Acyclic diene metathesis (ADMET) segmented copolymers

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Acyclic diene metathesis (ADMET) segmented copolymers
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Thesis (Ph.D.)--University of Florida, 1999.
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Includes bibliographical references (leaves 116-122).
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by Debra Tindall.
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ACYCLIC DIENE METATHESIS (ADMET) SEGMENTED COPOLYMERS


By

DEBRA TINDALL













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






























Measured against that which we desire,
our knowledge is clearly limited,
and if in this context we regard ourselves as children,
then we know that we are growing.

Justus Liebig













ACKNOWLEDGMENTS


The work described in this dissertation would not have been possible without the

support and guidance of so many people. First I wish to thank my advisor, Professor

Kenneth B. Wagener for his patience, guidance, and understanding. He has always been

supportive toward my pursuits of high-risk projects, but at the same time has known

when to move on, always with the success of his students as his highest priority. Thanks

are also extended to the members of my committee, Professors James M. Boncella,

Anthony Brennan, Lisa McElwee-White, and John R. Reynolds.

For assistance with the polymerization of isobutylene, I wish to thank Professor

Robeson Storey, Chris Curry, and Bryan Brister of the University of Southern

Mississippi. The preparation of these polymers would not have been possible without

their generosity and cooperation, and I hope that this interaction has opened the door for

further collaboration between our groups.

Thanks are also extended to Krystyna Brzezinska who began the pursuit of

ADMET segmented copolymers with her work the copolymerization of

polytetrahydrofuran with decadiene. Krystyna provided me with my very first sample

of ca,c-dienyl telechelic polytetrahydrofuran, thereby initiating my research that is

described herein.








I also wish to acknowledge Eddie Forbes, Peter Shang, and Dave Clavert at

Eastman Chemical Company for thermal analysis of some of my ester and carbonate

copolymers.

The National Science Foundation is acknowledged for supporting this work and

for their continual support of ADMET chemistry.

Jennifer Batten is recognized for her editorial assistance with this document. Her

patience and helpful suggestions, as well as her continued friendship, are very much

appreciated.

Enough thanks cannot be expressed to Lorraine Williams and Donna Balkcom for

facilitating all the administrative issues associated with graduate school, and for always

doing so with smiles, M&M's, and Girl Scout Cookies. I also wish to express my

appreciation to all the support staff at the University of Florida, particularly Joe

Carusone, for all the miles of ethernet cable he has strung throughout the Polymer Floor;

Joe Caruso, for all the speedy glass repairs; and the business office for putting up with all

the Polymer Floor computer orders.

Graduate school is about more than just conducting experiments isolated in a fume

hood, and one's surroundings and peers can lighten the arduous journey. The Butler

Polymer Labs have provided a friendly, supportive atmosphere in which to pursue

graduate studies. George and Josephine Butler deserve volumes of thanks for creating the

environment we know as the "Polymer Floor" and for their generous and unwavering

support of polymer chemistry at the University of Florida.








I wish to acknowledge all the members of the Wagener group and the Butler

Polymer Labs both past and present. Special thanks go to Dr. Tammy Davidson for

serving as my role model and "big sister" during my time in graduate school; Dr.'s David

and Jennifer Irvin and Dean and Annie Welsh for their special friendship and their talent

for bringing people together; Don Cameron for keeping the GPC running for us all; Mark

Watson for assistance with hydrogenations, microscopy, and writer's block and for the

many fruitful discussions about polymers, dissertations, and such; Femando G6mez, mi

complejo compafero de laboratorio, for all the hood-sash discussions, coffee, salsa, and

W&W's; Hiep Ly, co-founder of Polymer Floor Ice Cream Wednesdays, for his

friendship and photography expertise; and the infamous Dr. Jim Pawlow, future author of

"101 Amazing Jim Stories," for all the 5 k coaching sessions. Special thanks are also

extended to the recent Dr. Jon Penney for teaching me Schlenk techniques, and for doing

so with patience, not patients.

My family and friends have also provided volumes of support throughout my life.

I wish to thank my mother and father for nurturing the scientist in me for as long as I can

remember, and for supporting the decisions I have made in my life. Thanks are also

extended to Cindy for being not just my sister, but also my best friend. Finally I wish to

acknowledge my dear friends David Jedi Jelinek, Sam Pullara, and Nicole Watkins for

their longstanding friendship throughout all our life's changes.














TABLE OF CONTENTS

page


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

KEY TO ABBREVIATIONS......................... ....................................................ix

A B STRA CT.......................... .... ........................... ...............................


CHAPTERS

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

Block, Segmented, and Graft Copolymers.......................................... ................ 1
Phase Separation and Bulk Properties of Blends and Block Copolymers ................ 2
Phase Separation in Polymer Blends.......................................................... 3
Phase Separation in Block Copolymers........................... .......... ............... 4
Analysis of Phase Separated Materials............................ ............................ 6
Applications of Phase Separated Copolymer Materials.................................... 8
Synthesis of Block and Segmented Copolymers............................................ ..... 11
Sequential Monomer Addition Method .......................... ......................... 11
Reaction of End-Functionalized Oligomers.......................................................... 13
Limitations in the Synthesis of Segmented Copolymers....................................... 16
ADMET Segmented Copolymers...................................................................... 16
General Features of Acyclic Diene Metathesis Polymerization....................... 17
Mechanistic Features of ADMET Chemistry........................................ ......... .. 18
The Scope of ADM ET........................................................... ........................... 20
Producing Segmented Copolymers by ADMET.......................................... 21



2 SYNTHESIS AND CHARACTERIZATION OF DIENE
TELECHELOM ERS............................................................................................. 25

Poly(tetramethylene oxide) ca,B-Dienyl Telechelomers...................... ............ .. 25
Synthesis of a,o-Dienyl Poly(tetramehtylene oxide) Telechelomers................... 27








Polyisobutylene oa,-Dienyl Telechelomers......................... ....... ................... 31
Inifer Method for Polymerizing Isobutylene......................................... ............. 32
Functionalization with Allyltrimethyl Silane........................................ ............ .. 35
Synthesis of a,o-Dienyl Polyisobutylene............................................. 37
Metathesis Reactivity of a,o-Dienyl Polyisobutylene......................... ........... .. 40
Perspectives on PIB Telechelomers for Tailored Polymers.................................... 42



3 COPOLYMERIZATION OF POLYISOBUTYLENE WITH DECADIENE.......... 45

Synthesis of Segmented Copolymers of Decadiene and Polyisobutylene................ 46
Molecular Weight Analysis of Decadiene-PIB Segmented Copolymers................... 47
Thermal Analysis of Decadiene-PIB Segmented Copolymers.................................... 49
Hydrogenation of Segmented Copolymers.......................... ....................... 52



4 SEGMENTED ESTER POLYMERS...................................................................... 56

Synthesis of Ester ADMET Segmented Copolymers............................ ............ 57
Molecular Weight Analysis of Ester Segmented Copolymers.................................. 59
Thermal Analysis of the Ester Segmented Copolymers...................................... 61



5 SEGMENTED CARBONATE POLYMERS.................................................. 66

Synthesis of Carbonate ADMET Segmented Copolymers......................................... 66
Molecular Weight Analysis of Carbonate Segmented Copolymers........................ 67
Thermal Analysis of the Carbonate Segmented Copolymers................................... 70



6 SEGMENTED URETHANE POLYMERS................................................. 75

Synthesis of Urethane ADMET Segmented Copolymers ........................................ 77
Synthesis of Urethane Diene Monomers ........................................... ............ .... 77
Molecular Weight Analysis of Carbonate Segmented Copolymers.......................... 79
Thermal Analysis of the Carbonate Segmented Copolymers................................... 80








7 EXPERIMENTAL PROCEDURES........................... ............................. 85

General Experimental Procedures..................................................... 85
Synthesis of Diene Telechelic Oligomers................................................................. 86
Poly(tetramethylene oxide) Telechelomers ................................. ........... .. 87
Polyisobutylene Telechelomers.................................................. 88
Synthesis of Diene M onomers............................................. ................. .......... 91
Ester Diene Monomers..................................................... 92
Carbonate Diene Monomers....................................................... 93
Urethane Diene M onomers .............................................................. 94
Synthesis of Segmented Copolymers........................... ............................ 96
Polyisobutylene/Decadiene Segmented Copolymers .......................................... 96
Ester Segmented Copolymers...................................................... 101
Carbonate Segmented Copolymers............................. ........................ 103
Urethane Segmented Copolymers ................................... ...................... ... 107



8 SUM M ARY.................... ......................................... ............................. 111



LIST OF REFERENCES.................... ........................................................ 116

BIOGRAPHICAL SKETCH .................................................................................... 123

























viii













KEY TO ABREVIATIONS


A,B generic repeat units or segments in a copolymer

Cl bis(3-butenyl) carbonate

C2 bis(5-hexenyl) carbonate

Cy cyclohexyl, C6H,

DD 1,9-decadiene

El bis(5-hexenyl) terephthalate

E2 bis(5-hexenyl) phenylene diacetate

E3 3-butenyl 4-pentenoate

i-Pr isopropyl (C3H,)

L, generic ligands about a transition metal

Me methyl CH3

OTf triflate, O3SCF,

Ph phenyl C6H,

PIB 1 a,o-dienyl polyisobutylene with M= 1700

PIB2 ca,o-dienyl polyisobutylene with M,=3100

PIB3 a,w-dienyl polyisobutylene with M,=5800

PTHF1 ta,o-dienyl poly(tetrahydrofuran) with M,=1800

PTHF2 a,w-dienyl poly(tetrahydrofuran) with M,=3600

PTHF3 a,o-dienyl poly(tetrahydrofuran) with M,=1700








R generic alkyl group

U1 bis(5-hexenyl) 1,4-phenylenedicarbamate

U2 bis(5-hexenyl) methylene bis(4-phenylenecarbamate)

U3 bis(5-hexenyl) 4-methyl- ,3-phenylenedicarbamate

X,Y generic functional groups (eg. groups that can react with eachother to form
a link between monomers in step-growth polymerization)













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) SEGMENTED COPOLYMERS


By

Debra Tindall

May 1999


Chairman: Professor Kenneth B. Wagener
Major Department: Chemistry


A series of segmented copolymers was synthesized by using acyclic diene

metathesis (ADMET) to copolymerize a,o-dienyl polyether or polyisobutylene telechelic

oligomers with a,(o-diene comonomers possessing ester, carbonate, or urethane

functionality. The a,oa-diene telechelomers were synthesized by cationic polymerization

of tetrahydrofuran and isobutylene, capping with 5-hexen-l-ol and allyltrimethylsilane,

respectively. Polyisobutylene telechelomers were copolymerized with decadiene,

bis(5-hexenyl) terephthalate, bis(3-butenyl) carbonate, bis(5-hexenyl) carbonate,

bis(5-hexenyl) methylene-p-diphenylenedicarbamate, and 2,4-bis(5-hexenyl)tolyene

dicarbamate. Poly(tetramethylene oxide) telechelomers were copolymerized with

bis(5-hexenyl) terephthalate, bis(5-hexenyl) phenylene diacetate, 3-butenyl 4-pentenoate,

bis(3-butenyl) carbonate, bis(5-hexenyl) carbonate, bis(5-hexenyl) methylene-p-








diphenylene dicarbamate, and 2,4-bis(5-hexenyl)tolyene dicarbamate. In each case

conversion was good, with the number average molecular weight increasing to

approximately 20000 to 30000 g/mol, and in most cases only negligible unreacted parent

oligomer could be detected.

Differential scanning calorimetry (DSC) was used to study the thermal behavior

of the segmented copolymers. Segmented copolymers of polyisobutylene with ester or

carbonate comonomers showed both a Tg near -70 'C, corresponding to polyisobutylene,

and a melting point that correlated to the homopolymer of the second segment.

Segmented copolymers of polyisobutylene with decadiene showed intermediate phase

separation. Segmented copolymers of poly(tetramethylene oxide) with decadiene had

been shown previously by Brzezinska to have two melting points at 25 and 55 "C,

indicating immiscibility of the polyether and polyoctenamer segments. However,

copolymers of poly(tetramethylene oxide) with ester, carbonate, and urethane

comonomers gave materials showing some degree of phase miscibility, as indicated by

multiple melting points, and in some cases an increase in the T, of poly(tetramethylene

oxide). Segmented copolymers of poly(tetramethylene oxide) with the more flexible

esters, bis(5-hexenyl) phenylene diacetate and butenyl pentenoate, as well as the two

carbonate comonomers gave materials showing an intermediate melting point, indicating

a high degree of miscibility of the two segments. The more rigid

terephthalate as well as the two urethane monomers gave copolymers that appeared to

have an intermediate degree of phase separation. Hydrogenation of the carbonate

copolymers and the decadiene-polyisobutylene copolymers led to an increase in the

melting points of these materials.














CHAPTER 1
INTRODUCTION



In the quest for new, high-performance polymers, the novel arrangement of

standard monomers or repeat units can be as significant as the invention of new

monomers.',2 Drawing from the variety of possible polymer architectures along with the

wide range of different mechanisms available for assembling monomers to polymers, a

myriad of macromolecular structures are available to today's polymer chemist.




Block. Segmented and Graft Copolymers


Block, graft, and segmented copolymers are related types of copolymers, similar

in that there are distinct lengths of two or more homopolymer backbones incorporated

into one copolymer macromolecule. 1-1 Using the nomenclature of "A" and "B" to refer

to different homopolymer chains, diblock, terblock, segmented (multiple blocks), and

graft copolymers are depicted in Figure 1-1. Block and segmented copolymers are

characterized by two or more polymer chains joined covalently in an end-to-end fashion.

Block copolymers typically have fewer, longer chains and are synthesized by chain

polymerization methods, while segmented copolymers have several shorter chains in each

macromoleculeand are synthesized by step-growth mechanisms, as described below.4'5








In graft copolymers, chains of one polymer are bound pendant at intervals along a

backbone of a second polymer chain.6 Multi-block copolymers that employ more than

two types of constituent homopolymer backbones are also known, but these are beyond

the scope of this discussion.

a ,NvA-A-A-A-A-A-A-A-A--A-A-A-A- A-A-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B.BNw


b M.B-B-B-B-B-B-B-B-B-B(A-A-A-A-A-A-A-A-A-A)B-B-B-B-B-B-B-B-B-B,',




d ,/VB-B- B- B-B-BB-B-B -BB- B- B-B-B-B-B- BB- -B- B-BB
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A
A A A



Figure 1-1. Different copolymer arrangements: a) Diblock; b) Terblock; c) Segmented;
d) Graft copolymers.






Phase Separation and Bulk Properties of Blends and Block Copolymers


Copolymers are most useful when the properties desired in a material cannot be

attained from a single homopolymer. Since block, segmented, and graft copolymers are

composed of distinct segments of each parent homopolymer, these copolymers can have

theological and mechanical properties that are quite different from either parent








homopolymer or the corresponding random and alternating copolymers.4,5,8'9 For

example, while random and alternating copolymers typically have thermal transitions that

are intermediate to the two parent polymers, the thermal behavior of block copolymers

reflects that of each parent polymer, rather than an average of the two. With certain

compositions, the mechanical and theological properties can be greatly different from

either parent homopolymer. These unique properties are a result of the phase separation,

which arises from the sequenced arrangement of monomers in block copolymers.8



Phase Separation in Polymer Blends

The mixing of two homopolymers to make a polymer blend is one of the simplest

ways to alter the bulk properties of a polymer."-16 However, in order for a mixture of

two species to be miscible, the Gibbs free energy of mixing, AGmix, must be negative

(Equation 1-1). The mixing of small molecules is aided by an increase in entropy.

However, due to their large size, polymers gain little or no entropy when mixed, which

results in a positive AGmix unless a very negative enthalpy of mixing can offset this

unfavorable entropy.'4 Mixtures of polymers, polymer blends, are therefore miscible

only in a few cases, usually requiring secondary interactions such as hydrogen bonding

between the two polymer chains to produce a more favorable AHmx,.


AGmix = AHmix TASmix


(Equation 1-1)








This positive AGmix, which is typically observed, results in a demixingof the two

components into domains within the bulk material.14 (Figure 1-2a) Phase separation can

affect both the optical and mechanical qualities of the bulk blended material. The

interfacial boundaries between domains represent weak points in the material, and the

more distinct the two parent homopolymers, the less interfacial cohesion holds these

differing domains together.













a b

Figure 1-2. Phase separation in a) polymer blends compared with b) segmented
copolymers.





Phase Separation in Block Copolvmers

The tendency for phase separation is also present in block copolymers, since

these types of polymers are composed of distinct sequences of two parent

homopolymers within each macromolecular chain. However, the nature of phase

separation observed in block copolymers is slightly different than that observed for the

corresponding blend.'1417 The differing blocks still prefer to separate into domains, but at





5

the same time the covalent bonds between the blocks prevent complete phase separation

as would occur with the corresponding blend. (Figure 1-2b) This drive toward demixing

coupled with the molecular connectivity between blocks, leads to microphase separation

in block and segmented copolymers. The covalent bonding holding the different blocks

together tends to reduce the size of the phase separated domains on the order of 10-2 Pm,

and creates connectivity at the interface between domains. As a result, block copolymers

do not make the sacrifice in overall mechanical strength that is observed with polymer

blends.

Microphase separation can lead to unique bulk properties for block copolymer

materials. Within each microscopic domain, the polymer resembles the bulk parent

homopolymer. Thermal characteristics, as well as other properties characteristic of the

parent polymer can be retained in the copolymer, while theological properties can be

quite unique.8'10,14

The size and nature of the phase separation are influenced by the miscibilitiy of

the two blocks, as well as by the lengths and relative volumes of the two species.

Temperature and pressure also influence the tendency for phase separation, and it should

be noted that not all block copolymers exhibit phase separation.'1 Generally, for shorter

blocks, such as in segmented copolymers, the domains tend to be smaller, and below a

certain block length phase mixing will be less disfavored. Often for segmented

copolymers, the domain size is smaller than the wavelength of light, so these materials can

be transparent unlike many polymer blends. The influence of the relative volume of the








components on phase separation has been studied in depth.5-20 The general

morphologies for a two component system at differing relative volume percent is depicted

in Figure 1-3. Domains of the minor component take on differing forms within a matrix

of the major component or continuous phase, such that the interfacial area between the

two is minimized. With increasing amount, the minor component, A, forms spherical

then cylindrical domains. Further increasing the proportion of A, a tetrapodal

bicontinuous double diamond lattice morphology has been observed to occur in some

systems between the rod and column morpohologies.19.20 As the two components A and

B approach nearly equal proportions, a layered, lamellae, morphology is observed, and

further increasing the proportion of A leads to phase inversion with A becoming the

continuous phase. Phase separation for block copolymers consisting of more than two

different component blocks has also been studied, but is beyond the scope of this

discussion.







a b c d

Figure 1-3. Primary modes of phase separation in two-component block copolymer
system: a) spherical; b) cylindrical (rods); c) bicontinuous double diamond;
d)lamellae(layered).








Analysis of Phase Separated Materials

There are many analytical techniques available for studying heterogeneous and

phase separated polymer materials.' 15,20-22 Traditional polymer analyses, such as gel

permeation chromatography (GPC) can provide information on the molecular weight and

distribution of the copolymer. Depending on the method of synthesis, a bimodal peak is

often observed for block copolymers by GPC corresponding to a fraction of low

molecular weight homopolymer species in addition to the copolymer.4

Information can also be gained about the size and shape of the phase separated

domains. Small angle X-ray scattering (SAXS) can be used to elucidate the size of the

domains, particularly for copolymers in which one or both of the component polymers is

crystallizable or in cases where the morphology is in a very ordered matrix.22"24 Light

scattering and neutron scattering can also be useful in providing information about the

phase separation.

Electron microscopy is perhaps the most compelling method for studying

microphase separated materials, as this technique can provide an actual imageof the size

and shape of morphological features.24 Scanning electron microscopy (SEM) can provide

information on the surface structure, while transition electron microscopy (TEM) can be

used to elucidate the bulk structure of a material. TEM usually requires selective

"staining" of one component of the material to impart a contrast in the electron densities

between the two blocks. Osmium tetroxide or ruthenium tetroxide are two common

stains that selectively react with the double bonds such as those of alkenes and carbonyls.








Differential thermal analysis (DSC, DTA, DMA) can also provide information on

phase separated materials, and these methods require less expertise and sample

preparation than electron microscopy methods.21,24 The greater the degree of phase

separation in the material, the more the distinctly the thermal transitions corresponding

homopolymers will be retained in the copolymer. Thermal analysis can be used to detect

both Tg and Tm, so copolymers of all combinations of crystallizable and amorphous

blocks can be studied.



Applications of Phase Separated Copolvmer Materials

The phenomenon of phase separation can impart interesting and useful bulk

properties to copolymers, making these useful both as materials themselves and as agents

in modifying the properties of other homopolymers. Block and segmented copolymers

are usually more expensive to synthesize than homopolymers, so their use is mainly in

specialty applications or as additives to commodity polymers. The combination of soft

and hard blocks can give properties ranging from toughened, impact resistant

thermoplastics to thermoplastic elastomers as described in detail below. Other specialty

applications include uses which require the combination of certain properties of each

parent homopolymer are desired. For example, the hydrophobicity of one homopolymer

could be combined with the toughness and chemical resistance of a second homopolymer.4








Thermoplastic elastomers

One of the most important applications of phase separated block copolymers is

as thermoplastic elastomers.4,'89,14 A thermoplastic elastomer is a material that can be

reversibly elongated when tension is applied, but unlike thermoset elastomers such as

vulcanized natural rubber, these materials can be melted and processed. Thermoplastic

elastomers require at least three blocks in each polymer chain.4 For block copolymers,

this requires a terblock copolymer with central blocks of a highly amorphous, low Tg,

"soft," polymer flanked by blocks of a glassy (high Tg ) or crystalline, "hard," polymer.

Segmented copolymers, with their multiple short blocks, can also behave as thermoplastic

elastomers, and a classic example is the poly(urethane-ether) or poly(ester-ether)

segmented copolymers (e.g. LycraTM and HytrelTM).25"28

The Tg or Tm of the "hard" block parent polymer needs to be above the use

temperature of the material, yet low enough to allow for melt processing. The "soft"

parent polymer is an amorphous polymer with a low Tg, such as polybutadiene,

polyisoprene, or polyisobutylene or a semicrystalline polymer with a low melting point

such as an aliphatic polyether.2325 The relative proportion of hard and soft phases is also

important in achieving elastomeric behavior, where the continuous phase needs to be

amorphous, and typically volume proportions of 20-40% hard phase are used. The

chains of the amorphous continuous phase can slip past each other, allowing the material

to elongate, but the hard domains act as physical anchors, preventing the soft phase

chains from stretching beyond the point of recovery. These physical crosslinks are

thermally reversible, allowing the material to be melted and easily processed, whereas in








traditional thermoset rubbers the crosslinks are chemical, and heating does not melt these

materials.



Modifiers and compatibilizing agents

Segmented copolymers can also serve as compatibilizing agents.8"9 Commodity

polymers are often blended with other polymers, plasticizers, or other additives to

modify the properties of the parent material. However, these additives can be immiscible

with the polymer for reasons mentioned above, often compromising the mechanical

strength and optical clarity of the material.

Segmented copolymers can help to homogenize polymer blends.12 One approach

is to mix the homopolymer with a copolymer in which one of the blocks is compatible

with the homopolymer and the second component acts as a modifier. Another approach

employs block copolymers as macromolecular "surfactants" in homogenizing a mixture of

two dissimilar hompolymers. The blocks or segments are chosen such that each favors

one of the polymers being mixed. Phase separation may still occur in the bulk material,

but the added covalent bonding between segments of the block copolymer not only

reduces domain size, but helps to retain the physical strength of the material by adding

extra connectivity throughout the material.








Coatings and adhesives

Segmented copolymers are an important component of many coatings and

adhesives.1'29 Again, the ability to combine the distinct compositions and properties of

two different homopolymers into a single macromolecule chain allows these unique

properties. Theoretically, segmented copolymers can be tailored according to substrate

and surface quality desired. One component favors adhesion to the substrate while the

other segment either favors adhesion to a different substrate or has the surface quality

desired for a coating.




Synthesis of Block and Segmented Copolymers


The synthesis of block and segmented copolymers requires controlled

polymerization methods.2"4'30 Several options are possible, yet each has its limitations on

the possible combinations of homopolymer blocks.



Sequential Monomer Addition Method

The synthesis of block and segmented copolymers can be divided into two general

approaches. The first involves the sequential addition of monomers in a well-controlled

or living chain polymerization.-3a35 This method is suited to the formation of diblock and

terblock copolymers, giving controlled and predictable polymer structures, molecular

weights, and weight distributions. Many ring-opening or chain polymerizations, such as

anionic, cationic, transition metal coordination, and controlled radical polymerization








mechanisms, can be modified to disfavor termination and chain transfer reactions.32 The

best results employ living polymerizations, such that once monomer is consumed the

reactive end of the polymer chain is stable, but remains active toward the insertion of

more monomer.32 After consumption of the first monomer, A, a second monomer, B, can

be added, with polymerization of the second block resuming from the active end on the

first block of the polymer chain (Figure 1-4). Similarly, terblock copolymers can be

made by starting from a diinitiator.



1* mA IA/A-A-A-A-A-A-A-A-A-A-A-A-A-A-A*

InB

I-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-B-B-B-B-B-B-B-B-B-B-B-B-B-B-B*

Figure 1-4. Synthesis of diblock copolymer by sequential monomer addition method.


However, it should be noted, that the order of addition of monomers is often

limiting.30 For example, the active lithium anion chain end of polystyrene can initiate

polymerization of methyl methacrylate, but the acrylate anion can not initiate

polymerization of styrene. This is usually not a limitation in the formation of diblock

copolymers, but may require extra steps to produce certain terblock copolymers.

Terblock copolymers that contain a block arrangement that can not be made using a

diinitiator can sometimes be made by coupling two growing diblock copolymers, such as

using a di-electrophile to couple two anionically grown chains.4








Another limitation to the sequential addition method is that the monomers used

for each block must both be active toward the same polymerization mechanism.

However, studies in "propagation transformation" have shown that monomer reactivity

does not always have to be a limitation.30'3640 Propagation transformation involves

changing the nature of the active end of a growing polymer in situ before adding a second

monomer to grow the second block of the copolymer. Endo and coworkers have reduced

the cationic endgroup of polymerizing ethylene oxide to an anionic site capable of

initiating methyl methacrylate or caprolactone.36-37 Grubbs and coworkers have switched

from ring-opening metathesis polymerization (ROMP) to Ziegler-Natta polymerization

by reacting the growing transition metal alkylidene with an alcohol to give the metal-alkyl

species, which can initiate polymerization ethylene.38 Block copolymers of

polynorbomene with polyethylene have been made by this approach. Additionally, Guo

and coworkers performed radical to cationic transformation polymerization. The radical

chain end of AIBN-initiated p-methoxystyrene was transformed in situ to a cationic

center capable of polymerizing cyclohexene oxide by Ph2I+PF6.39



Reaction ofEnd-Functionalized Oligomers

An assortment of block and segmented copolymers can be made by starting with

an oligomer in which one or both ends are capped with an appropriate functional

group.3'30 The oligomer is typically grown by chain methods, and a number of scenarios

are possible for the synthesis of these end-functionalized, telechelic, oligomers.3'30

Functionalization of one end of the oligomer can be achieved by using either an initiator or








a capping agent that possesses the desired functionality. Telechelic oligomers

functionalized at both ends, a,o-telechelic oligomers, are best made by using a diinitiator

then terminating polymerization with a functionalized capping agent. These could also be

made by using a functionalized capping agent in addition to a functionalized initiator.

This route would also allow the creation of a,o-heterofunctionalized oligomers, but these

are beyond the scope of this discussion.

The functional group of a telechelic oligomercan be activated to form an initiator

for the chain polymerization of another monomer, which can provide an additional route

to obtaining diblock and terblock copolymers of monomers that are reactive toward a

different polymerization mechanism (Figure 1-Sa). An example is the ROMP-group

transfer radical polymerization (GTRP) block copolymers studied by Matyjezweski and

coworkers.40 Polynorborene is capped with 4-chloromethyl benzaldehyde, to give a

benzylchloride endgroup, which, upon activation by various transition metals, creates an

initiating site for the group transfer polymerization of methyl methacrylate.

The most common route to segmented, or multi-block, copolymers is by the

copolymerization of an a,co-difunctional telechelic oligomer along with difunctional

comonomers in a step-growth process (Figure 1-5b).27'28 These difunctional oligomers

function essentially as large monomers in step-growth polymerizations. As in all step-

growth polymerizations, the polymer chain is built through a series of coupling reactions,

and the growth of high molecular weight, linear polymer requires careful control of the








stoichiometry of perfectly difunctional monomers such that none of the reactants is in

excess and serves as a chain limiter.



X-AAAAAAA-X
difunctional telechelic oligomer

act iin Y-B-Y + (difunctional
ab \ X-A'-X comonomers)


*X-AAAAAAA-X* Segmented (A-B)n Copolymer
I (Figure 1-1c)
nB

Terblock B-A-B Copolymer
(Figure 1-lb)


Figure 1-5. Synthesis of block copolymers from a telechelic oligomer. a) Initiation of a
second chain polymerization; b) incorporation in step-growth
polymerization with difunctional comonomers.



Thus, by replacing a portion of one difunctional monomer by a stoichiometrically

equivalent amount of an oligomer possessing the same difunctionality, a copolymer can be

formed with oligomer segments incorporated periodically along the backbone of the

original step-polymer backbone. The two most common examples of these are the

poly(ester-ether) and the poly(urethane-ether) segmented copolymers derived from the

copolymerization of at,co-hydroxyl telechelic poly(oxytetramethylene) along with a glycol

(ethylene glycol or 1,4-butane diol) and terephthaloyl chloride or diisocyanates,

respectively.27-28








Limitations in the Synthesis of Segmented Copolymers

With the numerous potential applications for segmented copolymers, it can be

envisioned that segmented copolymers could be tailor-made according to the particular

combination of compatibilities desired. However, even given the variety of methods

known for making block copolymers, there remain limitations on the block combinations

that can be achieved. If chain polymerization is used, both monomers must be reactive

toward the same mechanism except for a few specialized cases mentioned above.

Methods for coupling two end-reactive polymers or for using step-growth techniques

require careful control of stoichiometry and functionality.

The synthesis of perfectly difunctional telechelic oligomers requires a diinitiated

polymerization and high-yielding capping reaction to place the desired functionality on

the end of the polymer chain. However, few polymerizations lend themselves to the

synthesis of perfectly difunctional ca,o-telechelomers. Further, the reactivity of the

capping reagent toward selectively terminating the polymerization is dependant on the

polymerization mechanism used to grow the oligomer.




ADMET Segmented Copolymers


The synthesis of segmented copolymers is also subject to the practical limitations

of step polymerization. Monomer and telechelicoligomermust be perfectly difunctional

or the molecular weight will be reduced due to chain termination by monofunctionalized

species.' Furthermore, if the polymerization is of the XX + YY type, in which an X








functionality can only react with a Y functionality, then stoichiometry balance between

the two functional groups is also crucial in achievinghigh molecular weight, as an excess

of either functionality will again act as a chain limiter. Acyclic diene metathesis

(ADMET) polymerization, has the potential to overcome some of these limitations in

stoichiometry and backbone combinations.41



General Features of Acyclic Diene Metathesis Polymerization

As mentioned above, segmented copolymers are produced by step-growth

polymerization methods. Acyclic diene metathesis (ADMET) polymerization is a step

growth, condensation polymerization mechanism that was developed in the Wagener

group and has been used to polymerize a number of oao-diene functionalized monomers

(Figure 1-6).42-43 In the presence of an appropriate catalyst, olefin reacts with olefin to

form the polymer linkages, obviating the stoichiometry issues inherent in XX + YY step

systems. Polymer can be formed from the reaction of a single diene monomer.

Furthermore, in ADMET copolymerizations, the stoichiometry of the two monomers can

be varied over all ranges without limiting the molecular weight.


SCHCH2 -x CH2CH2


Figure 1-6. ADMET conversion of generic diene monomer to unsaturated polymer.








Mechanistic Features of ADMET Chemistry

ADMET is a variation of the olefin metathesis reaction.41 Olefin metathesis is

mediated by certain transition metal alkylidene complexes, and two common ones are

illustrated in Figure 1-7.46-49 The alkylidene can be pre-formed as in the well-defined

Schrock tungsten and molybdenum systems and the Grubbs ruthenium complexes,4447 or

it can be generated in situ.4849 Strained cyclic olefins can undergo ring-opening metathesis

polymerization (ROMP) and acyclic dienes can undergo either ring closing metathesis

(RCM) reactions or step-growth polymerization (ADMET) depending on the diene and

reaction conditions.41



i-Pr i-Pr PCy3

H3C(F3C)2CO'" CH3 PCy h
H3C(F3C)2CO a Ph b


Figure 1-7. Two common well-defined alkylidene catalysts for ADMET
polymerization, a) Schrock molybdenum and b) Grubbs ruthenium
catalysts (Cy=C6jH-1)


The olefin metathesis reaction can be used to generate polymers in a step-growth

fashion by employing diene monomers, and the reaction may be easily driven toward

polymer by using terminal diene monomers such that the condensate is ethylene. The

mechanism for ADMET polymerization is illustrated below and can be viewed in two

steps, beginning with olefin coordination to the original metal alkylidene. (Figure 1-8)








R LnM R' / \ ,

diene monomer Ln +


LnM=CH2
1 2

Figure 1-8. Two regiochemical possibilities for reaction of catalyst precursor with
monomer



Two metallocyclobutane species are formed, depending on the regiochemistry of olefin

addition. Productive cleavage of the metallacyclobutanes gives two new alkylidenes, 1

and 2, which enter the catalytic cycle. (Figure 1-9) Starting from the methylidene, 2,

olefin adds to form a metallacyclobutane 4, which cleaves to give alkylidene 1. A second

monomer coordinates and forms metallacyclobutane 3. Productive cleavage of this ring

forms a link between the two monomer units while regenerating methylidene 2. The

dimer formed can enter the catalytic cycle on subsequent cycles. As with other step-

growth polymerizations, polymer is built as the result of a series of coupling reactions,

and high molecular weight polymer is only achieved after high conversion of the reactive

olefin groups.


















Symer LM H





CH2=CH2
condensate ln


Figure 1-9. The catalytic cycle for ADMET polymerization showing productive
reactions that lead to polymer formation.





The Scope of ADMET

Since the discovery of ADMET as a viable route to forming polymer from diene

monomers, the scope of this polymerization has been explored.41,5052 Diene monomers

containing a variety of different functional groups, including a variety of different atoms

such as oxygen, sulfur, silicon, germanium, phosphorous and nitrogen, have been

successfully polymerized by ADMET techniques. However, a few guidelines must be

followed to ensure successful ADMET polymerization. Studies have shown that the

reacting olefin must be spaced at least two methylenes away from any functional group.53

Sterics are also a factor, and substitution of the internal carbon of the metathesizing olefin

prohibits metathesis.4 Furthermore, metathesis is hindered for internal olefins or olefins





21

with substitution on the carbon alpha to the double bond.55 Heeding these restrictions, a

number of functional groups have been found to be amenable to ADMET polymerization,

including ester, carbonate, siloxane, boronate, alcohol, and amine groups. The several

reviews have summarized the breadth of ADMET, and the references therein may be

consulted for specific details.5"52

Many diene monomers are accessible through relatively straightforward

syntheses, making ADMET attractive as a route to a variety of polymer backbones not

attainable by other means. Furthermore, ADMET has seen recent application in the

formation of tailored polymer backbone structures.50



Producing Segmented Copolymers by ADMET

Given the versatility of ADMET polymerization for small diene

monomers, it is reasonable that ADMET may likewise be amenable to the polymerization

of macrodienes. Further, ADMET copolymerization of an a,o)-dienyl telechelic oligomer

along with known diene monomers could provide a route to the synthesis of segmented

copolymers. The general approach to ADMET segmented copolymers is illustrated in

Figure 1-10, which shows the condensation of a macrodiene with a small molecule diene

comonomer to make a copolymer with a segmented structure.56" Alternately a single

monomer could be used and that is the approach of Qiao and Baker. The ADMET

homopolymerization of short a,to-pentenyl glymes produced produced segmented ether-

ethylene copolymers.61'63









+ -(olgomer)--
Functionalized Diene
Diene Comonomer Telechelomer

ADMET



R oligomer. + CH2CH2







Segmented ADMET Copolymer


Figure 1-10. Synthesis of ADMET segmented copolymers-the essence of this study.





The key to using ADMET to make segmented copolymers lies in the ability to

synthesize a,co-diene telechelic oligomers and in the reactivity of these diene

telechelomers toward olefin metathesis with the catalysts used for ADMET

polymerization. Theoretically, if the same steric and electronic restrictions known for

small molecule dienes are observed, then the olefin functionality in of an ot,o-diene

telechelomer should be reactive toward ADMET polymerization.

To date, three oa,o-diene telechelic oligomers, poly(oxytetramethylene),

polysiloxane, and polyisobutylene have been synthesized and all three were found to be

reactive toward ADMET polymerization (Figure 1-11). 56-6 These telechelic oligomer

provide three very different backbone structures and different corresponding properties,








and their use in segmented copolymers could lead to unique combinations not possible by

other polymerization routes.




a



b



c






Figure 1-11. Diene telechelic oligomers. a) Poly(oxytetramethylene; b) Poly(dimethyl
siloxane); c) Poly(isobutylene).



Brzezinska and coworkers studied the copolymerization of ac,m-dienyl

poly(tetramethylene oxide) with decadiene to generate segmented copolymers .56-58 The

copolymerization of xa,-dienyl poly(oxytetramethylene) and polyisobutylene telechelic

oligomers with carbonate, ester, and urethane-functionalized diene comonomers is the

essence of the research described herein.59-60 Additionally, the ADMET reactivity and

copolymerization of the polyisobutylene telechelomer with decadiene was studied.

Although the ester, carbonate, and urethane functionalities were chosen for this study of

segmented ADMET copolymers, theoretically any diene monomer could be incorporated








with these or other diene telechelomers to form additional combinations of segments,

provided the diene functionality is amenable to ADMET chemistry.

The syntheses of poly(tetramethylene oxide) and polyisobutylene a,(o-dienyl

telechelomers are discussed in Chapter 2. The reactivity of polyisobutylene toward

metathesis chemistry and its copolymerization with decadiene are discussed in Chapters

2 and 3, respectively. It was shown that the polyether and polyisobutylene a,w-dienyl

telechelomers could indeed be incorporated into copolymers with the ester, carbonate, and

urethane monomers, and these copolymers are discussed in Chapters 4, 5, and 6,

respectively. Experimental details for this study are described in Chapter 7.

The structures of the copolymers were verified by 'H NMR, 13C NMR, and IR

spectroscopy, as well as gel permeation chromatography (GPC). Furthermore, the

thermal behavior of these copolymers was studied by differential scanning calorimetry

and thermogravimetric analysis.














CHAPTER 2
SYNTHESIS AND CHARACTERIZATION OF DIENE TELECHELOMERS




As mentioned in Chapter 1, the key to ADMET segmented copolymers lies in the

synthesis and reactivity of xa,w-diene functionalized telechelic oligomers. Two such

telechelomers were chosen for this study, poly(tetramethylene oxide) and

polyisobutylene. Each was synthesized by cationic polymerization followed by

controlled termination with a suitable capping agent bearing the olefin functionality.




Poly(tetramethvlene oxide) a.co-Dienvl Telechelomers


Strong protonic acids, such as trifluoromethanesulfonic acid, can be used to initiate

the ring-opening polymerization of cyclic ethers such as tetrahydrofuran.33'6465 Initiation

involves protonation of tetrahydrofuran to form a secondary oxonium ion. Nucleophilic

attack of monomer at either carbon alpha to the oxonium ion opens the first ring,

reforming a tertiary oxonium ion (Figure 2-1).





Figure 2-1. Initiation of tetrahydrofan polymerization with protonic acid, HA.

Figure 2-1. Initiation of tetrahydrofuran polymerization with protonic acid, HA.








The corresponding anhydrides and esters of strong protonic acids can likewise

initiate polymerization of cyclic ethers.33"34 Triflic anhydride is a particularly interesting

initiator, because it acts as a diinitiator for cyclic ethers, growing the polymer chain from a

central point with two identical ends, as illustrated in Figure 2-2.

/^.\ ,,, OSO2CFs
+ (CF3SO2)O F3CSOs S3v v







OTf "OTf

Figure 2-2. Diinitiation with triflic anhydride to produce two propagating ends.



Propagation proceeds through oxonium and ester end groups, rather than the more

reactive carbenium species, which reduces the propensity for side reactions. During the

polymerization, the oxonium end groups are subject to nucleophilic attack by monomer,

ether groups within the polymer chain, and counterion. In the polymerization of

tetrahydrofuran with triflate as the counterion, the combination of counterion with chain

end is a reversible reaction, and both the oxonium and the covalent ester species are active

toward nucleophilic attack by monomer (Figure 2-3). Reaction with polymer is also

reversible in these polymerizations, but since these chain transfer reactions lead to the

formation of cyclics (through intramolecular backbiting) or chain scrambling (through

intermolecular reactions), the molecular weight distribution can be broadened if these

reactions compete with propagation. To minimize the amount of nonproductive








reactions, the polymerization is best performed with high concentrations of monomer and

at lowered temperatures.


+-OS02CF3 O'-".."F SO2CF3






--oOSOCF3


Figure 2-3. Equillibrium between oxonium and ester endgroups.


Quenching this polymerization with water yields the dihydroxyl terminated

polyether. However, other nucleophiles such as alcohols, Grignard reagents, or alkali

metal reagents can also be used to terminate the polymer chain, and the use of a

functionalized nucleophile imparts functionality to the polymer chain end.3366



Synthesis of c.to-Dienvl Polv(tetramehtvlene oxide) Telechelomers

The diene functionalized polyether telechelomers used for this study were

synthesized from the triflic anhydride initiated ring-opening polymerization of

tetrahydrofuran followed by capping with 5-hexen-l-ol (Figure 2-4).








(CF3SO2)O












Figure 2-4. Diene functionalized poly(tetramethylene oxide).





A summary of the molecular weight data for the three polyether telechelomers

synthesized for this study is given in Table 2-1. The values for M, obtained by GPC

relative to polystyrene standards are a little over twice those determined by endgroup

analysis. The functionality, F, was determined by comparing the integration of terminal

olefin signals to signals arising from OH endgroup, which were undetectable in PTHF1

and PTHF2.


Table 2-1. Poly(tetramethylene oxide) telechomers synthesized.
Telechelomer Xn M, NMRa Mn GPCb M/Mn F

g/mol g/mol

PTHF1 25 1900 3900 1.11 >1.94

PTHF2 46 3600 7400 1.07 >1.94

PTHF3 21 1700 3800 1.7 1.94

a. Integration of internal CH2 to olefin endgroups.
b. Molecular weight relative to polystyrene standards.








The poly(tetramethylene oxide) used for the polymerizations with ester

monomers described in Chapter 4, PTHF3, was kindly provided by Krystyna

Brzezinska. Brzezinska polymerized tetrahydrofuran at room temperature in methylene

chloride, using triflic anhydride as the initiator.7 After proceeding for 12 hours at room

temperature, 5-hexenol was added to terminate the polymerization, thereby generatingthe

diene functionalized telechelomer.

All subsequent poly(tetramethylene oxide) telechelomers were synthesized by an

alternate method based on that of Smith and Hubin.6'68 Rather than using a solvent,

triflic anhydride was added to neat, chilled tetrahydrofuran. In the Brzezinska method,

the polymerization is allowed to reach equilibrium, and the relative concentrations of

monomer and initiator determine the resulting molecular weight of the oligomer.

However, by performing the polymerization in the bulk, at low temperatures, and with a

fixed amount of monomer and initiator, the molecular weight becomes a function of time.

The polymerization is purposely allowed to only proceed to a very low degree of

conversion, and on this time frame the polymerization approaches livingness. Indeed the

molecular weight distributions of PTHF1 and PTHF2 were narrower than PTHF3.57

Telechelomers used for the work described in Chapters 5 and 6 were synthesized

by adding 1.0 mL triflic anhydride to 36.0 mL tetrahydrofuran chilled to -13 "C.

Reaction for 25 minutes gave Mn=1800 (PTHF1), while reaction for 45 minutes increased

the molecular weight to M,=3600 (PTHF2). As above, the polymerizations were

terminated by adding 5-hexenol. The 'H NMR and 3C NMR spectra for PTHF1 are









shown in Figure 2-5 and Figure 2-6, respectively, and the GPC chromatograms for

PTHF1 and PTHF2 are shown in Figure 2-7.


a c e / h

b d f 9 25








b a



6Fi 5 4 NR of P

Figure 2-5. H NMR ofPTHF1 telecheloni


a c e h

b d f 9 25



CDC13




b a
I


120 100 80


g,f








c e


6b 4b


Figure 2-6. 'C NMR of PTHF1 telechelomer.


g,f h










c3 2 ppm 1


h








d


20 pbm


" o;


w>J













PTHF2 1 I1 1 PTHF1


7.0 8.0 9.Q 10.0
retention volume

Figure 2-7. GPC ofpoly(tetramethylene oxide) telechelomers. PTHFI: Mn=1800,
PDI=I.11; PTHF2: M,=3600, PDI=1.07.






Polvisobutvlene a.co-Dienvl Telechelomers


Polyisobutylene is an amorphous, rubbery polymer used in elastomers and for

gas barrier applications.'68 This polymer is attractive as a soft phase for segmented and

block copolymers because it is an amorphous, hydrocarbon polymer with a

Tg of between -67 and -73 'C.

Isobutylene is a monomer that can only be polymerized by cationic routes.'

Chain transfer events are prevalent in classical cationic polymerizations, so in order to

obtain control over the polymerization, systems employing Lewis acid catalysts are used

to mediate the reactivity of the propagating cationic site.3'33 Lewis acids such as BCl3 or

TiCI4 in the presence of a chloride initiator are most commonly used to polymerize

isobutylene in a controlled fashion. Under certain conditions, initiation, transfer, and








termination reactions can be controlled, and this has been termed the inerferter or inifer

method.23



Inifer Method for Polymerizing Isobutvlene

The titanium activated system developed by Kennedy and used extensively by

Storey was used to synthesize three a,(-dienyl polyisobutylene samples of differing

molecular weights.69'73 This system is attractive not only because it provides a clean,

controlled polymerization with narrow molecular weight distributions, but also because it

allows for capping of the polymer with allyl trimethylsilane to give terminal olefin end

groups.369

The inifer method involves the use of a chloride functionalized species that can

form a carbenium species when activated with a Lewis acid. Many such initiators, both

aromatic and aliphatic, and mono-, di-, and tri-functionalized in chloride have been

developed. Difunctionalized initiators, such as 5-tert-butyl dicumyl chloride, can initiate

polymer growth from two sites on a central headgroup, allowing the formation of

difunctional telechelic oligomers (Figure 2-8).70"71 The tert-butyl group meta to the

initiating groups is necessary to block electrophilic aromatic substitution on the aromatic

ring after the first addition of monomer, which would result in an indanyl structure.3





33

H3 H3 H3 H3
C CI


t (CH3)3

Figure 2-8. Blocked dicumyl chloride initiator used for polymerization ofisobutylene.


Titanium tetrachloride activates the chloride functionality of the initiator, and

establishes an equilibrium between a weak covalent chlorine-carbon bond and a tight ion

pair between the carbocation chain end and a dimeric titanium anion, Ti2C19 (Figure 2-9).

Titanium tetrachloride is unique compared to other Lewis acid polymerization catalysts

in that it is more reactive as its dimer.73'77 This equilibrium between dormant covalent

species and contact ion pair mediates the polymerization, reducing chain transfer and

other side reactions. Isobutylene can insert into this activated chain end, but the close

proximity of the bulky titanium counterion hinders other reactions.







H3 H3 H3 H3
C I TiC4 + + T12C19
2,6-dimethylpyridine Ti2CI9
CH3CI, hexane
C(CH3)3 C(CH3)3


-<




TiC4 TiC14
C(CH3)3

Figure 2-9. Polymerization of isobutylene using the t-butyl-dicumyl chloride initiator,
and TiC14 cocatalyst.


Titanium tetrachloride is necessary to activate the chloride bonds of the initiator,

but this compound is also extremely reactive toward the trace amounts of water that are

in the reaction medium, even under normal drybox conditions. The reaction of TiCI4 with

water produces HC1, which can also initiate polymerization of isobutylene, so a hindered

base, such as 2,6-dimethylpyridine, is added to the system to scavenge HC1. The

function of this base is twofold. In addition to preventing unwanted initiation by HCI, it

is believed that this base interacts with the titanium to mediate the nucleophilicity of the

counterion species. Some studies have indicated a reduction in chain transfer and

termination events upon adding pyridine and substituted pyridines. The propagation rate

is slowed, but narrower molecular weight dispersity can be achieved.7879








Side reactions are also minimized by conducting the polymerization at -80 'C.

The activation energy for chain transfer events is higher than for propagation, so the

polymerization is actually faster when run at very low temperatures. Indeed, at this

temperature, the polymerizations are complete in a matter of seconds or minutes. At

-80 'C, and with the appropriate amounts of initiator, activator, and Lewis base, side

reactions are minimized such that this system approaches livingness. The low

temperature also facilitates the handling of the isobutylene and solvent, methyl chloride,

which are gases at room temperature.



Functionalization with Allyl trimethvl Silane

Controlled termination of olefins polymerized by the inifer technique is not as

straightforward as for the ring-opening polymerizations of the cyclic ethers described

above. Addition of most nucleophiles, such as water or alcohols, yields the chloride

terminated polymer because the nucleophile attacks the Lewis acidic titanium species

rather than reacting with the carbenium end of the growing polymer chain. However,

reaction is possible between the growing polymer chain end and allyltrimethyl silane or

other allyl transfer agents.6 The overall result is the transfer of an allyl group to the end

of the polymer chain with trimethylsilyl chloride formed as a side product.

There is no detailed report on the mechanism for the allyl group transfer.3'69 It is

allyl silanes as well as allyl germanes and stannanes can transfer an allyl group to

electrophillic species (Figure 2-10).80









E+iR3 E,_ ,, ,R A- E..
+
A-SiR3

Figure 2-10. Reaction of electrophilic center with allylsilane followed by demetallation.



Titanium tetrachloride is used to facilitate the reaction of allyltrimethylsilane to

carbonyl compounds by coordinating to the carbonyl oxygen,80 and TiCI4 activates the

polymer chain end toward reaction with electron rich species.

However, there is also the possibility that the titanium tetrachloride plays a more

involved role. There is evidence that there is some degree ofalkene monomer coordination

to titanium when TiCI4 is used as the catalyst in cationic polymerization, although the

extent of olefin coordination and its effect on polymerization has not been elucidated.

Therefore interaction of the allyltrimethylsilane with the Lewis acidic titanium is not

unreasonable. Further, it is known that transition metal allyl complexes can be formed

from the combination of allyltrimethylsilane with the metal chloride.8"85 If a titanium

allyl complex were to form, there is ample evidence that this species could transfer the

allyl group to the polymer chain end. It has been demonstrated that the use of allyl

borane, allyl aluminum, or cyclopentadienyl aluminum species as activators in cationic

alkene polymerization results in allyl or cyclopentadienyl terminated polymer,

respectively.8'" It is therefore difficult to determine the degree of involvement of TiCI4

in the allylation without performing a mechanistic study of this reaction. The simple and

generally accepted mechanism for end-capping the polyisobutylene with allyltrimethyl







silane is the direct attack of the allyl with the activated carbon center via a six membered

transition state as illustrated in Figure 2-11.


+ Ti2Cl9


I SAi(CH3)3


Figure 2-11. Capping polyisobutylene with allyl trimethylsilane.




Synthesis of a.mr-Dienvl PolviqnhiutvlPn


The inifer method allows for well-controlled polymerization of isobutylene and

endcapping to obtain terminal olefin groups. These olefin end groups can be used as is or








reacted further to generate other end-functionality on these telechelic oligomers. Three

polyisobutylene telechelomers with three different molecular weights were synthesized

using the inifer method and allylation described above (Figure 2-12).



n n


C(CH3)3


Figure 2-12. a,(o-Dienyl polyisobutylene synthesized for this study. (n=12, 25, 49)



The molecular weight data are summarized in Table 2-2 and the GPC curves for

the three samples are shown in Figure 2-13. There is actually good agreement between

the molecular weight determined by light scattering, NMR integration, and that

determined relative to polystyrene standards. The telechelomers produced were of

narrow molecular weight distribution and by 'H NMR integration of the terminal olefin

groups vs. the three aromatic protons indicates that the functionality,F, is close to 2.0.


Table 2-2. Polyisobutylene telechomers synthesized.
Telechelomer IB units Mn NMRa Mn GPCb Mn GPC' Mw/M, Fa

(2n) g/mol g/mol g/mol

PIB1 24 1700 1700 1800 1.15 1.94

PIB2 50 3100 3100 3200 1.12 1.95

PIB3 98 5800 5800 5900 1.03 2.0

a. Integration of aromatic H to olefin endgroups.
b. Molecular weight by light scattering.
c. Molecular weight relative to polystyrene standards.














PIB2


PIB3


PIB1


10 15
retention volume
Figure 2-13. GPC ofPIB telechelomers: PIB1 (Mn=1700); PIB2 (Mn=3100); PIB3
(M,=5800)



The 'H NMR and 13C NMR spectra are shown below in Figure 2-14 and

Figure 2-15, respectively.

e d






C(CH3)3 h



9


CDC6 c
b a



7 6 5 4 3 2 1 ppm

Figure 2-14. 'H NMR of PIB2 telechelomer.









b d g

c k ke5f g i
gg
C(CH3)3 k
h


CDCI3

i b ga


140 120 100 80

Figure 2-15. 3C NMR of PTHF2 telechelomer.


60 40


d










20


Metathesis Reactivity of c.o-Dienvl Polvisobutylene


The shortest oligomer (Mn~1700) was used to obtain an estimate of the reactivity

of the terminal allyl groups toward the ruthenium and molybdenum metathesis catalysts.

Metathesis polymerization of the alkene terminated polyisobutylene generates a polymer

consisting of polyisobutylene segments interrupted periodically by 2-butenyl units as

well as the aromatic initiating fragment associated with each chain (Figure 2-16).





ADMET
-J!A 'PIB)-Ar-(PIB
F n o x


Figure 2-16. ADMET polymerization of a,co-dienyl polyisobutylene telechelomers.


20








Polymerizations were conducted using both Schrock's molybdenum

((Mo(NC6H3-2,6-i-Pr)(OCCH3(CF3)2)2(CHC(CH3)2C6H5)) and Grubbs's ruthenium

((Ru(P(C6H I)3)2CI2(CHPh)) alkylidene catalysts, Figure 1-7. ADMET

polymerizations were conducted in the bulk with 1:200 catalyst to monomer ratio under

vacuum. The ruthenium reactions were begun at 40 'C for 24 hours then warmed to 75 "C

for two additional days. The molybdenum catalyst is generally faster than the ruthenium

systems, but one drawback of the molybdenum catalyst is its lower tolerance toward

heating, so these reactions were performed at 40 "C for 3 days. Conversion was

estimated by 'H NMR end-group analysis and gel permeation chromatography and is

summarized in Table 2-3.


Table 2-3. Molecular weight data for metathesis conversion of polyisobutylene
telechelomers.(g/mol).
Ruthenium Molybdenum

Telechelomer 'H NMRa GPCb 'HNMR" GPCb

PIB(1700) 16,000 17,000 15,000 16,000

a. Molecular weight calculated from ratio of terminal to internal endgroups.
b. Molecular weight vs. polystyrene standards.


Metathesis polymerization of the polyisobutylene telechelomers is slow

compared to many of the small diene monomers typically used in ADMET

polymerization, and this reduced reactivity could be attributed to a number of factors.

Firstly the concentration of reacting olefin groups is small due to the large size of the

telechelomers. This situation can be related to a step polymerization at high conversions.








Catalyst plus two polymer end groups must find each other for each new connection to

occur. Further, the polyisobutylene oligomers are very viscous materials as opposed to

the liquid monomers typically used in ADMET polymerization, which may also hinder

the required convergence ofolefin groups and the reactive catalyst sites. Additionally, the

steric influence of the methyl groups on the carbon 3 to the reacting olefin could slow

olefin metathesis. Studies by Konzelman and Wagener have shown that placing bulky

substituents near the metathesizing olefin hinders metathesis.55 Another factor that could

slow the metathesis polymerization of these telechelomers arises from polyisobutylene's

low gas permeability. Polyisobutylene is such a good barrier to air that it is used as liner

material in tires and inflated balls.65 If the ethylene that is given off in the metathesis

reaction is trapped and kept in close proximity to the catalyst, it could re-enter the

catalytic cycle in depolymerizing reactions with the growing polymer.




Perspectives on PIB Telechelomers for Tailored Polymers


Both the molybdenum and ruthenium catalysts were effective toward the

metathesis conversion of the polyisobutylene telechelomers. Under the reaction

conditions used, polymerization was not complete, as conversion of this telechelomer

appears to be slower than that of many small molecule aliphatic diene monomers due to a

number of contributing factors described above. Subsequent metathesis reactions with

these telechelomers will need to be conducted for longer reaction times and higher

temperatures, if possible, to achieve adequate conversion.








Despite their slowed reactivity, the ability of xa,o-dienyl polyisobutylene to

undergo metathesis reactivity opens the door to many possible uses for these

telechelomers (Figure 2-17). For example, olefin metathesis chemistry could be used to

introduce new endgroups to these oligomers by reaction with an excess of functionalized

mono-olefin capping agents. Further, metathesis could be used to couple these

polyisobutylene telechelomers with diene telechelomers of a differing backbone (e.g. the

poly(tetramethlyene oxide) telechelomers described above), and this reaction would

produce a segmented copolymer.




n n


(CH3)3
X\ PTHF)n~-
a c b




telechelics segmented copolymers




segmented copolymers


Figure 2-17. Some of the possibilities for metathesis conversion of cawdienyl
polyisobutylene telechelomers. a) end-functionalization b) reaction with
other diene telechelomers c) reaction with diene comonomers.



Alternatively, copolymerization of these a,o-dienyl polyisobutylene

telechelomers with small molecule diene monomers could also lead to segmented





44

copolymers, and this is the approach explored in the subsequent chapters of this

dissertation. Copolymerization with decadiene is discussed in Chapter 3, while Chapters

4-6 present copolymerization with carbonate, ester, and urethane functionalized diene

comonomers to produce several new segmented copolymers.













CHAPTER 3
COPOLYMERIZATION OF POLYISOBUTYLENE WITH DECADIENE



Decadiene is the benchmark monomer for acyclic diene metathesis polymerization.

Not only was this the first monomer utilized in ADMET polymerization,43 but it has

been used to determine the reactivity of new catalysts47"4886 as well as to study the

kinetics of ADMET polymerization.87 Further, it was the successful copolymerization

of decadiene with poly(tetramethylene oxide) diene telechelomers that initiated the

research effort in ADMET segmented copolymers.57

The copolymerization of decadiene with the polyisobutylene telechelomers would

create segmented copolymers in which both blocks are aliphatic hydrocarbon chains.

However, it is the hydrogenated analogs of these polyoctenamer-isobutylene segmented

copolymers, which approximate segmented polyethylene-isobutylene structures, that are

particularly interesting. Although alternating copolymers of isobutylene-ethylene have

been reported, to date no chain polymerization mechanism has been able to generate

copolymers of ethylene and isobutylene arranged as blocks.8889








Synthesis of Segmented Copolymers of Decadiene and Polvisobutylene


Nine different segmented copolymers were synthesized from the

copolymerization of diene polyisobutylene with decadiene. The unsaturated

poly(isobutylene-octenamer) copolymers were then hydrogenated using the methods

developed by Watson and coworkers9 to give the nine corresponding saturated polymers,

which approximate a poly(isobutylene-ethylene) segmented structure (Figure 3-1).



PIB1
DD PIB2
PIB3
ADMET


^^^--(PIBl4

Poly(octenamer-b-isobutylene)
Segmented Copolymers

Hydrogenation


(PIB z
[I 4x1.

Poly(ethylene-b-isobutylene)
Segmented Copolymers

Figure 3-1. Copolymerization of polyisobutylene with decadiene followed by
hydrogenation.



Polyisobutylene diene oligomers with parent molecular weights of 1700 (PIB1)

3100 (PIB2) and 5800 (PIB3) were copolymerized in three different ratios with

decadiene. The proportions used are abbreviated as 1:2, 1:4, and 1:6, which refer to the

target compositions of the final copolymer containing one octenamer unit per every two,





47

four, or six isobutylene repeat units, respectively. Upon hydrogenation each octenamer

repeat unit is converted to four ethylene repeat units, which changes the proportions of

hard phase repeat unit with respect to isobutylene repeat units, as summarized in

Table 3-1. However, to avoid confusion, the copolymers will be referred throughout

this text as 1:6, 1:4, and 1:2 for the same copolymer sample both before and after

hydrogenation.


Table 3-1. Target proportions of octenamer and isobutylene in copolymers, and the
calculated conversion of these proportions in terms of ethylene repeat
units upon hydrogenation.
Poly(octenamer-IB) After hydrogenation
copolymer

mol octenamer: mol mol ethylene: mol IB wt ethylene: wt IB
IB

1:6 2:3 1:3

1:4 1:1 1:2

1:2 2:1 1:1



Molecular Weiaht Analysis of Decadiene-PIB Segmented Copolvmers


The unsaturated copolymers containing a largest fraction of polyisobutylene

(1:6) were sticky, viscous materials, resembling the parent polyisobutylene, and even

after hydrogenation, these remain very soft and tacky and transparent. The 1:4

copolymers based on PIB2 and PIB3 were soft, tacky semisolids and remained soft

translucent to transparent tough rubbery substances upon hydrogenation. A higher





48

degree of conversion was achieved with the PIB1 1:4 polymerization, which was a

resilient soft solid. The 1:2 copolymers were soft, waxy translucent materials, and

hydrogenation yielded soft white powders. Upon hydrogenation all materials became

more firm and the 1:4 and 1:2 became noticeably less soluble in common organic solvents.

Much like the homopolymerizations of polyisobutylene described in Chapter 2,

the copolymerizations of decadiene with polyisobutylene telechelomers were slow,

although improved molecular weight was achieved by allowing the reactions to proceed

for at least 7-10 days. Upon copolymerization the molecular weights of the resulting

copolymers increased relative to the parent homopolymer, and in each case there was

only negligibleunreacted parent oligomer as detected by GPC of the filtered reaction

product prior to precipitation. Molecular weight data is summarized in Table 3-2 and

indicates that copolymers of modest molecular weight (up to 22,000 vs. polystyrene

standards) were obtained in all but one case. The polydispersity (Mw/Mn) of the

copolymers was found to be lower than the expected 2.0 for step-growth polymerization,

but is still broader than the parent telechelomer.

Molecular weight was measured only for the unsaturated polyoctenamer-

polyisobutylene copolymers due to the reduced solubility of the materials after

hydrogenation. The 1:2 and 1:4 copolymers were insoluble in chloroform or other

common solvents at room temperature, precluding gel permeation chromatography or

NMR analysis at room temperature. However, while some studies have shown a change

in the hydrodynamic volume of an unsaturated polymer after hydrogenation,62 other








studies have shown that the hydrogenation procedure has little effect on the molecular

weight of the polymer.53



Table 3-1. Summary of molecular weight data for decadiene-PIB segmented copolymers.

Copolymer M, Mw Mw/M,

(ratiowt:wt) x103 g/mol x103 g/mol

PIB1-DD (2:1) 20 36 1.8

PIB2-DD (2:1) 14 20 1.4

PIB3-DD (2:1) 20 26 1.3

PIB1-DD (4:1) 35 47 1.4

PIB2-DD (4:1) 22 29 1.4

PIB3-DD (4:1) 22 29 1.5

PIB1-DD (6:1) 21 29 1.5

PIB2-DD (6:1) 23 34 1.5

PIB3-DD (6:1) 28 37 1.6


Thermal Analysis of Decadiene-PIB Segmented Copolymers


Thermal gravimetric analysis (TGA) of the segmented copolymers is summarized

in Table 3-2. The thermal stability of the copolymers in nitrogen is comparable to that

of the respective homopolymers, with all copolymers showing 50 % weight loss in the

range of 410-425 C. The length of the oligomer produced no significant effect on thermal

weight stability.








Table 3-2. Thermal gravimetric analysis of decadiene-PIB segmented copolymers:
Temperatures of onset, 50%, and 90% weight loss. 20 "C/min.
Copolymer Onset 50% 90%

(wt ratio) "C "C 'C

PIB1-DD (2:1) 380 410 434

PIB2-DD (2:1) 392 417 438

PIB3-DD(2:1) 381 410 434

PIB1-DD (4:1) 381 426 458

PIB2-DD (4:1) 384 412 436

PIB3-DD (4:1) 394 410 435

PIBI-DD (6:1) 378 409 431

PIB2-DD (6:1) 382 412 436

PIB3-DD (6:1) 387 415 438



Differential scanning calorimetry was used to study the phase separation in the

copolymers both before and after hydrogenation, and Figures 3-2 through 3-6 show

some of the trends that were observed. The 1:6 copolymers, which contain the largest

fraction of polyisobutylene, are amorphous, sticky materials displaying only a glass

transition temperature near the expected -70 'C corresponding to polyisobutylene.

Increasing the proportion ofdecadiene in the polymerization led to the formation of soft

waxes for the 1:4 copolymer and finally soft white solids for the 1:2 copolymers, which

displayed melting points corresponding to their polyoctenamer segments.

As illustrated in Figure 3-2, as the proportion of decadiene is increased, the

product changes from an amorphous material to a more solid semicrystalline material. For

the copolymers with PIBI, the 1:6 copolymer is a viscous liquid. Increasing the








proportion of decadiene to 1:4 gives a soft wax with a melting point of 44 "C. Further

increasing the amount of decadiene gives a copolymer with a melting point close to that

expected for a decadiene homopolymer.

a 5
-69 51 C









67 'C



-16o -f5 -50 -5 5 25 50 75
Temperature

Figure 3-2. DSC trace showing the effect of proportion of hard phase on unsaturated
PIB-octenamer copolymers: copolymers of PIBI with a) 1:6, b) 1:4, and
c) 1:2 proportions of octenamer.



The effect of increasing the amount of hard phase is also reflected in the change in

glass transition temperature. The samples with the lowest proportion of polyoctenamer,

are completely amorphous with the glass transition temperature elevated from that of the

polyisobutylene homopolymer. Presumably there is too little polyoctenamer to be able

to separate into crystalline domains. However, the increase in the soft phase Tg is

consistent with mixing of the amorphous polyoctenamer with the amorphous

polyisobutylene. The introduction of these less flexiblesegments could have an overall

stiffening of the bulk material, similar to what is observed for commercialpolyester-ether








segmented copolymers upon varying the proportions of hard and soft segments.2 As the

amount of polyoctenamer increases, the two components are able to phase separate into

crystalline and amorphous domains. With less polyoctenamer present in the soft phase,

the glass transition temperature decreases, approaching that of the PIB homopolymer.

Similar results are observed for the other copolymer combinations, and these are

summarized in Table 3-3.


Table 3-3. Differential scanning calorimetry analysis of decadiene-PIB segmented
copolymers. Data from second heating scan at 20 'C/min.
Copolymer T, T. ("C) T, after H2 T. after H2

(wt ratio) "C onset/peak "C onset/peak

PIB1-DD (2:1) -69 62/67

PIB2-DD (2:1) -69 60 / 67

PIB3-DD (2:1) -69 48 / 56 -63 120/ 125

PIB1-DD (4:1) -54 44 -60 88

PIB2-DD (4:1) -54 -- -59 85 /100

PIB3-DD (4:1) -68 36 -64 120

PIB1-DD (6:1) -51 -- -53 --

PIB2-DD (6:1) -59 -- -60 --

PIB3-DD (6:1) -66 -- -62 --


Hvdrogenation of Segmented Copolvmers


Hydrogenation of the segmented copolymers effectively converts the

polyoctenamer segments to polyethylene segments. In each case an increase in the








melting point of these segments was observed upon hydrogenation, while the T, remains

essentially unchanged. The effect of hydrogenating the copolymers is illustrated with the

copolymer of PIB3 with 2:1 decadiene (DD) (Figure 3-3) and with PIB2 with decadiene

1:4 (Figure 3-4). Upon hydrogenating the 2:1 PIB3/DD copolymer, not only is the

melting point elevated from 56 'C to 125 "C, but also the enthalpy associated with this

transition increases.

125'C
ir -63 'C d-=74
56 "C
--^ ----^56*
S-69*C *C




29 'C
AH= -25 J/g




-100 -50 0 50 100
Temperature


Figure 3-3. DSC trace showing the effect of hydrogenation on melting point:
a) PIB3/DD 2:1 before hydrogenation and b) after hydrogenation.



Hydrogenation has an even more pronounced effect in the case of the 4:1

PIB2/DD copolymer, which displays only a glass transition temperature for the

unsaturated copolymer. Upon hydrogenation, a weak melting endotherm appears at

100 'C.























Figure 3-4. DSC trace showing the effect of hydrogenation on melting point:
a) PIB2/DD 4:1 before hydrogenation and b) after hydrogenation.



Similar results are observed with the other copolymers upon hydrogenation. The

melting points of the hydrogenated polyoctenamer segments are much lower than that of

high molecular weight linear polyethylene, which is in the range of

135-140 'C. This depression from the expected melting point may be due to either

incomplete hydrogenation or to the short length of the polyethylene segments. If the

segment length is very short, as would be expected for a segmented copolymer, then the

polymer chains will not form the same type of crystal morphology as long-chain

polyethylene.

The effect of hard phase proportion observed with the

polyoctenamer/polyisobutylene copolymers is also seen their saturated analogs.

Figure 3-5 shows the hydrogenated copolymers of PIB3 with the three different

proportions of hard phase. The copolymers with the highest proportion of PIB remain

amorphous, even after hydrogenation. However, decreasing the amount of PIB reveals a





55

melting point for the polyethylene segments which increases with increasing

incorporation of hard phase. With the highest incorporation of ethylene segment, a

melting point is observed at 125 C.


a -62 C


Sb 64 C
120'C


C 63 C -.VJ125 *C




-100 -50 Temperature0 100


Figure 3-5. DSC trace showing the effect of proportion of hard phase for
hydrogenated copolymers: Saturated copolymers of PIB3 with a)l :6;
b) 1:4; and c) 1:2 to octenyl repeat unit.



Despite the fact that both segments are composed of hydrocarbon parent

polymers, the data for both the PIB-polyoctenamer and the PIB-polyethylene

copolymers indicates that by incorporating a high enough proportion of hard segment, a

copolymer with thermal properties consistent with phase separation can be obtained.

Most of the copolymers obtained were too low in molecular weight to be useful as

materials. However, the PIB1/DD 1:4 demonstrated that with high enough molecular

weight, these polyisobutylene-ethylene copolymers could be potentially interesting

materials.














CHAPTER 4
SEGMENTED ESTER COPOLYMERS



Segmentedpolyether-ester copolymers, such as Du Pont's HytrelTM, have been

commercially known since the early 1970's.28 These polymers are typically based on

aromatic ester repeat units such as ethylene or butylene terephthalates or 2,6-napthalene

dicarboxylates combined with soft polyethers, such as poly(tetramethylene oxide) or

poly(ethylene oxide). (Figure 4-1).


MeO2C-Ar-CO2Me + HO-(CH2)nrOH + H H

Ar=





+ LA 9-LO(CH2) } -t Ar-
C ------- /m"-






Figure 3-1. General scheme for synthesis of commercial poly(ester-ether) segmented
copolymers. m= 13; n=2,4.



The rigid, crystalline carboxylate segments impart high melting points and good

thermal stability to these copolymers. Segmented ester-ether copolymers range from

toughened thermoplastics to thermoplastic elastomers depending on the weight percent of








ester to ether. The noncrystalline portions of the polyester are incorporated into the

amorphous soft phase along with the polyether, allowing some copolymers with up to

50 % ester to show elastomeric behavior.




Synthesis of Ester ADMET Segmented Copolymers


Ester dienes are not new to ADMET chemistry.91 Patton and Wagener studied

the viablity of the ester functionality in ADMET monomers and found that terephthalate

dienes as well as aliphatic esters are reactive toward metathesis chemistry provided the

functionality is separated by at least two methylene units from the metathesizing olefin.

For this study, three ester diene monomers were copolymerized with

polyisobutylene PIB1 and poly(tetramethylene oxide) PTHF3 diene telechelic oligomers

to make four different segmented copoolymers (Figure 4-2). The polyisobutylene diene

oligomers with parent molecular weights of 1700 (PIB1) and poly(tetramethylene oxide)

oligomers with molecular weights of 1700 (PTIF3) were used, and the synthesis of these

telechelomers is described in Chapter 2.

The monomers, shown in Figure 4-3, were synthesized via standard

esterification methods. The bis(5-butenyl) terephthalate (El) was synthesized according

to the literature procedure by the reaction of terephthaloyl chloride with 5-hexen-l-ol,91

while the bis(5-hexenyl) phenylene diacetate (E2) was synthesized from the condensation

of 1,4-phenylene diacetic acid with 5-hexen-l-ol. The 3-butenyl 4-pentenoate (E3) was

kindly provided by M. Watson.








Ester + (oligoner)-v

E1,E2,E3 PTHF3
PIB1

ADMET


(PE) A(oligomer),

Ester Segmented Copolymers

Figure 4-2. Synthesis of carbonate segmented copolymers. (PE) = polyester segment,
(oligomer) = polyether or polyisobutylene segment.





SEl


^HHO2-C0CHH E2



SE3


Figure 4-3. Ester monomers used to make segmented copolymers.



Poly(tetramethylene oxide) (PTHFl) diene telechelomer was copolymerized in a

1:1 wt:wt ratio with bis(5-hexenyl) terephthalate, El, bis(l-hexenyl)phenylene diacetate,

E2, and 3-butenyl 4-pentenoate, E3. The terephthalate copolymer was a soft white solid,

while the phenylene diacetate copolymer was a soft, tacky material, and the butenyl

pentenoate copolymer was a sticky viscous liquid. Polyisobutylene telechelomer(PIB1)

was copolymerized with bis(5-hexenyl) terephthalate, El to give a soft waxy solid.











Molecular Weight Analysis of Ester Segmented Copolymers


The molecular weight of the resulting copolymers increases relative to the parent

telechelomers in each case with negligibleunreacted parent oligomer as detected by GPC,

and the chromatograms comparing parent telechelomer to final copolymer are shown in

Figure 4-4 and Figure 4-5 for the THF and PIB copolymers, respectively. Molecular

weight data is summarized in Table 4-1 and indicates that copolymers of modest

molecular weight (M, in the range of 15,000 to 24,000 vs. polystyrene standards) were

obtained in each case. The polydispersity (M,/Mn) of the copolymers was found to

approach 2.0 which is consistent for step-growth polymerization.




Mn=3800 Mn=3800 Mn3800
Mn=15000 Mn-23000 Mn=24000




a b c

6 7 8 9 10 7 8 9 10 7 8 9 10
Elution Volume Elution Volume Elution Volume

Figure 4-4. GPC ofpoly(tetramethylene oxide) oligomer before and after
copolymerization with a) El; b) E2; and c) E3. (M, value vs.
polystyrene standards.)





60

Table 4-1. Summary of molecular weight data for ester segmented copolymers.a
Copolymer Mn Mw Mw/Mn

x103 g/mol x103 g/mol

PTHF1-E1 15 29 2.0

PTHF1-E2 23 39 1.7

PTHF1-E3 24 32 1.4

PIB1-E1 19 32 1.7

a Molecular weight vs. polystyrene standards.




Polymerization using the polyisobutylene oligomer appeared to proceed more

slowly than those using the polyether telechelomer, and this decreased reactivity of

polyisobutylene diene is discussed in Chapter 2. Integration of the terminal to internal

olefin end groups by 'H NMR confirms that the polymerization is less complete for the

copolymerizations using polyisobutylene.


5 6 7 8 9 10
elution volume


Figure 4-5. GPC of PIB1 telechelomer before and after copolymerization with El.








Thermal Analysis of the Ester Segmented Copolymers


Thermal gravimetric analysis (TGA) data for the segmented copolymers under

nitrogen atmosphere are summarized in Table 4-2. The polymers have varied thermal

stabilities with 50 % weight loss in the range of 385-420 "C.


Table 4-2. TGA data for ester segmented copolymers.a
Copolymer Onset ("C) 50% (C) 90 % (*C)

PTHF1-E1 397 421 451

PTHF1-E2 394 418 454

PTHF1-E3 345 385 415

PIB1-E1 378 409 433
a heating at 20 "C/min under nitrogen atmosphere




Differential scanning calorimetry was used to study the phase separation of the

copolymers. The polyether segments should display Tg at -90 "C as well as a melting

endotherm around 25 'C on the second heating scan while the polyisobutylene has a glass

transition temperature near -70 'C. The transitions of the parent isobutylene, ester and

ether homopolymers are summarized in Table 4-3.

The observed thermal data for the copolymers is summarized in Table 4-4. The

DSC thermograms for the polyether/polyester segmented copolymers heated at 20 'C/min

or 10 'C/min for did not show the melting endotherms that would be expected if the

material were completely phase separated (Figure 4-6).








Table 4-3. Thermal transitions for parent ether, isobutylene, and ester homopolymersa
Ester homopolymer Tg T,

PTHF1 -93 "C 25 'C

PIB -70 'C --

E2 -- 110 C

E3 -- 35 'C

E4 -15 'C -9 "C

aScanning rate 20 'C/min. Data collected on second heating cycle.



The poly(ether-terephthalate) copolymer showed the expected melting endotherm

for the PTHF3 segment at 24 'C. However, rather than a single sharp melting point at

110 'C that would correspond to a phase-separated polyester segment, a melting peak at

103 'C was observed on the first heating scan, which split into two lower temperature

endotherms at 88 and 74 'C on subsequent heating scans. Additionally, a glass transition

was observed at -78 'C for this polymer when heated at 20 'C from a quenched melt, and

this is slightly higher than the expected -90 'C for the polyether homopolymer.

These results suggest a certain degree of mixing between the polyester and

polyether segments. It can be rationalized that three phases exist in the bulk material,

including an ester-rich phase (Tm=88 'C), and ether-rich phase (Tm=24 'C), and a mixed

interfacial phase with an intermediate melting point. As mentioned in Chapter 1, the

sharpness of the boundaries between two phases varies depending on the nature, length,

and proportion of the two components.








88 C
74 'C I

24 'C




I
200'C



br- isc

c ____---'- --

-50 -25 0 25 50 75 100
Temperature ('C)

Figure 4-6. DSC's for polyether-ester copolymers. a) PTHF3+E1; b) PTHF3+E2;
c) PTHF3+E3. Heating rate 10 'C/min.



The copolymers of poly(tetramethylene oxide) with the more flexible ester

monomers behave similarly. The E2 copolymer showed a T, at -64 'C with a single

melting endotherm at 20 'C, while the copolymer with 3-butenyl 4-pentenoate, E3,

displays a Tg at -93 'C and single melting peak at 15 "C. The convergence of the

expected melting peaks for the ester and ether segments is consistent with phase mixing of

the polyether and polyester segments to give an intermediate melting point. Additionally,

the Tg for the El and E2 copolymers is higher than that of the polyether homopolymer,

and this is consistent with phase mixing of amorphous portions of the polyester into the

amorphous polyether phase to give an intermediate Tg.

These observations of the thermal behavior for these copolymers are consistent

with data that is observed in the commercialpolyether-ester copolymers.28 For many of

the commercialsystems it is observed that the noncrystalline portions of the polyester








are incorporated into the soft phase along with the polyether segments, and increasing

increasing the amount of hard phase ester leads to an increase in not only the Tm but also

the Tg upon. Therefore, it is reasonable to assume that a similar effect will be observed in

the ADMET generated polyether-ester copolymers. This indicates that the ADMET

segmented ether-ester copolymers are phase mixed to differing extents, thus leading

toward an averaging of the thermal transitions of the two components. A small amount of

phase mixing leads to melting point depression for the El segments when combined with

the polyether, while phase mixing seems to be even greater for the more flexible E2 and E3

copolymers.


Table 4-4. DSC analysis of ester segmented copolymers.
Copolymer Tg Tm 1 Tm 2

PTHF1-E1 -78 'Ca 20 *Ca 78 'Ca

103 'Ca
PTHF1-E2 -64 'Ca 24 'C --

PTHF1-E3 -93 "C 15 "C --

PIBl-E2 -73"C -- Ill 'C

aScanning rate 20 'C/min. Data collected on second heating cycle.
bScanning rate 10 "C/min. Data collected on second heating cycle.


Thermal analysis of the polyisobutylene segmented ester copolymer showed the

expected glass transition at -73 C for the polyisobutylene segments along with the

expected melting point for the respective polyester segments (Figure 4-6).









Tm=111 C





Tg=-73 '0
-----------





-100 -75 -25 25 75 125
Temperature

Figure 4-6. DSC for polyisobutylene PIB1 copolymer with El.
Heating rate 20 "C/min.





The sharpness and temperature of the melting peak are combined with the low Tg,

are consistent with a high degree of phase separation for these polyisobutylene/polyester

copolymers, which is in contrast to what was observed for the polyether segmented

copolymers. The differing behavior of the two sets of segmented copolymers can be

correlated to the polarity of their parent homopolymers. Both the polyether and the

polyester contain polar groups along their backbone and it is reasonable to suggest that

these could participate in secondary dipole-dipole interactions that would facilitate the

enthalpy of mixing of the two segments. However, polyisobutylene is a purely

hydrocarbon backbone and would be expected to be less miscible with the polar polyester

segments.














CHAPTER 5
SEGMENTED CARBONATE COPOLYMERS




Carbonates are another common class of step-growth polymers, with the aromatic

polycarbonates based on bisphenol A as important thermoplastic materials. The use of

carbonates in segmented copolymers is not as extensive as that of esters or urethanes.

Hydroxyl-capped aliphatic polycarbonates have been used as the soft segment in

polyurethane segmented copolymers, and polyester-polycarbonate segmented

copolymers are also commercially known.92

Carbonates are not new to ADMET chemistry, as Patton and coworkers

demonstrated that aliphatic carbonate dienes with two to four methylene spacers between

the carbonate functionality and the reacting olefin are amenable to ADMET

polymerization.93 Patton also explored the ADMET polymerization of a diene monomer

whose homopolymerization gave an alternating bisphenol-A/3-hexenyl copolycarbonate

structure.




Synthesis of Carbonate ADMET Segmented Copolvmers


For the synthesis of ADMET segmented polycarbonates, the monomers

bis(3-butenyl) carbonate (C1) and bis(5-hexenyl) carbonate (C2) were chosen. The








carbonate monomers were synthesized by a modification of the published synthesis.93

Dimethyl carbonate was condensed with either 3-buten-l-ol or 5-hexen-l-ol in the

presence of sodium metal to make C1 and C2, respectively.

Diene telechelomers ofpolyisobutylene, with M,=1700 (PIBl) and 3100 (PIB2),

as well as poly(tetramethylene oxide), with Mn=1800 (PTHF1) and 3600 (PTHF2), were

used. These diene oligomers were copolymerized in a 1:1 wt:wt ratio with either Cl or

C2 to give a total of eight different carbonate segmented copolymers (Figure 5-1).





nO O+ -(oligomer^)
n PTHF1
PTHF2
C1 n=l PIB1
C2 n=2 PIB2

1ADMET


(PC)x-(oligomer)y
Carbonate Segmented Copolymers

Figure 5-1. Synthesis of carbonate segmented copolymers. (PC) = polycarbonate
segment, (oligomer) = polyether or polyisobutylene segment.





Molecular Weight Analysis of Carbonate Segmented Copolymers


Upon copolymerization the molecular weight of the resulting copolymers

increases relative to the parent homopolymer in each case as measured by GPC.








Molecular weight data is summarized in Table 5-1 and indicates modest molecular

weights (M, in the range of 25,000 vs. polystyrene standards) with polydispersities

(Mw/Mn) approximately 2 were found for the copolymers, which is consistent for step-

growth polymerization.



Table 5-1. Summary of molecular weight data for carbonate segmented copolymers.a

Copolymer M, Mw Mw/Mn

x103 g/mol x103 g/mol

PTHF1-C1 7 13 1.88

PTHF2-C1 6 10 1.75

PTHF1-C2 9 19 2.11

PTHF2-C2 11 16 1.47

PIB1-C1 4 8 1.93

PIB2-C1 5 11 2.37

PIB1-C2 8 14 1.76

PIB2-C2 10 22 2.07

a. Determined by GPC relative to polystyrene standards



Polymerizations using polyisobutylene oligomer appeared to proceed more

slowly than those using the polyether telechelomer, as discussed previously. Integration

of the terminal olefin end groups by 'H NMR confirms the polymerization is less

complete for these copolymerizations. It was also found that the copolymerizations

involving bis(3-butenyl) carbonate were much slower than those with bis(5-hexenyl)

carbonate. These showed incomplete conversion even after several days of exposure to








catalyst and vacuum. Homopolymerization of each of these carbonate monomers

confirmed that the butenyl carbonate monomer is less reactive than hexenyl carbonate to

ADMET polymerization.

Although this reactivity difference is not addressed in the original work concerning

the ADMET polymerization of carbonate monomers, it is reasonable to suggest that the

growing chain end derived from the bis(3-butenyl) carbonate is more prone to chelation to

the transition metal catalyst to give a favorable 5 or 7 membered ring as shown in

Figure 5-2. The observation of hindered or prohibited ADMET polymerization by

polar functional groups close to the metathesizing double bond has been referred to as the

"negative neighboring group effect." 28-30


0













Figure 5-2. Potential chelation of C1 carbonate functionality to catalyst during
ADMET polymerization.








Thermal Analysis of the Carbonate Segmented Copolvmers


Thermal gravimetric analysis of the segmented carbonate copolymers under

nitrogen atmosphere is summarized in Table 5-2. The polyisobutylene copolymers

appear to be slightly more thermally stable, with all copolymers showed 50 % weight

loss in the range of 370-410 'C. The length of the oligomershowed no significant effect

on thermal stability.


Table 5-2. Thermal gravimetric analysis of carbonate segmented copolymers.
Copolymer Onset 50% 90%

(C) (C) ('C)
PTHF1-C1 320 369 413

PTHF2-C1 294 398 430

PTHF1-C2 381 414 441

PTHF2-C2 384 409 438

PIB1-C1 365 409 435

PIB2-C1 355 405 432

PIB1-C2 368 410 438

PIB2-C2 366 414 440


Differential scanning calorimetry was used to provide an indication of the phase

separation of the copolymers. As discussed previously, the presence of distinct phase

transitions corresponding to each parent homopolymer can be an indication of phase


separation in the material.








Differential thermal analysis was obtained for two of the unsaturated copolymers

employing the C2 carbonate segment. The polyether-carbonate copolymer shows three

melting endotherms on the first scan, including the two expected for a first scan of

poly(tetramethylene oxide) as well as a small peak at 19 "C. This additional peak could

be due to phases containing polycarbonate segments that are unable to recrystallize on the

timescale of the experiment. The stronger melting transition is slightly depressed from

the expected melting point for the polyether homopolymer, indicating a simple melting

point depression occurring from phase mixed polyether-carbonate (Table 5-3).

The polyisobutylene copolymer with C2 shows thermal behavior consistent with

a greater degree of phase separation. The Tg for the polyisobutylene is slightly higher

than PIB homopolymer, and the melting peak observed at 38 'C is slightly lower than the

40 "C for the homopolycarbonate. Once again a weak melting endotherm is observed at

14 'C only on the first scan. It is difficult to determine whether this peak can be

correlated to the peak at 19 "C observed for the polyether-C2 copolymer.








Table 5-3. Differential scanning calorimetry analysis of carbonate segmented
copolymers, before and after hydrogenation. Data obtained on second
heating scan at 20 *C/min. (Temps in 'C, AH in J/g))

Unsaturated Copolymer After Hydrogenation

Copolymer Tg T, AH J/g 2 H 2T Ti AH J/g H2 Tm2 AH J/g

poly Cl -57' 45' (47.2J)

poly C2 -- 39' (46.2J)

PTHF1-C1 -65' 23 (62.4J) -77' 22' (81.8J) 34 b

PTHF2-C1 --c 24 (43.0J) -74' 24' (68.1J) 45b (15.9J)

PTHF1-C2 -70' 14 (42.0J) -74' 15" (52.1J) 36" (31.8J)

PTHF2-C2 -76 (19')",23' (51.1J) -76' 25' (55.4J) 46' (36.8J)

PIBI-CI -66 -- -64' (7')b (12.0J) 50' (33.1J)

PIB2-C1 ? ? -65' -- 46' (19.1J)

PIB1-C2 -65 -- -66' -- 48' (35J)

PIB2-C2 -66 (14')a,38' (3.9J) -64 -- 48' (31.2J)

a. Only observed on first heating scan.
b. Very weak transition appearing as shoulder on primary melting peak.
c. No observable Tg above -15 'C


Further thermal analysis was performed on the hydrogenated analogs of the

carbonate copolymers. Hydrogenation of the copolymers has a firming effect on the

materials, similar to what is seen for the PIB/decadiene copolymers. All but one

copolymer displayed melting points that correlate to hydrogenated carbonate in addition

to the expected transitions of the parent telechelomers.

The effect of hydrogenation is illustrated with the PTHF2/C2 and PIB2/C2

copolymers, for which thermal data was collected for both the unsaturated and the

hydrogenated copolymers (Figure 5-4 and Figure 5-5). Hydrogenation appears to lead





73

to greater phase separation, even with the polyether. After hydrogenation, the saturated

carbonate segment readily crystallizes, and two peaks are seen on the heating scans at 25

'C (polyether) and 46 'C (saturated carbonate).


1-75.5 'C


-50 0
Temperature


Figure 5-3. Effect of hydrogenation on melting point: Copolymer of PTHF2/C2
a) before hydrogenation and b) after hydrogenation.



By comparison, the PIB2/C2 copolymer does display a consistent melting peak

for the unsaturated carbonate segment. This implies that the unsaturated carbonate is able

to recrystallize more easily when it has a higher degree of phase separation, as would be

expected when combined with the hydrocarbon PIB component vs. the more polar

polyether. Upon hydrogenation the carbonate melting peak increases from 38 'C to 48

'C, nicely matching the melting transition observed for the PTHF2/C2 copolymer.





74


48 'C




38'C




-65 'C

-64 'C
f b


-100 -50 Temperature 0 50

Figure 5-4. Effect of hydrogenation on melting point: Copolymer of PIB2/C2
a) before hydrogenation and b) after hydrogenation.














CHAPTER 6
SEGMENTED URETHANE COPOLYMERS




Segmented urethane-ether copolymers are well known as thermoplastic

elastomers, with LycraT as the classic example.27'68 Segmented poly(urethane-ether)s are

synthesized from the copolymerization of diisocyanates along with diols and an

a,(o-dihydroxyl polyether (Figure 6-1).


O=C=N--Ar-N=C=O + HO-(CH2)nOH + H OH

Ar = L "TDI"
HCH,




H-Ar-NH .(CH2)n -NH-Ar-NH---(CH2CH20)



Figure 6-1. General synthesis of aromatic poly(urethane-ether) segmented copolymer



Polyurethane-isobutylene copolymers are also known, and using polyisobutylene

offers some advantages over polyether as the soft segment.29 The polyisobutylene

imparts greater stability towards hydrolysis, oxidation, chemicals, and thermal

degredation, as well as offering good barrier and damping ability over a wide temperature

range. Poly(urethane-isobutylene)s are made from the condensation of ca,o-hydroxyl





76


polyisobutylene with diisocyanates and small glycols. However, the synthesis of the

dihydroxyl polyisobutylene telechelomer is a multistep process, as there is no direct way

to introduce the hydroxyl functionality onto polyisobutylene. Allyl-capped

polyisobutylene can be synthesized by simply quenching the polymerization with

allyltrimethyl silane. ADMET condensation of allyl-PIB with a,to-dienyl urethanes

would offer poly(urethane-isobutylene) segmented copolymers in a total of only three

steps as opposed to the five steps using the traditional method. A comparison of the two

approaches is shown in Figure 6-2.


a b
I -- a -- [ Dichloroinitiator } -
I IB Polymerization
IB Polymerization quenched with
terminated with MeOH (allyl)SiMe3


C -~-Pl)B-- I 3
-PIB-_
CH3 HH3
Dehydrochirination H3











PI HO-(CH2)n-OH PIB-PU Segmetned copolymer
Figure 6-2. Comparison of a) traditional method for the synthesizing PIB-PU

segmented copolymers vs. b) ADMET approach.DMET
Oxidation
H /-OH MDI
PI HO-(CH,)n-OH PIB-PU Segmetned copolymer




Figure 6-2. Comparison of a) traditional method for the synthesizing PIB-PU
segmented copolymers vs. b) ADMET approach.











Synthesis of Urethane ADMET Segmented Copolvmers


A series of eight different urethane segmented copolymers was synthesized from

the copolymerization of polyisobutylene and poly(tetramethylene oxide) diene telechelic

oligomers with bis(5-hexenyl)methylene-p-diphenylene dicarbamate and with tolyene-

2,4-bis(5-hexenyl) dicarbamate (Figure 6-3). Polyisobutylene diene oligomers with

parent molecular weights of 1700 (PIB1) and poly(oxytetramethylene) oligomers with

molecular weight of and 3600 (PTHF2) were used.


---Urethane-_ + ,(oligomer)

U1,U2,U3 PTHF2
PIB1


ADMET


-(PU)x-(oligomer)y

Urethane Segmented Copolymers



Figure 6-3. Synthesis of urethane segmented copolymers. (PU) = polyurethane
segment, (oligomer) = polyether or polyisobutylene segment.



Synthesis of Urethane Diene Monomers


The three urethane diene monomers used are shown in Figure 6-4. These were

synthesized from the reaction of 5-hexen-l-ol with the appropriate diisocyanates,








phenylene diisocyanate, methylene-p-diphenylene diisocyanate, and tolyene-2,4-

diisocyanate, respectively. Each urethane diene is a solid, which distinguishes these

monomers from the traditional liquid diene monomers studied for ADMET

polymerization. The p-phenylene dicarbamate, Ul, has a melting point too high to be

amenableto ADMET polymerization, while U2 and U3 melted near 70 'C and 90 "C

respectively. The phenylene dicarbamate monomer (Ul) did not polymerize under the

conditions used, so this monomer was not used for further investigation. The melt-

homopolymerization of U2 and U3 proceeded with poor conversion. However,

copolymerization with the poly(tetramethylene oxide) oligomer seemed to facilitate

mixing of the monomer with catalsyt.




O=C=N-Ar-N=C=O + 2 HO' -
SnR4



NH--- -
Ar= Ul


Ar= -- CH U2

Ar = U3





Figure 6-4. Urethane monomers tested for ADMET segmented copolymers.








Molecular Weight Analysis ofUrethane Segmented Copolymers


Poly(oxytetramethylene) (PTHF2) and polyisobutyene (PIB1) diene

telechelomers were copolymerized to target a ratio of 6 IB units to 1 urethane repeat in

the final copolymer. Upon copolymerization the molecular weight of the resulting

copolymers increases relative to the parent in each case with negligibleunreacted parent

oligomeras detected by GPC. Molecular weight data is summarized in Table 6-1 and

indicates copolymers of modest molecular weight (in the range of 25,000 to 30,000 vs.

polystyrene standards) were obtained in each case. The polydispersity (Mw/M,) of the

copolymers was found to be slightly greater than 2.0, and is in the range which is

consistent for step-growth polymerization. The broader distribution is probably due to

the decreased metathesis reactivity of the urethane, particularly in the reactions with

polyisobutylene where the molten urethane monomer is insoluble in the polyisobutylene.

The solid urethane monomers were, however, able to dissolve in the melted

poly(tetramethylene oxide) at 60 "C allowing for better mixing of the two reacting species.



Table 6-1. Summary of molecular weight data for urethane segmented copolymers.

Copolymer M, M, M,/M,

x103 g/mol x103 g/mol
PTHF2-U2 30 59 2.0

PTHF2-U3 29 56 1.94

PIB1-U2 25 49 2.03

PIB1-U3 26 50 2.0











Thermal Analysis of the Urethane Segmented Copolymers


As with the previously discussed systems, thermal analysis gave an indication of

the thermal stability and degree of phase separation of the polyurethane segmented

copolymers. Thermal gravimetric analysis of the segmented copolymers under nitrogen

atmosphere is summarized in Table 6-2. The urethane-ether copolymers show

interesting thermogravimetric behavior. The TGA scans showing the urethane monomer,

poly(tetramethylene oxide) telechelomer, and the copolymer of the two for both ether-

urethane copolymers are shown below (Figure 6-5). Rather than the relatively sharp

decrease in weight as observed for the other segmented copolymers studied,

decomposition of the ether-urethanes appears to occur in two stages, with the weight loss

trailing off gradually above 450 "C.


a U2 -PTHF2


S\ copolymer





200 400 600
Temperature ( C)


b U3--. \\ PTHF2



i\ copolymer




200 400 600
Temperature ('C)


Figure 6-5. TGA thermograms ofpoly(ether-urethane) copolymers. a) PTHF2/U2
copolymer; b) PTHF2/U3 copolymer. (20 'C/min, Nitrogen)





81


The polyisobutylene copolymers appear to be slightly more thermally stable,

with all copolymers losing 50 % of their weight in the range of 390-395 'C (Figure 6-6).

However, this resemblance to the thermal stability of the polyisobutylene homopolymer

could be merely due to the very low incorporation of urethane into the copolymer.


a \ ,-PIB1
U2 t'

i polymer





200 400 600
Temperature ('C)


b PIB1
U3-- i
S ,copolymer


l '


200 400 600
Temperature ('C)


Figure 6-6. TGA thermograms for polyisobutylene urehane segmented copolymers:
a) PIBI/U2 copolymer; b) PIB1/U3 copolymer. (20 "C/min, Nitrogen)


Table 6-2. Thermal gravimetric analysis of urethane segmented copolymers.
Copolymer Onset ('C) 50 % ('C) 90 % ('C)

PTHF2-U2 372 391 403

PTHF2-U3 384 395 407

PIB1-U2 387 392 404

PIB1-U3 389 396 408



Differential scanning calorimetry was used to provide an indication of the phase

separation of the copolymers. As discussed previously, the presence of distinct phase








transitions corresponding to each parent homopolymer can be an indication of phase

separation of the two segments in the bulk polymer. The observed thermal data for the

urethane copolymers are summarized in Table 6-3. The data reflect the first heating scan

because no melting peaks corresponding to the urethane segments were observed on the

second heating scan. Unfortunately, suitable samples of the homopolymers of the

urethanes were not able to be obtained via ADMET polymerization, so the expected

melting points of the urethane segment are unknown. The polyether/polyurethane

segmented copolymers each showed the expected first-scan melt of the polyether at

36 'C. The U2 based copolymer shows a weak melting endotherm at 138 "C, which

disappeared upon subsequent scans, while the U3 ether copolymer showed no detectable

melting endotherm above 36 'C even on the first scan (Figure 6-6). The copolymers

with polyisobutylene showed no observable melting peaks between 20 'C and 150 "C,

and this is perhaps due to the low incorporation of urethane into the copolymers after

workup.


Table 6-3. DSC thermal transitions for urethane segmented copolymers at 20 'C/min.a
Copolymer Tg ('C) T.i (*C) T.2 ('C)

PTHF2-U2 -- 36 "C 138 'C

PTHF2-U3 -- 36 'C --

PIB1-U2 -67 'C -- 148 'C

PIB1-U3 -61 'C -- -

a. Data obtained from first heating cycle.





83



138'C


a)PTHF2+U2-- "

36 C
0
b) PTHF2+U3






0 25 50 75 100 125 150 175
Temperature
Figure 6-6. First heating scan thermogram for polyether-polyurethane copolymers.
a) PTHF2 + U2; b) PTHF2 + U3.


Temperature


Figure 6-7. First heating scan thermogram for polyisobutylene-polyurethane
copolymers. a) PIB1 + U2; b) PIB1 + U3








The observed DSC data are difficult to interpret with this limited amount of data,

and comparison of samples with a higher incorporation of urethane would be helpful.

However, bulk ADMET polymerization of these solid urethane monomers is

problematic. Homopolymerization only proceeded to low conversion, especially in the

case of U2 which melts at 90 'C. The Grubbs catalyst is not stable over the long reaction

times at this temperature required. The copolymerizations with the polyether seemed to

perform better, as the molten poly(tetramethylene oxide) is able to dissolve the urethane

monomers. The polyisobutylene copolymerizations were never able to be completely

homogenized even after stirring several days. One possible approach to facilitating the

polymerization of these and high-melting ADMET monomers is to add a small amount of

a high-boilingplasticizer, such as diphenyl ether, to the polymerization mixture. This

would help to liquify the solid monomer and would keep the viscosity lower throughout

the polymerization.














CHAPTER 7
EXPERIMENTAL PROCEDURES




General Experimental Procedures


Spectra for 'H NMR (300 MHz) and '3C NMR (75 MHz) were obtained on a

VarianGemini-SeriesNMR superconducting spectrometer system. All NMR data were

generated in CDC13 as the solvent, and peaks are listed in ppm downfield from

tetramethyl silane. Infrared (IR) data were recorded neat, using KBr plates on a Perkin

Elmer 281 infrared spectrometer. Low and high resolution mass spectrometry was

recorded on a Finnigan 4500 Gas Chromatography/Mass Spectrometer using either

electron or chemical ionization conditions. Elemental Analyses were performed by

Atlantic Microlab, Inc., Norcross, GA.

Gel Permeation Chromatography (GPC) was performed of a Waters and

Associates model 590 chromatograph using a Phenomenex mixed bed column and

chloroform as the eluent at a flow rate of 1.0 mL/ min. Peaks were detected using both a

Waters Associates differential refractometer and a Perkin Elmer LC-75

spectrophotometric detector (250 nm), and calibrated with polystyrene standards.

Molecular weights of the three polyisobutylene telechelic oligomers were additionally

determined by GPC with light scattering detector.








Preparatory HPLC was performed on a Rainan Dynamax system equipped with

Dynamax 60 A silica preparative column and Dynamax spectophotometer set at 254 nm.

Thermal Gravimetric Analysis (TGA) was performed on a Perkin Elmer TGA7 as

a heating rate of 20 "C/min up to 800 'C. Differential Scanning Calorimetry (DSC) was

performed on a Perkin Elmer DSC7 at heating rates of 10 'C/min or 20 "C/min, as

indicated. Both TGA and DSC were interfaced to a TAC7/DX thermal analysis

controller. Some DSC were run on a TA Instruments Universal V2.5D at 20 C/min.

Samples were heated above their melting point, cooled, then data was collected for the

second heating and cooling scan unless otherwise indicated.

The Grubbs catalyst, RuCI2(P(C6HI1)3)2CHPh46 and the Schrock molybdenum

catalyst (Mo(NC6H3-2,6-i-Pr)(OCCH3(CF3)2)2CHC(CH3)2C6H5)4 were prepared

according to published procedures. Toluene and pentane were treated with concentrated

sulfuric acid prior to drying over sodium/potassium alloy. Diethyl ether, toluene, and

pentane were distilled from sodium/potassium alloy.




Synthesis of a.o-Dienvl Telechelic Oligomers


The diene telechelomers used for this study were synthesized by cationic

polymerization of tetrahydrofuran or isobutylene followed by capping with 5-hexen-l-ol

or allyltrimethyl silane, respectively.








Polv(tetramethvlene oxide) Telechelomers


Poly(oxytetramethylene) oligomers were synthesized by cationic ring-opening

polymerization of tetrahydrofuran initiated by triflic anhydride. Tetrahydrofuran was

dried over sodium/potassium amalgumand freshly distilled before use. Triflic anhydride

was freshly distilled before use, and 5-hexen-l-ol was distilled from calcium hydride.



Synthesis of a.o-dienvl polv(tetramethvlene oxide) (M,=1800) (PTHFl).

Dry, degassed tetrahydrofuran (36.0 mL, 0.44 mol) was placed in a Schlenk flask

and cooled to -13 'C with a benzonitrile slush bath. Triflic anhydride (1.0 mL, 5.9x103

mol) was added all at once by syringe. The reaction was maintained at -13 'C and stirred

for 25 minutes, then the polymerization was quenched by rapidly adding 5 mL (0.04 mol)

5-hexen-l-ol. The reaction was allowed to warm to room temperature and stirred 12

hours. Solvent was evaporated to reduce the volume in half, then the reaction mixture

was precipitated into methanol that contained 5 % w:v sodium bicarbonate to yield a

white solid. The solid was collected by filtration and redissolved in chloroform and

reprecipitated in methanol twice more to ensure complete removal of the triflic acid. The

precipitate was dried under vacuum to give a soft white powder. Anal. Calc. for

Cl12H222026: 11.27 %H, 67.77 %C. Found: 11.27 %H, 67.31 %C. Dp-25 M,~ 1700 by

'H NMR, mp = 25, 35 'C; 'H NMR 1.42 (m, 4H), 1.60 (s, 98H, CH2), 1.81 (m, 4H),

2.07 (q, 4H), 3.41 (s, 102H, OCH2), 4.97 (m, 4 =CH2), 5.80 (m, 2=CH); "C NMR 138.7

(=CH), 114.4 (CH2), 70.5 (OCH2), 33.5 (CH2), 29.2 (CH2), 26.4 (CH2), 25.4 (CH2).










Synthesis of .co-dienyl poly(tetramethylene oxide) (Mn = 3600) (PTHF2).

The synthesis of the largerpoly(oxytetramethylene) oligomeris identical to that

described above with the exception of reaction time. After adding the triflic anhydride

(1.0 mL, 5.9x10"3 mol) to 36 mL tetrahydrofuran at -13 'C, the reaction was allowed to

stir for 45 minutes before quenching with 5-hexen-l-ol. After three precipitations, and

drying under vacuum, the oligomer was obtained as a soft white powder. Anal. Calc. for

C204H406049 : 67.25 %C, 11.23 %H; Found: 66.54 %C, 11.20 %H; Dp-48 Mn- 3600

by 'H NMR, Mn-, PDI -1.10 by GPC. mp = 25, 35 'C; 'H NMR 1.42 (m, 4H), 1.60

(s, 200H, CH2), 1.81 (m, 4H), 2.07 (q, 4H), 3.41 (s, 202H, OCH2), 4.97 (m, 4 =CH2),

5.80 (m, 2=CH); 13C NMR 138.7 (=CH), 114.4 (CH2), 70.5 (OCH2), 33.5 (CH2), 29.2

(CH2), 26.4 (CH2), 25.4 (CH2).



Polyisobutvlene Telechelomers


Isobutylene was polymerized cationically using the inifer method described by

Storey and coworkers, using the facilities and expertise of the Storey research group.72

The initiator, 5-tert-butyl-l,3-bis(2-chloro-2-propyl) benzene, was prepared in three

steps from 5-t-butyl isophthalic acid, according to published procedures.707' n-Hexane

was freshly distilled from calcium hydride. Titanium tetrachloride and anhydrous

2,6-dimethyl pyridine were used as received. Isobutylene and methylchloride were dried

by passage through a column packed with BaO and CaCl2. Polymerizations were




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