equation which calculates

the degree of polymerization (DP) as it relates to the extent of reaction (p)
(equation 4).51 The number of these repetitive condensations



DP- = (4)
(1-p)








(DP) is also related to the stoichiometric balance of the system. However, the

ADMET system typically involves condensing two identical functional

groups in an A-B type manner, which eliminats the stoichiometry concerns.
ADMET polymerizations also follow other notable stepwise constraints,

including the formation of molecules during equilibrium conditions that
have a most probable distribution (polydispersity index (PDI)) of 2. This
distribution is commonly referred to as a Flory distribution, and is
represented in Equation 5 as the weight-average molecular weight (M,)
divided by the number-average molecular weight (M,).51 Fortuitously, PE

samples synthesized by various metallocenes have a similar most probable

distribution. This will allow for better comparisons between the step samples
of ADMET polymerization and those produced by metallocenes.


M" =2.0 (5)


ADMET: Step Condensation Method to Producing a-Olefin Precursor
Polymers


The establishment of ADMET occurred via the metathesis
polymerization of 1,9-decadiene using the tungsten96 and molybdenum
versions of Schrock's alkylidene. The investigation of this and other
hydrocarbon monomers has demonstrated the clean conversion of a, (o-
hydrocarbon dienes into linear unsaturated polymers.97,98 Using Grubbs'
ruthenium alkylidenes, similar results showing the clean conversion of
hydrocarbons can also be obtained.99 The resulting polymers again, like the
ROMP polymers, produce linear unsaturated carbon backbone polymers
similar to their ct-olefin counterparts (Figure 1.16). For example, the
quantitative hydrogenation of polyoctenelene produced via ADMET results






35

in a saturated hydrocarbon chain that is analogous to completely linear PE.100

This dissertation is an extension of this work, using the same well established

clean conversion of a, co-hydrocarbodienes in order to produce PE samples

with inter and intramolecular homogeneity of branch inclusion. The

durability of Grubbs' ruthenium benzylidene toward alcohol functionalities is

also investigated as a means to directly synthesize well defined models of

alcohol functionalized a-olefin polymers similar to those of

polyvinylalcohol-polyethylene copolymers.















CHAPTER 2

EXPERIMENTAL
Instrumentation and Analysis


1H NMR 300 MHz and 13C NMR 75 MHz spectra were recorded on a
General Electric QE-Series NMR Superconductiong Spectrometer system or a
Varian Associates Gemini 300 Spectrometer. All NMR spectra were recorded
in CDC13 with v/v 0.03% TMS as an internal reference. Chemical shifts

reported were internally referenced to residual chloroform. Infrared data was

recorded on a BioRad FTS/40A infrared spectrometer. Analyses were

performed between NaC1 plates neat or with chloroform as a solvent. Purity

of compounds and reaction conversions were determined on either a

Hewlett-Packard HP5880A gas chromatograph using a capillary column with a

flame ionization detector or on silica coated tic plates with mixtures of

pentane and ethyl acetate as the mobile phase. Micro-extractions were used in

order to monitor reactions by GC. This was done in order to remove all water

soluble salts before injection into the GC. All pertinent GC peaks were
confirmed by mass spectrometry or NMR on the isolated compound. Low

and high Resolution Mass Spectrometry (LRMS), (HRMS) was recorded on a
Finnigan 4500 Gas Chromatography/Mass Spectrometer using either electron
ionization or chemical ionization conditions. Elemental analyses were

performed by Atlantic Microlab, Inc., Norcross, GA.








Gel permeation chromatography (GPC) was performed using a Waters
Associates liquid chromotograph U6K equipped with a tandem ABI

Spectroflow 757 UV absorbance detector and a Perkin-Elmer LC-25 RI detector.
All molecular weights are relative to polybutadiene or polystyrene standards.
Polymer samples were prepared in HPLC grade THF or CHC13 (-1% w/v) and
filtered before injection (a volume of 20-40 uL). The GPC was equipped with a
Ultrastyragel linear mixed bed column (CHC13) or two successive 5 x 103 A
and 5 x 104 A (THF) Phenogel columns (crosslinked polystyrene gel). HPLC

grade chloroform or THF were used as the eluent at a constant flow rate of 1.0
ml/min. Retention times were calibrated against polystyrene standards

(Scientific Polymer Products, Inc.) or polybutadiene standards (Polysciences,

Inc.) All standards Mp or Mw were selected to be well beyond the expected
polymers range. A minimum of 5 data points were achieved for a calibration
curve. On noted samples an internal standard of acetone was used.

Differential scanning calorimetry (DSC) analysis were performed using
a Perkin-Elmer DSC 7 at a heating rate varying between 20- 2'C/min. All
samples were first cooled to -120 "C (using liquid nitrogen as the coolant with
a helium flow at a rate of 30 ml/min.) and underwent isothermal cooling for

2 5 minutes before scanning up to 200 C followed by isothermal heating for
2 5 minutes. Multiple cycles were performed with data collection on the

second heating cycle or later. When transitions were identified the samples
were then slowly scanned over the pertinent temperature range. Reported
values are Tm peak (first order transition peak position), Tm onset and Tg
(glass transition). Thermal calibrations were done using indium and
cyclohexane as standards for both peak temperature transitions as well as for
heats of fusion. All samples were run using an empty pan as a reference and
empty cells as a subtracted baseline. Thermogravimetric analysis was








performed on a Perkin-Elmer TGA 7. All samples were heated from room
temperature to 700 C in nitrogen at a scan rate of 10 'C/min. The onset of

weight loss was taken as the reported value.




Materials and Techniques


Schrock's molybdenum metathesis catalyst [(CF3)2CH3CO]2(N-2,6-C6H3-
i-Pr2)Mo=CHC(CH3)2Ph, was synthesized according to published methods.101

Grubbs' ruthenium catalyst, RuCl2(=CHR)(PCy3)2 were Cy = cyclohexyl, was
provided by the Wagener group members, specifically Mark Watson, Shane
Wolfe, and Dr. John D. Anderson via literature procedure.89 All catalyst
systems employed in this study will be graphically depicted during their
pertinent discussions. p-Toluenesulfonohydrazide (TSH) was purchased
from Aldrich and was recrystallized from methanol prior to use.

Tripropylamine (TPA) and 0-xylene were purchased from Aldrich and
distilled from CaH2 prior to use. Two molar potassium tert-butoxide was

prepared in a dry schlenk tube by combining the salt (Aldrich) with THF
distilled from NaK alloy. 5-bromo-l-pentene, 8-bromo-l-octene (Aldrich) and

10-bromo-l-decene (Alfa Aesar) were used without further purification.
Tetrahydrofuran THF and dimethoxyethane DME were first distilled from

NaK alloy using benzaldehyde as an indicator. "Super dry" ethanol was
prepared as described in the literature.102 All other reagents mentioned in
the experimental were used as received.
Micro-extractions were done by using approximately 1/2 ml of the
reaction mixture with an equal amount of water or acid, followed by
vibration. Frequently 1/2 ml of diethyl ether would also be added to this








solution. After vibrating for 1 min. the mixture was allowed to separate into

layers with the upper (organic) layer used for GC analysis.


Synthesis and Characterization


Synthesis of Symmetrical Alkyl-Substituted Terminal Dienes


Step A (one pot two step synthesis): Synthesis of ethyl-2-acetyl-2-(4-
pentene)-6-heptenoate (la). 10.9g (84 mmoles) of ethyl acetoacetate (Aldrich)

and 200 ml of dry DME (Aldrich) were placed in an argon purged 500 ml three
neck flask equipped with a magnetic stir bar and condenser. To this stirring
solution, 42 ml of a 2 molar solution of potassium tert-butoxide in THF was

added. Upon this addition the solution turned lime-green in color. This

solution was allowed to stir for 0.5 hours at room temperature followed by
slowly adding 12.5g (84 mmoles) of 5-bromo-l-pentene by syringe and raising
the temperature to reflux. White salts were formed upon reflux. The first

addition was complete in 18 hrs as shown by GC. The reaction was then
cooled to room temperature and the second addition of 42 ml of the 2 molar
solution of potassium tert-butoxide in THF was added followed by the alkenyl
bromide as above. The reaction was again followed by GC with the majority
of product formation done in 24 hrs. The reaction was then quenched with
3M HCI and extracted with ether. The ether was dried over MgSO4 and then

evaporated yielding -80% of la. The following spectral properties were
observed: 1H NMR 1.11 ppm (m, br, 4H), 1.19 ppm (t, 3H), 1.79 ppm (m, br,
4H), 1.98 ppm (q, 4H), 2.04 ppm (s, 3H), 4.12 ppm (q, 2H), 4.91 ppm (m, 4H), 5.70

ppm (m, 2H); 13C NMR 14.06 ppm, 23.21, 26.62, 30.79, 33.84, 61.09, 63.36, 115.1,








137.94, 172.5, 205.1. The Low Resolution Mass Spectrum (LRMS, EI) also
confirms structure with a parent ion at 266, calcd for C16H2603 266.

Ethyl-2-acetyl-2-(7-octene)-9-decenoate (Ib). Synthesized as above.

Product not isolated for NMR spectral analysis. LRMS (EI) 350, calcd. for

C22H3803 350.
Ethyl-2-acetyl-2(9-decene)-11-dodecenoate (Ic). Synthesized as above.

Product not isolated before subsequent step. The product of this reaction was

a thick oil. GC retention times were consistent with what was expected for

this compound and the resulting side products.


Step B: Retro-Claisen condensation: Synthesis of ethyl-2-(4-pentene)-6-
heptenoate (2a). In an argon purged dry 250 ml 3 neck round bottom flask,

equipped with a condenser and a magnetic stir bar, 22.34g (84 mmoles) of 1
and 100 ml of dry ethanol were added. To this solution 35ml of a 21%

solution of sodium ethoxide in ethanol (Aldrich) was added. (This solution

was also prepared by the addition of 21 weight percent of sodium metal into

"dry" ethanol. Caution: This addition should be done under an inert

atmosphere using "super dry" ethanol. Any contact with water in the

presence of oxygen can likely result in a fire. Super dry ethanol was prepared

as described in the purification of organic compounds.102) The solution was

allowed to reflux for 3.5 hours and turned a dark yellow in color. After

cooling to room temperature the solution was quenched with water and 3M
HC1 followed by extraction with pentane or ether. The organic layer was then
dried over MgSO4 and evaporated under reduced pressure yielding -90% of

ester 3. The product was vacuum distilled through a short path vacuum
distillation apparatus. The product was collected between 130-150 "C at
4mmHg. The following spectral properties were observed: 1H NMR (CDC13):








1.25 ppm (t, 3H), 1.40 ppm (m, br, 6H), 1.62 ppm (m, br, 2H), 2.05 ppm (q, 4H),
2.31 ppm (m, 1H), 4.14 ppm (q, 2H), 4.95 ppm (m, 4H), 5.79 ppm (m, 2H); 13C

NMR: 14.5 ppm, 26.9, 32.0, 33.8, 45.5, 60.0, 114.9, 138.6, 176.0. The Low

Resolution Mass Spectrum (LRMS, EI) also confirms structure with a parent
ion at 244, calcd for C14H2502 244.

Ethyl-2-(7-octene)-9-decenoate (2b). Synthesized as above with high
conversion indicated by GC. 1H NMR (CDC13): 1.24- 1.55 ppm (m, br, 24H),

2.01 ppm (q, 4.6H), 2.28 ppm (m, 1H) 4.10 ppm (m, 2H) 4.92 ppm (m, 4H) 5.75

ppm (m, 2H); 13C NMR: 14.31, 25.80, 27.31, 28.09, 28.79, 28.89, 29.33, 32.44,
32.61, 33.70, 45.69, 46.50, 59.88, 64.05, 114.12, 139.04, 175.93, 176.54. Spectra

consistent with structure. LRMS 308, calcd. for C20H3602 308. HRMS 308.2739,
calcd. for C20H3602 308.2715.

Ethyl-2-(9-decene)-11-dodecenoate (2c). Synthesized as above with high
conversion indicated by GC. Product not isolated before subsequent step.

Product was a thick oil with consistent GC retention times with what was
expected.


Step C: Reduction of ester: Synthesis of 2-(4-pentene)-6-heptene-l-ol
(3a). In a flamed dry 250 ml three neck round bottom flask equipped with a
stir bar and condenser, 9.301g of 2 and 125 ml of dry THF were placed. This
solution was kept under an inert atmosphere and cooled to 0 'C. To this
stirring solution, 25 ml (2 eq) of a 1M solution of LiAIH4 (Aldrich) in THF

was added over a period of 5 min. Some bubbling was observed during this
addition. The reaction was allowed to warm to room temperature and stirred
for 2 hours. The reaction was then slowly quenched with water followed by
3M HC1. The solution was extracted with ether dried over MgSO4 and rotary

evaporated. A clear oil was recovered and vacuum distilled at 69-72 "C at








1mm Hg. The reduction resulted in 91% yield. The following spectral
properties were observed: 1H NMR (CDC13): 1.18 ppm (m, br, 9H), 1.79 ppm

(s, 1H), 1.98 ppm (q, 4H), 3.49 ppm (d, 2H), 4.88 ppm (m, 4H) 5.78 ppm (m 2H);
13C NMR: 26.08 ppm, 30.29, 33.98, 34.01, 40.22, 65.36, 114.28, 138.74. IR (CDCl3,

cm-1): 3383.8 (br), 3078.1, 3013.4, 2931.0, 2860.9, 1640.4, 1460.3, 1217.1, 1030.5,
996.1, 913.1, 759.5. Elemental analysis C12H230 C(calc=79.06, found=78.99),

H(calc=12.16, found=12.16).

2-(7-octene)-9-decene-l-ol (3b). Synthesized as above with high
conversion by GC. Short path vacuum distillation was done for purification
with the main fraction collected at -100-110 'C at lmmHg. Gas cromatograph

showed a purity of 98%. Isolated yield was 61%. Spectral analysis: 1H NMR

1.27 ppm (m, br, 22H), 2.03 ppm (br, 4H), 3.50 ppm (m, 2H) 4.93 ppm (m, 4H),
5.78 ppm (m, 2H); 13C NMR: 26.77 ppm, 28.87, 29.05, 29.84, 30.86, 33.72, 40.45,

65.50, 114.06, 139.06.
2-(9-decene)-11-dodecene-1-ol (3c). Synthesized as above with high
conversion by GC. Due to the size, and therefore the boiling point, of this
product a high vacuum short path distillation was done using a short path
high vacuum distillation apparatus equipped with a dry ice isopropanol

condenser. The product, while stirring with a Teflon stir bar, was brought to
full vacuum (>10-5 mmHg) at room temperature. The solution was then

slowly heated until condensing was observed. Due to the design of this
apparatus the temperature of the condensing gas could not be measured.
During the distillation three fractions were taken. The temperature of the oil
bath was approximately 180 'C. A purity of 96% was determined by GC.
Spectral analysis: 1H NMR (CDC13): 1.29 ppm (s, br, 32H), 1.71 ppm (s, 1H),

2.02 ppm (q, 4H), 3.49 ppm (d, 2H), 4.95 ppm (m, 4H), 5.38 ppm (br, 0.2H,
elimination product), 5.78 ppm (m, 2H); 13C NMR: 25.71, 26.83, 28.88, 29.09,








29.45, 29.54, 30.02, 30.88, 32.72, 33.75, 40.46, 65.51, 114.03, 139.08. LRMS (CI)

M+1=323, calcd. for C22H420 322.


Step D: Tosylation: 6-p-toluenesolfonyl methyl-l,10-undecadiene (4a).
In a flame dried and argon purged 100 ml three neck flask, 8.290g of the

alcohol 3a (46 mmoles) and 60 ml of CHC13 were added with a stir bar. This

solution was then cooled to 0 "C followed by the addition of 7.28g (92

mmoles) of pyridine. After stirring for 15 min., 13.03g (69 mmoles) of p-
toluenesolfonyl chloride (Aldrich) dissolved in 35 ml of CDCL3 was slowly
added (15 min.) by syringe or addition funnel. A brown yellow color was

observed following this addition. This solution was then allowed to warm to
room temperature and stirred for 8 hours. The reaction was followed by GC
until high conversions were observed. The reaction was then stopped and

washed with 3 M HCI to remove the pyridine. The organic layer was then
washed with water followed by a wash with K2C03 sat. in order to remove
unreacted tosyl-chloride. The water layers were all extracted with chloroform

which was then combined with the original organic layer. The organic layer
was then dried over MgSO4, filtered through a glass fitted funnel followed by

rotary evaporation. The resulting product was a viscous oil with a yellow

tint. The product was not further purified due to fear of elimination. A yield
of -30% was determined by GC with solvent subtraction. The following
spectral properties were observed: 1H NMR (CDC13): 1.29 ppm (m, 9H) 1.79

ppm (s, br, 1H), 1.97 ppm (s, br, 4H), 2.45 ppm (s, 3H), 3.92 ppm (m, 2H), 4.94
ppm (m, 4H), 5.72 ppm (m, 2H), 7.35 ppm (d, 2H), 7.80 ppm (d, 2H); 13C NMR:
21.62 ppm, 25.73, 30.07, 33.79, 37.47, 72.63, 114.62, 127.85, 127.91, 129.81, 138.46,
144.67. LRMS 336, calcd for C19H28SO3 336.








9-p-toluenesolfonyl methyl-1,16-heptadecadiene (4b): Synthesized as
above, with similar yields. The crude product had the appearance of a viscous
brown cloudy solution. Product not isolated before subsequent reaction.
11-p-toluenesolfony methyl-1,18-uneicosadiene (4c) Synthesized as
above. Yield was not determined by GC due to its high boiling point. The
crude product had the appearance of a viscous brown cloudy solution.
Spectral analysis: 1H NMR (CDC13): 1.23 ppm (m, br, 46H), 2.05 ppm (q, 5H),
2.42 ppm (s, 5.4H) 3.50 ppm (d, unreacted alcohol) 3.90 ppm (d, 0.9H), 4.95 ppm
(m, 4H), 5.40 ppm (s, br, blip, elimination product), 5.80 ppm (m, 1.6H), 7.33

ppm (d, 2.9H), 7.79 ppm (d, 2.66H), some unreacted tosyl chloride or acid was
also detectable in this region of the proton NMR.


Step 6: 6-methyl-l,10-undecadiene (5a). Approximately 9.66g (27
mmoles) of 4a was placed in a flame dried argon purged 250 ml three neck
flask equipped with a condenser and stir bar. 100 ml of dry THF was then
added and the solution was cooled to 0 "C. To this stirring solution 20 ml
(16.2 mmoles) of a 1 molar solution of lithium aluminum hydride (LAH) was
slowly syringed in (15 min.). Bubbling occurred upon first addition. After the
complete addition of the LAH the solution was brought to reflux for 5 hours
and monitored by GC. A white precipitate was formed during the reflux. The
reaction was then cooled and quenched slowly, first with water, followed by 3
N HCI (Caution: Addition of water and HC1 should be done slowly due to the
highly exothermic reaction and the copious production of hydrogen gas).
This mixture was then extracted three times with ether, followed by the
washing of the ether layer with sat K2C03. (In some cases the washing with
K2CO3 was omitted without change.) The organic layer was then dried over
MgSO4 and then filtered through a glass fritted funnel and rotary evaporated.








The product was a clear oil and isolated by short path vacuum distillation (28-

30'C at 2 mmHg) in approximately 60% yield. The following Spectral

properties were observed: 1H NMR (CDC13): 0.77 ppm (d, 3H), 1.09 ppm (m,

1H), 1.32 ppm (m, br, 10H), 1.99 ppm (q, 4H), 4.91 ppm (m, 4H), 5.78 ppm (m,

2H); 13C NMR 19.50 ppm, 26.29, 32.46, 33.98, 36.39, 113.99, 139.06, 139.11. Low

resolution mass spectrometry (EI) = 166, calcd for C12H22 166.

9-methyl-1,16-heptadecadiene (5b). Synthesized as above. Spectral

properties: 1H NMR 0.79 ppm (d, 3H), 1.29 ppm (m, br, 22H), 2.01 ppm (q, 4H),

4.94 ppm (m, 4H), 5.79 ppm (m, 2H); 13C NMR 19.74 ppm, 27.07, 29.01, 29.26,

29.91, 32.78, 33.87, 37.12, 114.12, 139.28. Elemental analysis C18H34 C(calc=86.32,

found=86.31) H(calc=13.68, found=13.60).

11-methyl-1,20-uneicosadiene (5c). Synthesized as above with only

three hours of reflux. Spectral properties: 1H NMR 0.82 ppm (d, 3H), 1.23

ppm (br, m, 40H), 2.05 ppm (q, 4.5H), 4.98 ppm (m, 4H), 5.49 ppm (m, 0.09H),
5.81 ppm (m, 2H); 13C NMR 19.55 ppm, 26.91, 28.83, 28.98, 29.33, 29.43, 29.46,

29.83, 32.65, 33.60, 36.98, 65.39, 113.84, 139.01. Low resolution mass

spectrometry (EI) = 306, calcd for C22H42 306. High resolution mass

spectrometry (CI M+1) = 307.3396, calcd for C22H43 = 307.3365.



Alternative enolate displacement reactions for the synthesis of compounds
la, and lb


Ethyl-2-acetyl-6-heptenoate (ml) was prepared by an enolate
displacement of a alkenyl bromide. Approximately 100 ml of "super dry"
ethanol was distilled into a 200 ml three neck flask with a condenser. Na

metal (Aldrich 1.035 g, 0.04501 moles) was then added to the argon filled flask
at room temperature. Caution: This addition should be done under an inert








atmosphere using "super dry" ethanol. Any contact with water in the

presence of oxygen can likely result in a fire. This was then refluxed until all

of the Na dissolved (1 hour). The solution was allowed to cool then ethyl

acetoacetate (Aldrich 9.0 g, 0.069 moles) was added slowly via an addition

funnel or syringe. This solution was then allowed to reflux for 1 hour. A

color change from colorless to lime green was observed. The solution was

allowed to cool to room temperature and then 5-bromo-l-pentene (Aldrich

6.7 g, 0.045 moles) was added over a period of 30 min. A color change to

milky yellow was observed (incipient precipitation of NaBr salts). This
solution was allowed to reflux for 24 hours. The solution was transferred to a

200 ml RB flask and the ethanol evaporated off. The remaining oil was then
extracted with water and ether. The ether layer was then dried with MgSO4

followed by rotary evaporation. A crude yield of 94% was attained. The

product was then purified by short path vacuum distillation. The products

fraction came over at the range 70-74C at a pressure of -2mmHg. The
following spectral properties were observed: 1H NMR(CDC13) 1.28 ppm (t,

3H), 1.39 ppm (m, 2H), 1.85 ppm (m, 2H), 2.08 ppm (q, 2H), 2.23 ppm (s, 3H),

3.41 ppm (t, 1H), 4.20 ppm (q, 2H), 5.00 ppm (m, 2H), 5.78 ppm (m, 1H); 13C

NMR: 13.96 ppm, 14.14, 20.96, 30.04, 50.02, 59.74, 61.18, 89.65, 166.96, 200.22,
200.26.

Ethyl-2-(4-pentene)-6-heptenoate (2a) and ethyl-2-acetyl-2-(4-pentene)-6-

heptenoate (la) were prepared and worked up in the same manner as 6.
Compound 6 was used as a reactant in place of ethyl acetoacetate. Upon

addition of 6 the solution turned from clear to a dark red. After the addition
of 5-bromo-l-pentene the solution again turned a milky yellow due to

precipitating salts. The reaction was refluxed for 112 hours, followed by

evaporation, extraction, and distillation. A GC trace showed that there were 2








major products, 34% (2a) and 47% (la). The following spectral properties were
observed: (2a) 1H NMR (CDC13): 1.25 ppm (t, 3H), 1.40 ppm (m, br, 6H), 1.62

ppm (m, br, 2H), 2.05 ppm (q, 4H), 2.31 ppm (m, 1H), 4.14 ppm (q, 2H), 4.95
ppm (m, 4H), 5.79 ppm (m, 2H); 13C NMR: 14.5 ppm, 26.9, 32.0, 33.8, 45.5, 60.0,
114.9, 138.6, 176.0. LRMS: 224 calcd. for C14H2502 224. (la) 1H NMR 1.11

ppm (m, br, 4H), 1.19 ppm (t, 3H), 1.79 ppm (m, br, 4H), 1.98 ppm (q, 4H), 2.04
ppm (s, 3H), 4.12 ppm (q, 2H), 4.91 ppm (m, 4H), 5.70 ppm (m, 2H); 13C NMR
14.06 ppm, 23.21, 26.62, 30.79, 33.84, 61.09, 63.36, 115.1, 137.94, 172.5, 205.1.
LRMS 266, calcd for C16H2603 266.

The above reactions using ethanol and Na metal, was also done in
order to produce 2a in a one pot procedure. After the first addition of Na and
alkene bromide (as stated above) the reaction was allowed to cool to room
temperature followed by an addition of a second equivalent of Na metal. The
solution was allowed to stir for 1/2 hour forming a dark orange color. The
solution was then brought to reflux, dissolving the remaining sodium,
followed by the slow addition of one equivalent of 5-bromo-l-pentene (1/2
hour). The reaction was followed by GC producing both products 2a and la.
All of the product could then be converted to 2a by an addition (1/2
equivalent) of sodium metal. The reaction was then cooled to room
temperature followed by quenching with water and 3N HCL. The reaction
was extracted as listed above followed by isolation by vacuum distillation as
listed before. An isolated yield of 36% was obtained using this method.
Spectral analysis was consistent with the structure and as listed before.


Ethyl-2-acetyl-2-(4-pentene)-6-heptenoate (la) was also pursued by an
enolate displacement of a bromine in an aprotic solvent. Sodium ethoxide
was made by the addition of sodium (Aldrich, 0.116g 0.005 moles) into a 100








ml three neck flask containing 50 ml of "super dry" ethanol under argon.

Caution: This addition should be done under an inert atmosphere using
"super dry" ethanol. Any contact with water in the presence of oxygen can

result in a fire. This mixture was allowed to mix until all of the sodium

dissolved. The ethanol was then distilled off under reduced pressure. 6 (1.00g

0.005 moles) and an excess of diethyl carbonate was added to the cooled solid.

This was then mixed at room temperature until most of the salt dissolved.
This solution was then fractionated under reduced pressure (150 mmHg at 60-

70C) to remove any formed ethanol. 5-Bromo-l-pentene (0.0745g 0.005
moles) was then added to the solution. A condenser was then placed in the
center neck and the temperature was then raised to 1150C at standard
pressure. The solution was then stirred at this temperature for 104 hours.
The diethyl carbonate was then evaporated off and water was added, la was
extracted with ether and dried over MgSO4. A GC trace was done, which

showed two products. The products were distilled under reduced pressure
(10-2 mmHg 90-100C). The spectral properties were the same as 2a, and la

above. The yield on this reaction was 13% for la and 4% for 2a. The yields
were never optimized. Spectral analysis was the same as reported before.

Compound la was pursued again by use of a hydride base and an
aprotic solvent. A solution of 6 (3.0 g 0.015 moles) in dry 1,2-
dimethoxyethane (DME) (20 ml) was added dropwise under nitrogen to a
stirred mixture of potassium hydride (1.72 g of 35% suspension 0.015 moles
Aldrich) in DME (100 ml). When evolution of hydrogen stopped a solution
of 5-bromo-l-pentene (2.31 g 0.015 moles Aldrich) in DME (20 ml) was added
dropwise. The solution was heated under reflux for 24 hours. The DME was
then evaporated and la was again worked up as before. Compound la was








recovered in a 50% yield before optimizing. The spectral properties were the

same as reported before.


Ethyl-2-acetyl-2-(4-pentene)-6-heptenoate (la) and ethyl-2-(4-pentene)-6-
heptenoate (2a) using KH (one pot two step method): In flame dried argon
purged 100 ml 3 neck round bottom flask with condenser, 3.5 g (0.03M) of a
35% dispersion of KH in mineral oil was washed three times with 20 ml of

dry pentane. The remaining white salt was pumped to dryness under
vacuum. Approximately 50 ml of dry dimethoxy ethane (DME) was then

cannula transferred to this flask followed by stirring. No evolution of
hydrogen was observed. To this stirring solution 3.9g (0.03M) of

ethylacetoacetate was slowly added (20 min.) resulting in the evolution of a

gas (H2) and a change from colorless to a clear lime green color. The solution
was then heated to 70 *C followed by the slow addition (15 min.) of 4.47g

(0.03M) 5-bromo-l-pentene. Upon this addition the mixture turned yellow in
color with a suspension of white salts. The solution was refluxed for 20 hours
followed by cooling to 50 'C. A second equivalent of washed KH was added
under argon. Vigorous bubbling was observed with a darkening of the yellow
color to an orange. The second addition of 5-bromo-l-pentene was then
added followed by refluxing for 72 hrs. The reaction was then cooled followed

by evaporation of the solvent. The remaining orange liquid was then
extracted 3 time with water and ether. The organic layer was dried over

MgSO4 and rotary evaporated. A 60% yield was obtained (41% la, 18% 2a by
GC). A high vacuum distillation and a low temperature recrystallization
were attempted with poor results. A column was run on 200 mg of the
product using 80% pentane and 20% ethyl acetate through silica gel. A purity
of 94.4 was attained for la as determined by GC. 1H and 13C NMR are








consistent with structure la. This procedure was also done in two steps with

complete isolation of 6 and la after each step. Yields were lower due to loss

during isolation.


Ethyl-2-(4-pentene)-6-heptenoate (2a) using NaH (one pot two step
method): In a 500 ml 3 neck flask equipped with a condenser and stir bar,

10.9g (0.085 M) of ethylacetoacetate and 250 ml of DMF were stirred. To this

solution 8.16g (4 equivalents) of powdered sodium hydride was added.

Bubbling (H2 gas) occurred immediately upon this addition. The solution

was stirred at room temperature for 0.5 hours followed by the addition of 25g

(0.17 M) of 5-bromo-l-pentene. The temperature of the solution was then

raised to 120 "C. The reaction was followed by GC, using micro-extractions,

showing the production of both 2a and la. The reaction was continued for 20

hrs. At this time GC showed almost full conversion to the ester 2a. Full

conversion was often achieved by the addition of dry ethanol to the basic

solution. The solution was then cooled to room temperature followed by

slowly quenching with water and 3N HCL (Caution: Addition of water and

HCI should be done slowly due to the highly exothermic reaction and the

copious production of hydrogen gas.) The solution was then extracted 3 times

with 250 ml portions of ether. The organic phase was then dried over MgSO4

followed by filtering and rotary evaporation. GC showed that all the product

had been converted to 4. The product was isolated by a short path vacuum
distillation (74-85 "C at lmmHg) with approximately a 51% yield. Spectral
analysis was consistent with the structure and as listed before.


Ethyl-2-acetyl-2-(4-pentene)-6-heptenoate (la) and ethyl-2-(4-pentene)-6-
heptenoate (2a) using KOH, NaOH or 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)








(one pot two step method); general procedure. In a 500 ml three neck flask

10.9g (0.085 moles) of ethyl acetoacetate and 250 ml of DMF (anhydrous) were

stirred. Approximately 23.8g (5 eq) of potassium hydroxide pellets were added

followed by the addition of 25g (0.17 moles) of 5-bromo-l-pentene. The

solution was then stirred and heated to 120 'C upon which all of the KOH

pellets dissolved. A yellow brown color was observed. After three hours GC

showed the productions of both products with product (la) in majority. After
24 hours the pH of the solution was taken resulting in a pH of -10. No

change in the product ratio was detected by GC. More KOH was then added

until the pH was over 12. The reaction was then allowed to stir for 12 more

hours. At this time GC showed a mixture of products with the majority

product being 2a when the bases KOH of NaOH were used. When DBU was

used alone, only product la was formed. The reaction was then cooled to

room temperature and quenched with 3M HCL and water. This solution was

then extracted three times with 100 ml portions of ether. The organic layer

was then dried with MgS04 followed by rotary evaporation. The neat product
was dark brown orange in color. A short path vacuum distillation was then
done with the ester product distilling between 90-110 "C at 6 mmHg. An

isolated yield of 43% was obtained. The remaining product was not

identified. Spectral analysis was consistent with the structure and as listed
before.


Ethyl-2-acetyl-2-(4-pentene)-6-heptenoate (la) using NaNH2. In a dry
100 ml 3 neck flask with stir bar and condenser, 2g (0.015 moles) of ethyl
acetoacetate was mixed with 50 ml of dry dimethoxy ethane (DME). To this

stirring argon purged solution, 1.2 g (0.015 moles) of NaNH2 in a 50% weight

solution in toluene, was pipetted in. A lime green color appeared








immediately upon this addition. The solution was then heated to 60 'C

followed by the addition of 0.015 moles of the alkene-bromide. The

production of white salts upon this addition was immediately observed. The

solution was then allowed to reflux for 8 hrs. and followed by GC. The

reaction mixture was then cooled to room temperature followed by a second

addition of base and alkene-bromide in the same manner as before. A yellow

color and a significant production of salts were observed. The product

mixture was again followed by GC and the reaction was stopped after 12 hrs.

of reflux. The reaction was then quenched under an inert atmosphere using 3

M HC1. Diethyl ether was then added to this solution and 3 extractions were

done. The organic layer was then dried over anhydrous magnesium sulfate,
followed by filtration and evaporation. A EI-GC/MS was done showing that

the crude solution was a mixture of previously isolated products and a tri-

alkylated product. The product mixtures are illustrated in Figure 3.14. No

further isolation was done on the mixture.


Alternative Methods for the Synthesis of Compounds 5a-5c


Attempted decarbonylation of ethyl-2-acetyl-2-(4-pentene)-6-heptenoate
to form 6-acetyl-l,10-undecadiene (7). The decarbonylation was attempted by

the addition of an acid, base or a salt with the appropriate solvent (DMF,

DMSO, H20). These reactions were brought to reflux and monitored by

micro-extractions followed by GC. After the reactions were cooled to room
temperature, they were extracted with pentane and water. The pentane was
then rotary evaporated followed by spectral analysis if appropriate. No
reaction or decomposition was observed for these reactions. When base

(KOH) was used the expected increase in (2a) was observed by GC.










6-acetyl-l,10-undecadiene (7). In a 25 ml round bottom flask with 10 ml
of NMP and 0.5g of water, 2g of LiCI and Ig of the keto-ester (la) was added.

The solution was heated to reflux noting a color change from colorless to

yellow by 150 "C. All salts were dissolved by 160 C. Reflux was maintained

for 6 h forming a brown solution. The reaction was monitored by GC using

micro-extractions and showed the disappearance of the starting material and

the appearance of a new peak with a retention time of 10.78 minutes. The

starting material has a retention time of 12.77 minutes. The reaction was

allowed to reflux for a total of 9 hours. The reaction was cooled to room

temperature and extracted with 200 ml of water and 50 ml of pentane. The

organic layer was then dried over anhydrous magnesium sulfate followed by

filtering and rotary evaporation. A crude yield of 90% was obtained. Low

resolution mass specrometry calculated M + 1 = 195 actual M + 1 = 195. 1H
NMR:1.19 ppm (m, br, 8H), 1.51 ppm (m, 2H), 1.96 ppm (q, 4H), 2.04 ppm (s,

3H), 4.89 ppm (m, 4H), 5.69 ppm (m, 2H).


Wittig Method


(1-Pentene)triphenylphosphonium bromide (8) was synthesized as a
Wittig salt. 5-Bromo-l-pentene (Aldrich, 15 ml, 0.1 moles) was added to a 250

ml 3-neck flask containing 145 ml DMF and triphenylphosphine (Aldrich,
28.85 g, .11 moles). A TeflonTM coated stir bar and a condenser were then
added. The solution was refluxed at 1700C for 20.5 hours. The salt was then

precipitated out with diethyl ether. The salt was vacuum filtered and the
filtrate was treated again with ether for further precipitation. A yellow white
solid was recovered. The salts were then washed with hot THF then mixed in








this solvent until they dissolved partially. The solution was then allowed to

cool to room temperature and then cooled in a freezer. The salts were then

collected cold by vacuum filtration to give 1 as white crystals in a 93% yield.
Compound 1 was dried in a schlenk tube at room temperature at 10-2 mmHg
for 12 hours. 1H NMR (CDC13): 1.68 ppm (m, 2H), 2.23 ppm (q, 2H), 3.80 ppm

(m, 2H), 5.02 ppm (t, 2H), 5.65 ppm (m, 1H), 7.80 ppm (m, 15H). Elemental
calcd: C, 67.00; H, 6.11; P, 7.51; Br, 19.38. Obsd: C, 67.07; H, 6.05.


Tertiary Alcohol Synthesis and Reduction


6-methyl-l,10-undecadiene-6-ol (9), was synthesized by the Grignard
reaction with the ethyl acetate. 5-Bromo-l-pentene was dried over freshly
ground CaH2 for 3 hrs, then vacuum transferred to a schlenk flask with 4 A

molecular sieves. In a flame dried 100 ml three neck round bottom flask 1.63g
(67 mmoles) of freshly ground magnesium turnings were placed followed by
the addition of 50 ml of dry ether. A crystal of iodine, and a small amount of
the bromide was added in order to initiate the reaction. The balance of the
bromide was then added at such a rate as to maintain reflux. After complete
addition, the mixture was stirred and refluxed for 0.5 hours. After cooling to

room temperature 33.5 mmoles of dry ethyl acetate was added to produce (9).
Refluxing occurred upon addition of the electrophiles and was maintained by

heating for 2 hours. The reaction was then cooled and quenched with 3
molar HC1. The reaction mixture was extracted with ether and dried over

anhydrous magnesium sulfate, followed by filtering and evaporation yielding
5.18g (84%) of a clear liquid 9. The monomer was distilled under reduced
pressure (70-80 'C at lmmHg) using a short path distillation apparatus. The
following spectral properties were observed: 1H NMR (9) 1.14 ppm (s, 3H) 1.43








ppm (m, 9H), 2.05 ppm (m, 4H), 4.98 ppm (m, 4H), 5.80 ppm (m, 2H); 13C
NMR: 23.12 ppm, 26.80, 34.07, 41.21, 72.52, 114.48, 138.61; Elemental calcd: C,
79.06; H, 12.16; 0, 8.78. Obsd: C, 79.16; H, 12.15.


5-methyl-1,9-decadiene-5-ol (10) was prepared by using a Grignard
reagent with a ketone. 1-pentene-5-magnesium bromide (0.1 moles) was

prepared in the usual manner as a Grignard reagent. The reagent was
prepared in a 200 ml three neck flask and condenser with 20 ml of dry ether.

5-hexene-2-one (Aldrich 9.8 g, 0.1 moles) and 20 ml of ether were then slowly
added via an addition funnel. A 15 min. reflux and a color change from

brown to green was observed. The solution was allowed to stir for 7 hours
and then transferred to a 250 ml Erlenmeyer. Approximately 10 ml of 1N
H2S04 was added and 10 was extracted using water and ether. The ether layer
was dried over MgSO4, evaporated, and then vacuum distilled using a short

path vacuum apparatus. The alcohol fraction came over at 900C at 10-1
mmHg. 10 was recovered in a 78% yield and a 99.92% purity determined by
GC. The following spectral properties were observed: 1H NMR (CDC13): 1.17

ppm (s, 3H), 1.45 ppm (d, br, 4H), 1.55 ppm (p, 2H) 2.10 ppm (m, 4H), 5.00 ppm
(m, 4H), 5.82 ppm (m, 2H); 13C NMR: ppm 23.20, 26.75, 26.81, 28.29, 34.13,
40.80, 41.37, 72.55, 114.30, 114.6, 138.6, 138.9. Elemental calcd: C, 79.51; H, 11.98;

0, 9.51. Obsd: C, 76.16; H, 11.36.


Attempted synthesis of 5-methyl-1,9-decadiene (11) or 6-methyl-l,10-
undecadiene (5a) (Carey method). In a dry 250 ml 3 neck flask 0.786 (4.6
mmoles) of 2-(3-butene)-6-heptene-2-ol (10) and 1.34g (5.1 mmoles) of
triphenyl silane (weighed out in nitrogen purged glove bag) were placed with
15 ml of methylene chloride. To this stirring solution 0.80g (7.0 mmoles) of








trifloroacetic acid was dripped in. No physical change was observed upon

addition. The reaction was followed by GC using micro-extractions. After 24

hours no significant reduction in the starting material was observed so an

additional 1.5 equivalents of trifloroacetic acid was added. This solution was

then allowed to mix for an additional 12 hours. The reaction was then

quenched with an excess of saturated potassium carbonate followed by

extraction with 3 equivalent amounts of diethyl ether. The organic phase was

then dried over anhydrous magnesium sulfate followed by filtration then

rotary evaporation. The crude reaction mixture was then run through an

alumna column using pentane as the mobile phase. A GC/MS-CI/methane

was done showing that one of the minor products (5%) had a base peak of 165.

This indicates that there is some eliminated product present. 1H NMR was

relatively messy, but the olefin region did show some internal olefin

resonance's at 5.6 ppm. The target product could not be identified by GC/MS

or NMR. The reaction was repeated again using the same scale with shorter

reacting times, but resulting in the same results.


Attempted synthesis of 5-methyl-1,9-decadiene or 6-methyl-l,10-
undecadiene (5a) (Ireland method). Approximately Ig (5.5 mmoles) of

alcohol 9 was placed in a 100 ml three neck flask containing 40 ml of a 4 : 1

mixture of dry THF and tetramethylethylene diamine (TMEDA) respectively.

To this stirring solution at room temperature 2.5 ml (6 mmoles) of n-butyl
lithium in hexanes was slowly added by syringe. After mixing for 20 min. 0.9

ml (5.5 mmoles) of Diethyl chlorophosphate was dripped in via syringe.
After the first 0.5 hour white salts were noticed. The solution was allowed to
mix at room temperature for 3 hours followed by quenching with excess 1 M

HCI in anhydrous ether. This was done in order to remove the TMEDA and








LiCI salts. After the addition of the acid, large amounts of salt precipitated out

which were then filtered by using a fine frit funnel. The pH was taken

followed by additional acid washes until the solution was acidic. The ether

was then evaporated giving 850 mg of the crude reaction mixture. A GC/MS

was done on this crude mixture. The crude mixture was then dissolved in 20

ml of THF and 800 mg of t-butanol. This solution was then dripped into a

mixing solution of 20 ml EtNH2 with 200 mg of Li metal cooled to 0 'C.

Some bubbling was noted upon this addition. The reaction was stirred for 3

hours without dissolving the lithium metal. The reaction was quenched

with water and the excess lithium metal was filtered out. The reaction was

extracted with ether, dried, filtered and rotary evaporated. A GC and a

GC/MS was done showing no conclusive results of product formation.


ADMET Polymerizations of Monomers 5a and 5b


General Metathesis Conditions


All glassware was thoroughly cleaned and flame dried under vacuum
before use. The monomers were vacuum fractionally distilled or column

chromatographed to a purity of > 99% as determined by GC and elemental

analysis. The monomers were then dried over calcium hydride for a

minimum of 8 hours and then vacuum transferred onto a sodium-potassium
alloy to insure dryness. They were stirred on this alloy for a minimum of 4
hours. During this period the clear solutions would turn blue in color.
Monomers were degassed by subjecting them to several freeze pump thaw
cycles under high vacuum (<10-4 torr). The dry degassed monomers were








then vacuum transferred into a clean dry flask fitted with a TeflonTM vacuum

valve.

All metathesis reactions were initiated in the bulk, under argon glove
box conditions. Monomers were introduced into a 25 or 50 ml round-

bottomed flask equipped with a high vacuum TeflonTM valve and magnetic

stir bar. On occasion, treatment with catalyst for purification was necessary.

All monomers (0.4-2.0 g) were opened in the dry box followed by the addition

of catalyst (2-20 mg). After the addition of catalyst, the reactions were exposed

to intermittent vacuum at room temperature, until a noticeable increase in

viscosity was apparent. When the stirring of the reaction became hindered it

was then placed under high vacuum in order to remove the continuous

generation of ethylene. All the reactions were started at room temperature

then ramped to 60 "C over a period of 2 to 3 days. When no further

evolution of ethylene was apparent (bubbling stopped) the solutions were

then cooled to room temperature and quenched by exposure to air. Polymers

were isolated in high yield (-90%), followed by NMR, GPC, and elemental

analysis on the crude reaction mixture. The polymers were then precipitated

from toluene into cold methanol producing a clear, colorless to white

semisolid. If the polymer retained any color (due to catalyst) it could be

removed by dissolving the sample into toluene followed by passing it

through a short alumina column.


Polymerization of 6-methyl-l,10-undecadiene (P5a). The addition of
approximately 5-10 mg of Schrock's Mo catalysts resulted in the immediate

evolution of ethylene. The reaction was then placed onto a high vacuum
line and exposed to intermittent vacuum until there was a noticeable increase

in viscosity (30 min.). The reaction was then exposed to high vacuum (<10-5








mmHg) and stirred. As the viscosity of the system increased the solution was
slowly heated in order to facilitate stirring, in the manner stated above. After
precipitation the polymer was a clear white nonflowable tacky solid. The

polymer was dried by exposure to schlenk line vacuum at approximately
60'C. The following spectral analysis were observed: 1H NMR 0.78 ppm (d,
3H), 1.03 ppm (m, 1H), 1.28 ppm (m, 8H), 1.89 ppm (m, br, 4H), 5.29 ppm (m,

2H); 13C NMR 19.68 ppm, 27.13, 27.54, 32.58, 32.95, 36.54, 36.70, 129.92, 130.38.
Elemental analysis for repeat C10H18 C(calc=86.88 found=85.59) H(calc=13.12

found=13.01). Molecular weight determination for all the batches is discussed

in the results and discussion (Table 4.1).


Polymerization of 9-methyl-1,16-heptadecadiene (P5b). The same
general procedure was followed as for P5a. In this batch of monomer, some
impurities were present so the reaction was restarted by further addition of
Schrock's Mo catalyst in order to purify. The polymer was precipitated and
dried as stated above. A clear to white tacky solid was obtained with the
following spectral analysis: 1H NMR 0.81 ppm (d, 3H), 1.06 ppm (s, br, 1H),
1.29 ppm (s, br, 10H), 1.98 ppm (m, br, 4H), 4.94 ppm (m, end group) 5.37 ppm

(m, br 2H), 5.80 ppm (m, br, =CH2); 13C NMR 19.53 ppm 26.91, 27.10, 29.04,
29.19, 29.54, 29.64, 29.72, 32.39, 32.67, 37.00, 129.73, 130.21. Elemental analysis

for repeat C16H30 C(calc=86.4 found=84.9) H(calc=13.6 found=13.4). Molecular
weight determination for all the batches is discussed in the results and
discussion (Table 4.2).








Hydrogenation of Polymers P5a and P5b


Hydrogenation of poly [6-methyl-l,10-undecadiene] (HP5a). The
hydrogenation was performed in a flame dried, 20 ml round-bottom three-
neck flask equipped with a reflux condenser, TeflonTM stir bar, and supplied
with a positive Argon pressure. To this flask 50 mg of polymer P5a, 5 ml of
dry reagent grade o-xylene, 135 mg (2.5 eq) of TSH, and 103 mg (2.5 eq) of TPA
were added. The mixing solution was then heated to reflux. All of the TSH
did not dissolve until the solution was close to reflux. Upon heating some
gas evolution could be observed (bubbling of N2) before reflux was achieved.
The solution was allowed to reflux for 6 hours followed by cooling to room
temperature. Some white precipitation was noted at this time. A second
addition of 68 mg (1.25 eq) of TSH, and 51 mg (1.25) of TPA was administered,
followed by refluxing for 3 hours. The polymer was then precipitated in cold
methanol. The methanol was then decanted off followed by drying the
polymer in a schlenk flask under reduced pressure at 60 'C for 18 hours.
Approximately 70% of the polymer was recovered. A semi-clear tacky solid
was recovered with the following spectral analysis: 1H NMR 0.83 ppm (3H,
d), 1.10 ppm (2H, br), 1.27 ppm (14H s); 13C NMR 18.8 ppm, 26.2, 28.8, 29.5, 30.0,
36.3. Molecular weight determination is displayed in Figure 4.14.


Hydrogenation of poly [9-methyl-1,16-heptadecadiene] (HP5b). The
hydrogenation was performed in a flame dried, 100 ml round-bottom three-
neck flask equipped with a reflux condenser, TeflonTM stir bar, and supplied
with a positive Argon pressure. To this flask 500 mg of polymer P5b, 30 ml of
dry reagent grade o-xylene, 1.05g (2.5 eq) of TSH, and 0.80g (2.5 eq) of TPA
were added. The mixing solution was then heated to reflux. All of the TSH








did not dissolve until the solution was close to reflux. Upon heating some

gas evolution could be observed (bubbling of N2) before reflux was achieved

-110 C. The solution was allowed to reflux for 3 hours followed by cooling

to room temperature. Some white precipitation was noted at this time. A
second addition of 1.05g (2.5 eq) of TSH, and 0.8g (2.5 eq) of TPA was

administered, followed by refluxing for 3 more hours. The polymer was then
precipitated twice from cold methanol. The methanol was then decanted off

followed by drying the polymer in a schlenk flask under reduced pressure at

80 "C for 24 hours. Approximately 70% of the polymer was recovered. A

opaque yellow brown hard waxy solid was recovered with the following

spectral analysis: 1H NMR 0.83 ppm (3H, d), 1.09 ppm shoulder, 1.27 ppm

(28H s); 3C NMR 18.8 ppm, 26.1, 28.7, 29.1, 31.9, 36.2. Molecular weight

determination is discussed in Figure 4.15.




Alcohol Monomer Synthesis


6-methyl-l,10-undecadiene-6-ol (A3), and 1,10-undecadiene-6-ol (A2)
were synthesized by the Grignard reaction with the appropriate ester. 5-
Bromo-1-pentene was dried over freshly ground CaH2 for 3 hrs, then vacuum

transferred to a schlenk flask with 4 A molecular sieves. In a flame dried 100

ml three neck round bottom flask 1.63g (67 mmoles) of freshly ground
magnesium turnings were placed followed by the addition of 50 ml of dry

ether. A crystal of iodine, and a small amount of the bromide was added in

order to initiate the reaction. The balance of the bromide was then added at
such a rate as to maintain reflux. After complete addition, the mixture was
stirred and refluxed for 0.5 hours. After cooling to room temperature 33.5








mmoles of either dry ethyl format was slowly added to produce (A2), or

alternatively dry ethyl acetate was added to produce (A3). Refluxing occurred

upon addition of the electrophiles and was maintained by heating for 2 hours.
The reaction was then cooled and quenched with 3 molar HC1. The reaction

mixture was extracted with ether and dried over anhydrous magnesium
sulfate, followed by filtering and evaporation yielding 5.18g (84%) of a clear

liquid A2. Similar yields were obtained for A3. Both monomers were

distilled under reduced pressure (70-80 "C at ImmHg) using a short path

distillation apparatus. The secondary alcohol diene (A2) was further purified
by column chromatography using silica gel with a solvent gradient elution
using 1-5% ethyl acetate and pentane. The column was monitored by TLC
using a 5% ethyl acetate 95% pentane mobile phase on silica plates. The
following spectral properties were observed: 1H NMR (A2) 1.35 ppm (m, 9H),
1.99 ppm (m, 4H), 3.54 ppm (s, 1H), 4.89 ppm (m, 4H), 5.73 ppm (m, 2H); 13C
NMR: 24.79, 33.56, 36.79, 71.53, 114.41, 138.54; Elemental Calcd: C, 78.51; H,
11.98; 0, 9.51. Obsd: C, 77.61; H, 11.80. 1H NMR (A3) 1.14 ppm (s, 3H) 1.43

ppm (m, 9H), 2.05 ppm (m, 4H), 4.98 ppm (m, 4H), 5.80 ppm (m, 2H); 13C
NMR: 23.12 ppm, 26.80, 34.07, 41.21, 72.52, 114.48, 138.61; Elemental calcd: C,

79.06; H, 12.16; 0, 8.78. Obsd: C, 79.16; H, 12.15.


Synthesis of 6-(4-pentene)-l-heptene-7-ol (Al) was synthesized in a
three step reaction sequence as shown below.


Step 1: Synthesis of ethyl-2-acetyl-2-(4-pentene)-6-heptenoate (la).
10.9g (84 mmoles) of ethyl acetoacetate (Aldrich) and 200 ml of dry DME were
placed in an argon purged 500 ml three neck flask equipped with a stir bar and
condenser. To the stirring solution 42 ml of a 2 molar solution of potassium








tert-butoxide in DME was added. Upon addition the solution turned a lime

green color and was allowed to stir for 0.5 hours at room temperature.

Approximately 12.5g (84 mmoles) of 5-bromo-l-pentene was then slowly

added and the temperature raised to reflux upon which white salts began to
precipitate. The first addition was complete in 18 h as shown by GC. The

reaction was then cooled to room temperature and the second addition of the
alkenyl bromide was repeated as above and completed in 24 h. The reaction
was then quenched with 3M HCI and extracted with ether. The ether was
dried over MgSO4 and then evaporated yielding -80% of la. The following

spectral properties were observed: 1H NMR 1.11 ppm (m, br, 4H), 1.19 ppm (t,

3H), 1.79 ppm (m, br, 4H), 1.98 ppm (q, 4H), 2.04 ppm (s, 3H), 4.12 ppm (q, 2H),
4.91 ppm (m, 4H), 5.70 ppm (m, 2H); 13C NMR 14.06 ppm, 23.21, 26.62, 30.79,

33.84, 61.09, 63.36, 115.1, 137.94, 172.5, 205.1. The Low Resolution Mass

Spectrum (LRMS) also confirms structure with a parent ion at 266, calcd for

C16H2603 266.


Step 2: Retroclaisen condensation: Synthesis of ethyl-2-(4-pentene)-6-
heptenoate (2a). In an argon purged dry 250 ml 3 neck round bottom flask

equipped with a condenser and a stir bar, 22.34g (84 mmoles) of la and 100 ml
of dry ethanol were added. To this solution 35ml of a 21% solution of sodium
ethoxide in ethanol was added. The solution was allowed to reflux for 3.5

hours and turned a dark yellow in color. After cooling to room temperature
the solution was quenched with water and 3M HCI then extracted with
pentane. The organic layer was then dried over MgSO4 and evaporated

yielding 90% of ester 2a. The following spectral properties were observed: 1H
NMR: 1.25 ppm (t, 3H), 1.40 ppm (m, br, 6H), 1.62 ppm (m, br, 2H), 2.05 ppm

(q, 4H), 2.31 ppm (m, 1H), 4.14 ppm (q, 2H), 4.95 ppm (m, 4H), 5.79 ppm (m,








2H); 13C NMR: 14.5 ppm, 26.9, 32.0, 33.8, 45.5, 60.0, 114.9, 138.6, 176.0. The Low

Resolution Mass Spectrum (LRMS) also confirms structure with a parent ion
at 224: calcd. for C14H2502 = 224.


Step 3: Reduction of ester: Synthesis of 6-(4-pentene)-l-heptene -7-ol

(3a) (Al). Approximately 9.301g of 2a and 125 ml of dry THF were placed in a
flamed dried 250 ml three neck round bottom flask with stir bar and

condenser. This solution was kept under argon and cooled to 0 "C. To this
stirring solution, 25 ml of a 1M solution of LiAlH4 in THF was added over a

period of 5 min. Some bubbling was observed during this addition. The

reaction was allowed to warm to room temperature and stirred for 2 hours.

The reaction was then slowly quenched with water followed by 3M HC1. The
solution was extracted with ether, dried over MgSO4 and evaporated. A clear

oil was recovered and vacuum distilled at 69-72 "C at 1mm Hg. The
following spectral properties were observed: 1H NMR (CDC13): 1.18 ppm (m,

br, 9H), 1.79 ppm (s, 1H), 1.98 ppm (q, 4H), 3.49 ppm (d, 2H), 4.88 ppm (m, 4H)
5.78 ppm (m 2H); 13C NMR: 26.08 ppm, 30.29, 33.98, 34.01, 40.22, 65.36, 114.28,
138.74. IR (CHC13, cm-1): 3383.8 (br), 3078.1, 3013.4, 2931.0, 2860.9, 1640.4,

1460.3, 1217.1, 1030.5, 996.1, 913.1, 759.5. Elemental analysis C12H230

C(calc=79.06, found=78.99), H(calc=12.16, found=12.16).


ADMET Polymerizations of Alcohol Monomers Al, A2, A3


General Metathesis Conditions


All glassware was thoroughly cleaned and flame dried under vacuum
before use. The monomers were vacuum fractionally distilled (from CaH2 if








needed) prior to polymerization. The monomers, if stored, were placed over

4A molecular sieves in order to preserve dryness. The purity of the

monomers was >98% as determined by GC. Monomers were degassed by

subjecting them to several freeze pump thaw cycles under high vacuum (<10-
4 torr). The dry, degassed monomers were then vacuum transferred into a

clean dry reaction flask fitted with a TeflonTM vacuum valve and containing a

magnetic stir bar.

All metathesis reactions were initiated in the bulk, in an argon glove
box conditions. The addition of a few drops of dry CDC13 was occasionally
done in order to help initiate the reaction. Monomers (0.5-1.5 g), while in the

glove box, were introduced into a 25 or 50 ml round-bottomed flask equipped

with a high vacuum TeflonTM valve and magnetic stir bar. After the addition

of catalyst (catalyst to monomer ratios discussed below), the reactions were

first exposed to intermittent vacuum until the viscosity increased, followed

by exposure to high vacuum in order to remove the continuous generation of

ethylene. All the reactions were started at room temperature and maintained

there until the increase in viscosity prevented stirring. At this time the

reaction temperature was slowly ramped to 70 "C over a period of 2 to 3 days.

The solutions were then cooled to room temperature and quenched by the
addition of excess ethyl vinyl ether or by exposure to air. Reactions were run

on a 0.5 1.5g scale, with a monomer to catalyst ratio of 500:1, 300:1 or 200:1, as
noted.


Polymerization of [6-(4-pentene)-l-heptene-7-ol] (PAl). The monomer
Al was synthesized and dried as previously described. For a monomer to

catalyst ratio of 200:1, 23 milligrams of catalyst, RuC12(=CHPh)(PCy3)2 (C3), was

added to 1 g of the monomer. The reaction was performed under typical








metathesis conditions, until the contents could no longer be stirred or

ethylene evolution had stopped. The reaction was quenched by exposure to
air. The polymers were not precipitated before undergoing characterization.

The following spectral properties were observed: 1H NMR (CDC13): 1.09 ppm
(br, 8H); 1.35 (br, 1H); 1.71 (br, 4.4H); 3.19 (br, 1.9H); 4.67 (br, 0.04H end group);

5.15 (br, 2H); 5.60 (br, 0.003H end group). 13C NMR: Anal. Calcd for CloH10s:
C, 77.87; H, 11.76. Found: C, 75.55; H, 11.41. For GPC analysis see table 5.1. IR

(neat, cm-1) 3341, 3005, 2926, 2856, 1726, 1457, 1440, 1036, 967, 511.


Polymerization of [1,10-undecadiene-6-ol] (PA2). The monomer A2
was synthesized and dried as previously described. For a monomer to catalyst

ratio of 200:1, 24 mg of catalyst, RuCl2(=CHPh)(PCy3)2, was added to Ig of the
monomer. The procedure was followed as in (PA1). The following spectral

properties were observed: 1H NMR: 1.45 ppm (br, d, 9H); 2.00 (br, 4H); 3.55
(br, .7H); 4.98 (br, 0.29H end group); 5.40 (br, 2H); 5.80 (br, m, 0.04H end group).
13C NMR: 24.8-33.4 (multiple signals), 36.4, 71.0, 129.5-130.5 (multiple signals).

Anal. Calcd for C9H160: C, 77.09; H, 11.50. Found: C, 76.48; H, 11.33. For GPC
analysis see table 5.1.


Polymerization of [6-methyl-l,10-undecadiene-6-ol] (PA3) The
monomer A3 was synthesized and dried as previously described. For a
monomer to catalyst ratio of 500: 15 mg of catalyst C3 was added to 500 mg of
the monomer. The procedure was followed as in PA1. The following spectral
properties were observed: 1H NMR: 1.12 ppm (s, 3H); 1.40 (br, 8H); 1.99 (br,
4H); 4.94 (br, m, 0.25H end group); 5.39 (br, 2H); 5.79 (br, m, 0.09H end group).
13C NMR: 23.90, 26.94, 27.67, 33.01, 41.37, 72.72, 129.92, 130.42. Anal. Calcd for








C10H180: C, 77.87; H, 11.76. Found: C, 76.61; H, 11.50. For GPC analysis see
table 5.1.


Hydrogenation of Poly [1,10-Undecadiene-6-ol] (HPA2)


The hydrogenation was performed in a flame dried, 50 ml round-

bottom three-neck flask equipped with a reflux condenser, TeflonTM stir bar,

and supplied with a positive Argon pressure. To this flask 266 mg of

polymer PA2, 25 ml of dry reagent grade toluene, 907 mg of TSH, and 0.932 ml
of TPA were added. The mixing solution was then heated to reflux. All of

the TSH did not dissolve until the solution was close to reflux. Upon heating
some gas evolution could be observed (bubbling of N2) before reflux was

achieved. The solution was allowed to reflux for 6 hours followed by cooling

to room temperature. Some white precipitation was noted at this time

(insoluble hydrogenated polymer). A second addition of 907 mg of TSH, and

0.932 ml of TPA was administered, followed be refluxing for 3 hours. Once

the solution cooled to room temperature the product could be observed as a

white precipitant. The polymer was then precipitated in cold methanol.

Approximately 60% of the polymer was recovered. The following spectral

properties were observed: 1H NMR (Toluene d8 at 100 'C): 1.55 ppm and 1.62

ppm (br, s, 18H); 3.72 (s, 1H); 5.18 (br, m, residual vinilic CH2); 5.62 (br, m,
residual internal olefin). 13C NMR: 26.60, 30.50, 30.66, 38.67, 72.41. GPC
analysis was not performed due to the insoluble nature of this polymer.








Preliminary Alcohol Dimerization Experiments


Dimerization of 4-pentene-l-ol (12). Monoene 12 was purchased from

Aldrich in Ig bottles and used on that scale with no further purification. The

monoene was placed in a 50 ml reaction flask followed by degassing under

high vacuum using three freeze pump thaw cycles. The monoene was then

placed into the dry box along with the addition of a magnetic stir bar. To this

stirring liquid, 23 mg of Grubbs' ruthenium catalyst C3 (a monoene to catalyst

ratio of 400 : 1) was added. Upon this addition the reaction turned purple

brown in appearance follow by a small amount of bubbling. The reaction was

then removed from the dry box, placed on the high vacuum line, followed by

intermittent exposure to low vacuum (<10-2 torr) while stirring. At this time

noticeable degassing (bubbling) occurred and continued. After two hours the

solution turned an orange in color followed by a yellow color with a white

precipitate after 18 hours. After 18 hours a sample was taken for a proton

NMR. Approximately 80% conversion was determined by proton NMR.

This was determined by the ratio (proton integration) of internal to external

olefin peaks. 1H NMR peaks of the mixture are as follows: 1.56 ppm (qn), 2.05

ppm (m), 2.17 ppm (qrt.), 2.25 ppm (qrt.), 2.75 ppm (br OH), 3.54 ppm (d), 4.93

ppm (m, =CH2), 5.38 ppm (m, trans internal olefin), 5.47 ppm (m, cis internal
olefin), 5.72 ppm (m, CH= terminal olefin).


Attempted dimerization of 2-propene-l-ol (allylic alcohol) (13). The

attempted dimerization was performed in a similar manner as that described
for monoene 12. The addition of 35 mg of catalyst C3 (M : C = 400 : 1) resulted
in an immediate color change to yellow with what appeared to be a white
precipitate. The evolution of ethylene (bubbling) was not observed upon this








addition. Some bubbling was noticed while exposure to the intermittent
vacuum. The reaction was allowed to stir for 18 hours, followed by NMR
analysis. The 1H NMR represents a mixture of isomers: 0.94 ppm (m), 1.10

ppm (m), 1.61 ppm (br, m), 2.32 ppm (qrt.), 2.47 ppm (qrt.), 3.72 ppm (br, OH),
4.12 ppm (shp, m), 5.20 ppm (m), 5.82 ppm (s), 5.97 ppm (m), 9.78 ppm (shp, s).


Dimerization of 5-hexene-2-ol (14). The monoene 14 was provided by
Shane Wolfe fully characterized and at a purity of >99% by GC. This sample
was degassed and placed in a dry box atmosphere as before. To this stirring
liquid 21 mg of catalyst C3 (M : C = 200 : 1) was added followed by immediate
bubbling and an orange purple color. The reaction was then exposed to
intermittent vacuum as before with a noticeable increase in the evolution of
gas. Samples were taken for NMR after 1 hour and after 24 hours showing a
52 and 97% conversion, respectively. 1H NMR peaks of the mixture after 24
hours are as follows: 1.18 ppm (d), 1.49 ppm (m), 1.61 ppm (d of d), 2.10 ppm
(br, m), 3.78 ppm (q), 4.98 ppm (m) (unreacted =CH2), 5.40 ppm (m) (cis and
trans), 5.8 ppm (m) (terminal =CH).


Attempted dimerization or polymerization of 1, 5-hexadiene-2, 3-diol
(15). Monoene 15 (Aldrich) was purchased in Ig bottles and used on that scale
with no further purification. One gram of 15 was placed into a reaction flask
with a stir bar and degassed as before. Under dry box conditions 42 mg of
catalyst C3 (M : C = 200 : 1) was added to this stirring solution. Upon this
addition the catalyst and solution maintained there original color (purple).
No bubbling was observed upon this addition. The reaction was transferred
to the vacuum line as before, and allowed to stir for 12 hours. No outward
sign of condensation was observed (increase in viscosity and bubbling). After








12 hours an aliquot was removed for NMR analysis. No reaction was

observed by NMR at this time. The reaction was returned to dry box

conditions upon which a few drops (-0.3 ml) of CDC13 was added. This was

done in order to solvate the catalyst. Upon this addition the solution

immediately turned brown in color. This mixture was allowed to stir for an

additional 12 hours. 1H NMR analysis again showed no detectable reaction

(no detection of internal olefin). The NMR was consistent with the unreacted
monoene.


Attempted dimerization of 1, 5-hexadiene-3-ol (16). As stated before Ig

of 16 (Aldrich) was degassed and placed in dry box conditions. To this stirring
solution 42 mg (M: C = 200: 1) of catalyst C3 was added. Upon this addition

the reaction immediately turned brown in color with no detectable evolution

of gas (bubbling of ethylene). Intermittent vacuum was applied with no

increase in viscosity or continued bubbling. After 12 hours an aliquot was

removed for 1H NMR analysis. A small amount of internal olefin was

detected at 5.5 ppm. The remaining proton shifts remained consistent with
the starting material.














CHAPTER 3


DESIGN AND SYNTHESIS OF SYMMETRICAL ALKYL-SUBSTITUTED
TERMINAL DIENES


This chapter is concerned with the design and synthesis of the
symmetrical alkyl substituted monomers that are required for the productive

conversion towards a linear regular branched acyclic diene metathesis

(ADMET) polymer (Figure 3.1).




,,C, Catalyst c ~ + CH-CH2C


Figure 3.1. ADMET polymerization of terminal dienes



The goal of this research has been to model branching in polyethylene
in order to better understand how branching affects the physical properties of

a polymer. The branching of linear polyethylene that is induced by the
random copolymerization of a-olefins or chain transfer events can be

mimicked by the ADMET condensation of alkyl substituted dienes followed
by hydrogenation. The resulting copolymer is the product of a
homopolymerization; therefore, the amount and location of the branch
points is controlled by the monomer used. The synthetic methodology
presented, via the homopolymerization of ADMET monomers, provides
both inter and intramolecular homogeneity with regard to branch








distributions (imperfections) along the polymer backbone. Polymer samples

containing these qualities are excellent models for the study of structure-

property relationships with regard to branching in polyethylene. This type of
system with a perfectly-spaced alkyl branch is illustrated in Figure 3.2.



H





Control over # of methylenes

Control over length and identity of "R"

Figure 3.2. Target polymer for the synthesis of perfectly branched
polyethylene.


Designing the Target Monomers


The clean nature of polymers produced by the homopolymerization of

a, co-dienes, enables the design of the appropriate monomer to be deduced

from the target unsaturated polymer (prepolymer). This is represented by the

retrosynthesis of a target prepolymer in Figure 3.3.



H H



Figure 3.3. The retrosynthesis of the target prepolymer.



To achieve control over the distribution of branch points in the

resulting polymer, it is necessary to design a synthetic methodology that will









produce symmetrical hydrocarbon a, co-dienes. This type of synthesis is

challenging due to the lack of functional groups present and the symmetrical

nature of the final product (Figure 3.4). Further, it is necessary to be able to

synthesize a homologous series of the models in which both the frequency

and identity of this branch point can be varied (Figure 3.4).

A symmetrically substituted diene is necessary to prevent the
scrambling of branches (imperfections) in the polymer chain. The metathetic



H


R
Control over the frequency R= Variable length alkyl groups;
of the branch -\Control over the branch identity


Figure 3.4. Target monomer; symmetrically substituted diene


reactivity of the terminal olefins in alkyl substituted dienes is essentially

equivalent. Therefore, the polymerization of an unsymmetrical diene lacks

the necessary head to tail preference required for ordered assembly. The

resulting placement isomerism can be demonstrated by the

homopolymerization of 4-alkyl-1,8-nonadiene (Figure 3.5). This isomerism is

illustrated by the 1,6 and 1,7 placement of the alkyl branch in a trimer that

contains one head to head (HH) and one tail to head (TH) connection (Figure

3.5). Due to functional group equivalence, these types of connections will

occur in a random fashion providing only intermolecular homogeneity. This

type of distribution would be considerably more ordered than that obtained in

a-olefin copolymerizations, but precise control cannot be achieved.









H
I
R

Mo

H H



HH THR

1. 6 placement
1,7 placement

Figure 3.5. Trimer of unsymmetrical 4-alkyl-1,8-nonadiene; 1,6 and 1,7
placement of branch due to head to head (HH) and tail to head (TH) type
placements.


Purification is also an important consideration during the design of the

monomers due to the need for 99%+ purity in order for polycondensation to

proceed to high molecular weights. This is a result of the statistics involved

in step polymerizations as defined by the Carothers equation (equation 4

chapter 1). Further, the catalyst used for ADMET polymerizations (Figure 3.5.)

is vulnerable to attack by Lewis bases.







CF3 N
CCF ,CH3
CHO 0 NH3

CH3 F3 Ph
CF3
C1
Figure 3.5. ADMET catalyst; Schrock's Molybdenum Alkylidene.








Synthesizing the Target Monomer


Various synthetic methods were investigated toward the production of

a homologous series of target monomers. The priorities in this consideration

were to obtain a relatively high yielding procedure with the variability to

synthesize a reasonable number of the desired monomer derivatives (Figure

3.4). The synthetic methods that were attempted (Figure 3.6) have displayed

interesting mechanistic implications that were considered in the

development and optimization of monomer construction.


P-Keto Ester Substitution Method


The carbon-carbon bond-forming reaction of enolate substitutions has
been shown to be a synthetically useful method toward the production of the

target monomer. Carbanions or enolates can be formed by the deprotonation

of an a-carbon by a strong Br6nsted base. These protons exhibit significantly

higher acidities compared to hydrocarbons, where their increased acidity

results from a combination of the inductive effect from the alpha carbonyl

and the resonance stabilization of the anion formed by removal of a proton
(Figure 3.7). The formation of a significant concentration of the enolate

requires that the base used has a weaker conjugate acid than the active

methylene compound.103 The solvent must also be a weaker acid than the
conjugate acid of the base to avoid solvent deprotonation.'03

Enolate anions are useful in a variety of base catalyzed condensation
reactions of carbonyl compounds, specifically aldol/Claisen condensations

and alkylations. This type of enolate substitution is common for the anions









O2Et

H + =CH, Br
c= n


CH


3



Dicarbonyl substitution t



/ Wittig chemistry


R

H2 H2
H


Malonic ster


0 R 0

RO- k(CHY -CH2 "OR
1 n v n


DiGrignard coupling


Lactone ubstitution





R


R
BrMg V L MgBr + BCH2')B


Figure 3.6. Pursued routes of monomer synthesis.




of P-ketoesters with the majority of the examples involving the

monosubstitution of stabilized enolates with alkyl halides.103 The di-


0

LCHig + RC-OEt

M=Li.MgX


Organometallic/ter


t-alcohol


/


-^,








alkylation of ethyl acetoacetate, via enolate anions, is the basis for a multistep

synthetic procedure for the generation of the target monomer.






/C-OC2H /C-OC2HS C-OCH5
H2C\ CH -CH3
CCH3 CCH3 \ CH3



Figure 3.7. The equilibrium and resonance structures of enolate formation.



A general procedure for the synthesis of the target monomer was
devised which involved the enolate displacement of terminal alkene

bromides. This method of synthesizing the target monomer is illustrated in

Figure 3.8 and is termed the p-keto-ester method. The first reaction, (A)

Figure 3.8, involves the generation of the anion from a diprotic active

methylene group followed by subsequent alkylation of the 0-keto-ester with

an alkene bromide forming the mono-substituted p-keto-ester. This can then

be repeated for the other proton forming the dialkylated product (1). This

method provides a single center were both alkylations can occur creating a

symmetrical intermediate. The frequency of the repeat unit in the target

polymer can be controlled by the alkylation of various length alkenyl

bromides. The intermediate (1) could then follow two routes (B or C) to

generate the alkyl group. Route B is the process of eliminating the acetyl

group by the use of a retro-Claisen condensation reaction. The ester

produced, (2), can then be reduced to form the primary alcohol (3), which can

be removed by conversion to a leaving group (tosylate) followed by hydride














'O2Et

H2 + ^;Hk Br
C= O
CH3


COEt


H 2
Reduction D
OH
CH,

H
3


R

H
target monomer
0
COEt
Base H H
A O Dealkoxycarbonylation
D CH3 c
Deacylation CHC 1
B H


c=o 6
CH3
E Reduction
Sto Methylene

1. Tosylation- H J.z -~jH-
2. Reduction 2yn 11

5 CH
7


Figure 3.8. P-Keto-ester method: synthesis of target monomer.



displacement to form the methyl substituted target monomer (5). The

alternative route, C, removes the ester group via dealkoxycarbonylation. This

can be done directly or by decarboxylation of the saponified ester. The

resulting ketone (6) can then be reduced to the methylene by a Wolf-Kishner

reaction to form the ethyl substituted target monomer (7). Both

intermediates (3) and (6) can be used to extend the symmetrical alkyl

substituent via further alkylations.

Route B (Figure 3.8) provided the means to construct a series of the

target monomers and was used to synthesize monomers 5a, 5b, and 5c (where









C(O)OCHCH
A CH3CHOO)C-CH,-C(O)CH, 2 eq (CH)CO-K/DME
2 eq CH--CH(CHI,,Br +(CH,)n (CH2)n''
C(O)CH,
1





C(O)OCH2CH3 C(O)OCHCH3
B (CH)n (CH2n E Na / OH (CH)n C

C(O)CH3
1 2





OH
C(O)OCH,CH3 IH
S (CH) (CH) LiAIH4/THF 2
(CH). ( (CH2) (CH,)./,-


2 3





OH OTs
CH2 CH,
D ..(CH) 2(CH2) TosC I/Et3N (CH 2)n
D --(CH2) l^(CH,),-`- --- .)---- t(CH2) j,) (CH,).----


OTs

E '(CH. CH,


CH3
LiAIH4/THF .
---------- '^CH-^tC^-


Figure 3.9. The synthesis of the methyl substituted target monomer.








n=3, 6, and 8 respectively). The reactions used to accomplish this 6 step

conversion are shown in Figure 3.9.


Enolate Alkylation of Ethyl Acetoacetate and the Retro-Claisen Condensation


The enolate anion of ethyl acetoacetate was investigated as a means to
add alkene halides via subsequent nucleophilic displacements. The anion

generated by deprotenation of a p-keto-ester can exist in two resonance

structures (Figure 3.7); the anion on the oxygen, or the anion on the carbon.

The type of base and solvent used in these reactions can favor either O-

alkylation or C-alkylation, and has a direct effect on competing side reactions.

If the base is too nucleophilic (Lewis basic), the direct displacement of the

alkene bromide or the deacylation of the P-keto-ester by a reverse Claisen

condensation can occur. If the base exhibits a strong Bronsted basicity,

elimination of the alkene bromide, alkylation of the ketone, or dianion

formation of the P-keto ester can occur.

In order to optimize the conditions for this substitution reaction, both
the type of base and solvent were investigated using 5-bromo-l-pentene as the
halo-alkene (Figure 3.10). The major products in these reactions were the di-

alkylated P-keto ester (A Figure 3.10) and the di-alkylated ester (B Figure 3.10).

These products correspond to compounds la, b, c and 2a, b, c in the

experimental section.

The syntheses of la, Ib, and Ic were designed to be a one pot, two step
procedure (A Figure 3.9), which involved the deprotonation of ethyl
acetoacetate by the bulky Br6nsted base potassium tert-butoxide in dimethoxy

ethane (DME) (entry 12 Figure 3.10). This was accomplished by the room









O 0
H2Et COEt COEt
2 H Br5--BS^ ICH.-(CH2 3.CH,)--(CH
0 +2 CHBr +Bae H 1 +iH
c=o 3 C-=0 H
CH, CH3

A B

Entry Base Solvent A% B%
1 2 eq EtO-Na+ EtOH 17 22
2 4 eq EtO-Na+ EtOH 0 48
3 2 eq EtO-Na+ EtO(CO)OEt 13 4
4 2eqKH THF 69 4
5 4 eq NaH DMF 16 51
6 3 eq NaH DMF 60 0
7 2 eq NaH EtO(CO)OEt 42 0
8 4 eq NaOH DMF 0 52
9 2 eq KOH DMF 39 21
10 2 eq DBU DMF 42 0
11 2 eq NaNH2 THF 57 7
12 1.9 eq (CH3)3CO- K+ DME 86 0

Figure 3.10. The enolate displacement reaction of 5-bromo-l-pentene.
Displayed percentages were attained by GC and show % of A or B within each
sample.



temperature addition of one equivalent of base to a stirring solution of the P-

keto-ester. Formation of the enolate could be detected by the lime green color

of the solution, which is the apparent result of the highly delocalized anion of

a p-keto ester. After acid-base equilibrium was obtained, 5-bromo-l-pentene

was added (or higher homologue) to the basic solution. The reaction was

monitored by GC using a micro-extraction method and was allowed to

continue until a high conversion was achieved. Mono-alkylation of the keto-

ester was a relatively fast reaction as shown by detection by GC within the first

10 minutes of refluxing. A small amount of the di-alkylated product was

detected before the addition of a second equivalent of base or alkene-bromide.








The second alkylation was facilitated by the addition of another

equivalent of base at room temperature, followed by a second equivalent of

the alkene-bromide. Again, the enolate was detected by a dark green color but

was usually only evident at increased temperatures, due to the decreased

acidity of the second proton. The second alkylation was also monitored by GC

and required much longer reaction times to achieve good conversions. The

retardation of the second alkylation probably is due to a more sterically

hindered enolate anion and a shifted acid-base equilibrium. A large amount

of potassium bromide salt was apparent by the end of the second reaction.
Product, la, was isolated using high vacuum distillation via a short path

distillation apparatus and resulted in a 65% yield, while products lb and Ic

were not isolated due to their low vapor pressures. GC retention times of the

crude products were consistent with what was expected, and mass spectra

were consistent with their formula weight. The crude mixtures were used in

subsequent reactions without further purification.

The addition of excess base (potassium tert-butoxide), or increased
reaction times also resulted in the conversion of la to the deacylated product

2a (Figure 3.10). Similar conversions occurred for lb and Ic consequently

producing compounds 2a, b, c, as the major products. Cooler temperatures
and longer reaction times may facilitate the production of the keto-ester only.

This deacylation of a P-keto esters was identified as a retro-Claisen

condensation.104,105,106 The cleavage of P-keto esters at the ketone has been
observed during alkylation reactions and was most pronounced when the
alkylated product had two alpha substituents,107 as do products la, b, and c.
Literature reports that this cleavage can be minimized by three methods; low

temperature reactions using sodium ethoxide, the use of sterically hindered

bases such as potassium tert-butoxide,10s or the use of sodium hydride109 in








polar aprotic solvents. The extended exposure of nonenolizable ketones to

tert-butoxide in DME has also shown a similar ketone cleavage.110111 The

proliferation of this cleavage has become the basis for the second step in the

synthetic sequence (Figure 3.11).



0 o
OEt Et o
SH BOCC

EtO CH3 H'
la 2a
Figure 3.11. The conversion of la to 2a by the reverse Claisen condensation.



The retro-Claisen condensation of the products la, Ib, and Ic, was

induced by the addition of an excess of sodium ethoxide (Figure 3.11 and

Figure 3.9 B). This deacylation occurred with near quantitative conversion,

i.e. > 95% and was monitored by GC (Figure 3.12). Chromatogram A is the

product mixture after the enolate alkylation reaction and chromatograms B-D

are the product mixtures after 1, 2, and 3 hours of exposure to sodium

ethoxide, respectively. Compound percentages were determined by

subtracting out the known solvent peaks. The GC peaks were assigned by the

isolation and characterization of the compounds by NMR and GC/MS. It was

also demonstrated the conversion could be obtained by direct addition of

sodium ethoxide to the reaction pot after the completion of the di-alkylation.

Higher yields were achieved, though, by first isolating the crude products. It

was also observed that the use of more nucleophilic bases for the enolate

alkylation resulted in higher percentages of the deacylated product before the

addition of sodium ethoxide.









2a la 2a la 2a la 2a
78% 16.8% 82% 13% 94% 5.3% 99%







i i I I la
1%





A B C D

Figure 3.12. Gas chromatograms demonstrating the conversion of la to 2a by
a reverse Claisen condensation using sodium ethoxide.


Other less successful methods of di-alkylating P-keto esters were

examined with their respective results listed in the table of Figure 3.10.

Entries 1 and 2 show the results when sodium ethoxide was used as the base

in the two step reaction where both the mono and di-alkylated products were

isolated between steps. The monoalkylated product was isolated with

relatively high yields (-80%) while the dialkylated product was isolated with a

yields of 30% or less. Previous investigators have shown that the failure to

efficiently di-alkylate was due to the incomplete formation of the sodio

derivative of the mono-alkylated product,112 which leaves large amounts of

sodium ethoxide in solution which could then directly displace the alkyl

bromide. A modification of this reaction presented by Wallingford et a112 is

shown in entry 3. In this case the reaction is performed in a high boiling

aprotic solvent where ethanol is distilled off as it is formed therefore driving

the reaction toward the production of the sodio derivative. However, poor








yields were also obtained using this technique. Both of these methods using

sodium ethoxide, resulted in deacylation of the product in a uncontrollable

fashion, which is consistent with the use of a nucleophilic base.

The use of dimethylformamide (DMF) and other aprotic solvents
results in the acceleration of enolate alkylations.113 Aprotic solvents show a

clear advantage over the use of protic solvents for the alkylation of enolates

of monosubstituted acetoacetic esters,114 but occasionally have the

detrimental effect of favoring alkylation at the oxygen rather than at the

carbon. Zaugg et al offers an excellent review of specific solvent effects in the

alkylation of enolate anions.115

Zaugg115 also demonstrates the use of hydride as the base in DMF.
Hydride has the advantage of shifting the acid base equilibrium in favor of

the enolate anion due to the release of hydrogen upon deprotenation. Entries

4-7 (Figure 3.10) are the results of using a hydride base with ethyl acetoacetate

in an aprotic solvent. The yields were moderate to low and varied with

reaction times. These reactions were repeated multiple times and were

performed as either a two step process with isolation of each step or as a one

pot synthesis. If an excess of hydride was used and or reaction times were

dramatically increased, the deacylated product 2a was the major product.

Further, the production of 2a was improved by the addition of ethanol after

alkylation was complete. Higher boiling residues were detected for each of
these runs.

The di-alkylation of activated methylenes is reported to react in the
presence of 1,8-diazabicyclo[5.4.0]undec-7-en (DBU) and DMF.116 Using this
method (entry 10, Figure 10), longer reaction times were required for the di-
alkylation, while producing only monomer la. This retention of the P-keto








ester functionality is consistent with the use of the non-nucleophilic base

DBU.

The use of potassium and sodium hydroxide in DMF was investigated

as an alkylating medium (entries 8 and 9, Figure 10). Usually, these types of

bases are avoided due to their tendency to cause saponification and

decarboxylation of the ester group.103 The nucleophilic nature of the

hydroxide can also induce cleavage of the ketone functionality.103 The di-

alkylated product la was obtained using this method but resulted in low

yields. Quantitative conversion, as monitored by GC, of la to 2a was obtained

and was promoted by increasing the pH of the solution. The production of

the keto acid and the decarboxylated product was not investigated.

Sodium amide, due to its high Brbnsted basicity, was investigated as a

means to increase the rate of the second alkylation. Its basicity also creates the

possibility of forming the dianion of the 1, 3,-keto ester. It has been shown

that the addition of two equivalents of sodium amide to ethyl acetoacetate can

be used to generate the dianion which results in the activation of the acetyl

methylene for displacement reactions (Figure 3.13).117 The acetyl anion will

be the "hotter" anion and will usually undergo a high yielding alkylation.



0 O0 O 0 0
0 NaNH,
COACH5 NH OCH5 ----- OC2H

Figure 3.13. The generation of the enolate dianion by sodium hydride.


Results obtained from using sodium amide as the base in a two step
method (entry 11, Figure 10), resulted in acetyl substitution. The products

masses (GC/MS) were consistent with a mixture of the mono, di, di-
deacylated, and tri-alkylated products (Figure 3.14 A, B, C, D respectively). The









percentages of products were determined by GC with subtraction of the

known solvent peaks.




coEt COEt COEt COEt

C--o C- 3 H 3 C-O
CH3 CH3 CH

A B C
20% 50% 6.6% II


D
16%
Figure 3.14. Product percentages of the enolate displacement using NaNH2.


Reduction, Tosylation, and Hydride Displacement



The reduction of 2a, b, and c was accomplished by the addition of excess

lithium aluminum hydride (LAH) (> 2 eq) to a solution of the ester in THF118

(Figure 3.9 C). This reaction proceeded as expected with near quantitative

conversion at room temperature producing the alcohols 3a, b, and c. The

reduction did not require the extensive purification of the ester starting

material before reacting. Due to the high boiling points of the other alcohols,

only the intermediate 3a was purified by vacuum distillation. Alcohols 3b

and 3c were characterized and used in their crude form in the subsequent

reaction.

Now that the primary alcohol could be obtained, it was necessary to

remove the alcohol functionality so that the methyl substituted target

monomer could be synthesized. This was accomplished by first converting

the alcohol into a tosylate and then displacing it by a hydride.








Tosylation of the alcohol (Figure 3.9 D) was achieved by using a
technique similar to that developed by Kabalka et al,119 in which the tosylates

of long chain aliphatic alcohols were obtained by reacting the alcohols with a

1 : 1.5 : 2 ratio of alcohol/tosyl chloride/pyridine in chloroform. These

reactions were cooled to 0 "C for the addition of reagents followed by

warming to room temperature. This was done to avoid the undesirable

elimination product. The reaction was followed by GC until no further

conversion was observed (approx. 12 hrs.). The products recovered (4a, b, c)

were thick oils and were used without further purification. The tosylate (4a)

was purified by column chromatography for complete characterization.

Tosylation methods using different equivalent amounts of reactant
and reagents were also attempted. Using THF as the solvent and NaH or

triethyl amine as bases were somewhat successful but resulted in relatively

low yields.

The final reaction was the nucleophilic displacement of the tosyl group
by a hydride (Figure 3.9 E). Two equivalents of lithium aluminum hydride in

THF were added to a mixing solution of compound 4 followed by refluxing.

The conversion was complete in less than 5 hours and gave moderate yields

of the target monomers 5a, b, and c. The monomers 5a and 5b were purified

by short path vacuum distillation to a purity of 99% by GC, followed by full

characterization. The 1H NMR spectra of the target methyl substituted

monomers 5a, 5b and 5c are shown in Figure 3.15.


Dealkoxycarbonylation of the Keto Ester

Route C (Figure 3.8) was investigated as a means to produce the ethyl
substituted monomer 7. Alkylated products of P-keto esters may be
hydrolyzed and decarboxylated to form the corresponding acids and ketones,















CH,

-(CH2,)3 ,-(CH2)f-

5a









ppm




CH3

"'-(CH2) (CH2)6 I

5b











CH3

',-(CH2) 3(CH2)g

5c





ppm
Figure 3.15. 1H NMR of the methyl substituted target monomers 5a and 5b.








respectively.103 The decarboxylation of saponified esters (acids) is known to

proceed through a six-center transition state which initially forms the enol

(Figure 3.16).107


R- C-- CHC0,H A M H2
SHH
R--C-CcoH RC O 2C- R--=CH, R-C--CH,


Figure 3.16. Decarboxylation of 1, 3-keto acid.


Saponification of di-substituted p-keto esters is often complicated by the
competing attack of the hydroxide anion at the ketone functionality, which
leads to the reverse-Claisen cleavage instead of the saponification. This is due

to the presence of a nucleophilic group with a dialkylated 1, 3-keto ester.
Hydrolysis and decarboxylation are typically accomplished with aqueous acid
and heat to avoid this side reaction.107

Decarbonylation of la to 6 (C Figure 3.8) was attempted by heating la in
the presence of either an acid, base, or salt (NaC1) in DMF, DMSO, or H20. No
detectable reaction or significant decomposition was observed using these

methods. The expected conversion of la to 2a (deacylation) was observed
with the addition of KOH and heating.

Krapcho reports a method to affect dealkoxycarbonylation of
disubstituted p-keto esters by the use of a salt such as lithium chloride or
sodium cyanide in a dipolar aprotic media.120 This method has the
advantage of proceeding with neutral conditions, therefore preventing side
reactions such as acid addition to olefins and ketone cleavage. Using this
method, la was reacted with LiC1 salts in NMP and water under reflux
conditions. The GC results showed the appearance of a new major peak.
Further, low resolution GC/MS resulted in a M+1 ion that was consistent
with the production of 7. The 1H NMR showed the retention of a 3 proton








singlet at 2.04 ppm from the retention of the methyl ketone as well as the

disappearance of the ethoxy protons. Work on the dealkoxycarbonylation was

stopped due to the difficulty in isolating large amounts of la.

The P-keto ester substitution method has provided the most success in

the generation of the target monomers. Target symmetrical methyl

substituted monomers 5a, 5b, and 5c have been generated using the general

methodology outlined in Figure 3.9. The following discussions are based on

other synthetic methods that have been investigated but are currently not

being pursued.


Wittig Method


The Wittig reaction between a phosphorus ylid and an aldehyde or
ketone results in carbon-carbon bond-formation and is extensively employed

in synthesis. The use of this reaction was investigated for the synthesis of the

target monomers.

The synthetic design was to first make a phosphonium salt from an
alkene bromide followed by the formation of the ylid and the coupling with

an alkene-one (Figure 3.17). The carbon-carbon bond-formation results in the
formation of an olefin at the joining site. The product, therefore, contains a

tri-substituted olefin in place of the carbonyl (Figure 3.17 C).

This method provides the ability to make monomers of multiple sizes
and variable length branches. The size (length) and symmetry of the diene

product can be modified by choosing longer chain functionalized alkenes.
The branch point identity can be varied by modification of the alkane side of
the ketone. Figure 3.17 demonstrates this utility with the synthesis of a
methyl branched monomer by reacting the ylid with a methyl ketone.




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