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Synthesis and characterization of stereoblock polymers of poly(methyl methacrylate)

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Synthesis and characterization of stereoblock polymers of poly(methyl methacrylate)
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Doherty, Martin A., 1956-
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xii, 86 leaves : ill. ; 28 cm.

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Block copolymers ( jstor )
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Methacrylates ( jstor )
Molecular weight ( jstor )
Money market accounts ( jstor )
Monomers ( jstor )
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Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
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Thesis:
Thesis (Ph. D.)--University of Florida, 1984.
Bibliography:
Includes bibliographical references (leaves 83-85).
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Typescript.
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Vita.
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by Martin A. Doherty.

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University of Florida
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SYNTHESIS AND CHARACTERIZATION OF
STEREOBLOCK POLYMERS OF POLY(METHYL METHACRYLATE)






By

MARTIN A. DOHERTY






















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 1984




























To my parents, Joseph and Geraldine Doherty
















ACKNOWLEDGEMENTS

The author wishes to thank his supervisory committee, Dr.

Charles Beatty, Dr. Wallace Brey, and Dr. William Jones, for their assistance and support. The author personally wishes to thank Dr. George Butler for his discussions on areas both related and not related to chemistry. Special thanks and deep appreciation are directed to Dr. Thieo Hogen-Esch for his moral support, encouragement, patience, and friendship.

The author would also like to acknowledge Marlene Hawthorne, Mark Eller, Ish Khan, and Patty Hickerson, for their assistance in maintaining the author's sanity throughout his graduate studies.

Most of all, the author wishes to thank his parents, for without them, none of this would be possible.


















iii















TABLE OF CONTENTS

Page

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

LIST OF TABLES . . . . . . . . . . . . . . . . . . . . . . . . vii

LIST OF FIGURES. . .................. .... ix

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . xi

CHAPTER

I INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . 1

II EXPERIMENTAL . . . . . . . . . . . . . . . . . . . . . . 11

Initiator Syntheses . ................. 12

Diphenylmethane and Diphenylethylene Purification. . 12 Diphenylmethyllithium (Monofunctional Initiator) . 12 1,1,4,4-Tetraphenylbutane Dianion Lithium. ...... 16

Monomer Synthesis and Purifications . ......... 19

Methyl Methacrylate (MMA). . .......... ... 19

Silver Methacrylate (AgMA) . ............ 22

Trityl Methacrylate (TrMA) . . ............ . 22

Diphenyl Methyl Methacrylate (DMA) . ........ 24

Polymerization Reactions. . ............... 25

Formation of Homopolymers. . ............. 25

Block Copolymer Reactions. . ............. 28

PDMA, TrMA Random Copolymers . ........... 30



iv










CHAPTER Page

Polymer Hydrolysis ................... . 30

PTrMA.. ................... .... 30

PDMA. ................... ......33

Random Copolymers (PDMA-TrMA) . ............ 33

PDMA-TrMA Block Copolymers. . .............. 33

PMMA-TrMA Block Copolymers. . ............. . 33

Diazomethane Methylation . ................ 34

Instrumentation ...................... 36

Gas Chromatography. .................. 36

Nuclear Magnetic Resonance (NMR). . .......... . 36

Differential Scanning Calorimetry (DSC) . ....... 37 Gel Permeation Chromatography (GPC) . ......... 37

Segment Molecular Weight Calculations. . .......... 38

III POLYMER SYNTHESES AND CHARACTERIZATIONS. . ......... 41

PMMA Homopolymers Synthesized From TrMA, DMA and MMA . . . 42

Homopolymers Prepared With Monofunctional Initiators. . 42 Homopolymers Prepared With Bifunctional Initiators. .. 44

PMMA From Random Copolymerization of DMA and TrMA. . ... 47

AB Stereoblock PMMA Synthesized From DMA and TrMA . . . 51 AB Stereoblock PMMA Synthesized From MMA and TrMA . . . 53 ABA Stereoblock Polymers From DMA and TrMA. . ...... 55

IV STEREOCOMPLEX ANALYSIS OF STEREOBLOCK POLYMERS OF PMMA
AND PMMA HOMOPOLYMERS. . .................. 59

Introduction . . . . . . . . . . . . . . . . . . . . . . . 59





v










CHAPTER Page

Stereocomplex Formation Studies . ............ 60

Investigation of the Stereocomplex Equilibrium . . . . 60 Homocomplexation of S-PMMA and I-PMMA in DMSO ..... 62

Comparison of Stereocomplexation Between Stereoblock Polymers of PMMA With Mixtures of I-PMMA
and S-PMMA ................... ... 64

Concentration Effects on Stereocomplex Formation . . . 69

Effect of PMMA Stereoregularity on Stereocomplex
Formation . . . . . . . . . . . . . . . . . . . . . . . . 69

Determination of S-PMMA/I-PMMA Stereocomplex Ratios
for PMMA Homopolymers Synthesized From DMA and TrMA. . 69 Mixtures of I-PMMA and S-PMMA With At-PMMA ...... 73

Analysis of Stereocomplex Formation From SAtSand IAtI-PMMA Stereoblock Polymers . ......... 74

Effect of Segment Molecular Weight on Stereocomplex
Formation . . . . . . . . . . . . . . . . . . . . . . . . 75

DSC Investigation on Stereoblock Polymers . ....... 81 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . .. . 83

BIOGRAPHICAL SKETCH. . .................. ... 86

















vi
















LIST OF TABLES

Table Page

1 PMMA Homopolymer Analyses From TrMA, DMA, and MMA ..... 42

2 Molecular Weight Data for PMMA Homopolymers Synthesized
From TrMA, DMA, and MMA .................. 44

3 PMMA Tacticity Using Sodium Counterion Initiators .... . 45

4 Stereochemistry and GPC Data for PMMA Prepared With Mono- and Bifunctional Lithium Initiators . ........ 46 5 Random Copolymers From TrMA and DMA ............ 48

6 Effect of DMA Polymerization Time on Stereoblock PMMA . . . 52 7 AB Stereoblock Polymers of PMMA From TrMA and DMA .... . 54 8 A-B Stereoblock Polymers of PMMA From MMA and TrMA. ..... 56 9 Various ABA Stereoblock Copolymers of PMMA. ......... 57 10 Homocomplexation Analyses of S-PMMA and I-PMMA. . ...... 63 11 Samples Used in Series A and Series B ........ . . . . 65

12 Fraction of Complexed Polymer for Mixtures of PMMA
Homopolymers and for Stereoblock PMMA in Series A and
Series B at Various Temperatures. . ............. 65

13 I- and S-PMMA Tacticities Accounting for Differences
in S/I Ratios in CD3CN. .................. 72

14 NMR Results for I-PMMA and S-PMMA Mixed With At-PMMA
in CD3CN . . . . . . . . . . . . . . . . . . . . . . . . . . 73

15 Temperature and Tacticity Study on Mixture of IAtIand SAtS-PMMA Stereoblock Polymers in a Complexing
Solvent . . . . . . . . . . . . . . . . . . . . . . . . . . 75




vii










Table Page

16 GPC and NMR Analyses on Stereocomplex Formation on SI-PMMA Stereoblock Polymers . .............. 76

17 DSC Analysis for Various PMMA Samples. .... ....... 81










































viii















LIST OF FIGURES

Figure Page

1 Schematic representation of stereocomplex of isotactic PMMA and syndiotactic PMMA . ............ 2

2 Configuration of stereoblock polymer . ......... 5

3 Schematic representation of a mixture of IAtI- and
SAtS-PMMA stereoblock polymers . ............ 7

4 Apparatus for vacuum line purification of diphenylmethane and diphenylethylene . ............. 13

5 Apparatus for the synthesis and purification of diphenylmethyllithium (DPML) . .............. 14

6 Apparatus for the synthesis of 1,1,4,4-Tetraphenylbutane dianion lithium (DPE-Li)2 . ........... 17

7 Apparatus for the purification of 1,1,4,4-Tetraphenylbutane dianion lithium (DPE-Li+)2 ......... 18

8 Apparatus for the vacuum line drying of methyl methacrylate over CaH2 ...................20

9 Apparatus for the vacuum line drying of methyl methacrylate over a sodium mirror. . ............. 21

10 Apparatus for the storage of solid materials under
high vacuum . . . . . . . . . . . . . . . . . . . . . . . 23

11 Apparatus used to prepare THF solutions of diphenylmethyl methacrylate or trityl methacrylate . ...... 26

12 Apparatus used in the homopolymerizations of diphenylmethyl methacrylate or trityl methacrylate . ...... 27

13 Apparatus used in the homopolymerization of methyl
methacrylate . . . . . . . . . . . . . . . . . . . . . . 29




ix










Figure Page
14 Apparatus used in the synthesis of poly(methyl
methacrylate)-trityl methacrylate block copolymers . . .. 31

15 Apparatus used in the synthesis of poly(diphenylmethyl methacrylate)-trityl methacrylate block
copolymers . . . . . . . . . . . . . . . . . . . . . . . . 32

16 Apparatus used in the generation of diazomethane .... . 35

17 Schematic representation for intramolecular association for bifunctional sodium initiator in THF. . ...... 45

18 Random syndiotactic placement of DMA into PTrMA. ...... 50

19 100 MHz 1H-NMR spectra of sample PMT-2 (syndiotactic
segment molecular weight = 4160; isotactic segment
molecular weight = 4960) recorded at various temperatures. . . . . . . . . . . . . . . . . . . . . . . . .. . 61

20 Complexation as a function of temperature for samples A-B and A+B in series A................... 67

21 Complexation as a function of temperature for samples A-B and A+B in series B. . ................. 68

22 Complexation effects with dilution of samples A-B and A+B in series A. . .................. . . 70

23 Effects of S-PMMA/I-PMMA weight ratios on a-methyl proton absorptions from 100 MHz 1H-NMR spectra at 250C
in CD3CN . . . . . . . . . . . . . . . . . . . . . . . . . 71

24 GPC chromatograms run in THF and CHC13 for samples a) PDT-4 and b) PDT-8. .................. 78

25 Room temperature and high temperature 100 MHz 1H-NMR spectra for samples a) PDT-1 and b) PMT-2 (solvent
DMSO-d6) . . . . . . . . . . . . . . . . . . . . . . . . . 80











x
















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


SYNTHESIS AND CHARACTERIZATION OF
STEREOBLOCK POLYMERS OF POLY(METHYL METHACRYLATE)

By

Martin A. Doherty
December 1984

Chairman: Thieo E. Hogen-Esch Major Department: Chemistry

It is well known that the isotactic and syndiotactic forms of poly(methyl methacrylate) (PMMA) differ considerably in their physical properties. For example, the glass transition temperature of syndiotactic PMMA (S-PMMA) is about 670C higher than that of isotactic PMMA (I-PMMA).

Several authors have shown that mixtures of S-PMMA and I-PMMA in certain solvents (i.e., DMSO, DMF, and CH3CN) result in stereocomplex formation. This stereocomplex is believed to reflect a physical association between the tactic homopolymers where I-PMMA helices are surrounded by S-PMMA helices.

Stereoblock polymers are unique materials, because they are homopolymers with long sequences of tactically distinct segments. The scientific literature has shown no examples of monodisperse stereoblock polymers with well-defined block integrity.


xi










In this investigation, the synthetic pathway for well-defined stereoblock polymers of PMMA was developed using anionic techniques. Using monofunctional anionic initiators, SI-PMMA stereoblock polymers were synthesized. These materials were then investigated with respect to their stereocomplexing ability. Comparisons between the SI-PMMA stereoblock polymer and mixtures of S- and I-PMMA homopolymers showed that intramolecular stereocomplexation occurred in the block polymer in addition to the established intermolecular stereocomplexation.

From bifunctional anionic initiators, both SIS- and ISI-PMMA stereoblock polymers were synthesized. A synthetic procedure was also developed for the synthesis of atactic PMMA (At-PMMA). Again, using a bifunctional anionic initiator, both SAtS- and IAtI-PMMA stereoblock polymers were synthesized. NMR analysis of a mixture of these two polymers in complexing solvents revealed that stereocomplexation occurred only between the isotactic and syndiotactic segments.

















xii
















CHAPTER I

INTRODUCTION

The homopolymers of syndiotactic poly(methyl methacrylate) (SPMMA) and isotactic poly(methyl methacrylate) (I-PMMA) are different not only with respect to the configurations of their pendant groups along the polymer backbone,1 but also with respect to many physical properties.2-4 For example, the temperature at which an amorphous polymer changes from a glassy solid to a rubbery material, called the glass transition temperature (T ), is 1050C for S-PMMA and 380C for I-PMMA.2

In 1961, it was demonstrated that mixtures of I-PMMA and S-PMMA in selected solvents resulted in gel formation5 This physical association between these tactic polymers, called stereocomplex formation,6 was shown to occur exothermically.7 X-ray data revealed that the stereocomplex resulted from an inner helix of I-PMMA surrounded by a helix of S-PMMA6'8 as illustrated in Figure 1.

The specific polymer interactions responsible for stereocomplex formation have been discussed by several authors.8-11 From their work involving complexation propensity between various isotactic and syndiotactic poly(alkyl methacrylates), Challa and Bosscher concluded that Van der Waals interactions between the I-PMMA methyl ester and the S-PMMA a-methyl group were responsible for stereocomplex



1







2



















Figure 1. Schematic representation of stereocomplex of isotactic
PMMA and syndiotactic PMMA







3



formation.8'9 Spevacek, who analyzed stereocomplex PMMA using NMR, concluded associations were due to ester group interactions.10'11 Regardless of the specific interactions, it appears that an optimum steric fit exists between the polymers comprising stereocomplex PMMA.

A result of stereocomplex formation is that the physical properties of the isolated complex are different from its constituent homopolymers.12'13 Specifically, differential scanning calorimetry (DSC), which detects thermal transitions, has shown that the T of both IPMMA and S-PMMA disappear with complexation. At the same time, a new thermal transition is detected at 205%C which has been attributed to the "melting" or decomposition temperature of the stereocomplex.12

There is also disagreement involving the stoichiometric ratio, (syndiotactic/isotactic) (S/I), for stereocomplex formation. From X-ray diffraction data on solid stereocomplexes, Liquori et al.6 proposed a S/I ratio of 2:1. Challa concluded from both DSC12 and reduced viscosity13,14 measurements that complexation also occurs at a S/I ratio of 2:1. Spevacek's NMR work suggested that S/I ratios depend on specific complexation solvents and the polymer tacticities involved in the complexation.10,11,15 For example, using the same IPMMA homopolymer, complexation ratios (S/I) changed from 1:1 to 2.2:1 when a S-PMMA polymer with an 88.5% syndiotactic triad content was replaced with one with 65%.15 With respect to complexation solvents, for the same I-PMMA and S-PMMA samples, the S/I complexation ratios were 2.2:1 in CD 3CN and 2:1 in CC4.15







4



Challa has classified solvents by their abilities to promote stereocomplex formation. He noted DMF, DMSO, THF and CH3CN were all strongly complexing solvents. Both CHC13 and CH2Cl2 were classified as non-complexing solvents.16

An interesting application resulting from the tendency of S-PMMA and I-PMMA to associate in particular solvents is the phenomenon of template polymerization.14,16-19 The radical polymerization of methyl methacrylate (MMA) in DMF, a complexing solvent, produces PMMA that is 64% triad syndiotactic. The same radical polymerization carried out in the presence of an I-PMMA matrix yields a PMMA that is 90% triad syndiotactic.17 By replacing the I-PMMA matrix with an S-PMMA matrix, I-PMMA is synthesized.1 7191n non-complexing solvents, in the presence of either I-PMMA or S-PMMA matrices, only conventional PMMA is synthesized.16

Stereoblock polymers (Figure 2) are unique systems because they are at the same time both homopolymers and block copolymers. They are homopolymers in the sense that the polymer chain contains a single monomer type. However, because the pendant groups along the backbone are arranged in distinctly different tacticities, they can be considered block copolymers.

Several authors20-23 have claimed to have synthesized stereoblock polymers of PMMA using Grignard initiators. However, their polymers contained randomly sequenced isotactic and syndiotactic segments of varying lengths. The polydispersities of their resulting polymers were large and often polymodal.




















R R




RR R R R

Figure 2. Configuration of stereoblock polymer.






6



Well-defined stereoblock polymers of PMMA would be interesting materials for several reasons. It is well established that in selected solvents I-PMMA and S-PMMA form stereocomplexes by intermolecular association.5-19 In an A-B24 stereoblock polymer of PMMA possessing well-defined isotactic (I) and syndiotactic (S) segments, because a covalent linkage connects tactic segments, there now exists the capability of forming intramolecular as well as intermolecular stereocomplexes.

An ABA24 stereoblock polymer of SIS-PMMA could be a very interesting material because the architecture places a segment of I-PMMA (soft segment, low T ) between segments of S-PMMA (hard segment, higher T ). If phase separation were to occur between the tactic segments (incompatability), the potential exists for the formation of thermoplastic elastomers. However, such behavior would only be exhibited at intermediate temperatures between the Tg's of the block segments and in polymers cast from a non-complexing solvent.

If stereocomplex formation were to occur only between I-PMMA and S-PMMA, then the mixing of isotactic-atactic-isotactic (IAtI) and syndiotactic-atactic-syndiotactic (SAtS) PMMA stereoblock polymers in complexing solvents should result in stereocomplexes embedded in an atactic matrix (Figure 3). Here the stereocomplexes would act as physical cross-links providing a network structure from a single chemical composition. From an application viewpoint, such a material should possess enhanced properties compared to conventional PMMA.






7

































Figure 3. Schematic representation of a mixture of IAtI- and SAtSPMMA stereoblock polymers ( boPcbo7 = stereocomplex, = At-PMMA).






8


Yuki et al.25,26 demonstrated that trityl methacrylate (TrMA) polymerized with anionic initiators in THF at -780C yielded isotactic poly(trityl methacrylate) (I-PTrMA). Under the same conditions, they showed that diphenylmethyl methacrylate yielded predominantly syndiotactic poly(diphenylmethyl methacrylate) (S-PDMA).26 Both these polymers could be hydrolyzed and methylated to PMMA (Scheme 1). Because hydrolysis and methylation does not involve the asymmetric backbone carbons responsible for chain tacticity, the original polymer tacticity is maintained during conversion to PMMA.27 Therefore, I-PMMA and S-PMMA can be synthesized from TrMA and DMA, respectively. It has also been demonstrated that under the same polymerization conditions (THF solvent at -780C), MMA can be polymerized to yield S-PMMA.28 However, PMMA obtained from MMA is less syndiotactic than PMMA obtained using DMA.


Scheme 1


In + TrMA THF I-PTrMA N I-PMMA
n - 7800 2 CH 1 H


I + DMA THFOH S-PDMA 1) H S-PMMA


There are several additional features which make anionic polymerization techniques attractive. First, it has been demonstrated by several workers that the anionic polymerization of various alkyl methacrylates leads to polymers having approximately the same size chain lengths or narrow molecular weight distributions.29-34 This






9


is an important quality if unambiguous correlations between polymer molecular weight and physical properties are to be determined. Second, in anionic polymerizations, selected monomers can be sequentially polymerized to yield block copolymers.35'36 AB block copolymers can be synthesized from the sequential polymerization of two monomers using a monofunctional initiator. ABA block copolymers can be synthesized using a bifunctional initiator (Scheme 2).

Scheme 2

AB Block Copolymer Synthesis:

+ M1 + M2 1
" +MI--> I-_M1 T I'I n 2+m_CH30H
+ - > I-M1N)-M2) H


ABA Block Copolymer Synthesis:

I + M1 Ml Ti-_1 I-1i1-A

+ M2
2 -M2 (M2 m-_(M 1 1I MI-~-M2-Tm 2

CH30H


I = initiator; CH30H = terminating agent; M1 = monomer 1;M2= monomer 2

By the sequential polymerization of TrMA to either DMA or MMA (or vice versa), the subsequent hydrolysis and methylation of the resulting block copolymer should yield stereoblock polymers of PMMA. Polymer






10



architecture can be controlled with selection of either monofunctional or bifunctional initiators. Segment distribution can be controlled by original initiator and monomer concentrations.

The purpose of this investigation can be described as follows:

1. Prepare a series of I-PMMA samples synthesized from TrMA

and S-PMMA samples synthesized from both MMA and DMA.

Examine these samples to determine polymer stereochemistry and molecular weight distributions.

2. Develop and optimize conditions necessary for the syntheses of well-defined AB and ABA stereoblock polymers

of PMMA containing S-PMMA and I-PMMA sequences.

3. Determine S/I complexation ratios using S-PMMA and IPMMA homopolymers for several strongly complexing solvents.

4. Study and compare stereocomplex formation between SIstereoblock PMMA and the corresponding I-PMMA and SPMMA homopolymers of the same tactic lengths.

5. Synthesize SI stereoblock polymers of PMMA with syndiotactic segments originating from both DMA and MMA.

Determine tacticity effects on stereocomplex formation

by comparison of these stereoblock polymers.

6. Develop a synthetic procedure for At-PMMA. Then, synthesize IAtI and SAtS ABA stereoblock polymers and

examine the mixture of these polymers in complexing

solvents.
















CHAPTER II

EXPERIMENTAL

All work involving carbanions was carried out under high vacuum

(10-6 mm Hg). The vacuum was generated by the combination of a mechanical pump (Welch Duo-Seal Vacuum Pump) and a mercury diffusion pump. All stopcocks and ground glass joints were lubricated with Dow Corning high vacuum silicone grease.

All glassware was constructed from pyrex using a natural gas/ oxygen torch. For work involving carbanions, glassware was treated in the following manner. First, an apparatus was rinsed successively with 2% HF, H20, and acetone. Then it was dried at 1100C in the drying oven. Prior to all reactions, further drying was carried out on the vacuum line by flame degassing which involved heating an evacuated apparatus with a torch.

THF was used as the solvent in all reactions involving carbanions. Three liters of THF were refluxed over Na/K alloy for several days. Two liters were then collected by distillation onto freshly cut Na metal. Additional Na and K were added to the THF along with 0.5 g of benzophenone. The solvent flask was attached to the vacuum line and degassed. After several hours the solvent became purple indicating presence of the benzophenone dianion which indicated the absence of water and oxygen.



11






12


Initiator Syntheses
Diphenylmethane and Diphenylethylene Purification

Both diphenylmethane (Eastman) and diphenylethylene (Aldrich) used in initiator syntheses were purified in the following manner. The initiator precursors (10 ml) were refluxed overnight on CaH2 in a 25 ml flask equipped with a reflux condenser and a CaSO4 drying tube. Both samples were then distilled under vacuum (pressure unrecorded) onto fresh CaH2. The precursors were then placed on an apparatus shown in Figure 4, attached to the vacuum line (10-6 mm Hg), and allowed to stir for several hours. Both samples were degassed and distilled into breakseal-equipped ampoules. Distillation was facilitated by the use of a hot air gun. Diphenylmethyllithium (Monofunctional Initiator)

Diphenylmethyllithium (DPML) was synthesized and purified in an apparatus illustrated in Figure 5. The apparatus was placed on the vacuum line (10-6 mm Hg) and flame degassed. The apparatus was then charged with argon, and 2.5 ml (4.0 x 10-3 mol) of n-butyllithium (1.6 M in hexane) was injected through a serum cap into the apparatus. Both argon and hexane were removed by distillation into a liquid nitrogen trap leaving behind the viscous yellow n-butyllithium. The apparatus was cooled to -780C using a dry ice-isopropanol bath, and the serum cap was sealed from the apparatus.

Dry THF was distilled into the apparatus, and 0.8 g (4.76 x 10-3 mol) of diphenylmethane was added from an ampoule through a breakseal. The reaction solution slowly turned orange and was allowed to stir at






13


































Figure 4. Apparatus for vacuum line purification of diphenylmethane
and diphenylethylene.






14














Diphenyln-BuLi methane













Wash
Ampoule





Figure 5. Apparatus for the synthesis and purification of
diphenylmethyll ithium (DPML).






15


room temperature for eight hours. THF was distilled from the apparatus leaving the solid yellow DPML salt. The apparatus was cooled to

-780C, and hexane (dried over Na/K alloy) was distilled into the flask. The apparatus was sealed from the vacuum line by torch, and the hexane was used to wash the hexane-insoluble DPML salt. Washings were carried out by pouring the hexane through a coarse fritted filter into a wash ampoule and then redistilling the hexane into the main body of the apparatus. After several washings the hexane was removed from the main body of the apparatus in the wash ampoule.

The apparatus was reattached to the vacuum line and cooled to

-780C. About 70 ml of THF was vacuum distilled into the apparatus to dissolve the DPML salt. The initiator was poured into a separate ampoule, removed by torch, and stored in the freezer at -200C.

DPML initiator concentrations were determined by gas chromatography (GC) using the following procedure. About a milliliter of DPML was terminated on the vacuum line with dry Mel (MeI dried over CaH2). The terminated DPML initiator was analyzed by GC to determine the presence of unreacted diphenylmethane (not removed in the hexane washings). In all analyses only negligible amounts of diphenylmethane were detected. A volume of the Mel terminated DPML salt was then mixed with an equal volume of diphenylmethane-THF solution of known concentration. The mixture was analyzed by GC, and the concentration of the unknown DPML initiator was determined by direct comparison of Mel-terminated DPML with diphenylmethane standard solution. Even though the GC used employed a flame ionization detector which responded to the number of carbon atoms a molecule possessed







16


(diphenylmethane, 13 C; DPML + Mel, 14 C), no corrections were made for detector response in the concentration determination of DPML.

To verify the use of the above concentration determination procedure, two solutions of known concentration were prepared: diphenylethylene (5.66 x 10-2 M) and diphenylmethane (5.26 x 10-2 M). The assumption was made that the diphenylethane was of unknown concentration. Using the above procedure and diphenylmethane as a standard, the concentration of diphenylethylene was determined to be 5.72 x 10-2 M.

1,1,4,4-Tetraphenylbutane Dianion Lithium

Lithium metal (-~1 g, 0.14 mol) was cut into small pieces and

placed through opening A into the apparatus shown in Figure 6 under Ar atmosphere. Opening A was sealed with a torch. The apparatus was attached to the vacuum line (10-6 mm Hg), flame degassed, and cooled to -780C. Dry THF was distilled into the vessel, and 0.9 g (0.005 mol) of diphenylethylene was added from an ampoule through a breakseal. The reaction mixture slowly became blood-red and was allowed to stir overnight at room temperature.

The apparatus was sealed from the line by a torch, and the bloodred 1,1,4,4-tetraphenylbutane lithio dianion (DPE Li+)2 was poured through a coarse fritted filter into a breakseal-equipped ampoule. The (DPE-Li+)2 ampoule was then separated by a torch from the main body of the apparatus. The (DPE-Li )2 was reattached to an apparatus (Figure 7) where it was purified using the same procedure used to purify DPML (see diphenylmethyllithium).






17












Diphenylethylene

























Figure 6. Apparatus for the synthesis of 1,1,4,4-Tetraphenylbutane
dianion lithium (DPE-Li+)2.






18










(DPE Li+ )

















Wash
Ampoule Figure 7. Apparatus for the purification of 1,1,4,4-Tetraphenylbutane dianion lithium (DPE-Li+)2.






19


The concentration of (DPE'Li )2 was determined by GC using the same procedure used to determine DPML concentrations. However, since the number of carbon atoms of each sample detected by the GC's flame ionization detector differed to a large extent (diphenylmethane standard, 13 C; CH3I terminated initiator, 30 C), direct comparisons between GC integrated intensities could not be made. Therefore, the uneven detector response was compensated for by multiplying the directly determined initiator concentration (from integrated peak intensities) by a factor of 13/30.

Monomer Synthesis and Purifications Methyl Methacrylate (MMA)

In a 100 ml round-bottom flask equipped with a reflux condenser and a CaSO4 drying tube, 50 ml of methyl methacrylate (Aldrich) was stirred over CaH2 at room temperature for eight hours. The methyl methacrylate (MMA) was then distilled under reduced pressure (unrecorded), and CaH2 was added to the distillate. The distillate was then attached to the apparatus shown in Figure 8, placed on the vacuum line, and allowed to sit for several hours. The monomer was then degassed and distilled at room temperature into a breaksealequipped ampoule cooled to O'C. The ampoule was then removed from the line by a torch.

The MMA ampoule was attached to an apparatus (Figure 9) capable of generating a sodium mirror. With the apparatus open to the vacuum line (10-6 mm Hg), the reservoir containing Na metal (-1.0 g) was heated with a torch until sodium vapors condensed in the main body of the apparatus. The deposited sodium resembled a mirror surface. The







20



































Figure 8. Apparatus for the vacuum line drying of methyl methacrylate
over CaH2.







21










Methyl
methacrylate





















Sodium metal Figure 9. Apparatus for the vacuum line drying of methyl methacrylate
over a sodium mirror.






22


apparatus was closed to the vacuum line, and the MMA was introduced onto the metal. After 30 minutes the MMA was distilled at room temperature and subdivided into ampoule-equipped breakseals cooled to 00C. The MMA was stored in the freezer at -200C. Silver Methacrylate (AgMA)37

Methacrylic acid (49.02 ml, 0.57 mol) was placed in a 500 ml

three-neck flask equipped with a mechanical stirrer and two addition funnels. The flask was placed in an ice bath, and 34.6 ml (0.57 mol) of NH40H was added dropwise. Ammonium methacrylate precipitated as a white solid, and the reaction was stirred at OOC for 15 minutes. The reaction was warmed to room temperature, and 96.96 g (0.57 mol) of AgNO3 (dissolved in 100 ml of deionized water) was added dropwise to the ammonium methacrylate. The reaction was stirred for two hours, and the silver methacrylate (AgMA) product was a gray precipitate.

AgMA was separated by filtration and recrystallized from boiling H20. The final product was first dried in the vacuum oven overnight at room temperature then further dried on the vacuum line (10-6 mm Hg) for 24 hours. The AgMA was stored under high vacuum in flasks equipped with high vacuum stopcocks (Figure 10). Yields of 65% were obtained after purification.

Trityl Methacrylate (TrMA)37

Tritylchloride (50 g, 0.180 mol) was recrystallized from a mixture of 20 ml benzene and 5 ml acetyl chloride8 The tritylchloride was allowed to recrystallize for two hours at 00C and then collected by filtration. The yellow trityl chloride crystals were washed with cold petroleum ether which contained several drops of acetyl chloride.







23
























0


















Figure 10. Apparatus for the storage of solid materials under high
vacuum.







24


The trityl chloride was then stored under high vacuum in flasks equipped with high vacuum stopcocks (Figure 10).

AgMA (32 g (1.6 mol) suspended in dry ether (freshly distilled from CaH2) was placed in a 500 ml three-neck flask equipped with an addition funnel, a reflux condensor (with CaSO4 drying tube), a mechanical stirrer, and a heating mantel.

Trityl chloride (34.7 g, 0.125 mole) (dissolved in 100 ml of dry ether) was added to the AgMA-ether suspension. The reaction was refluxed for three hours. AgCl was collected by gravity filtration, and the ether filtrate was condensed on the rotoevaporator. The crude trityl methacrylate (TrMA) was purified first by a hot filtration using dry ether and activated charcoal then two simple recrystallizations from dry hexane. Final product yields were 62% or less. The TrMA was ground to a fine powder and stored under high vacuum (Figure 10). TrMA was characterized by melting point, elemental analysis, and 60 MHz 1H NMR.

m.p.: 100-101C (literature 101-103�C).39

Elemental Analysis Found: C, 84.26; H, 6.29%. Calculated for C23H2002: C, 84.12; H, 6.14%.
1H NMR: 7.30 ppm, multiplet (15 H); 6.20 ppm, singlet (1 H);

5.50 ppm, singlet ( H); 2.0 ppm, singlet (3 H). Diphenyl Methyl Methacrylate (DMA)26

AgMA (38.5 g, 0.200 mol) and dry ether were placed in a 500 ml

three-neck flask equipped with a reflux condenser, mechanical stirrer, addition funnel, and heating mantle. Diphenylmethylchloride (31.31 g, 27.46 ml, 0.155 mol, Aldrich) was added to the flask at room







25


temperature. The reaction mixture was refluxed for eight hours with stirring. AgCl was separated by filtration, and the concentration of the ether filtrate yielded the crude diphenylmethyl methacrylate (DMA). The DMA was purified by two hot filtrations using hexane and activated charcoal. Product yields were 74% or less. DMA was characterized by melting point, elemental analysis, and 100 MHz 1H NMR.

m.p.: 790C (literature 790C).26

Elemental Analysis Found: C, 80.58; H. 6.52%. Calculated for C17H1602: C, 80.92; H, 6.39%.

1H NMR: 7.30 ppm, multiplet (10 H); 6.93 ppm, singlet (1 H), 6.52 ppm, singlet (1H), 5.63 ppm, singlet (1H); 2.00 ppm, singlet (3 H).

Polymerization Reactions

Formation of Homopolymers

Polymerizations were carried out by two methods depending on whether the monomer was solid (DMA or TrMA) or liquid (MMA).

Poly(diphenylmethyl methacrylate) (PDMA) and Poly(trityl methacrylate) (PTrMA). A predetermined amount of solid monomer was placed in a vessel illustrated in Figure 11, and the monomer addition opening was sealed with a torch. The monomer vessel was evacuated on the vacuum line (10-6 mm Hg) for several hours. The ampoule was then cooled to -780C, and THF was distilled through the vacuum line into it. The vessel was sealed from the line and stored in the freezer at

-200C.

DMA and TrMA homopolymerizations were carried out in an apparatus depicted in Figure 12. The apparatus was placed on the vacuum line







26


































Figure 11. Apparatus used to prepare THF solutions of diphenylmethyl
methacrylate or trityl methacrylate.







27








Diphenylmethyl methacrylate or Trityl methacrylate Initiator


























Figure 12. Apparatus-used in the homopolymerizations of diphenylmethyl methacrylate or trityl methacrylate.







28


(10-6 mn Hg), cooled to -780C, and approximately 100 ml of dry THF was vacuum distilled into it. The apparatus was sealed from the line by torch and warmed to room temperature. A THF solution containing the initiator [DPML or (DPE'Li+)2] was then added to the flask through a breakseal. Any residual initiator clinging to the ampoule was washed into the THF by application of a cold dauber to the initiator ampoule. The vessel was cooled to -780C, and the monomer solution was added to the initiator. After monomer addition, the colored initiator solution immediately became colorless (a slight yellow color was observed sometimes in TrMA polymerizations). After allowing the reaction to proceed for a given time, the apparatus was reattached to the vacuum line. Termination was accomplished by the distillation of MeOH into the reaction.

The polymer solution was precipitated in a 10-fold volume excess of either MeOH or hexane. The polymer was collected by filtration and dried in the vacuum oven at room temperature for several days.

Poly(methyl methacrylate) (PMMA). Purified MMA was divided in vacuo (10-6 mm Hg) into ampoules equipped with breakseals. The MMA homopolymerizations and polymer workups were similar to those of the DMA and TrMA homopolymerizations, with the exception that MMA was added to the initiator solution by an in vacuo distillation into the reaction vessel (Figure 13).

Block Copolymer Reactions

Block copolymers were synthesized by the sequential polymerization of either DMA and TrMA or MMA and TrMA. DPML initiator was used to synthesize AB block copolymers, and (DPE-Li+)2 initiator was used to synthesize ABA triblock copolymers.






29










Initiator Methyl methacrylate



















Figure 13. Apparatus used in the homopolynierization of methyl
methacrylate.







30


All block copolymer reactions (either AB or ABA) were carried out in apparatus depicted in Figures 14 and 15. The apparatus shown in Figure 14 was designed for the synthesis of block copolymers synthesized from MMA and TrMA and the apparatus in Figure 15 for block copolymers synthesized from DMA and TrMA. Block copolymerizations were carried out as described previously for the homopolymer reactions with the additional step that after the first monomer had been allowed to polymerize for a specific time, the second monomer was added and allowed to polymerize. Polymer terminations and workups were identical to those described for the homopolymer syntheses. PDMA, TrMA Random Copolymers

The same procedures used in the syntheses of PDMA and PTrMA

homopolymers were employed in the syntheses of PDMA, TrMA random copolymers. The only modification in the random copolymer syntheses was that predetermined amounts of DMA and TrMA monomers were mixed together and stored in the same ampoule prior to polymerization.

Polymer Hydrolysis

PTrMA26

About one gram of PTrMA was refluxed in 50 ml of methanol containing 5% HC1 for four hours. During the hydrolysis the originally insoluble PTrMA went into solution. The solution was condensed, and the residue was dissolved in a minimum amount of MeOH. The resulting polymethacrylic acid (PMA) was precipitated in cold ether and collected by vacuum filtration. The polymer was dried overnight in a vacuum oven at room temperature. NMR measurements of the corresponding PMMA (see diazomethane methylation) indicated quantitative hydrolysis.






31







Initiator Trityl methacrylate Methyl
methacrylate















Figure 14. Apparatus used in the synthesis of poly(methyl
methacrylate)-trityl methacrylate block copolymers.






32




Initiator Diphenylmethyl methacrylate
Trityl
methacrylate
























Figure 15. Apparatus used in the synthesis of poly(diphenylmethyl
methacrylate)-trityl methacrylate block copolymers.







33


PDMA

Approximately one gram of PDMA was refluxed in 50 ml of methanol containing 10% HCl for at least seven days. During the first five days, the originally insoluble polymer slowly went into solution. After hydrolysis, the solution was condensed and dissolved in a minimum amount of MeOH. The PMA was precipitated in ether and collected by vacuum filtration. The polymer was dried overnight at room temperature in a vacuum oven. Incomplete hydrolysis was detected by two methods. First, ether is a good solvent for PDMA and a poor solvent for PMA; therefore, any difficulty precipitating PMA in ether suggested incomplete hydrolysis. Second, NMR analysis of the corresponding PMMA (see diazomethane methylation) would exhibit larger than expected aromatic absorptions. Some aromatic absorptions are expected because both initiators, DPML and (DPE Li+)2, contain phenyl substituents. For incompletely hydrolyzed PDMA samples, the hydrolysis procedure was continued for several more days. Random Copolymers (PDMA-TrMA)

Random PDMA-TrMA was hydrolyzed by the same procedure used for the hydrolysis of PDMA.

PDMA-TrMA Block Copolymers

The hydrolysis procedure used for PDMA was also employed for all block copolymers containing PDMA segments. PMMA-TrMA Block Copolymers

Block copolymers containing PMMA and PTrMA segments were hydrolyzed in the same manner as PTrMA homopolymers. Under these conditions, only the PTrMA segments hydrolyzed resulting in a PMMA-MA block







34


copolymer. This polymer was difficult to separate from other hydrolysis products because good solvents for one polymer segment are poor solvents for the other. PMMA-MA was finally isolated by washing the condensed hydrolysis product in a mixture of ether and slightly acidic H20. The polymer precipitated at the solvent interface, was collected by filtration, and dried overnight in a vacuum oven.

Diazomethane Methylation40

Poly(methacrylic acid) and PMA copolymers were methylated to PMMA using the following procedure. A diazomethane (CH2N2) generating apparatus (Figure 16) was constructed from three 250 ml thick-wall centrifuge bottles, condensing jacket with screw cap fittings, long-stem separatory funnel with a teflon stopcock, rubber stoppers, and firepolished glass tubing.

Approximately 10 ml of ether was placed in both collection vessels (B and C) which were cooled in an ice-salt bath. KOH (2.0 g,

0.036 mol), 4 ml H20, 4 ml ether and 13 ml (0.097 mol) of 2-(2-ethoxyethoxy)ethane (Kodak) were placed in centrifuge bottle A. The solution was heated to 700C using a H20 bath. N-methyl-N-nitroso-p-toluene-sulfonamide (Diazald, Aldrich) dissolved in 40 ml of ether was added dropwise to A, and immediately CH2N2 was generated and distilled with ether into B and C.

The CH2N2-ether solution was added to hydrolyzed polymer samples40 (0.1 g polymer suspended in 10 ml of ether). Gas evolution was detected, and the polymer samples slowly dissolved. Additional CH2N2 was added to each sample, and the samples were allowed to sit overnight.































B C Stirring hot plate




Figure 16. Apparatus used in the generation of diazomethane.






36


The samples were then condensed, and their residues dissolved in CHC13. The polymers were precipitated in cold hexane, collected by vacuum filtration, and dried for several days in the vacuum oven.

Instrumentation

Gas Chromatography (GC)

Gas chromatographic analyses were carried out on a Hewlett Packard Model 5880A instrument equipped with a flame ionization detector. Separations were made on a 50 meter SE-54 silicone gum capillary column (Hewlett Packard) using helium as a carrier gas. Nuclear Magnetic Resonance (NMR)

Proton NMR spectra were obtained on either a Varian EM-360L or a JEOL FX-100 high resolution spectrometer. Chemical shifts are expressed in parts per million (ppm) downfield from tetramethylsilane (TMS) unless otherwise stated. Polymer proton spectra were carried out with a 1.985s acquisition time and a 100 ms pulse delay.

NMR studies of PMMA stereochemistry were carried out in either CDC13 (55�C) or DMSO-d6 (120%C). For a given sample, the tacticity measurements were identical in either solvent. For PMMA the chemical shifts of the a-methyl protons are most sensitive to polymer configuration. Therefore, triad tacticity information was obtained by integration of the a-methyl resonances. All polymer configurations are expressed in terms of triad tacticities.

All expected tacticities of the stereoblock polymers were calculated from the following equations:






37


I = lI1 + n 212

H = nlH1 + n2H2

S = nlS1 + n2S2

I, H, S = expected triad tacticities of the stereoblock polymer; I1, H1, SI = triad tacticities of PMMA homopolymer represented in

segment 1;

12, H2, S2 = triad tacticities of PMMA homopolymer represented in

segment 2;

n1, n2 = mole fractions of monomer 1 and monomer 2, respectively,

used in the synthesis of the stereoblock polymer. Differential Scanning Calorimetry (DSC)

DSC measurements were obtained on a Perkin Elmer DSC-1B model calorimeter. Scan speeds of 100C per minute were used. The glass transition temperatures (T ) were recorded at the onset on that thermal transition. Indium metal was used for machine calibration. Gel Permeation Chromatography (GPC)

GPC analyses were carried out at room temperature using a Waters 6000 liquid chromatograph. Two w-styragel columns of 103 and 104 A permeability ranges were used in series. Samples were detected by a Waters differential refractometer or a Perkin Elmer LC-75 UV spectrometric variable wavelength detector. Polymer solutions (200 ul, 0.2 g/dl) were analyzed in either CHC13 or THF. Samples run in CHC13 were detected using both the refractive index and UV (240 nm) detectors. Samples run in THF were detected with the UV detector.(214 nm).






38


From the GPC chromatogram, number average molecular weights (Mn), weight average molecular weights (Mw) and molecular weight distributions (Mw/Mn) were determined. The Mn represents a molecular weight value for an average chain in a polymer sample. The number average molecular weight is defined as

Mn = ENxMx

where Nx is the number fraction of molecules of size Mx.

The Mw places emphasis on the weight fraction of molecules in a polymer sample. The weight average molecular weight is defined as


Mw = EX Mx

where Xx is the weight fraction of molecules whose weight is MxThe Mw/Mn reflects the polydispersity for a polymer sample. A value of Mw/Mn = 1 represents a monodisperse sample where all polymer molecules are of the same chain length.

Mn and MW values were determined by computer analysis41of a GPC chromatogram using a PMMA calibration curve. In all analyses, corrections were made for column band broadening caused by diffusion. The PMMA calibration curve (molecular weight versus retention volume) was generated from a universal calibration curve based on polystyrene standards and appropriate Mark-Houwink constants for both polystyrene and PMMA.42

Segment Molecular Weight Calculations

The isotactic and syndiotactic relative segment molecular weights were calculated from the stereochemical composition of the stereoblock






39


polymers and the tacticities of the respective PMMA homopolymers comprising the individual segments of the stereoblock polymer.

The triad tacticities of the stereoblock polymers are a weighted average of the tacticities in the individual segments so that: MI = M1 1 + M212 (1) where M, M1 and M2, and I, Il and 12 refer to the molecular weights and isotactic content of the stereoblock polymer and the two tactic segments, respectively. M was assumed to be equal to Mn obtained from GPC analysis.

Since M = M1 + M2, and letting p = M2/M1, the relationship


p = (11 - 1)/( -12) (2) can be derived from Equation 1.

Similarly, Equations 3 and 4 can be derived in an analogous manner:

p = (SI - S)/(S - S2) (3) p = (H1 - H)/(H - H2) (4) where S, S1 and S2, and H, H1 and H2 refer to the syndiotactic and heterotactic contents of the stereoblock polymers and their corresponding segments.

For AB stereoblock polymers, the reported segment molecular weights were obtained from averaging values determined from I and S analysis.






40



For ABA stereoblock polymers, the total segment molecular weights were determined in the same manner as the AB stereoblock polymers. The reported values for the individual A segments were obtained by dividing the total A molecular weight by two.
















CHAPTER III

POLYMER SYNTHESES AND CHARACTERIZATIONS

In order to gain an understanding of the stereoblock polymers of PMMA and to determine conditions necessary for their syntheses, the monomers corresponding to the possible block segments (TrMA, DMA and MMA) were homopolymerized and converted to PMMA. These PMMA homopolymers were then analyzed for tacticity, initiator efficiency and molecular weight distributions.

The stereochemical assignments obtained from PMMA prepared from TrMA, DMA or MMA provide information that can ascertain the block integrity of stereoblock PMMA. Any deviations between expected tacticity values and actual NMR determined tacticity values can be explained by incomplete monomer polymerization of either segment.

Initiator efficiency and corresponding PMMA molecular weight

distributions from the homopolymer experiments can provide information as to whether a monomer can be polymerized to a predetermined segment length. Good agreement between a targeted and actual PMMA molecular weight coupled with a narrow molecular weight distribution suggests a fast and efficient initiation process. Such results indicate that the subsequent polymerization proceeds in the absence of any chain transfer reactions. This information in turn would suggest stereoblock polymers can be synthesized with monodisperse segments of varying lengths.

41






42


PMMA Homopolymers Synthesized From TrMA, DMA and MMA Homopolymers Prepared With Monofunctional Initiators

Diphenylmethyllithium (DPML) was used to initiate the homopolymerizations of TrMA, DMA, and MMA in order to prevent initiator attack at the monomer carbonyl carbon.3 Table 1 lists the results for PMMA synthesized from TrMA, DMA, and MMA. In all cases, each polymer is monodisperse, and there is generally good agreement between the calculated Mn and the Mn obtained from GPC analyses. These results suggest an efficient initiation process.

Table 1

PMMA Homopolymer Analyses From TrMA, DMA, and MMAa PMMA M Triad Tacticity Mb (GPC) Sample Monomer I H S n (calc.) Mn

PT-1 TrMA 91 8 1 4200 3950 1.11 PD-1 DMA 2 14 84 8300 6780 1.07 PM-1 MMA 2 24 74 3300 2679 1.17 a All polymerizations carried out in THF at -780C. b Determined from degree of polymerization ([monomer]/[initiator])

x 100 (molecular weight of MMA).


The tacticity values for the PMMA homopolymers synthesized from DMA and TrMA agree with literature values.26 However, the 74% syndiotactic content obtained from MMA is noteworthy, because literature values for MMA polymerized in THF at -780C are often much lower (e.g.,







43


56%).28 The reasons for these discrepancies can be attributed to the manner in which the monomer is added to the reaction flask. The literature values reflect the addition of MMA in large quantities; this causes a warming of the reaction solution due to the exothermicity of the reaction. Thus, the higher syndiotactic content probably reflects a better temperature control caused by the slow vapor distillation of MMA into the reaction vessel.

In order to demonstrate the effect of reaction temperature on PMMA polymer tacticity, MMA was polymerized at -1030C in an etherliquid N2 bath. The polymer was 80% syndiotactic, and the polydispersity was very large as determined by visual inspection of the GPC chromatogram.

Table 2 lists additional PMMA samples synthesized from TrMA, DMA, and MMA. All samples have narrow molecular weight distributions, and PMMA tacticities for the various monomers are identical to those listed in Table 1. Discrepancies between calculated and GPC Mn values are probably due to inaccuracies in initiator concentrations.

In the homopolymerization of TrMA to high degrees of polymerization (DP), the polymer reaction often turned white and in some cases became viscous, almost gel-like. This was not surprising because Okamoto et al.44 have demonstrated that PTrMA becomes insoluble in common organic solvents with DP's greater than 60. Nevertheless, in a TrMA homopolymerization, the product was readily hydrolyzed and converted to I-PMMA. Tables 1 and 2 show that the resulting PMMA's







44



Table 2

Molecular Weight Data for PMMA Homopolymers
Synthesized From TrMA, DMA, and MMA

M M M (GPC) M Sample n w M G n
Designation Monomer (GPC) (GPC) n (Calculated)a

PT-2 TrMA 26,800 31,900 1.19 15,000 PT-3 TrMA 12,500 13,500 1.08 23,000

PD-2 DMA 18,900 20,400 1.07

PD-3 DMA 21,500 24,700 1.15 7,800 PM-2 MMA 3,447 3,982 1.15 7,000 PM-3 MMA 11,739 13,234 1.12 15,000 PM-4 MMA 77,653 90,234 1.24 80,000

a Determined from degree of polymerization ([monomer]/[initiator])

x 100 (molecular weight of MMA).


are monodisperse indicating that the apparent inhomogeneity in the polymerization mixture did not adversely affect the molecular weight distributions.

Horopolymers Prepared With Bifunctional Initiators

Warzelhan et al.45 showed that the syndiotactic content of PMMA was significantly lowered in going from a monofunctional to a bifunctional sodium initiator in THF at low temperatures (Table 3).

Since syndiotactic content in PMMA generally increases with de28
creasing reaction temperature, the differences here cannot be due to different reaction temperatures. The differences were attributed to






45



Table 3

PMMA Tacticity Using Sodium Counterion Initiators

Temperature Triad Tacticity Counterion Solvent (C) I H S

Na THF -61 4 36 58 Na Bifunctional THF -75 39 41 20


intramolecular association of ion pairs for the bifunctional sodium initiator (Figure 17). This was claimed to result in an alteration at the propagation site.




CH3 OCH3

C: Na 0O C
C--I
C=0 Na :C

OCH3 CH3


Figure 17. Schematic representation for intramolecular association
for bifunctional sodium initiator in THF.

In order to determine if tacticity is maintained in changing from a monofunctional lithium initiator to a bifunctional lithium initiator, DMA, TrMA and MMA were all homopolymerized using 1,1,4,4tetraphenyl butane lithium dianion (DPE-Li+)2. (DPE-Li+)2 was synthesized by the reaction of Li metal with diphenylethylene (Scheme

3).







46


Scheme 3


Ph Ph




Ph Ph
+j L , LiLi



S h, Li+ + Ph , Li Li Ph, Li+ Ph
Ph = phenyl Ph

Table 4 lists the tacticity and GPC data for the corresponding PMMA samples synthesized from DMA, TrMA, and MMA using (DPE'Li +)2 For comparison, data obtained from the DPML- initiation of these monomers are provided.

Table 4
Stereochemistry and GPC Data for
PMMA Prepared With Mono- and Bifunctional Lithium Initiators
Monofunctional Bifunctional
Initiator Initiator
PMMA PMMA
Monomer Triad Tacticity GPC Triad Tacticity GPC
I H S I H S

TrMA 91 8 1 Ma 90 7 3 Mb DMA 2 14 84 Ma - 17 83b Mb MMA 2 24 74 Ma - 17 83 Bc a (M) = Monomodal
b Measurement done PDMA c (B) - Bimodal







47



From Table 4, both TrMA and DMA show no major differences

between tacticity measurements or GPC results using monofunctional or bifunctional lithium initiators. Interestingly, with MMA, the syndiotactic content was somewhat higher, and the polymer had a bimodal distribution when the bifunctional lithium initiator was used. Whether these results indicate intramolecular associations of ion pairs is not entirely clear. In any event, subsequent reactions with bifunctional initiators were carried out with DMA and TrMA.

PMMA From Random Copolymerization of DMA and TrMA

The syntheses of well-defined block copolymers presupposes a complete polymerization of the first monomer prior to the addition of the second monomer. Anything short of complete conversion would result in a random copolymerization between the two monomers, and this could affect the block integrity of the second segment.

In order to determine how the stereochemistry of the second block segment in stereoblock PMMA is affected by incomplete polymerization of the first monomer, two random copolymers were synthesized using different molar ratios of DMA and TrMA. The corresponding PMMA tacticities are listed in Table 5. For comparison, PMMA tacticities obtained from DPML initiated monomers are provided.







48


Table 5

Random Copolymers From TrMA and DMA Monomer PMMA
Molar Ratios Triad Tacticities Sample DMA TrMA I H S

Random PDMA-TrMA 1 9 63 28 9 Random PDMA-TrMA 1 1 15 50 35 PTrMA 0 1 91 8 1 PDMA 1 0 1 15 84



The random copolymerization, at a TrMA/DMA molar ratio of 9:1,

illustrates the importance of complete monomer conversion of the first segment. In this experiment, only 10% DMA is present, but this translates into a 28% decrease in isotactic content compared to a segment polymerized from only TrMA. This sharp drop in isotactic content suggests considerable disruption in the stereoregularity of the chain upon DMA addition. This is not surprising, because several stereochemical consequences may result from DMA incorporation.

First, the addition of DMA to a predominantly isotactic living

chain may affect the stereochemistry of the last TrMA-TrMA (T-T) placement:





T T T T T T 0
m m m or
r
T = TrMA; D = DMA; m = meso; r = racemic






49


Second, the subsequent additions of the next few TrMA monomers may be influenced by the newly formed living DMA chain end and the stereochemistry resulting from its addition. These subsequent TrMA additions are likewise stereochemically distinct:






T T T D T T T D T
m m m m m
or or or
r r r





T T T D T T
m m m m
or or or
r r r

T = TrMA; D = DMA; m = meso; r = racemic


In all likelihood then, the random copolymerization between TrMA and DMA is a complex process, and the present data does not allow an unambiguous interpretation for DMA incorporation. However, by assuming that DMA units are randomly positioned in the polymer chain, the above results suggest DMA is incorporated in a syndiotactic fashion into a predominantly isotactic polymer backbone. This placement is depicted in Figure 18.







50



T T T T T T T T T





m m m m r r m m m m Tr = TrMA; D = DMA; m = meso; r = racemic

Figure 18. Random syndiotactic placement of DMA into PTrMA.

For each DMA addition, two mr and one rr triad sequences are

generated. This is not surprising because DMA has been shown to homopolymerize in a highly syndiotactic fashion under similar reaction conditions. The seven remaining triad sequences would reflect tacticities generated from TrMA homopolymerization (91% mm, 8% mr and 1% rr).

Based on these assumptions which suggest a syndiotactic placement of DMA into a predominantly isotactic PTrMA backbone (Figure 18), a random copolymerization of TrMA/DMA of 9:1 molar ratio is predicted to have the triad tacticities of 64%, I; 26%, H; 10% S. These predicted values are in excellent agreement with the experimentally determined results. It should be emphasized that similar tacticities could be generated by alternate mechanistic schemes.

The random copolymerization, TrMA/DMA of 1:1, provides a valuable approach for the synthesis of atactic poly(methyl methacrylate) (AtPMMA). This is shown by the 50% heterotactic content in the corresponding PMMA. By having the capability of generating At-PMMA sequences, the stereoblock copolymers of SAtS and IAtI can be synthesized.






51


An important finding from both random copolymerization experiments is that the copolymerization of TrMA with small amounts of DMA results in larger heterotactic content than PMMA homopolymers synthesized from only TrMA. AB Stereoblock PMMA Synthesized From DMA and TrMA

From the homopolymer studies, it was noted that viscous to gellike mixtures were observed in the polymerization of TrMA. Therefore, DMA was chosen as the first monomer to be polymerized in the AB PMMA stereoblock polymer syntheses. Scheme 4 depicts this overall process.
Scheme 4


-CH3 THF 3 -3 TrMA
hLi + P-0 iH2 HO iM "'DM O '0DM

CH CH CH
H21-Li+ MeOH
P--CH2----4CH2H--+--CHe-C L e PDMA-TrMA

02 '-ODM 0 'OTr 0 Tr

CH3 CH

PDMA-TrMA HC PCH-- C H
MeOH I ' n --- m C=O C=O
I I
OH OH

CH N CH3 CH3 Ph Ph CH2N2 1 1__, P
2 P-CH2 --(CH2 DM = -C-H ; Tr = -C-Ph

C= C=0 h Ph

CH3 CH3







52


From the random copolymer studies, it was demonstrated that small amounts of DMA could significantly alter the tacticity of I-PMMA synthesized from TrMA. With this understanding, well-defined block integrity depends on complete polymerization of the first monomer prior to the addition of the second monomer. In order to demonstrate this, three A-B stereoblock copolymers of PMMA were synthesized using different polymerization times of the PDMA segment (Table 6).

Table 6

Effect of DMA Polymerization Time on Stereoblock PMMA PMMA Triad Tacticities
Sample Expected Actual B.C.a M Desig. Sample I H S I H S Yield M n PDT-1 PDMA(60)b-TrMAc 39 12 49 21 17 62 86 1.09 PDT-2 PDMA(120)-TrMA 37 12 51 33 15 52 83 PDT-3 PDMA(145)-TrMA 46 11 42 44 11 45 87 a B.C. = DMIA-TrMA block copolymer b Polymerization time (minutes)

c TrMA polymerization time 180 minutes


When DMA was polymerized for 60 minutes, there was poor agreement between expected and actual NMR tacticity values. In view of the large heterotactic content displayed in the stereoblock copolymer, this suggests a random copolymerization between DMA and TrMA. By decreasing the DMA polymerization time to 120 minutes, this discrepancy between actual and expected tacticity values narrows considerably.







53



However, the larger than expected heterotactic content suggests some random copolymerization. Finally, a well-defined stereoblock copolymer of PMMA is produced by allowing DMA to polymerize for 145 minutes.

Table 7 lists several A-B stereoblock copolymers of PMMA synthesized from DMA and TrMA. The second two entries, samples PDT-4 and PDT-5, suggest some random copolymerization occurring between DMA and TrMA. For samples PDT-6 and PDT-7, the discrepancies between actual and expected triad tacticity data indicate an incomplete TrMA polymerization. This is reflected in lower than expected isotactic content coupled with expected heterotactic triad intensities. The much larger original block copolymer yield and closer agreement between expected and actual NMR data for PDT-7 as compared to PDT-6 is not readily explained. Even though TrMA was allowed to polymerize some 22 minutes longer in the former polymer, this does not appear to be sufficient reason to account for the observed differences. By allowing the TrMA block to polymerize for a long time (more than 12 hours), stereoblock copolymers having the desired tactic distributions were obtained (entries PDT-8 and PDT-9). AB Stereoblock PMMA Synthesized From MMA and TrMA

In order to determine how tacticity influences stereocomplex

formation, DMA was replaced by MMA in the syntheses of PMMA A-B stereoblock polymers. Homopolymer analysis showed that syndiotactic content was 10% lower for PMMA synthesized from MMA than that prepared from DMA. The A-B stereoblock polymers of PMMA obtained from MMA and TrMA were synthesized in the same manner as those obtained from TrMA and DMA (Scheme 4),the exception being thatMMAwas substituted for DMA.








Table 7

AB Stereoblock Polymers of PMMA From TrMA and DMA PMMA
Monomer Polymerization DMA-TrMA Block Triad Tacticities M Approximate
Sample Time (Hr) Copolymer Expected Actual Segment MW Designation DMA TrMA Yield I H S I H S n I S PDT-1 2.41 3.0 87 46 11 42 44 11 45 1.09 2070 2320 PDT-4 2.75 3.15 55 46 11 42 14 16 70 1.15 - PDT-5 2.3 3.0 66 46 11 42 21 19 60 1.23 PDT-6 3 2.75 50 46 11 42 15 13 74 - - PDT-7 2.75 3.15 89 31 13 56 27 10 63 1.24 8100 22200 PDT-8 3.6 >12 71 31 13 56 32 9 59 1.25 7093 15106 PDT-9 3 -24 95 37 12 51 38 14 48 1.22 9637 13361







55



In order to determine whether MMA polymerization time affects block integrity, two experiments were carried out in which only the polymerization time of MMA was varied. These results are listed as PMT-1 and PMT-2 in Table 8.

Both PMT-1 and PMT-2 show good agreement between actual and expected triad tacticities. Random copolymerization between monomers is not observed in either case. This is not surprising since the polymerization of MMA is expected to occur much faster than, for instance, that of DMA or TrMA.

Table 8 also lists additional PMMA stereoblock polymers synthesized from MMA and TrMA. None of the experiments indicate any random copolymerization between MMA and TrMA. Discrepancies between the expected and actual triad tacticities may be attributed to incomplete TrMA polymerizations.

ABA Stereoblock Polymers From DMA and TrMA

The syntheses of ABA stereoblock polymers of PMMA were carried out using the bifunctional initiator (DPE'Li+)2. Table 9 lists several ABA stereoblock polymers of PMMA synthesized from various combinations of DMA and TrMA. Because homopolymer analysis indicated a bimodal polymer distribution for bifunctionally initiated MMA, this monomer was not used in the ABA stereoblock polymer syntheses.

Deviations between expected and actual tacticity values can be explained either by incomplete polymerization of the second monomer (PTDT-1) or a random copolymerization between the two monomers (PDTD-2, PDTD-3).








Table 8

A-B Stereoblock Polymers of PMMA From MMA and TrMA MMA-TrMA PMMA M Approximate Monomer Polymerization Block Triad Tacticities w Segment
Sample Time (Hr) Copolymer Expected Actual - Molecular Weights Designation MMAa TrMA Yield I H S I H S n I S

PMT-1 0.5 3 46 16 37 49 15 36 1.11 5100 4620 PMT-2 1.0 3 - 46 16 37 51 12 37 1.13 4690 4160 PMT-3 0.75 3 51 32 18 50 17 15 68 1.13 2260 15740 PMT-4 0.75 3 45 46 16 37 23 15 62 1.12 2620 10480 PMT-5 0b 2.66 49 33 21 58 11 17 72 1.15 1100 16000 PMT-6 0b 6 81 33 18 49 26 15 59 1.16 3950 12750 a MMA polymerization time starts after total MMA added into reaction vessel. b TrMA added immediately after MMA monomer addition.








Table 9

Various ABA Stereoblock Copolymers of PMMA Original PMMA
PMMA Block Triad Tacticities MW
Sample Tactic Copolymer Expected Actual Approximate Designation Sequence Yield I H S I H n Segment Lengths PTDT-1 ISI 75 46 11 43 34 13 53 1.37 3.350-11,600-3,350 PDTD-2 SIS 85 26 13 61 14 25 61 1.18 PDTD-3 SIS 100 31 13 56 22 19 59 1.20 PT(DT)T-4 IAtI 91 48 31 21 51 30 19 1.31 2,000-4400-2,000a PD(DT)D-5 SAtS 94 8 32 60 6 31 63 1.19 3,000-4500-3,000b a Approximate segment lengths determined from isotactic analysis, p= (I1-)/I-12). b Approximate segment lengths determined from syndiotactic analysis, p = (S1-S)/(S-52).






58



Since it was demonstrated that equimolar quantities of DMA and TrMA randomly copolymerize to yield a corresponding atactic PMMA (At-PMMA), two stereoblock polymers were polymerized having atactic central segments [PT(DT)T-4 and PD(DT)D-5]. In both experiments, there was good agreement between expected and actual triad tacticity values.
















CHAPTER IV

STEREOCOMPLEX ANALYSIS OF STEREOBLOCK POLYMERS OF PMMA AND PMMA HOMOPOLYMERS

Introduction

In addition to the synthesis of stereoblock polymers of PMMA,

another key research objective was to compare stereocomplex formation resulting from stereoblock polymers with stereocomplex formation resulting from mixtures of isotactic and syndiotactic homopolymers. Because the respective tactic segments in the stereoblock polymer are covalently linked, stereocomplex formation is expected to be enhanced in this system. This results from the possibility that intramolecular associations can now occur in addition to the expected intermolecular association.

High resolution 1H-NMR has been shown to be a convenient technique for analyzing stereocomplex formation between I-PMMA and SPMMA.10,11,15 The mobilities of the protons involved in the stereocomplex are greatly reduced; therefore, the integrated intensities of these protons are broadened to such an extent that NMR detection does not occur. Only the protons corresponding to non-associated monomer units are observed.15

Stereocomplex formation has been shown to be a thermally reversible process. In certain solvents, the stereocomplexes are manifested



59






60



by the formation of visible gels. Several authors have observed that these gels dissociate over a very narrow temperature range.5'46 This dissociation has been interpreted as the "melting" of the stereocomplex. The actual temperature where "melting" occurs is influenced by the stereoregularity of the constituent homopolymers; the more stereoregular the polymer, the higher its dissociation temperature. At temperatures well above the dissociation temperature, it can be assumed that almost no complexed material exists. Because of this and since only uncomplexed PMMA is detected by the NMR, fractions of uncomplexed PMMA can be determined from the integrated peak intensities at any temperature. To illustrate the effects of temperature on stereocomplexed PMMA, Figure 19 shows the NMR of sample PMT-2 taken at various temperatures.

Stereocomplex Formation Studies

Investigation of the Stereocomplex Equilibrium

In order to study stereocomplex formation by NMR, it must first be determined whether the ratio of complexed and uncomplexed polymer reflects a true thermodynamic equilibrium. This appears to be the case. First, the changes observed in the NMR spectra when heating or cooling were always rapid and did not change once a constant temperature was attained. Second, the integrated intensities (relative to an internal standard) remained constant regardless of the preceding thermal treatment of the sample. Thus, the same integrated intensity was observed at a particular temperature regardless whether this temperature was reached by cooling or heating.
















Methylene a-Methyl proton
proton absorptions
absorptions








Temperature
(oC)
63


57



42

34

U- 25

2.5 2.0 1.5 1.0 0.5 ppm

Figure 19. 100 MHz 1H-NH'iR spectra of sample PMT-2 (syndiotactic segment molecular weight = 4160; isotactic segment molecular weight = 4960) recorded at
various temperatures. (* = solvent)






62


Homocomplexation of S-PMMA and I-PMMA in DMSO

A potential complication in analyzing stereocomplex formation between I- and S-PMMA is that these respective homopolymers have been shown to undergo self-association. Like stereocomplex formation, this self-association has been shown to be dependent on homopolymer tacticity as well as the particular solvent used in the analysis. For example, in toluene, more than 70% of the monomer units are associated in 85% triad syndiotactic PMMA. However, no complex formation is observed with 66% triad syndiotactic PMMA in the same solvent.47 The self-association process observed in S-PMMA has been shown to be thermally reversible with the aggregates dissociating between 406000.48

With respect to I-PMMA, about 20% of the monomer units are associated in CD3CN.49 These aggregates have been shown to be thermally stable, and they dissociate at temperatures in excess of 1600C.

To determine if self-association occurs in addition to stereocomplex formation, the integrated intensities of I-PMMA and S-PMMA were measured both at room temperature and at temperatures exceeding 800C. The samples were analyzed using various NMR acquisition times and pulse delays, and the results are listed in Table 10. All analyses were performed in DMSO-d6, and the reported intensity ratios were determined relative to an internal standard.

For all samples, the integrated intensities obtained at the higher temperatures are between 40-60% larger than those at room temperature. Since both I-PMMA and S-PMMA responded in a similar fashion,






63



Table 10

Homocomplexation Analyses of S-PMMA and I-PMMA Samples
PD-4a PT-2 PT-2 (S-PMMA) (I-PMMA) (I-PMMA) Intensity Ratiob 1.62c 1.40c 1.56d

Acquisition Time(s) 1.98 1.98 -~8 Pulse Delay(s) 0.1 0.1 ~2

a PD-4: GPC(M n) = 51,800.
b
Integrations were made from total a-methyl and methylene regions of PMMA spectra, and the reported ratio reflects
the high temperature intensity divided by the 250C intensity.
c High temperature intensity determined at 830C.

High temperature intensity determined at 930C.


and since I-PMMA self-association has been shown to break up at temperatures exceeding 160*C, these data suggest that self-association is not occurring for either I- or S-PMMA in DMSO. At this time, the larger integrated intensity values observed at higher temperatures cannot be adequately explained. However, since this intensity enhancement is observed, it can be expected to also occur in the temperature analyses of stereocomplex formation thereby rendering that analysis semi-quantitative at best.







64



Comparison of Stereocomplexation Between Stereoblock Polymers of
PMMA With Mixtures of I-PMMA and S-PMMA

In order to properly compare complexation in stereoblock PMMA with mixtures of syndiotactic and isotactic homopolymers, the individual segment lengths and segment tacticities of the stereoblock sample should be identical to those in the respective homopolymers.

Two sets of samples were analyzed in DMSO-d6. In the first set, designated Series A, a SI-PMMA stereoblock polymer was compared to a mixture of S- and I-PMMA homopolymers in which all tactic segments were synthesized from MMA or TrMA. In the second sample set, designated Series B, similar polymers were analyzed with the exception that the syndiotactic segments in both the stereoblock polymer and S-PMMA homopolymer were generated from DMA. Table 11 describes the individual samples in both Series A and Series B.

Each sample was analyzed at several temperatures, and peak integrations (representing uncomplexed material) were determined from the proton absorptions in the a-methyl region. In all measurements, peak integrations were calibrated with hexamethyldisiloxane or the residual DMSO solvent peak. For the sample measurements taken at 98*C, the corresponding integrations were assumed to represent the complete dissociation of the stereocomplex. The integrated intensities obtained at lower temperatures were then normalized to the integrated intensity obtained at 980C; these values represent the amount of uncomplexed material at that given temperature. The fractions of complexed material for the samples in Series A and Series B measured at various temperatures are given in Table 12.






65



Table 11

Samples Used in Series A and Series B Series A
Mn (GPC) of Sample Sample Sample Sample Tactic Segments Weight Concentration Designation Architecture I S (g) (Molar)a

PMT-6 SI-PMMA 3950 12,750 0.0198 0.396 PM-3 S-PMMA - 11,739 0.0135 0.270
+
PT-1 I-PMMA 4200 - 0.0058 0.116 Series B
PDT-8 SI-PMMA 7350 15,650 0.0110 0.22

PD-3 S-PMMA - 21,500 0.0071 0.142
+
PT-3 I-PMMA 12,500 - 0.0039 0.078 a Based on MW of methyl methacrylate.


Table 12

Fraction of Complexed Polymer for Mixtures of PMMA Homopolymers and for Stereoblock PMMA
in Series A and Series B at Various Temperatures Series A Series B Temperature Complexed Material Complexed Material
(�C) AB A+B AB A+B
25 0.90 0.81 0.991 0.865 39 0.87 0.71 0.974 0.837 54 0.73 0.43 0.895 0.790

67 0.61 0.12 0.95 0.38

98 0 0 0 0







66



Since the integrated intensities of the I- and S-PMMA homopolymers have been shown to increase at higher temperatures relative to an internal standard, the possibility of this occurring in the stereocomplex analysis cannot be ruled out. However, its effect should be relatively minor compared to the observed intensities that reflect the dissociation of the stereocomplex, and semiquantitative comparisons between the samples in Series A and Series B should be valid particularly since signal enhancement of I- and S-PMMA was shown to be almost identical.

From Figures 20 and 21 for Series A and Series B, respectively, it can be seen that complexation is more extensive for the PMMA stereoblock polymer than for the mixture of S-PMMA and I-PMMA homopolymers. This indicates that intramolecular complex formation is indeed occurring in the A-B stereoblock polymers in addition to the expected intermolecular stereocomplexation.

By extrapolation of the A+B sample curves in both Series A and Series B (Figures 20 and 21, respectively), it is predicted that these samples would be largely dissociated between 70-800C. In this temperature range, the stereocomplexes generated from the PMMA stereoblock polymers in both Series A and Series B would be approximately 60% complexed. These results suggest that intramolecular complexation results in a more thermally stable stereocomplex as compared to intermolecular complexation.

For Series B where the syndiotactic components are more stereoregular, Table 12 indicates that stereocomplex formation for both the
















1.0
g 0.9 A u 0.8 8
0.7 g A

0.6 A & 0.5
Uo 0.4
0.3 0.2 0.1

20 30 40 50 60 70 80 Temperature (OC) Figure 20. Complexation as a function of temperature for samples
A-B and A+B in series A. Sample A-B, A ; sample A+B,














1.0 yv
0.9 U0.8 0 u- 0.7

0.6

S0.5
E 0.4 0.3 0.2 0.1

20 30 40 50 60 70 80 Temperature (OC) Figure 21. Complexation as a function of temperature for samples A-B
and A+B in series B. Sample A-B, V ; sample A+B, .







69



block polymer and the homopolymer mixture is more extensive than for their respective counterparts in Series A. However, this assessment is strictly qualitative since different tactic lengths are being compared.

Concentration Effects on Stereocomplex Formation

In order to determine the effect of concentration with respect to stereocomplex formation, both the A-B and A+B samples in Series A were diluted fifteen-fold. The percent of complexed polymer for both concentrated and dilute samples as a function of temperature are given in Figure 22. By comparing the A+B concentrated sample to the A-B diluted sample, it can be seen that stereocomplex formation is more extensive in the stereoblock polymer. Whether this is due to intra- or intermolecular complex formation, or both, remains to be determined.

Effect of PMMA Stereoregularity on Stereocomplex Formation

Determination of S-PMMA/I-PMMA Stereocomplex Ratios for PMMA Homopolymers Synthesized From DMA and TrMA
Spevacek observed that the stereochemistry of both the S- and

I-PMMA homopolymers influenced the S-PMMA/I-PMMA (S/I) ratio observed in their resulting stereocomplex.10,11,15 In order to compare the S/I stereocomplex ratio between PMMA homopolymers synthesized from DMA and TrMA, various weight ratios of the corresponding S-PMMA and I-PMMA were analyzed by 1H-NMR in both CD3CN and DMSO-d6. The spectra obtained in CD3CN are shown in Figure 23, and similar spectra were obtained in DMSO-d6.













1.0
S0.9 A
0.8 9
0.7
T0.6
x0.5 A

S0.4 al
0.3

0.2 �
0.1

20 30 40 50 60 70 80 Temperature (OC)
Figure 22. Complexation effects with dilution of samples A-B
and A+B in series A. A-B concentrated, A ; A-B dilute,A ; A+B concentrated, V ; A+B dilute, m






71




















a.

b.




d.





Figure 23. Effects of S-PMMA/I-PMMA eight ratios on a-methyl proton
absorptions from 100 MHz H-NMR spectra at 250C in CD3CN.
Weight ratios: a) 1.5, b) 2.0, c) 2.5, d) 3.0.
Mn (GPC) for I-PMMA = 26,800; Mn (GPC) for S-PMMA = 51,800,
with exception of sample (d) where Mn (GPC) = 21,500.
(* = solvent)







72



In Figure 23a, where the weight ratio of S/I is 1.5:1, only IPMMA absorptions are observed. Apparently, at this ratio all the SPMMA is involved in the stereocomplex. At a S/I ratio of 2:1 (Figure 23b), no discernible absorptions are detected in the a-methyl region (0.8-1.2 ppm). This indicates that all polymeric species are involved in the formation of the stereocomplex. This suggests that complexation between I-PMMA and S-PMMA, synthesized from DMA and TrMA, respectively, occurs at a S/I ratio of 2:1.

At a S/I ratio of 2.5:1, it is interesting to note that no discernible peaks are observed. However, at a 3:1 ratio, absorptions from S-PMMA are visible. This indicates that I-PMMA is involved in stereocomplex formation and that observed S-PMMA is in excess of the complex.

Spevacek, who studied stereocomplex formation in CD3CN, reported a S/I ratio of 1:1. The reason for the discrepancy between Spevacek's ratios11 and the ratios reported here is probably due to differences in the stereoregularity of the polymers (Table 13).

Table 13

I- and S-PMMA Tacticities Accounting for
Differences in S/I Ratios in CD3CN Triad Tacticities
PMMA Study I H S I-PMMA This research 91 8 1 I-PMMA Ref. 11 97 3 0 S-PMMA This research 2 14 84

S-PMMA Ref. 11 2.5 9 88.5






73



All stereocomplexes generated in CD3CN resulted in visible gel formation as evidenced by precipitation of the stereocomplex. However, as Figure 23 indicates, no excessive peak broadening or loss in resolution was observed. With DMSO-d6, no precipitates were observed.

Mixtures of I-PMMA and S-PMMA With At-PMMA

Stereocomplex formation has been shown to occur only between S-PMMA and I-PMMA, and the degree of complexation is influenced to a large extent by the stereoregularity of the polymer chains. Therefore, CD3CN solutions of I-PMMA and S-PMMA were mixed with At-PMMA, and the resulting mixtures were examined by NMR (Table 14).

Table 14

NMR Results For I-PMMA and S-PMMA Mixed With At-PMMA in CD3CN Expected NMR Observed Triad Tacticity Triad Tacticity Sample Mixture I H S I H S

I-PMMAa + At-PMMAb 57 24 19 57 24 19 S-PMMAc + At-PMMAb 12 35 53d 12 38 50

a I-PMMA: I, H, S of 91, 8, 1; M (GPC) = 26,800.

b At-PMMA: I, H, S of 16, 42, 42; Mn (GPC) = 23,200.

c S-PMMA: I, H, S of 2, 14, 84; M (GPC) = 51,800.

d Determined from high temperature tacticity analysis.


Because of the good agreement between the observed NMR tacticities and the expected values which were obtained assuming no complex formation, it appears that At-PMMA does not form stereocomplexes with







74



either I-PMMA or S-PMMA. The absence of complex formation is further suggested because no precipitation was observed in either CD3CN solution. This was not the case for mixtures of S-PMMA and I-PMMA in CD3CN, where stereoassociation resulted in precipitation of the stereocomplex.

Analysis of Stereocomplex Formation From SAtS- and IAtI-PMMA Stereoblock Polymers

The formation of stereocomplexes between PMMA stereoblock polymers having an IAtI and SAtS architecture would be of interest, because complex formation should involve only the isotactic and syndiotactic segments. In such a mixture, the stereocomplexed material would serve as physical crosslinks which would be superimposed on an At-PMMA matrix (Figure 3). From an application viewpoint, as a result of such crosslinks, the mechanical properties of these complexed polymers would be expected to be very different from the mechanical properties of conventional PMMA.

It was demonstrated in CD3CN that mixtures of I-PMMA and S-PMMA, synthesized from TrMA and DMA, respectively, complexed in an S/I ratio of 2:1 to 2.5:1. Also, neither of these tactic homopolymers appeared to form stereocomplexes with At-PMMA. Assuming that these observations hold for a mixture of CD3CN solutions of IAtI and SAtS stereoblock polymers, an expected triad tacticity value can be determined. By heating such a mixture above the melting temperature of the stereocomplex, the expected tacticity should reflect values assuming no complexation. The results of such an experiment are given in Table 15. Here equal weights of samples PT(DT)T-4 and PD(DT)D-5 were mixed







75



in CD3CN. The good agreement observed between expected and actual tacticity values,both at room temperature and at 700C, suggests that stereocomplex formation does occur between isotactic and syndiotactic segments.

Table 15

Temperature and Tacticity Study on Mixture of
IAtI- and SAtS-PMMA Stereoblock Polymers in a Complexing Solvent Triad Tacticity
I H S

PT(DT)T-4 (IAtI) Room Expecteda 23 45 32
+ NMRb 23 43 34 PD(DT)D-5 (SAtS) 70C Expectedc 30 30 40 NMR 27 33 40

a Calculated assuming S/I ratio of 2:1 and complete formation of
stereocomplex.
NMR sample tube contained visible precipitate. c Calculated assuming no stereocomplex formation.


Effect of Segment Molecular Weight on Stereocomplex Formation

The minimum I- and S-PMMA segment lengths required to generate stereocomplexes have been discussed by several authors.15'46 Spevacek suggested that for S-PMMA that is 66% syndiotactic, ten monomer units and three monomer units are necessary for complexation to occur in benzene and CH3CN, respectively.15 Spevacek's analyses employed the same I-PMMA sample (97% isotactic with respect to triad tacticity) in all his studies. Ryan, who studied complex formation of various samples of I-PMMA with a standard syndiotactic polymer, concluded that a






76



minimum of eight isotactic monomer units are required for stereocomplexation.46 It is interesting to note that almost all previous conclusions on minimum sequence lengths were deduced from studies performed on very high molecular weight polymers and polymers with broad molecular weight distributions.

To assess segment length effects on stereocomplex formation, both GPC and NMR analyses were employed. The samples involved in this study along with their GPC and NMR results are listed in Table 16.

Table 16

GPC and NMR Analyses on Stereocomplex Formation on SI-PMMA Stereoblock Polymers GPC (Mw/Mn)
Tactic Lengths CHC1 a b
Sample S I 3 THF NMR PDT-1 2320 2070 1.09 1.13a 1.68 PMT-2 4160 4690 1.13 1.55a 2.70

PDT-4c - - 1.15 Broadd

PDT-8 15102 7093 1.25 Broade 102.88 PDT-9 13361 9637 1.22 - 19.97

a Monomodal GPC chromatogram.

b Ratio of intensities at 830C and 250C; both intensities
were determined against an internal standard. All high temperature analyses were measured at 830C with the exception of PDT-8 whose high temperature analysis was
measured at 980C.
c Total polymer molecular weight (GPC in CHC13) = 18,000;
approximate segment lengths: I = 2,500; S = 16,500.
GPC chromatogram displayed a trimodal distribution.

e GPC chromatogram displayed three high molecular weight
shoulders.-






77



Although THF has been described as the most common GPC solvent, it nevertheless has pronounced effects on the analyses of the stereoblock polymers of PMMA. With the exception of sample PDT-1, the GPC.analyses for the samples listed in Table 16 show that those run in THF, cited as a strongly complexing solvent, have broad molecular weight distributions and in some instances display visible polymodality. The same samples run in CHCl3 are both monodisperse and monomodal.

The GPC analysis of sample PDT-1 is virtually identical in either THF or CHC13. These results suggest that the effects of complexation observed in THF for entries PMT-2, PDT-4, and PDT-8 are not occurring in sample PDT-1.

To illustrate the effects of complexation, Figure 24 depicts the GPC chromatograms of samples PDT-4 and PDT-8, both analyzed in THF and CHCl3. It is apparent from the THF analyses that complexation is manifested by both a broadening of the GPC chromatogram and also the appearance of additional peaks in the higher molecular weight region (lower count number). For the same samples run in CHC13, the resulting GPC chromatograms are both monomodal and monodisperse.

NMR was used to assess chain length effects in stereocomplex formation by comparing integrated peak intensities at room temperature with those obtained at temperatures exceeding 800C. From Table 16, with the exception of PDT-1 and PMT-2, all samples analyzed in DMSO-d6 by NMR showed large high temperature to low temperature integrated intensity ratios. This reflects extensive stereocomplexation processes in these samples.












I, II I * aI
I iI
I I












* ..... I ... I � 1 ai" "
I I, I I














a) PD- n ) D-.*On on 09a1
a 1
I I Il

I S
I a


II a.





ai a

i



- I



18 16 14 12 10 (counts) 10 12 14 16 1820(ons*


Figure 24. GPC chromatograms run in THF - and CHC13- for samples
a) PDT-4 and b) PDT-8. * One count =0.95 ri.







79



It is interesting to compare the NMR results listed in Table 16 for the samples PDT-1 and PMT-2. Over the temperature range studied, the integrated intensity for sample POT-1 increased by a factor of 1.68. However, it was previously shown that the integrated intensities increased by similar order of magnitudes for homopolymer samples, where it was concluded that no self-association was occurring. Therefore, this observation suggests little or no stereocomplex formation is occurring in PDT-I. The intensity increase by a factor of 2.7 for sample PMT-2 does suggest complexation is indeed occurring at room temperature.

Further evidence supporting the contention that complexation does occur in PMT-2 and not PDT-1 is shown by the NMR spectra of these two samples where one measurement was taken at room temperature and.the other at 125C (Figure 25).

For sample PDT-1, the isotactic, heterotactic, and syndiotactic c-methyl absorptions can clearly be distinguished at room and high temperatures. However, large differences can be detected for PMT-2 where all syndiotactic absorptions disappear at room temperature as a consequence of stereocomplex formation.

In conclusion, GPC and NMR evidence suggests sample PDT-1 undergoes very little or no room temperature complexation in DMSO-d6. Because the polymer contains approximately 20 monomer units in the isotactic segment and 23 monomer units in the syndiotactic segment, the minimum repeat unit responsible for complex formation is seemingly larger than what has been reported in the literature.






80






a) PDT-1 250C 1250C










2 1 ppm 2 1 ppm b) PMT-2 250C 1250C











I I I I
2 1 ppm 2 1 ppm



samples a) PDT-1 and b) PMT-2 (solvent DMSO-d6).







81



DSC Investigation on Stereoblock Polymers

Materials that exhibit thermoplastic elastomeric properties are usually ABA block copolymers. The central B block is often a segment having a low glass transition temperature, Tg, whereas the A segments often exhibit a much higher Tg. An important criterion for ABA thermoplastic elastomers is that the individual A and B segments must be incompatible with one another.

In order to determine if a PMMA stereoblock polymer with an SIS architecture could potentially exhibit thermoplastic elastomeric properties, the glass transition temperatures of several PMMA samples were determined by DSC. These results are listed in Table 17.

Table 17

DSC Analysis for Various PMMA Samples Polymer Segment Lengths Sample Architecture S I Tg (OC)

PM-5 S-PMMA 77,089 - 135 PI-1 I-PMMA - 35,000a 50 PDT-8 SI-PMMA 15,106 7,093 99

a PI-1 was synthesized by the reaction of MMA and diphenylhexyllithium in toluene. The reported Mn value was determined by the equation [monomer]/[initiator] x 100,
where 100 equals the molecular weight of a methyl methacrylate monomer unit.


The observed Tg for sample PDT-8 listed in Table 18 suggests

that the isotactic and syndiotactic segments in this PMMA stereoblock







82



polymer are compatible. This is concluded from the fact that only one Tg was observed in the DSC (if two polymers are incompatible, individual Tg's are observed). Also, the value of the observed Tg is approximately equal to a weighted average for the Tg's of its individual segments (see PM-5 and PI-1 for Tg's for S- and I-PMMA segments). Since the isotactic and syndiotactic segments in PDT-8 appear to be compatible, such compatibility would be expected to also exist in a SIS-PMMA stereoblock polymer. This then would rule out the possibility that these materials would act as thermoplastic elastomers.















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3. J.M. O'Reilly, H.E. Bair and F.E. Karasz, Macromolecules 15,
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8. F. Bosscher, G.T. Brinke and G. Challa, Macromolecules 15, 1442
(1982).

9. F. Bosscher, D.W. Keekstra and G. Challa, Polymer 22, 124 (1981). 10. J. Spevacek and B. Schneider, Makromol. Chem. 176, 729 (1975). 11. J. Spevacek and B. Schneider, Colloid and Polym. Sci. 258, 621
(1980).

12. E.L. Feitsma, A. deBoer and G. Challa, Polymer 16, 515 (1975). 13. E.J. Vorenkamp and G. Challa, Polymer 22, 1705 (1981). 14. R. Buter, Y.Y. Tan and G. Challa, J. Polym. Sci.-Polym. Chem. Ed.
11, 989 (1973).

15. J. Spevacek and B. Schneider, Makromol. Chem. 175, 2939 (1974). 16. R. Buter, Y.Y. Tan and G. Challa, J. Polym. Sci.-Polym. Chem. Ed.
11, 2975 (1973).



83







84


17. R. Buter, Y.Y. Tan and G. Challa, J. Polym. Sci. A-1 10, 1031
(1972).

18. G. Challa and Y.Y. Tan, Pure and Appl. Chem. 53, 627 (1981). 19. R. Buter, Y.Y. Tan and G. Challa, J. Polym. Sci.-Polym. Chem. Ed.
11, 1003 (1973).

20. P.E. Allen and C. Mair, Eur. Polym. J. 20, 697 (1984). 21. T. Miyamoto and H. Inagaki, Polym. J. 1, 46 (1970). 22. P.E. Allen and B.O. Bateup, Eur. Polym. J. 14, 1001 (1978). 23. A. Nishioka, H. Watanabe, K. Abe and Y. Sono, J. Polym. Sci. 48,
241 (1960).

24. AB and ABA designate polymer backbone architecture. Segment A
may be either chemically or configurationally distinct from
segment B.

25. H. Yuki, K. Hatada, Y. Kikuchi and T. Niinomi, J. Polym. Sci.,
Part B 6, 753 (1968).

26. H. Yuki, K. Hatada, T. Niinomi and Y. Kikuchi, Polym. J. 1, 36
(1970).

27. T. Tsuruta, T. Makimoto and H. Kanai, J. Macromol. Chem. 1, 31
(1966).

28. H. Yuki, K. Hatada, K. Ohta and Y. Okamoto, Appl. Polym. Symp.
26, 39 (1975).

29. A. Roig, J.E. Figueruelo and E. Llano, J. Polym. Sci., Part B 3,
171 (1965).

30. G.M. Guzman and A. Bello, Makromol. Chem. 107, 46 (1967). 31. G. Lohr and G.V. Schulz, Eur. Polym. J. 10, 121 (1974). 32. R. Kraft, A.H.E. Muller, V. Warzelhan, H. Hocker and G.V. Schulz,
Macromolecules 11, 1093 (1978).

33. A. Muller, Makromol. Chem. 182, 2863 (1981). 34. H. Jeuck and A.H. Muller, Makromol. Chem., Rapid Commun. 3, 121
(1982).

35. M. Szwarc, "Carbanions Living Polymers and Electron Transfer
Processes," John Wiley and Sons, Inc., New York, 1968, Chapter 2.






85



36. A. Noshay and J.E. McGrath, "Block Copolymers Overview and
Critical Survey," Academic Press, Inc., New York, 1977, Chapter4.

37. Synthetic procedures for both AgMA and TrMA were obtained by
personal communication with Professor Yoshio Okamoto of Osaka
University, Japan.

38. B.S. Furniss, A.J. Hannaford, V. Rogers, P.W.G. Smith and A.R.
Tatchell, "Vogel's Textbook of Practical Organic Chemistry,"
Fourth Edition, Longman Group Limited, London, 1978, p. 608.

39. N.A. Adrova and L.K. Prokhorova, Vysokomol. Soedin. 3, 1509
(1961).

40. A. Katchalsky and H. Eisenberg, J. Polym. Sci. 6, 145 (1951).

41. The computer program for GPC analyses was developed by Dr.
Teng-shau Young using techniques adapted from W.W. Yau, J.J.
Kirkland and D.D. Bly, "Modern Size-Exclusion Liquid Chromatography," John Wiley and Sons, Inc., New York, 1979.

42. J. Brandrup and E.H. Immergut, "Polymer Handbook," Second Edition,
John Wiley and Sons, Inc., New York, 1975, Chapter IV.

43. A. Muller in "Anionic Polymerizations, Kinetics, Mechanisms,
and Synthesis," ACS Symposium Series 166, American Chemical Society, Washington, D.C., 1981, p. 441.

44. Y. Okamoto, K. Suzuki and H. Yuki, J. Polym. Sci.-Polym. Chem.
Ed. 18, 3043 (1980).

45. V. Warzelhan, G.V. Schulz and H. Hocker, Makromol. Chem. 181,
149 (1980).

46. C.F. Ryan and P.C. Fleischer, Jr., J. Phys. Chem. 69, 3385
(1961).

47. J. Spevacek. J. Polym. Sci.-Polym. Phys. Ed. 16, 523 (1978).

48. J. Spevacek, B. Schneider, M. Bohdanecky and S. Sikora, J.
Polym. Sci.-Polym. Phys. Ed. 20, 1623 (1982).

49. J. Spevacek and B. Schneider, Makromol. Chem. 176, 3409 (1975).
















BIOGRAPHICAL SKETCH Martin A. Doherty was born in Syracuse, New York, on November 15, 1956, at 6:56 a.m. He has been growing ever since.






































86













I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate,in scope and quality, as a dissertation for the degree of Doctor of Philosophy.




T7ieo E. Hogen-Egh, Chairman Professor of Chemistry


I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate,in scope and quality, as a dissertation for the degree of Doctor of Philosophy.




Charles L. Beatty Professor of Materials Science and Engineering


I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate,in scope and quality, as a dissertation for the degree of Doctor of Philosophy.




Wallace S. Brey, Jr. Professor of Chemistry











I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate,in scope and quality, as a dissertation for the degree of Doctor of Philosophy.




George B. Butler
Professor of Chemistry


I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate,in scope and quality, as a dissertation for the degree of Doctor of Philosophy.




William M. Jones
Professor of Chemistry


This dissertation was submitted to the Graduate Faculty of the Department of Chemistry in the College of Liberal Arts and Sciences and to the Graduate School, and was accepted for partial fulfillment of the requirements of the degree of Doctor of Philosophy.




Dean for Graduate Studies
December 1984 and Research




Full Text

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SYNTHESIS AND CHARACTERIZATION OF STEREOBLOCK POLYMERS OF POLY(METHYL METHACRYLATE) By MARTIN A. DOHERTY 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 1984

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To my parents, Joseph and Geraldine Doherty

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ACKNOWLEDGEMENTS The author wishes to thank his supervisory committee, Dr. Charles Beatty, Dr. Wallace Brey, and Dr. William Jones, for their assistance and support. The author personally wishes to thank Dr. George Butler for his discussions on areas both related and not related to chemistry. Special thanks and deep appreciation are directed to Dr. Thieo Hogen-Esch for his moral support, encouragement, patience, and friendship. The author would also like to acknowledge Marlene Hawthorne, Mark Eller, Ish Khan, and Patty Hickerson, for their assistance in maintaining the author's sanity throughout his graduate studies. Most of all, the author wishes to thank his parents, for without them, none of this would be possible.

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TABLE OF CONTENTS Page ACKNOWLEDGEMENTS iii LIST OF TABLES vii LIST OF FIGURES ix ABSTRACT xi CHAPTER I INTRODUCTION 1 II EXPERIMENTAL 11 Initiator Syntheses 12 Diphenylmethane and Di phenyl ethylene Purification. . 12 Diphenylmethyl lithium (Monofunctional Initiator) . . 12 1,1, 4, 4-Tetraphenyl butane Dianion Lithium 16 Monomer Synthesis and Purifications 19 Methyl Methacrylate (MMA) 19 Silver Methacrylate (AgMA) 22 Trityl Methacrylate (TrMA) 22 Diphenyl Methyl Methacrylate (DMA) 24 Polymerization Reactions 25 Formation of Homopolymers 25 Block Copolymer Reactions 28 PDMA, TrMA Random Copolymers 30

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CHAPTER p^ Polymer Hydrolysis 30 PTrMA 30 PDMA 33 Random Copolymers (PDMA-TrMA) 33 PDMA-TrMA Block Copolymers 33 PMMA-TrMA Block Copolymers 33 Diazomethane Methyl ati on 34 Instrumentation 36 Gas Chromatography 36 Nuclear Magnetic Resonance (NMR) 36 Differential Scanning Calorimetry (DSC) 37 Gel Permeation Chromatography (GPC) 37 Segment Molecular Weight Calculations 38 III POLYMER SYNTHESES AND CHARACTERIZATIONS 41 PMMA Homopolymers Synthesized From TrMA, DMA and MMA . . . 42 Homopolymers Prepared With Monofunctional Initiators. . 42 Homopolymers Prepared With Bifunctional Initiators. . . 44 PMMA From Random Copolymerization of DMA and TrMA 47 AB Stereoblock PMMA Synthesized From DMA and TrMA ... 51 AB Stereoblock PMMA Synthesized From MMA and TrMA ... 53 ABA Stereoblock Polymers From DMA and TrMA 55 IV STEREOCOMPLEX ANALYSIS OF STEREOBLOCK POLYMERS OF PMMA AND PMMA HOMOPOLYMERS 59 Introduction 59

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CHAPTER p a g e Stereocomplex Formation Studies 60 Investigation of the Stereocomplex Equilibrium .... 60 Homocomplexation of S-PMMA and I-PMMA in DMSO 62 Comparison of Stereocomplexation Between Stereoblock Polymers of PMMA With Mixtures of I-PMMA and S-PMMA 54 Concentration Effects on Stereocomplex Formation ... 69 Effect of PMMA Stereoregularity on Stereocomplex Formation 69 Determination of S-PMMA/ I -PMMA Stereocomplex Ratios for PMMA Homopolymers Synthesized From DMA and TrMA. . 69 Mixtures of I-PMMA and S-PMMA With At-PMMA 73 Analysis of Stereocomplex Formation From SAtSand IAtl-PMMA Stereoblock Polymers 74 Effect of Segment Molecular Weight on Stereocomplex Formation 75 DSC Investigation on Stereoblock Polymers 81 REFERENCES 83 BIOGRAPHICAL SKETCH 86

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LIST OF TABLES Table Page 1 PMMA Homopolymer Analyses From TrMA, DMA, and MMA 42 2 Molecular Weight Data for PMMA Homopolymers Synthesized From TrMA, DMA, and MMA 44 3 PMMA Tacticity Using Sodium Counterion Initiators 45 4 Stereochemistry and GPC Data for PMMA Prepared With Monoand Bifunctional Lithium Initiators 46 5 Random Copolymers From TrMA and DMA 48 6 Effect of DMA Polymerization Time on Stereoblock PMMA ... 52 7 AB Stereoblock Polymers of PMMA From TrMA and DMA 54 8 A-B Stereoblock Polymers of PMMA From MMA and TrMA 56 9 Various ABA Stereoblock Copolymers of PMMA 57 10 Homocomplexation Analyses of S-PMMA and I-PMMA 63 11 Samples Used in Series A and Series B 65 12 Fraction of Complexed Polymer for Mixtures of PMMA Homopolymers and for Stereoblock PMMA in Series A and Series B at Various Temperatures 65 13 Iand S-PMMA Tacticities Accounting for Differences in S/I Ratios in CD 3 CN 72 14 NMR Results for I-PMMA and S-PMMA Mixed With At-PMMA in CD-CN 73 15 Temperature and Tacticity Study on Mixture of IAtland SAtS-PMMA Stereoblock Polymers in a Complexing Solvent 75

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Table 16 GPC and NMR Analyses on Stereocomplex Formation on SI-PMMA Stereoblock Polymers Page 17 DSC Analysis for Various PMMA Samples. 76 81

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LIST OF FIGURES Figure p age 1 Schematic representation of stereocomplex of isotactic PMMA and syndiotactic PMMA 2 2 Configuration of stereoblock polymer 5 3 Schematic representation of a mixture of IAtland SAtS-PMMA stereoblock polymers 7 4 Apparatus for vacuum line purification of diphenylmethane and diphenylethylene 13 5 Apparatus for the synthesis and purification of diphenylmethyllithium (DPML) 14 6 Apparatus for the synthesis of 1,1,4,4-Tetraphenylbutane diam'on lithium (DPE _ Li + )„ 17 7 Apparatus for the purification of 1,1,4,4-Tetraphenylbutane dianion lithium (DPE-Li + )„ 18 8 Apparatus for the vacuum line drying of methyl methacrylate over CaH„ 20 9 Apparatus for the vacuum line drying of methyl methacrylate over a sodium mirror 21 10 Apparatus for the storage of solid materials under high vacuum 23 11 Apparatus used to prepare THF solutions of diphenylmethyl methacrylate or trityl methacrylate 26 12 Apparatus used in the homopolymerizations of diphenylmethyl methacrylate or trityl methacrylate 27 13 Apparatus used in the homopolymerization of methyl methacrylate 29

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Figure Page 14 Apparatus used in the synthesis of poly(methyl methacrylate)-trityl methacrylate block copolymers .... 31 15 Apparatus used in the synthesis of poly(diphenylmethyl methacrylate)-trityl methacrylate block copolymers 32 16 Apparatus used in the generation of diazomethane 35 17 Schematic representation for intramolecular association for bifunctional sodium initiator in THF 45 18 Random syndiotactic placement of DMA into PTrMA 50 19 100 MHz 1 H-WR spectra of sample PMT-2 (syndiotactic segment molecular weight = 4160; isotactic segment molecular weight = 4960) recorded at various temperatures 61 20 Complexation as a function of temperature for samples A-B and A+B in series A 67 21 Complexation as a function of temperature for samples A-B and A+B in series B 68 22 Complexation effects with dilution of samples A-B and A+B in series A 70 23 Effects of S-PMMA/I-PMMA weight ratios on a-methyl proton absorptions from 100 MHz 1h-NMR spectra at 25°C in CD 3 CN 71 24 GPC chromatograms run in THF and CHC1, for samples a) PDT-4 and b) PDT-8 78 25 Room temperature and high temperature 100 MHz l H-NMR spectra for samples a) PDT-1 and b) PMT-2 (solvent DMS0-d 6 ) 80

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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 SYNTHESIS AND CHARACTERIZATION OF STEREOBLOCK POLYMERS OF POLY (METHYL METHACRYLATE) By Martin A. Doherty December 1984 Chairman: Thieo E. Hogen-Esch Major Department: Chemistry It is well known that the isotactic and syndiotactic forms of poly(methyl methacrylate) (PMMA) differ considerably in their physical properties. For example, the glass transition temperature of syndiotactic PMMA (S-PMMA) is about 67°C higher than that of isotactic PMMA (I -PMMA). Several authors have shown that mixtures of S-PMMA and I-PMMA in certain solvents (i.e., DMSO, DMF, and CH-CN) result in stereocomplex formation. This stereocomplex is believed to reflect a physical association between the tactic homopolymers where I-PMMA helices are surrounded by S-PMMA helices. Stereoblock polymers are unique materials, because they are homopolymers with long sequences of tactically distinct segments. The scientific literature has shown no examples of monodisperse stereoblock polymers with well-defined block integrity.

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In this investigation, the synthetic pathway for well-defined stereoblock polymers of PMMA was developed using anionic techniques. Using monofunctional anionic initiators, SI-PMMA stereoblock polymers were synthesized. These materials were then investigated with respect to their stereocomplexing ability. Comparisons between the SI-PMMA stereoblock polymer and mixtures of Sand I-PMMA homopolymers showed that intramolecular stereocomplexation occurred in the block polymer in addition to the established intermolecular stereocomplexation. From Afunctional anionic initiators, both SISand ISI-PMMA stereoblock polymers were synthesized. A synthetic procedure was also developed for the synthesis of atactic PMMA (At-PMMA). Again, using a bifunctional anionic initiator, both SAtSand IAtl-PMMA stereoblock polymers were synthesized. NMR analysis of a mixture of these two polymers in complexing solvents revealed that stereocomplexation occurred only between the isotactic and syndiotactic segments.

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CHAPTER I INTRODUCTION The homopolymers of syndiotactic poly(methyl methacrylate) (SPMMA) and isotactic poly(methyl methacrylate) (I-PMMA) are different not only with respect to the configurations of their pendant groups along the polymer backbone, but also with respect to many physical properties. 2 " 4 For example, the temperature at which an amorphous polymer changes from a glassy solid to a rubbery material, called the glass transition temperature (T ), is 105°C for S-PMMA and 38°C for I-PMMA. 2 In 1961, it was demonstrated that mixtures of I-PMMA and S-PMMA in selected solvents resulted in gel formation.^ This physical association between these tactic polymers, called stereocomplex formation, was shown to occur exothermically. 7 X-ray data revealed that the stereocomplex resulted from an inner helix of I-PMMA surrounded by a helix of S-PMMA 6 ' 8 as illustrated in Figure 1. The specific polymer interactions responsible for stereocomplex formation have been discussed by several authors. 8 " 11 From their work involving complexation propensity between various isotactic and syndiotactic poly(alkyl methacrylates) , Challa and Bosscher concluded that Van der Waals interactions between the I-PMMA methyl ester and the S-PMMA a-methyl group were responsible for stereocomplex

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Figure 1. Schematic representation of stereocomplex of isotactic PMMA 2IZZ: and syndiotactic PMMA ^^ .

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8 9 formation. Spevacek, who analyzed stereocomplex PMMA using NMR, concluded associations were due to ester group interactions. 10 ' 11 Regardless of the specific interactions, it appears that an optimum steric fit exists between the polymers comprising stereocomplex PMMA. A result of stereocomplex formation is that the physical properties of the isolated complex are different from its constituent homo12 13 polymers. ' Specifically, differential scanning calorimetry (DSC), which detects thermal transitions, has shown that the T of both IPMMA and S-PMMA disappear with complexation. At the same time, a new thermal transition is detected at 205°C which has been attributed to the "melting" or decomposition temperature of the stereocomplex. 12 There is also disagreement involving the stoichiometric ratio, (syndiotactic/isotactic) (S/I), for stereocomplex formation. From X-ray diffraction data on solid stereocomplexes, Liquori et al. 6 proposed a S/I ratio of 2:1. Challa concluded from both DSC 12 and reduced viscosity 13 ' 14 measurements that complexation also occurs at a S/I ratio of 2:1. Spevacek's NMR work suggested that S/I ratios depend on specific complexation solvents and the polymer tacticities involved in the complexation. 10 ' 11 ' 15 For example, using the same IPMMA homopolymer, complexation ratios (S/I) changed from 1:1 to 2.2:1 when a S-PMMA polymer with an 88.5% syndiotactic triad content was replaced with one with 65%. 15 With respect to complexation solvents, for the same I-PMMA and S-PMMA samples, the S/I complexation ratios were 2.2:1 in CD,CN and 2:1 in CC1 15 o 4

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Challa has classified solvents by their abilities to promote stereocomplex formation. He noted DMF, DMSO, THF and CH.CN were all strongly complexing solvents. Both CHC1 3 and CH 2 C1 2 were classified as non-complexing solvents.''' 6 An interesting application resulting from the tendency of S-PMMA and I-PMMA to associate in particular solvents is the phenomenon of template polymerization. 14,16 " 19 The radical polymerization of methyl methacrylate (MMA) in DMF, a complexing solvent, produces PMMA that is 64% triad syndiotactic. The same radical polymerization carried out in the presence of an I-PMMA matrix yields a PMMA that is 90% triad syndiotactic. 17 By replacing the I-PMMA matrix with an S-PMMA matrix, I-PMMA is synthesized. 17,19 In non-complexing solvents, in the presence of either I-PMMA or S-PMMA matrices, only conventional PMMA is synthesized. 16 Stereoblock polymers (Figure 2) are unique systems because they are at the same time both homopolymers and block copolymers. They are homopolymers in the sense that the polymer chain contains a single monomer type. However, because the pendant groups along the backbone are arranged in distinctly different tacticities, they can be considered block copolymers. Several authors " have claimed to have synthesized stereoblock polymers of PMMA using Grignard initiators. However, their polymers contained randomly sequenced isotactic and syndiotactic segments of varying lengths. The polydispersities of their resulting polymers were large and often polymodal .

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Well-defined stereoblock polymers of PMMA would be interesting materials for several reasons. It is well established that in selected solvents I-PMMA and S-PMMA form stereocomplexes by intermolecu5-19 24 lar association. In an A-B stereoblock polymer of PMMA possessing well-defined isotactic (I) and syndiotactic (S) segments, because a covalent linkage connects tactic segments, there now exists the capability of forming intramolecular as well as intermolecular stereocomplexes. 24 An ABA stereoblock polymer of SIS-PMMA could be a very interesting material because the architecture places a segment of I-PMMA (soft segment, low T ) between segments of S-PMMA (hard segment, higher T ). If phase separation were to occur between the tactic segments (incompatability) , the potential exists for the formation of thermoplastic elastomers. However, such behavior would only be exhibited at intermediate temperatures between the T 's of the block segments and in polymers cast from a non-complexing solvent. If stereocomplex formation were to occur only between I-PMMA and S-PMMA, then the mixing of isotactic-atactic-isotactic (IAtl) and syndiotactic-atactic-syndiotactic (SAtS) PMMA stereoblock polymers in complexing solvents should result in stereocomplexes embedded in an atactic matrix (Figure 3). Here the stereocomplexes would act as physical cross-links providing a network structure from a single chemical composition. From an application viewpoint, such a material should possess enhanced properties compared to conventional PMMA.

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Figure 3. Schematic representation of a mixture of IAtland SAtSPMMA stereoblock polymers ( WcXfiC = stereocomplex, ^-V-^ = At-PMMA).

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or nc Yuki et al. ' demonstrated that trityl methacrylate (TrMA) polymerized with anionic initiators in THF at -78°C yielded isotactic poly(trityl methacrylate) (I-PTrMA). Under the same conditions, they showed that diphenylmethyl methacrylate yielded predominantly syndiotactic poly(diphenylmethyl methacrylate) (S-PDMA). 26 Both these polymers could be hydrolyzed and methylated to PMMA (Scheme 1). Because hydrolysis and methylation does not involve the asymmetric backbone carbons responsible for chain tacticity, the original polymer tacticity is maintained during conversion to PMMA. 27 Therefore, I-PMMA and S-PMMA can be synthesized from TrMA and DMA, respectively. It has also been demonstrated that under the same polymerization conditions (THF solvent at -78°C) , MMA can be polymerized to yield S-PMMA. However, PMMA obtained from MMA is less syndiotactic than PMMA obtained using DMA. Scheme 1 tmp CH~0H 1 . u + I n + TrMA -i^> —1^ I-PTrMA *j j^> I-PMMA THF CH^OH , + I n + DMA 4^> _J_> S-PDMA \]^ R > S-PMMA There are several additional features which make anionic polymerization techniques attractive. First, it has been demonstrated by several workers that the anionic polymerization of various alkyl methacrylates leads to polymers having approximately the same size chain lengths or narrow molecular weight distributions. 29 " 34 This

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is an important quality if unambiguous correlations between polymer molecular weight and physical properties are to be determined. Second, in anionic polymerizations, selected monomers can be sequentially polymerized to yield block copolymers. ' AB block copolymers can be synthesized from the sequential polymerization of two monomers using a monofunctional initiator. ABA block copolymers can be synthesized using a Afunctional initiator (Scheme 2). Scheme 2 AB Block Copolymer Synthesis: r + M i -> HVrf + " 2 > I ^ M l• W 2Vl W 2 CH..0H + — " > HMlWi" ABA Block Copolymer Synthesis: "I" N, — > -M^^H^Vrt ^^ -M 2 (M 2 ^ rT (M 1 Vl^ 1 V M 2tl M 2 CH,0H 'm I initiator; CH,0H = terminating agent; M. monomer 1 ; M. = monomer 2 By the sequential polymerization of TrMA to either DMA or MMA (or vice versa), the subsequent hydrolysis and methylation of the resulting block copolymer should yield stereoblock polymers of PMMA. Polymer

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10 architecture can be controlled with selection of either monofunctional or Afunctional initiators. Segment distribution can be controlled by original initiator and monomer concentrations. The purpose of this investigation can be described as follows: 1. Prepare a series of I-PMMA samples synthesized from TrMA and S-PMMA samples synthesized from both MMA and DMA. Examine these samples to determine polymer stereochemistry and molecular weight distributions. 2. Develop and optimize conditions necessary for the syntheses of well-defined AB and ABA stereoblock polymers of PMMA containing S-PMMA and I-PMMA sequences. 3. Determine S/I complexation ratios using S-PMMA and IPMMA homopolymers for several strongly complexing solvents. 4. Study and compare stereocomplex formation between SIstereoblock PMMA and the corresponding I-PMMA and SPMMA homopolymers of the same tactic lengths. 5. Synthesize SI stereoblock polymers of PMMA with syndiotactic segments originating from both DMA and MMA. Determine tacticity effects on stereocomplex formation by comparison of these stereoblock polymers. 6. Develop a synthetic procedure for At-PMMA. Then, synthesize IAtl and SAtS ABA stereoblock polymers and examine the mixture of these polymers in complexing solvents.

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CHAPTER II EXPERIMENTAL All work involving carbanions was carried out under high vacuum (10 mm Hg). The vacuum was generated by the combination of a mechanical pump (Welch Duo-Seal Vacuum Pump) and a mercury diffusion pump. All stopcocks and ground glass joints were lubricated with Dow Corning high vacuum silicone grease. All glassware was constructed from pyrex using a natural gas/ oxygen torch. For work involving carbanions, glassware was treated in the following manner. First, an apparatus was rinsed successively with 2% HF, H 2 0, and acetone. Then it was dried at 110°C in the drying oven. Prior to all reactions, further drying was carried out on the vacuum line by flame degassing which involved heating an evacuated apparatus with a torch. THF was used as the solvent in all reactions involving carbanions. Three liters of THF were refluxed over Na/K alloy for several days. Two liters were then collected by distillation onto freshly cut Na metal. Additional Na and K were added to the THF along with 0.5 g of benzophenone. The solvent flask was attached to the vacuum line and degassed. After several hours the solvent became purple indicating presence of the benzophenone dianion which indicated the absence of water and oxygen. II

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12 Initiator Syntheses Pi phenyl methane and Diphen.ylethylene Purification Both diphenylmethane (Eastman) and diphenylethylene (Aldrich) used in initiator syntheses were purified in the following manner. The initiator precursors (10 ml) were refluxed overnight on CaH 2 in a 25 ml flask equipped with a reflux condenser and a CaSO. drying tube. Both samples were then distilled under vacuum (pressure unrecorded) onto fresh CaH_. The precursors were then placed on an apparatus shown in Figure 4, attached to the vacuum line (10 mm Hg), and allowed to stir for several hours. Both samples were degassed and distilled into breakseal -equipped ampoules. Distillation was facilitated by the use of a hot air gun. Diphenylmethyl lithium (Honofunctional Initiator) Diphenylmethyl lithium (DPML) was synthesized and purified in an apparatus illustrated in Figure 5. The apparatus was placed on the vacuum line (10" mm Hg) and flame degassed. The apparatus was then charged with argon, and 2.5 ml (4.0 x 10" 3 mol ) of n-butyllithium (1.6 M in hexane) was injected through a serum cap into the apparatus. Both argon and hexane were removed by distillation into a liquid nitrogen trap leaving behind the viscous yellow n-butyllithium. The apparatus was cooled to -78°C using a dry ice-isopropanol bath, and the serum cap was sealed from the apparatus. Dry THF was distilled into the apparatus, and 0.8 g (4.76 x 10" 3 mol) of diphenylmethane was added from an ampoule through a breakseal. The reaction solution slowly turned orange and was allowed to stir at

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13 Figure 4. Apparatus for vacuum line purification of di phenyl methane and diphenylethylene.

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14 ^ aft/ JZ u Di phenyl n-BuLi niethane Figure 5. Apparatus for the synthesis and purification of di phenyl methyl lithium (DPML).

PAGE 27

15 room temperature for eight hours. THF was distilled from the apparatus leaving the solid yellow DPML salt. The apparatus was cooled to -78°C, and hexane (dried over Na/K alloy) was distilled into the flask. The apparatus was sealed from the vacuum line by torch, and the hexane was used to wash the hexane-insoluble DPML salt. Washings were carried out by pouring the hexane through a coarse fritted filter into a wash ampoule and then redistilling the hexane into the main body of the apparatus. After several washings the hexane was removed from the main body of the apparatus in the wash ampoule. The apparatus was reattached to the vacuum line and cooled to -78°C. About 70 ml of THF was vacuum distilled into the apparatus to dissolve the DPML salt. The initiator was poured into a separate ampoule, removed by torch, and stored in the freezer at -20°C. DPML initiator concentrations were determined by gas chromatography (GC) using the following procedure. About a milliliter of DPML was terminated on the vacuum line with dry Mel (Mel dried over CaH ? ). The terminated DPML initiator was analyzed by GC to determine the presence of unreacted diphenylmethane (not removed in the hexane washings). In all analyses only negligible amounts of diphenylmethane were detected. A volume of the Mel terminated DPML salt was then mixed with an equal volume of diphenylmethane-THF solution of known concentration. The mixture was analyzed by GC, and the concentration of the unknown DPML initiator was determined by direct comparison of Mel-terminated DPML with diphenylmethane standard solution. Even though the GC used employed a flame ionization detector which responded to the number of carbon atoms a molecule possessed

PAGE 28

16 (diphenylmethane, 13 C; DPML + Mel, 14 C), no corrections were made for detector response in the concentration determination of DPML. To verify the use of the above concentration determination procedure, two solutions of known concentration were prepared: diphenylethylene (5.66 x 10" M) and diphenylmethane (5.26 x 10~ 2 M). The assumption was made that the diphenylethane was of unknown concentration. Using the above procedure and diphenylmethane as a standard, the concentration of di phenyl ethylene was determined to be 5.72 x 10" 2 M. ium 1,1, 4 ,4-Tetraphenyl butane Dianion Lithit Lithium metal (~1 g, 0.14 mol) was cut into small pieces and placed through opening A into the apparatus shown in Figure 6 under Ar atmosphere. Opening A was sealed with a torch. The apparatus was attached to the vacuum line (10" mm Hg), flame degassed, and cooled to -78°C. Dry THF was distilled into the vessel, and 0.9 g (0.005 mol) of di phenyl ethylene was added from an ampoule through a breakseal. The reaction mixture slowly became blood-red and was allowed to stir overnight at room temperature. The apparatus was sealed from the line by a torch, and the bloodred 1,1,4,4-tetraphenylbutane lithio dianion (DPE"Li + )„ was poured through a coarse fritted filter into a breakseal-equipped ampoule. The (DPE'Li ) 2 ampoule was then separated by a torch from the main body of the apparatus. The (DPE"Li + ) 2 was reattached to an apparatus (Figure 7) where it was purified using the same procedure used to purify DPML (see diphenylmethyllithium) .

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17 Figure 6. Apparatus for the synthesis of 1,1,4,4-Tetraphenylbutane dianion lithium (DPE"Li + ) 2 .

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18 Figure 7. Apparatus for the purification of 1,1,4,4-Tetraphem/lbutane dianion lithium (DPE"Li + )„.

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19 The concentration of (DPE~Li + ) 2 was determined by GC using the same procedure used to determine DPML concentrations. However, since the number of carbon atoms of each sample detected by the EC's flame ionization detector differed to a large extent (diphenylmethane standard, 13 C; CH 3 I terminated initiator, 30 C), direct comparisons between GC integrated intensities could not be made. Therefore, the uneven detector response was compensated for by multiplying the directly determined initiator concentration (from integrated peak intensities) by a factor of 13/30. Monomer Synthesis and Purifications Methyl Methacrylate (MMA) In a 100 ml round-bottom flask equipped with a reflux condenser and a CaS0 4 drying tube, 50 ml of methyl methacrylate (Aldrich) was stirred over CaH 2 at room temperature for eight hours. The methyl methacrylate (MMA) was then distilled under reduced pressure (unrecorded), and CaH 2 was added to the distillate. The distillate was then attached to the apparatus shown in Figure 8, placed on the vacuum line, and allowed to sit for several hours. The monomer was then degassed and distilled at room temperature into a breaksealequipped ampoule cooled to 0°C. The ampoule was then removed from the line by a torch. The MMA ampoule was attached to an apparatus (Figure 9) capable of generating a sodium mirror. With the apparatus open to the vacuum line (10 mm Hg), the reservoir containing Na metal (-1.0 g) was heated with a torch until sodium vapors condensed in the main body of the apparatus. The deposited sodium resembled a mirror surface. The

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20 Figure 8. Apparatus for the vacuum line drying of methvl methacrylate over CaH„.

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21 Sodium metal Figure 9. Apparatus for the vacuum line drying of methyl methacrylate over a sodium mirror.

PAGE 34

22 apparatus was closed to the vacuum line, and the MMA was introduced onto the metal. After 30 minutes the MMA was distilled at room temperature and subdivided into ampoule-equipped breakseals cooled to 0°C. The MMA was stored in the freezer at -20°C. Silver Methacrylate (AqMA) 3 7 Methacrylic acid (49.02 ml, 0.57 mol ) was placed in a 500 ml three-neck flask equipped with a mechanical stirrer and two addition funnels. The flask was placed in an ice bath, and 34.6 ml (0.57 mol) of NH 4 0H was added dropwise. Ammonium methacrylate precipitated as a white solid, and the reaction was stirred at 0°C for 15 minutes. The reaction was warmed to room temperature, and 96.96 g (0.57 mol) of AgN0 3 (dissolved in 100 ml of deionized water) was added dropwise to the ammonium methacrylate. The reaction was stirred for two hours, and the silver methacrylate (AgMA) product was a gray precipitate. AgMA was separated by filtration and recrystallized from boiling H 2 0. The final product was first dried in the vacuum oven overnight at room temperature then further dried on the vacuum line (10" 6 mm Hg) for 24 hours. The AgMA was stored under high vacuum in flasks equipped with high vacuum stopcocks (Figure 10). Yields of 65% were obtained after purification. Trit.yl Methacrylate (TrMA) 37 Tritylchloride (50 g, 0.180 mol) was recrystallized from a mixture of 20 ml benzene and 5 ml acetyl chloride? 8 The tritylchloride was allowed to recrystallize for two hours at 0°C and then collected by filtration. The yellow trityl chloride crystals were washed with cold petroleum ether which contained several drops of acetyl chloride.

PAGE 35

23 hj Figure 10. Apparatus for the storage of solid materials u vacuum. nder high

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24 The trityl chloride was then stored under high vacuum in flasks equipped with high vacuum stopcocks (Figure 10). AgMA (32 g (1.6 mol) suspended in dry ether (freshly distilled from CaH 2 ) was placed in a 500 ml three-neck flask equipped with an addition funnel, a reflux condensor (with CaSO. drying tube), a mechanical stirrer, and a heating mantel. Trityl chloride (34.7 g, 0.125 mole) (dissolved in 100 ml of dry ether) was added to the AgMA-ether suspension. The reaction was refluxed for three hours. AgCl was collected by gravity filtration, and the ether filtrate was condensed on the rotoevaporator. The crude trityl methacrylate (TrMA) was purified first by a hot filtration using dry ether and activated charcoal then two simple recrystallizations from dry hexane. Final product yields were 62% or less. The TrMA was ground to a fine powder and stored under high vacuum (Figure 10). TrMA was characterized by melting point, elemental analysis, and 60 MHz *H NMR. m.p.: 100-10rc (literature 101-103°C). 39 Elemental Analysis Found: C, 84.26; H, 6.29%. Calculated for C 23 H 20 2 : C, 84.12; H, 6.14%. H NMR: 7.30 ppm, multiplet (15 H); 6.20 ppm, singlet (1 H); 5.50 ppm, singlet (1H); 2.0 ppm, singlet (3 H). Pi phenyl Methyl Methacrylate (DMA) 26 AgMA (38.5 g, 0.200 mol) and dry ether were placed in a 500 ml three-neck flask equipped with a reflux condenser, mechanical stirrer, addition funnel, and heating mantle. Diphenylmethylchloride (31.31 g, 27.46 ml, 0.155 mol, Aldrich) was added to the flask at room

PAGE 37

25 temperature. The reaction mixture was refluxed for eight hours with stirring. AgCl was separated by filtration, and the concentration of the ether filtrate yielded the crude diphenylmethyl methacrylate (DMA). The DMA was purified by two hot filtrations using hexane and activated charcoal. Product yields were 74% or less. DMA was characterized by melting point, elemental analysis, and 100 MHz l H NMR. m.p.: 79°C (literature 79°C). 26 Elemental Analysis Found: C, 80.58; H. 6.52%. Calculated for C 17 H 16°2 : C ' 80,92; H > 6>39% H NMR: 7.30 ppm, multiplet (10 H); 6.93 ppm, singlet (1 H), 6.52 ppm, singlet (1H), 5.63 ppm, singlet (1H); 2.00 ppm, singlet (3 H). Polymerization Reactions Formation of Homopolymers Polymerizations were carried out by two methods depending on whether the monomer was solid (DMA or TrMA) or liquid (MMA). Poly(diphenylmethyl methacrylate) (PDMA) and Poly(trityl methacrylate) (PTrHA) . A predetermined amount of solid monomer was placed in a vessel illustrated in Figure 11, and the monomer addition opening was sealed with a torch. The monomer vessel was evacuated on the vacuum line (10" mm Hg) for several hours. The ampoule was then cooled to -78°C, and THF was distilled through the vacuum line into it. The vessel was sealed from the line and stored in the freezer at -20°C. DMA and TrMA homopolymerizations were carried out in an apparatus depicted in Figure 12. The apparatus was placed on the vacuum line

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26 Figure 11. Apparatus used to prepare THF solutions of diphenylmethyl methacrylate or trityl methacrylate.

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27 Diphenylmethyl methacrylate or Trityl methacrylate Figure 12. Apparatus used in the homopolymerizations of diphenylmethyl methacrylate or trityl methacrylate.

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28 (10 mm Hg), cooled to -78°C, and approximately 100 ml of dry THF was vacuum distilled into it. The apparatus was sealed from the line by torch and warmed to room temperature. A THF solution containing the initiator [DPML or (DPE"Li + ) 2 ] was then added to the flask through a breakseal. Any residual initiator clinging to the ampoule was washed into the THF by application of a cold dauber to the initiator ampoule. The vessel was cooled to -78°C, and the monomer solution was added to the initiator. After monomer addition, the colored initiator solution immediately became colorless (a slight yellow color was observed sometimes in TrMA polymerizations). After allowing the reaction to proceed for a given time, the apparatus was reattached to the vacuum line. Termination was accomplished by the distillation of MeOH into the reaction. The polymer solution was precipitated in a 10-fold volume excess of either MeOH or hexane. The polymer was collected by filtration and dried in the vacuum oven at room temperature for several days. Poly(methyl methacrylate) (PMMA) . Purified MMA was divided in vacuo (10" mm Hg) into ampoules equipped with breakseals. The MMA homopolymerizations and polymer workups were similar to those of the DMA and TrMA homopolymerizations, with the exception that MMA was added to the initiator solution by an in vacuo distillation into the reaction vessel (Figure 13). Block Copolymer Reactions Block copolymers were synthesized by the sequential polymerization of either DMA and TrMA or MMA and TrMA. DPML initiator was used to synthesize AB block copolymers, and (DPE~Li + ) 2 initiator was used to synthesize ABA triblock copolymers.

PAGE 41

29 no r\ Initiator Methyl methacrylate Figure 13. Apparatus used in the homopolymerization of methyl methacrylate.

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30 All block copolymer reactions (either AB or ABA) were carried out in apparatus depicted in Figures 14 and 15. The apparatus shown in Figure 14 was designed for the synthesis of block copolymers synthesized from MMA and TrMA and the apparatus in Figure 15 for block copolymers synthesized from DMA and TrMA. Block copolymerizations were carried out as described previously for the homopolymer reactions with the additional step that after the first monomer had been allowed to polymerize for a specific time, the second monomer was added and allowed to polymerize. Polymer terminations and workups were identical to those described for the homopolymer syntheses. PDMA, TrMA Random Copolymers The same procedures used in the syntheses of PDMA and PTrMA homopolymers were employed in the syntheses of PDMA, TrMA random copolymers. The only modification in the random copolymer syntheses was that predetermined amounts of DMA and TrMA monomers were mixed together and stored in the same ampoule prior to polymerization. Polymer Hydrolysis PTrMA 26 About one gram of PTrMA was refluxed in 50 ml of methanol containing 5% HC1 for four hours. During the hydrolysis the originally insoluble PTrMA went into solution. The solution was condensed, and the residue was dissolved in a minimum amount of MeOH. The resulting polymethacrylic acid (PMA) was precipitated in cold ether and collected by vacuum filtration. The polymer was dried overnight in a vacuum oven at room temperature. NMR measurements of the corresponding PMMA (see diazomethane methylation) indicated quantitative hydrolysis.

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31 Initiator Trityl methacrylate aft /\ Methyl methacrylate Figure 14. Apparatus used in the synthesis of poly(methyl methacrylate)-trityl methacrylate block copolymers.

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32 Initiator Di phenyl methyl methacrylate oa n Trityl methacrylate Figure 15. Apparatus used in the synthesis of poly(diphenylmethyl methacrylate)-trityl methacrylate block copolymers.

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33 PDMA Approximately one gram of PDMA was refluxed in 50 ml of methanol containing 10% HC1 for at least seven days. During the first five days, the originally insoluble polymer slowly went into solution. After hydrolysis, the solution was condensed and dissolved in a minimum amount of MeOH. The PMA was precipitated in ether and collected by vacuum filtration. The polymer was dried overnight at room temperature in a vacuum oven. Incomplete hydrolysis was detected by two methods. First, ether is a good solvent for PDMA and a poor solvent for PMA; therefore, any difficulty precipitating PMA in ether suggested incomplete hydrolysis. Second, NMR analysis of the corresponding PMMA (see diazomethane methylation) would exhibit larger than expected aromatic absorptions. Some aromatic absorptions are expected because both initiators, DPML and (DPE~Li + ) 2 , contain phenyl substituents. For incompletely hydrolyzed PDMA samples, the hydrolysis procedure was continued for several more days. Random Copolymers (PDMA-TrMA) Random PDMA-TrMA was hydrolyzed by the same procedure used for the hydrolysis of PDMA. PDMA-TrMA Block Copolymers The hydrolysis procedure used for PDMA was also employed for all block copolymers containing PDMA segments. PMMA-TrMA Block Copolymers Block copolymers containing PMMA and PTrMA segments were hydrolyzed in the same manner as PTrMA homopolymers. Under these conditions, only the PTrMA segments hydrolyzed resulting in a PMMA-MA block

PAGE 46

34 copolymer. This polymer was difficult to separate from other hydrolysis products because good solvents for one polymer segment are poor solvents for the other. PMMA-MA was finally isolated by washing the condensed hydrolysis product in a mixture of ether and slightly acidic H 2 0. The polymer precipitated at the solvent interface, was collected by filtration, and dried overnight in a vacuum oven. Diazomethane Methylation 40 Poly(methacrylic acid) and PMA copolymers were methylated to PMMA using the following procedure. A diazomethane (CH 2 N 2 ) generating apparatus (Figure 16) was constructed from three 250 ml thick-wall centrifuge bottles, condensing jacket with screw cap fittings, long-stem separatory funnel with a teflon stopcock, rubber stoppers, and firepolished glass tubing. Approximately 10 ml of ether was placed in both collection vessels (B and C) which were cooled in an ice-salt bath. KOH (2.0 g, 0.036 mol), 4 ml H 2 0, 4 ml ether and 13 ml (0.097 mol) of 2-(2-ethoxyethoxy)ethane (Kodak) were placed in centrifuge bottle A. The solution was heated to 70°C using a H 2 bath. N-methyl-N-nitroso-p-toluene-sulfonamide (Diazald, Aldrich) dissolved in 40 ml of ether was added dropwise to A, and immediately CH 2 N 2 was generated and distilled with ether into B and C. The CH 2 N 2 -ether solution was added to hydrolyzed polymer samples 40 (0.1 g polymer suspended in 10 ml of ether). Gas evolution was detected, and the polymer samples slowly dissolved. Additional CH„N was added to each sample, and the samples were allowed to sit overnight.

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35 p C_J 1 J -— X CO c/i

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36 The samples were then condensed, and their residues dissolved in CHC1 3 . The polymers were precipitated in cold hexane, collected by vacuum filtration, and dried for several days in the vacuum oven. Instrumentation Gas Chromatography (GC) Gas chromatographic analyses were carried out on a Hewlett Packard Model 5880A instrument equipped with a flame ionization detector. Separations were made on a 50 meter SE-54 silicone gum capillary column (Hewlett Packard) using helium as a carrier gas. Nuclear Magnetic Resonance (NMR) Proton NMR spectra were obtained on either a Varian EM-360L or a JEOL FX-100 high resolution spectrometer. Chemical shifts are expressed in parts per million (ppm) downfield from tetramethylsilane (TMS) unless otherwise stated. Polymer proton spectra were carried out with a 1.985s acquisition time and a 100 ms pulse delay. NMR studies of PMMA stereochemistry were carried out in either CDC1 3 (55°C) or DMSO-dg (120°C). For a given sample, the tacticity measurements were identical in either solvent. For PMMA the chemical shifts of the a-methyl protons are most sensitive to polymer configuration. Therefore, triad tacticity information was obtained by integration of the a-methyl resonances. All polymer configurations are expressed in terms of triad tacticities. All expected tacticities of the stereoblock polymers were calculated from the following equations:

PAGE 49

37 I i^Ij +n 2 I 2 H = n 1 H 1 + n 2 H 2 S = rijSj + n 2 S 2 I, H, S = expected triad tacticities of the stereoblock polymer; 'l' H l' S l = trlad tacticities of PMMA hotnopolymer represented in segment 1; I 2 , H 2 , S 2 = triad tacticities of PMMA homopolymer represented in segment 2; "p "2 = mo ^ e fractl ' on s of monomer 1 and monomer 2, respectively, used in the synthesis of the stereoblock polymer. Differential Scanning Calorimetry (DSC) DSC measurements were obtained on a Perkin Elmer DSC-1B model calorimeter. Scan speeds of 10°C per minute were used. The glass transition temperatures (T ) were recorded at the onset on that thermal transition. Indium metal was used for machine calibration. Gel Permeation Chromatography (GPC) GPC analyses were carried out at room temperature using a Waters 6000 liquid chroma tograph. Two u-styragel columns of 10 3 and 10 4 A permeability ranges were used in series. Samples were detected by a Waters differential refractometer or a Perkin Elmer LC-75 UV spectrometry variable wavelength detector. Polymer solutions (200 ul , 0.2 g/dl) were analyzed in either CHC1 3 or THF. Samples run in CHC1. were detected using both the refractive index and UV (240 nm) detectors. Samples run in THF were detected with the UV detector (214 nm).

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38 From the GPC chromatogram, number average molecular weights (M ), weight average molecular weights (MJ and molecular weight distributions (M w /M n ) were determined. The M p represents a molecular weight value for an average chain in a polymer sample. The number average molecular weight is defined as M ZH M n —xx where N x is the number fraction of molecules of size M The M w places emphasis on the weight fraction of molecules in a polymer sample. The weight average molecular weight is defined as w *x x where x x is the weight fraction of molecules whose weight is M . The M w /M n reflects the polydispersity for a polymer sample. A value of M w /M n 1 represents a monodisperse sample where all polymer molecules are of the same chain length. M n and M w values were determined by computer analysis 41 of a GPC chromatogram using a PMMA calibration curve. In all analyses, corrections were made for column band broadening caused by diffusion. The PMMA calibration curve (molecular weight versus retention volume) was generated from a universal calibration curve based on polystyrene standards and appropriate Mark-Houwink constants for both polystyrene and PMMA. 42 Segment Molecular Weight Calculations The isotactic and syndiotactic relative segment molecular weights were calculated from the stereochemical composition of the stereoblock

PAGE 51

39 polymers and the tacticities of the respective PMMA homo polymers comprising the individual segments of the stereoblock polymer. The triad tacticities of the stereoblock polymers are a weighted average of the tacticities in the individual segments so that: MI = M 1 I 1 + M 2 I 2 (1) where M, Mj and M 2> and I, l % and I g refer to the molecular weights and isotactic content of the stereoblock polymer and the two tactic segments, respectively. M was assumed to be equal to M obtained from GPC analysis. Since M Mj + M 2> and letting p = lyiHj, the relationship p = (Ij I)/(I I 2 ) (2) can be derived from Equation 1. Similarly, Equations 3 and 4 can be derived in an analogous manner: p -.($! S)/(S S 2 ) (3) P = (Hj H)/(H H 2 ) (4) where S, Sj and S 2 , and H, h^ and H 2 refer to the syndiotactic and heterotactic contents of the stereoblock polymers and their corresponding segments. For AB stereoblock polymers, the reported segment molecular weights were obtained from averaging values determined from I and S analysis.

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40 For ABA stereoblock polymers, the total segment molecular weights were determined in the same manner as the AB stereoblock polymers. The reported values for the individual A segments were obtained by dividing the total A molecular weight by two.

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CHAPTER III POLYMER SYNTHESES AND CHARACTERIZATIONS In order to gain an understanding of the stereoblock polymers of PMMA and to determine conditions necessary for their syntheses, the monomers corresponding to the possible block segments (TrMA, DMA and MMA) were homopolymerized and converted to PMMA. These PMMA homopolymers were then analyzed for tacticity, initiator efficiency and molecular weight distributions. The stereochemical assignments obtained from PMMA prepared from TrMA, DMA or MMA provide information that can ascertain the block integrity of stereoblock PMMA. Any deviations between expected tacticity values and actual NMR determined tacticity values can be explained by incomplete monomer polymerization of either segment. Initiator efficiency and corresponding PMMA molecular weight distributions from the homopolymer experiments can provide information as to whether a monomer can be polymerized to a predetermined segment length. Good agreement between a targeted and actual PMMA molecular weight coupled with a narrow molecular weight distribution suggests a fast and efficient initiation process. Such results indicate that the subsequent polymerization proceeds in the absence of any chain transfer reactions. This information in turn would suggest stereoblock polymers can be synthesized with monodisperse segments of varying lengths. 41

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42 PMMA Homo polymers Synthesized From TrMA, DMA and MMA Homopolymers Prepared With Monofunctional Initiators Diphenylmethyl lithium (DPML) was used to initiate the homopolymerizations of TrMA, DMA, and MMA in order to prevent initiator attack at the monomer carbonyl carbon. 43 Table 1 lists the results for PMMA synthesized from TrMA, DMA, and MMA. In all cases, each polymer is monodisperse, and there is generally good agreement between the calculated M n and the M n obtained from GPC analyses. These results suggest an efficient initiation process. Table 1 PMMA Homopolymer Analyses From TrMA, DMA, and MMA a PMMA M Sample Monomer TrMA Triac I 91 1 Tact H icity S M n (calc.) b M n (GPC) w M n PT-1 8 1 4200 3950 1.11 PD-1 DMA 2 14 84 8300 6780 1.07 PM-1 MMA 2 24 74 3300 2679 1.17 a b All polymerizations carried out in THF at -78°C. Determined from degree of polymerization ([monomer]/[initiator]) x 100 (molecular weight of MMA). The tacticity values for the PMMA homopolymers synthesized from DMA and TrMA agree with literature values. 26 However, the 74% syndiotactic content obtained from MMA is noteworthy, because literature values for MMA polymerized in THF at -78°C are often much lower (e.g.,

PAGE 55

43 56%). The reasons for these discrepancies can be attributed to the manner in which the monomer is added to the reaction flask. The literature values reflect the addition of MMA in large quantities; this causes a warming of the reaction solution due to the exothermicity of the reaction. Thus, the higher syndiotactic content probably reflects a better temperature control caused by the slow vapor distillation of MMA into the reaction vessel. In order to demonstrate the effect of reaction temperature on PMMA polymer tacticity, MMA was polymerized at -103°C in an etherliquid N 2 bath. The polymer was 80% syndiotactic, and the polydispersity was very large as determined by visual inspection of the GPC chromatogram. Table 2 lists additional PMMA samples synthesized from TrMA, DMA, and MMA. All samples have narrow molecular weight distributions, and PMMA tacticities for the various monomers are identical to those listed in Table 1. Discrepancies between calculated and GPC M n values are probably due to inaccuracies in initiator concentrations. In the homopolymerization of TrMA to high degrees of polymerization (DP), the polymer reaction often turned white and in some cases became viscous, almost gel-like. This was not surprising because Okamoto et al. 44 have demonstrated that PTrMA becomes insoluble in common organic solvents with DP's greater than 60. Nevertheless, in a TrMA homopolymerization, the product was readily hydrolyzed and converted to I-PMMA. Tables 1 and 2 show that the resulting PMMA's

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44 Table 2 Molecular Weight Data for PMMA Homopolymers Synthesized From TrMA, DMA, and MMA Sample Designation Monomer M n (GPC) M w (GPC) M w (GPC) M n (GPC) M n (Calculated) 3 PT-2 TrMA 26,800 31,900 1.19 15,000 PT-3 TrMA 12,500 13,500 1.08 23,000 PD-2 DMA 18,900 20,400 1.07 PD-3 DMA 21,500 24,700 1.15 7,800 PM-2 MMA 3,447 3,982 1.15 7,000 PM-3 MMA 11,739 13,234 1.12 15,000 PM-4 MMA 77,653 90,234 1.24 80,000 a Determined from degree of polymerization ([monomer]/[initiator]) x 100 (molecular weight of MMA). are monodisperse indicating that the apparent inhomogeneity in the polymerization mixture did not adversely affect the molecular weight distributions. Honiopolyme rs Prepared with Bifunctional Initiators Warzelhan et al. 45 showed that the syndiotactic content of PMMA was significantly lowered in going from a monofunctional to a bifunctional sodium initiator in THF at low temperatures (Table 3). Since syndiotactic content in PMMA generally increases with decreasmg reaction temperature," the differences here cannot be due to different reaction temperatures. The differences were attributed to

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45 Table 3 PMMA Tacticity Using Sodium Counterion Initiators Counterion Solvent Temperature Triad Tacticity CO I_ H S Na Na Bifunctional THF THF -61 -75 4 39 36 41 58 20 intramolecular association of ion pairs for the bifunctional sodium initiator (Figure 17). This was claimed to result in an alteration at the propagation site. — CH, I < C: Na I C = I OCH, OCH. 0=C Na T CH, Figure 17. Schematic representation for intramolecular association tor bifunctional sodium initiator in THF. In order to determine if tacticity is maintained in changing from a monofunctional lithium initiator to a bifunctional lithium initiator, DMA, TrMA and MMA were all homopolymerized using 1,1,4,4tetraphenyl butane lithium dianion (DPE"Li + ) 2 . (DPE"Li + ). was synthesized by the reaction of Li metal with di phenyl ethylene (Scheme 3).

PAGE 58

46 Scheme 3 /h Ph X ~> . J< Li + Ph Ph Ph , Li + ^> M + 1 + Ph J^\/'\VPh . Li Ph Ph Table 4 lists the tacticity and GPC data for the corresponding PMMA samples synthesized from DMA, TrMA, and MMA using (DPE~Li + ) ? . For comparison, data obtained from the DPML" initiation of these monomers are provided. Table 4 Stereochemistry and GPC Data for PMMA Prepared With Mono and Bifunctional Lithium Initiators Monofunctional Bifunctional Initiator Initiator PMMA PMMA Monomer Triad Tacticity GPC Triad Tacticity GPC I H S I H TrMA 91 8 1 M a 90 7 3 M b DMA 2 14 84 M a 17 83 b M b MMA 2 24 74 M a 17 83 B C (M) Monomodal Measurement done PDMA C (B) Bimodal

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47 From Table 4, both TrMA and DMA show no major differences between tacticity measurements or GPC results using monofunctional or Afunctional lithium initiators. Interestingly, with MMA, the syndiotactic content was somewhat higher, and the polymer had a bimodal distribution when the Afunctional lithium initiator was used. Whether these results indicate intramolecular associations of ion pairs is not entirely clear. In any event, subsequent reactions with Afunctional initiators were carried out with DMA and TrMA. PMMA From Random Copolymerization of DMA and TrMA The syntheses of well-defined block copolymers presupposes a complete polymerization of the first monomer prior to the addition of the second monomer. Anything short of complete conversion would result in a random copolymerization between the two monomers, and this could affect the block integrity of the second segment. In order to determine how the stereochemistry of the second block segment in stereoblock PMMA is affected by incomplete polymerization of the first monomer, two random copolymers were synthesized using different molar ratios of DMA and TrMA. The corresponding PMMA tacticities are listed in Table 5. For comparison, PMMA tacticities obtained from DPML initiated monomers are provided.

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48 Table 5 Random Copolymers From TrMA and DMA Sample Monomer Random PDMA-TrMA 1 9 Random PDMA-TrMA 1 1 PTrMA o 1 PDMA l o PMMA Molar Ratios Triad Tacticities DMA TrMA I H S 63 28 9 15 50 35 91 8 1 1 15 84 The random copolymerization, at a TrMA/DMA molar ratio of 9:1, illustrates the importance of complete monomer conversion of the first segment. In this experiment, only 10% DMA is present, but this translates into a 28% decrease in isotactic content compared to a segment polymerized from only TrMA. This sharp drop in isotactic content suggests considerable disruption in the stereoregularity of the chain upon DMA addition. This is not surprising, because several stereochemical consequences may result from DMA incorporation. First, the addition of DMA to a predominantly isotactic living chain may affect the stereochemistry of the last TrMA-TrMA (T-T) placement: /wv\_ + D /VVNAT = TrMA; D = DMA; m = meso; r = racemic T T m or r

PAGE 61

49 Second, the subsequent additions of the next few TrMA monomers may be influenced by the newly formed living DMA chain end and the stereochemistry resulting from its addition. These subsequent TrMA additions are likewise stereochemical ly distinct: T T m or r + T •WU T D m m or or r r + T -i> ,VVW T D m m m or or or r r r T = TrMA; D = DMA; m meso; r = racemic In all likelihood then, the random copolymerization between TrMA and DMA is a complex process, and the present data does not allow an unambiguous interpretation for DMA incorporation. However, by assuming that DMA units are randomly positioned in the polymer chain, the above results suggest DMA is incorporated in a syndiotactic fashion into a predominantly isotactic polymer backbone. This placement is depicted in Figure 18.

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50 D mmm mrrmmmm Tr = TrMA; D = DMA; m = meso; r = racemic Figure 18. Random syndiotactic placement of DMA into PTrMA. For each DMA addition, two mr and one rr triad sequences are generated. This is not surprising because DMA has been shown to homopolymerize in a highly syndiotactic fashion under similar reaction conditions. The seven remaining triad sequences would reflect tacticities generated from TrMA homopolymerization (91% mm, 8% mr and 1% rr). Based on these assumptions which suggest a syndiotactic placement of DMA into a predominantly isotactic PTrMA backbone (Figure 18), a random copolymerization of TrMA/DMA of 9:1 molar ratio is predicted to have the triad tacticities of 64%, I; 26%, H; 10% S. These predicted values are in excellent agreement with the experimentally determined results. It should be emphasized that similar tacticities could be generated by alternate mechanistic schemes. The random copolymerization, TrMA/DMA of 1:1, provides a valuable approach for the synthesis of atactic poly(methyl methacrylate) (AtPMMA). This is shown by the 50% heterotactic content in the corresponding PMMA. By having the capability of generating At-PMMA sequences, the stereoblock copolymers of SAtS and IAtl can be synthesized.

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51 An important finding from both random copolymer! zation experiments is that the copolymerization of TrMA with small amounts of DMA results in larger heterotactic content than PMMA homopolymers synthesized from only TrMA. AB Stereoblock PMMA Synthesized From DMA and TrMA From the homopolymer studies, it was noted that viscous to gellike mixtures were observed in the polymerization of TrMA. Therefore, DMA was chosen as the first monomer to be polymerized in the AB PMMA stereoblock polymer syntheses. Scheme 4 depicts this overall process. Scheme 4 ? H 3 f H 3 Tiff S P-ITM J_i ru J-, «+ TrMA :,C— ODM 'ODM PDMA-TrMA O^N^DM 0^ x 0Tr cr^tlTr CH 3 f H 3 PDMA-Trm ^-^ P^-^H^-^ c=o c=o I I OH OH CH, CH, CH N | 3 j 3 Ph p h ~> ^"z-f-hr-f^rf-y* ™ -C-H i Tr -C-Ph C=0 C=0 P" Ph 0CH 3 dcH 3

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52 From the random copolymer studies, it was demonstrated that small amounts of DMA could significantly alter the tacticity of I-PMMA synthesized from TrMA. With this understanding, well-defined block integrity depends on complete polymerization of the first monomer prior to the addition of the second monomer. In order to demonstrate this, three A-B stereoblock copolymers of PMMA were synthesized using different polymerization times of the PDMA segment (Table 6). Table 6 Effect of DMA Polymerization Time on Stereoblock PMMA PMMA Triad Tacticities Sam P le Expected Actual B.C. 3 tt , b Desig. Sample I H S I H S Yield M w /M n Nb T ..„„c PDT-1 PDMA(60r-TrMA c 39 12 49 21 17 62 86 1.09 PDT-2 PDMA(120)-TrMA 37 12 51 33 15 52 83 PDT-3 PDMA(145)-TrMA 46 11 42 44 11 45 87 a B.C. = DMA-TrMA block copolymer Polymerization time (minutes) TrMA polymerization time 180 minutes When DMA was polymerized for 60 minutes, there was poor agreement between expected and actual NMR tacticity values. In view of the large heterotactic content displayed in the stereoblock copolymer, this suggests a random copolymerization between DMA and TrMA. By decreasing the DMA polymerization time to 120 minutes, this discrepancy between actual and expected tacticity values narrows considerably.

PAGE 65

53 However, the larger than expected heterotactic content suggests some random copolymerization. Finally, a well-defined stereoblock copolymer of PMMA is produced by allowing DMA to polymerize for 145 minutes. Table 7 lists several A-B stereoblock copolymers of PMMA synthesized from DMA and TrMA. The second two entries, samples PDT-4 and PDT-5, suggest some random copolymerization occurring between DMA and TrMA. For samples PDT-6 and PDT-7, the discrepancies between actual and expected triad tacticity data indicate an incomplete TrMA polymerization. This is reflected in lower than expected isotactic content coupled with expected heterotactic triad intensities. The much larger original block copolymer yield and closer agreement between expected and actual NMR data for PDT-7 as compared to PDT-6 is not readily explained. Even though TrMA was allowed to polymerize some 22 minutes longer in the former polymer, this does not appear to be sufficient reason to account for the observed differences. By allowing the TrMA block to polymerize for a long time (more than 12 hours), stereoblock copolymers having the desired tactic distributions were obtained (entries PDT-8 and PDT-9). AB Stereoblock PMMA Synthesized From MMA and TrMA In order to determine how tacticity influences stereocomplex formation, DMA was replaced by MMA in the syntheses of PMMA A-B stereoblock polymers. Homopolymer analysis showed that syndiotactic content was 10% lower for PMMA synthesized from MMA than that prepared from DMA. The A-B stereoblock polymers of PMMA obtained from MMA and TrMA were synthesized in the same manner as those obtained from TrMA and DMA (Scheme 4) , the exception being that MMA was substituted for DMA.

PAGE 66

u s. i— OJ CQ E -o — > "~ «< i— OJ E o • SQ->Io 1 o 54 01 -M E m > S 4J X C a L a rr a.
PAGE 67

55 In order to determine whether MMA polymerization time affects block integrity, two experiments were carried out in which only the polymerization time of MMA was varied. These results are listed as PMT-1 and PMT-2 in Table 8. Both PMT-1 and PMT-2 show good agreement between actual and expected triad tacticities. Random copolymerization between monomers is not observed in either case. This is not surprising since the polymerization of MMA is expected to occur much faster than, for instance, that of DMA or TrMA. Table 8 also lists additional PMMA stereoblock polymers synthesized from MMA and TrMA. None of the experiments indicate any random copolymerization between MMA and TrMA. Discrepancies between the expected and actual triad tacticities may be attributed to incomplete TrMA polymerizations. ABA Stereoblock Polymers From DMA and TrMA The syntheses of ABA stereoblock polymers of PMMA were carried out using the Afunctional initiator (DPE~Li + ) Table 9 lists several ABA stereoblock polymers of PMMA synthesized from various combinations of DMA and TrMA. Because homopolymer analysis indicated a bimodal polymer distribution for bifunctionally initiated MMA, this monomer was not used in the ABA stereoblock polymer syntheses. Deviations between expected and actual tacticity values can be explained either by incomplete polymerization of the second monomer (PTDT-1) or a random copolymerization between the two monomers (PDTD-2, PDTD-3).

PAGE 68

56 K f a s hn f= £ c o a) 4-> i—
PAGE 69

57 5£ E: Is: i— aj ,r— ro -— tu Or— O -rrCQ Q.>i O 3 CJ r(TJ Q. SZ E Ol a

PAGE 70

58 Since it was demonstrated that equimolar quantities of DMA and TrMA randomly copolymerize to yield a corresponding atactic PMMA (At-PMMA), two stereoblock polymers were polymerized having atactic central segments [PT(DT)T-4 and PD(DT)D-5]. In both experiments, there was good agreement between expected and actual triad tacticity values.

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CHAPTER IV STEREOCOMPLEX ANALYSIS OF STEREOBLOCK POLYMERS OF PMMA AND PMMA HOMOPOLYMERS Introduction In addition to the synthesis of stereoblock polymers of PMMA, another key research objective was to compare stereocomplex formation resulting from stereoblock polymers with stereocomplex formation resulting from mixtures of isotactic and syndiotactic homopolymers. Because the respective tactic segments in the stereoblock polymer are covalently linked, stereocomplex formation is expected to be enhanced in this system. This results from the possibility that intramolecular associations can now occur in addition to the expected intermolecular association. High resolution H-NMR has been shown to be a convenient technique for analyzing stereocomplex formation between I-PMMA and SPMMA. ' ' The mobilities of the protons involved in the stereocomplex are greatly reduced; therefore, the integrated intensities of these protons are broadened to such an extent that NMR detection does not occur. Only the protons corresponding to non-associated monomer units are observed. Stereocomplex formation has been shown to be a thermally reversible process. In certain solvents, the stereocomplexes are manifested 59

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60 by the formation of visible gels. Several authors have observed that these gels dissociate over a very narrow temperature range. 5 ' 46 This dissociation has been interpreted as the "melting" of the stereocomplex. The actual temperature where "melting" occurs is influenced by the stereoregularity of the constituent homopolymers; the more stereoregular the polymer, the higher its dissociation temperature. At temperatures well above the dissociation temperature, it can be assumed that almost no complexed material exists. Because of this and since only uncomplexed PMMA is detected by the NMR, fractions of uncomplexed PMMA can be determined from the integrated peak intensities at any temperature. To illustrate the effects of temperature on stereocomplexed PMMA, Figure 19 shows the NMR of sample PMT-2 taken at various temperatures. Stereocomplex Formation Studies Investigation of the Stereocomplex Equilibrium In order to study stereocomplex formation by NMR, it must first be determined whether the ratio of complexed and uncomplexed polymer reflects a true thermodynamic equilibrium. This appears to be the case. First, the changes observed in the NMR spectra when heating or cooling were always rapid and did not change once a constant temperature was attained. Second, the integrated intensities (relative to an internal standard) remained constant regardless of the preceding thermal treatment of the sample. Thus, the same integrated intensity was observed at a particular temperature regardless whether this temperature was reached by cooling or heating.

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61 Methylene proton absorptions ct-Methyl proton absorptions 2.5 Figure 19. 2.0 1.5 1.0 0.5 ppn 1, 100 MHz H-NKR spectra of sample PMT-2 (syndiotactic segment molecular weight = 4160; isotactic segment molecular weight = 4960) recorded at various temperatures. (* = solvent)

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62 Homocomplexation of S-PMMA and I-PMMA in DMSQ A potential complication in analyzing stereocomplex formation between Iand S-PMMA is that these respective homopolymers have been shown to undergo self-association. Like stereocomplex formation, this self-association has been shown to be dependent on homopolymer tacticity as well as the particular solvent used in the analysis. For example, in toluene, more than 70% of the monomer units are associated in 85% triad syndiotactic PMMA. However, no complex formation is observed with 66% triad syndiotactic PMMA in the same solvent. 47 The self-association process observed in S-PMMA has been shown to be thermally reversible with the aggregates dissociating between 4060°C. 48 With respect to I-PMMA, about 20% of the monomer units are asso49 ciated in CDjCN. These aggregates have been shown to be thermally stable, and they dissociate at temperatures in excess of 160°C. To determine if self-association occurs in addition to stereocomplex formation, the integrated intensities of I-PMMA and S-PMMA were measured both at room temperature and at temperatures exceeding 80°C. The samples were analyzed using various NMR acquisition times and pulse delays, and the results are listed in Table 10. All analyses were performed in DMS0-d g , and the reported intensity ratios were determined relative to an internal standard. For all samples, the integrated intensities obtained at the higher temperatures are between 40-60% larger than those at room temperature. Since both I-PMMA and S-PMMA responded in a similar fashion,

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63 Table 10 Homocomplexation Analyses of S-PMMA and I-PMMA .a Samples PD-4 a PT-2 PT-2 (S-PMMA) (I-PMMA) (I-PMMA) Intensity Ratio 1.62 c 1.40 c 1.56 d Acquisition Time(s) 1.98 1.98 ~3 Pulse Del ay (s) 0.1 0.1 -2 3 PD-4: GPC(M n ) = 51,800. Integrations were made from total a-methyl and methylene regions of PMMA spectra, and the reported ratio reflects the high temperature intensity divided by the 25°C intensity. High temperature intensity determined at 83°C. High temperature intensity determined at 93°C. and since I-PMMA self-association has been shown to break up at temperatures exceeding 160°C, these data suggest that self-association is not occurring for either Ior S-PMMA in DMS0. At this time, the larger integrated intensity values observed at higher temperatures cannot be adequately explained. However, since this intensity enhancement is observed, it can be expected to also occur in the temperature analyses of stereocomplex formation thereby rendering that analysis semi-quantitative at best.

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64 Comparison of Stereocomplexation Between Stereoblock Polymers of PMMA With Mixtures of I-PMMA and S-PMMA In order to properly compare complexation in stereoblock PMMA with mixtures of syndiotactic and isotactic homopolymers, the individual segment lengths and segment tacticities of the stereoblock sample should be identical to those in the respective homopolymers. Two sets of samples were analyzed in DMS0-d c . In the first b set, designated Series A, a SI-PMMA stereoblock polymer was compared to a mixture of Sand I-PMMA homopolymers in which all tactic segments were synthesized from MMA or TrMA. In the second sample set, designated Series B, similar polymers were analyzed with the exception that the syndiotactic segments in both the stereoblock polymer and S-PMMA homopolymer were generated from DMA. Table 11 describes the individual samples in both Series A and Series B. Each sample was analyzed at several temperatures, and peak integrations (representing uncomplexed material) were determined from the proton absorptions in the a-methyl region. In all measurements, peak integrations were calibrated with hexamethyldisiloxane or the residual DMSO solvent peak. For the sample measurements taken at 98°C, the corresponding integrations were assumed to represent the complete dissociation of the stereocomplex. The integrated intensities obtained at lower temperatures were then normalized to the integrated intensity obtained at 98°C; these values represent the amount of uncomplexed material at that given temperature. The fractions of complexed material for the samples in Series A and Series B measured at various temperatures are given in Table 12.

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65 Table 11 Samples Used in Series A and Series B Sample Designation Sample Architectu re Series A M n (GPC) of Tactic Segments I S Sample Weight (q) Sample Concentration (Molar)a PMT-6 SI-PMMA 3950 12,750 0.0198 0.396 PM-3 S-PMMA 11,739 0.0135 0.270 PT-1 I-PMMA 4200 0.0058 0.116 Series B PDT-8 SI-PMMA 7350 15,650 0.0110 0.22 PD-3 S-PMMA 21,500 0.0071 0.142 PT-3 I-PMMA 12,500 0.0039 0.078 Based on MW of methyl me thacrylate. Table 12 Fraction of Complexed Polymer for Mixtures of PMMA Homopolymers and for Stereoblock PMMA in Series A and Series B at Various Temperatures Series A Series B Temperature Complexed Material Complexed Material (°C) AB A+B AB A+B 25 0.90 0.81 0.991 0.865 39 0.87 0.71 0.974 0.837 54 0.73 0.43 0.895 0.790 67 0.61 0.12 0.95 0.38 98

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66 Since the integrated intensities of the Iand S-PMMA homopolymers have been shown to increase at higher temperatures relative to an internal standard, the possibility of this occurring in the stereocomplex analysis cannot be ruled out. However, its effect should be relatively minor compared to the observed intensities that reflect the dissociation of the stereocomplex, and semiquantitative comparisons between the samples in Series A and Series B should be valid particularly since signal enhancement of Iand S-PMMA was shown to be almost identical . From Figures 20 and 21 for Series A and Series B, respectively, it can be seen that complexation is more extensive for the PMMA stereoblock polymer than for the mixture of S-PMMA and I-PMMA homopolymers. This indicates that intramolecular complex formation is indeed occurring in the A-B stereoblock polymers in addition to the expected intermolecular stereocomplexation. By extrapolation of the A+B sample curves in both Series A and Series B (Figures 20 and 21, respectively), it is predicted that these samples would be largely dissociated between 70-80°C. In this temperature range, the stereocomplexes generated from the PMMA stereoblock polymers in both Series A and Series B would be approximately 60% complexed. These results suggest that intramolecular complexation results in a more thermally stable stereocomplex as compared to intermolecular complexation. For Series B where the syndiotactic components are more stereoregular, Table 12 indicates that stereocomplex formation for both the

PAGE 79

67 o o c= ^ • •4 • O CO si X -o < U0J43BJJ UOLq.BX9[duJ03

PAGE 80

68 I/) «< SQi O i— 4a » • w , < • CM t— I d d U0LJ3BJJ UOLJBXBldUlOO

PAGE 81

69 block polymer and the homopolymer mixture is more extensive than for their respective counterparts in Series A. However, this assessment is strictly qualitative since different tactic lengths are being compared. Concentration Effects on Stereocomplex Formation In order to determine the effect of concentration with respect to stereocomplex formation, both the A-B and A+B samples in Series A were diluted fifteen-fold. The percent of complexed polymer for both concentrated and dilute samples as a function of temperature are given in Figure 22. By comparing the A+B concentrated sample to the A-B diluted sample, it can be seen that stereocomplex formation is more extensive in the stereoblock polymer. Whether this is due to intraor intermolecular complex formation, or both, remains to be determined. Effect of PMMA Stereoreqularity on Stereocomplex Formation Determination of S-PMMA/I-PMMA Stereocomplex Ratios for PHHA Homopolymers Synthesized From DMA and TrMA ~~ Spevacek observed that the stereochemistry of both the Sand I-PMMA homopolymers influenced the S-PMMA/I-PMMA (S/I) ratio observed in their resulting stereocomplex. 10 ' 11,15 In order to compare the S/I stereocomplex ratio between PMMA homopolymers synthesized from DMA and TrMA, various weight ratios of the corresponding S-PMMA and I-PMMA were analyzed by X H-NMR in both CD 3 CN and DMSO-d,. The spectra obtained in CD 3 CN are shown in Figure 23, and similar spectra were obtained in DMSO-d,.

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70 ! -a t 4Q) o +-> * 5 I u c o u • « • «« • nj J ) sI. •re£ +J =5 S C (1) m (/) • (J tm M < c C.) o o p o •rC rt3 W X CO
PAGE 83

Figure 23. Effects of S-PMMA/I-PMMA weight ratios on a-methvl oroton from 100 MHz HI-NMR spectra at 25°C in CD-sCN. 1.5, b) 2.0, c) 2.5, d) 3.0. absorptions froiT Weight ratios: Mn (GPC) for I-PMKA = 26,800; M n (GPC)'for S-PMMA = 51,800, with exception of sample (d) where M n (GPcf (* " solvent) 21,500.

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72 In Figure 23a, where the weight ratio of S/I is 1.5:1, only IPMMA absorptions are observed. Apparently, at this ratio all the SPMMA is involved in the stereocomplex. At a S/I ratio of 2:1 (Figure 23b), no discernible absorptions are detected in the a-methyl region (0.8-1.2 ppm). This indicates that all polymeric species are involved in the formation of the stereocomplex. This suggests that complexation between I-PMMA and S-PMMA, synthesized from DMA and TrMA, respectively, occurs at a S/I ratio of 2:1. At a S/I ratio of 2.5:1, it is interesting to note that no discernible peaks are observed. However, at a 3:1 ratio, absorptions from S-PMMA are visible. This indicates that I-PMMA is involved in stereocomplex formation and that observed S-PMMA is in excess of the complex. Spevacek, who studied stereocomplex formation in CD 3 CN, reported a S/I ratio of 1:1. The reason for the discrepancy between Spevacek 's ratios and the ratios reported here is probably due to differences in the stereoregularity of the polymers (Table 13). Table 13 Iand S-PMMA Tacticities Accounting for Differences in S/I Ratios in CD 3 CN PMMA Study I-PMMA This research 91 I-PMMA Ref. 11 S-PMMA This research S-PMMA Ref. 11 Triad Tacticities I H S 91 8 1 97 3 2 14 84 2.5 9 88.5

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73 All stereocomplexes generated in CD 3 CN resulted in visible gel formation as evidenced by precipitation of the stereocomplex. However, as Figure 23 indicates, no excessive peak broadening or loss in resolution was observed. With DMSO-d., no precipitates were observed. Mixtures of I-PMMA and S-PMMA With At-PMMA Stereocomplex formation has been shown to occur only between S-PMMA and I-PMMA, and the degree of complexation is influenced to a large extent by the stereoregularity of the polymer chains. Therefore, CD 3 CN solutions of I-PMMA and S-PMMA were mixed with At-PMMA, and the resulting mixtures were examined by NMR (Table 14). Table 14 NMR Results For I-PMMA and S-PMMA Mixed With At-PMMA in CD 3 CN Expected NMR Observed Triad Tacticity Triad Tacticity Sample Mixture I H s I H S I-PMMA 3 + At-PMMA b 57 24 19 57 24 19 S-PMMA C + At-PMMA b 12 35 53 d 12 38 50 I-PMMA: I, H, S of 91, 8, 1; M n (GPC) = 26,800. b At-PMMA: I, H, S of 16, 42, 42; M n (GPC) = 23,200. c S-PMMA: I, H, S of 2, 14, 84; M R (GPC) = 51,800. Determined from high temperature tacticity analysis. Because of the good agreement between the observed NMR tacticities and the expected values which were obtained assuming no complex formation, it appears that At-PMMA does not form stereocomplexes with

PAGE 86

74 either I-PMMA or S-PMMA. The absence of complex formation is further suggested because no precipitation was observed in either CD,CN solution. This was not the case for mixtures of S-PMMA and I-PMMA in CD 3 CN, where stereoassociation resulted in precipitation of the stereocomplex. Analysis of Stereocomplex Formation From SAtSand IAtlPMMA Stereoblock Polymers ~ — The formation of stereocomplexes between PMMA stereoblock polymers having an IAtl and SAtS architecture would be of interest, because complex formation should involve only the isotactic and syndiotactic segments. In such a mixture, the stereocomplexed material would serve as physical crosslinks which would be superimposed on an At-PMMA matrix (Figure 3). From an application viewpoint, as a result of such crosslinks, the mechanical properties of these complexed polymers would be expected to be very different from the mechanical properties of conventional PMMA. It was demonstrated in CD 3 CN that mixtures of I-PMMA and S-PMMA, synthesized from TrMA and DMA, respectively, complexed in an S/I ratio of 2:1 to 2.5:1. Also, neither of these tactic homopolymers appeared to form stereocomplexes with At-PMMA. Assuming that these observations hold for a mixture of CD 3 CN solutions of IAtl and SAtS stereoblock polymers, an expected triad tacticity value can be determined. By heating such a mixture above the melting temperature of the stereocomplex, the expected tacticity should reflect values assuming no complexation. The results of such an experiment are given in Table 15. Here equal weights of samples PT(DT)T-4 and PD(DT)D-5 were mixed

PAGE 87

75 in CD 3 CN. The good agreement observed between expected and actual tacticity values, both at room temperature and at 70°C, suggests that stereocomplex formation does occur between isotactic and syndiotactic segments. Table 15 Temperature and Tacticity Study on Mixture of IAtland SAtS-PMMA Stereoblock Polymers in a Complexing Solvent Triad Tacticity I H S Room 23 45 32 PT(DT)T-4 (IAtl) j e Z__^^ Expected + ^/" NMR b 23 43 34 PD(DT)D-5 (SAtS) ^^^^ Expected 30 30 40 NMR 27 33 40 Calculated assuming S/I ratio of 2:1 and complete formation of stereocomplex. NMR sample tube contained visible precipitate. Calculated assuming no stereocomplex formation. Effect of Segment Molecular Weight on Stereocomplex Formation The minimum Iand S-PMMA segment lengths required to generate stereocomplexes have been discussed by several authors. 15 ' 46 Spevacek suggested that for S-PMMA that is 66% syndiotactic, ten monomer units and three monomer units are necessary for complexation to occur in benzene and CH 3 CN, respectively. 15 Spevacek's analyses employed the same I-PMMA sample (972 isotactic with respect to triad tacticity) in all his studies. Ryan, who studied complex formation of various samples of I-PMMA with a standard syndiotactic polymer, concluded that a

PAGE 88

76 minimum of eight isotactic monomer units are required for stereocom46 plexation. It is interesting to note that almost all previous conclusions on minimum sequence lengths were deduced from studies performed on very high molecular weight polymers and polymers with broad molecular weight distributions. To assess segment length effects on stereocomplex formation, both GPC and NMR analyses were employed. The samples involved in this study along with their GPC and NMR results are listed in Table 16. Table 16 GPC and NMR Analyses on Stereocomplex Formation on SI-PMMA Stereoblock Polymers Tactic S Lengths I GPC (M w /M n ) Sample CHC1 3 3 THF NMR b PDT-1 2320 2070 1.09 1.13 a 1.68 PMT-2 4160 4690 1.13 1.55 a 2.70 PDT-4 C 1.15 Broad d PDT-8 15102 7093 1.25 Broad e 102.88 PDT-9 13361 9637 1.22 19.97 Monomodal GPC chromatogram. Ratio of intensities at 83°C and 25°C; both intensities were determined against an internal standard. All high temperature analyses were measured at 83°C with the exception of PDT-8 whose high temperature analysis was measured at 98°C. Total polymer molecular weight (GPC in CHC1 3 ) = 18,000; approximate segment lengths: I = 2,500; S = 16,500. GPC chromatogram displayed a trimodal distribution. GPC chromatogram displayed three high molecular weight shoulders. -

PAGE 89

77 Although THF has been described as the most common GPC solvent, it nevertheless has pronounced effects on the analyses of the stereoblock polymers of PMMA. With the exception of sample PDT-1, the GPCanalyses for the samples listed in Table 16 show that those run in THF, cited as a strongly complexing solvent, have broad molecular weight distributions and in some instances display visible polymodality. The same samples run in CHC1 3 are both monodisperse and monomodal . The GPC analysis of sample PDT-1 is virtually identical in either THF or CHC1 3 . These results suggest that the effects of complexation observed in THF for entries PMT-2, PDT-4, and PDT-8 are not occurring in sample PDT-1. To illustrate the effects of complexation, Figure 24 depicts the GPC chromatograms of samples PDT-4 and PDT-8, both analyzed in THF and CHC1 3 . It is apparent from the THF analyses that complexation is manifested by both a broadening of the GPC chromatogram and also the appearance of additional peaks in the higher molecular weight region (lower count number). For the same samples run in CHC1,, the resulting GPC chromatograms are both monomodal and monodisperse. NMR was used to assess chain length effects in stereocomplex formation by comparing integrated peak intensities at room temperature with those obtained at temperatures exceeding 80°C. From Table 16, with the exception of PDT-1 and PMT-2, all samples analyzed in DMS0-d 6 by NMR showed large high temperature to low temperature integrated intensity ratios. This reflects extensive stereocomplexation processes in these samples.

PAGE 90

78 o *— ' 1 ° CO 03 t/> — 1 O) Q. / .^o e .— 1 to =3s_ r~H o 4OJ 1 t— 1 1 1 , — o CO 1 I—I i— lO o en o o -a ii c to +-> . E * 3 — > o to O +J | c c m r0 c: O <* 51 SZ hO LJ a. o O— < CD ro «J" CM
PAGE 91

79 It is interesting to compare the NMR results listed in Table 16 for the samples PDT-1 and PMT-2. Over the temperature range studied, the integrated intensity for sample PDT-1 increased by a factor of 1.68. However, it was previously shown that the integrated intensities increased by similar order of magnitudes for homopolymer samples, where it was concluded that no self-association was occurring. Therefore, this observation suggests little or no stereocomplex formation is occurring in PDT-1. The intensity increase by a factor of 2.7 for sample PMT-2 does suggest complexation is indeed occurring at room temperature. Further evidence supporting the contention that complexation does occur in PMT-2 and not PDT-1 is shown by the NMR spectra of these two samples where one measurement was taken at room temperature and the other at 125°C (Figure 25). For sample PDT-1, the isotactic, heterotactic, and syndiotactic a-methyl absorptions can clearly be distinguished at room and high temperatures. However, large differences can be detected for PMT-2 where all syndiotactic absorptions disappear at room temperature as a consequence of stereocomplex formation. In conclusion, GPC and NMR evidence suggests sample PDT-1 undergoes very little or no room temperature complexation in DMSO-d . Be6 cause the polymer contains approximately 20 monomer units in the isotactic segment and 23 monomer units in the syndiotactic segment, the minimum repeat unit responsible for complex formation is seemingly larger than what has been reported in the literature.

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80 a) PDT-1 25°C b) PMT-2 25°C pptn ppm 125°C ppm pprr. Figure 25. Room temperature and high temperature 100 MHz H-NMR spectra for samples a) PDT-1 and b) PMT-2 (solvent DMSO-d,).

PAGE 93

81 DSC Investigation on Stereoblock Polymers Materials that exhibit thermoplastic elastomeric properties are usually ABA block copolymers. The central B block is often a segment having a low glass transition temperature, Tg, whereas the A segments often exhibit a much higher Tg. An important criterion for ABA thermoplastic elastomers is that the individual A and B segments must be incompatible with one another. In order to determine if a PMMA stereoblock polymer with an SIS architecture could potentially exhibit thermoplastic elastomeric properties, the glass transition temperatures of several PMMA samples were determined by DSC. These results are listed in Table 17. Table 17 DSC Analysis for Various PMMA Samples Sample Polymer Architecture Segment Lengths S I Tq (°C) PM-5 S-PMMA 77,089 135 PI-1 I -PMMA 35,000 a 50 PDT-8 SI -PMMA 15,106 7,093 99 a PI-1 was synthesized by the reaction of MMA and diphenylhexyllithium in toluene. The reported M n value was determined by the equation [monomer]/[initiator] x 100, where 100 equals the molecular weight of a methyl methacrylate monomer unit. The observed Tg for sample PDT-8 listed in Table 18 suggests that the isotactic and syndiotactic segments in this PMMA stereoblock

PAGE 94

82 polymer are compatible. This is concluded from the fact that only one Tg was observed in the DSC (if two polymers are incompatible, individual Tg's are observed). Also, the value of the observed Tg is approximately equal to a weighted average for the Tg's of its individual segments (see PM-5 and PI-1 for Tg's for Sand I-PMMA segments). Since the isotactic and syndiotactic segments in PDT-8 appear to be compatible, such compatibility would be expected to also exist in a SIS-PMMA stereoblock polymer. This then would rule out the possibility that these materials would act as thermoplastic elastomers.

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REFERENCES 1. F.A. Bovey and G.V.D. Tiers, J. Polym. Sci. 44, 173 (1960). 2. J. Brandrup, E.H. Immergut, "Polymer Handbook," Second Edition, John Wiley and Sons, Inc., New York, 1975, p. II 1-148. 3. J.M. O'Reilly, H.E. Bair and F.E. Karasz, Macromolecules 15, 1083 (1982). — ' 4. H.E. Goode, F.H. Owens, R.P. Fellmann, W.H. Snyder and J.E. Moore, J. Polym. Sci. 46, 317 (1960). 5. W.A. Watanabe, C.F. Ryan, P.C. Fleischer and B.S. Garret, J. Phys. Chem. 65, 896 (1961). 6. A.M. Liquori, G. Anzuino, V.M. Corro, M. d'Alazni, P. de Santis and M. Savino, Nature 206, 358 (1965). 7. E. Killmann and K. Graun, Makromol . Chem. 185, 1199 (1984). 8. F. Bosscher, G.T. Brinke and G. Challa, Macromolecules 15. 1442 (1982). — 9. F. Bosscher, D.W. Keekstra and G. Challa, Polymer 22, 124 (1981). 10. J. Spevacek and B. Schneider, Makromol. Chem. 176, 729 (1975). 11. J. Spevacek and B. Schneider, Colloid and Polym. Sci. 258, 621 (1980). 12. E.L. Feitsma, A. deBoer and G. Challa, Polymer 16, 515 (1975). 13. E.J. Vorenkamp and G. Challa, Polymer 22, 1705 (1981). 14. R. Buter, Y.Y. Tan and G. Challa, J. Polym. Sci. -Polym. Chem. Ed 11, 989 (1973). 15. J. Spevacek and B. Schneider, Makromol. Chem. 175 , 2939 (1974). 16. R. Buter, Y.Y. Tan and G. Challa, J. Polym. Sci. -Polym. Chem Ed 11, 2975 (1973). S3

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84 17. R. Buter, Y.Y. Tan and G. Challa, J. Polym. Sci. A-l 10, 1031 18. G. Challa and Y.Y. Tan, Pure and Appl . Chem. 53, 627 (1981). 19 ' li B 1003'(1973) Tan and G ' Challa> J ' P ° lym " Sci -Pol y m Chem Ed. 20. P.E. Allen and C. Mair, Eur. Polym. J. 20, 697 (1984). 21. T. Miyamoto and H. Inagaki , Polym. J. 1, 46 (1970). 22. P.E. Allen and B.O. Bateup, Eur. Polym. J. 14, 1001 (1978). "' 241 N (196of' H ' Watanabe ' K ' Abe and Y Sono > J P 01 ^Sci. 48, 24. AB and ABA designate polymer backbone architecture. Segment A may be either chemically or configurationally distinct from segment B. 25 ' Part U B k1 6, K 753 a (1968)!" ^^ "* ^ " UmmU J " P ° lym Sc1 " 26 ' (iJo) 1 ' K " Hatada ' T ' Niinomi and Y Kikuchi, Polym. J. 1, 36 11 ' J, n IfV uta * T> Makimot ° and H. Kanai , J. Macromol. Chem. 1 31 28 ' 26, Y 3Ml975) atad * i K ' ° hta ^ YOkamot0 ' A PP K Po ^ m Symp. 29 ' 171 R (1965)' E ' F1gueruel ° and E " Llano > J Poly"Sci., Part B 3, 30. G.M. Guzman and A. Bello, Makromol . Chem. 107, 46 (1967). 31. G. Lohr and G.V. Schulz, Eur. Polym. J. 10, 121 (1974). 32. R. Kraft, A.H.E. Muller, V. Warzelhan, H. Hocker and G.V. Schulz Macromolecules 11, 1093 (1978). ^cnuiz, 33. A. Muller, Makromol. Chem. U!2, 2863 (1981). 34 ' (1982)^ and A ' H ' MUller ' Makr ™ 01 Chem -' RaDid Co ™ un 1, 121 35. M. Szwarc, "Carbanions Living Polymers and Electron Transfer Processes," John Wiley and Sons, Inc., New York, 196 8 " Chapter 2.

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85 36. A. Noshay and J.E. McGrath, "Block Copolymers Overview and Critical Survey," Academic Press, Inc., New York, 1977, Chapter 4. 37. Synthetic procedures for both AgMA and TrMA were obtained by personal communication with Professor Yoshio Okamoto of Osaka University, Japan. 38. 39. 40. B.S. Furniss, A.J. Hannaford, V. Rogers, P.W.G. Smith and A.R. Tatchell, "Vogel's Textbook of Practical Organic Chemistry," Fourth Edition, Longman Group Limited, London, 1978, p. 608. N.A. Adrova and L.K. Prokhorova, Vysokomol . Soedin. 3, 1509 A. Katchalsky and H. Eisenberg, J. Polym. Sci . 6, 145 (1951). 41. The computer program for GPC analyses was developed by Dr. Teng-shau Young using techniques adapted from W.W. Yau, J.J. Kirkland and D.D. Bly, "Modern Size-Exclusion Liquid Chromatography," John Wiley and Sons, Inc., New York, 1979. 42. J. Brandrup and E.H. Immergut, "Polymer Handbook," Second Edition, John Wiley and Sons, Inc., New York, 1975, Chapter IV. 43. A. Muller in "Anionic Polymerizations, Kinetics, Mechanisms, and Synthesis," ACS Symposium Series 166, American Chemical Society, Washington, D.C., 1981, p. 441. 44. Y. Okamoto, K. Suzuki and H. Yuki , J. Polym. Sci. -Polym. Chem. Ed. 18, 3043 (1980). 45. V. Warzelhan, G.V. Schulz and H. Hocker, Makromol. Chem. 181 149 (1980). 46. C.F. Ryan and P.C. Fleischer, Jr., J. Phys. Chem. 69, 3385 47. J. Spevacek. J. Polym. Sci. -Polym. Phys. Ed. J_6, 523 (1978). 48. J. Spevacek, B. Schneider, M. Bohdanecky and S. Sikora, J Polym. Sci. -Polym. Phys. Ed. 20, 1623 (1982). 49. J. Spevacek and B. Schneider, Makromol. Chem. JL76, 3409 (1975).

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BIOGRAPHICAL SKETCH Martin A. Doherty was born in Syracuse, New York, on November 15, 1956, at 6:56 a.m. He has been growing ever since. 36

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I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. y r // P a Thieo E. Hogert-E^Ch, Chairman Professor of Chemistry I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Charles L. Beatty Professor of Materials Science and Engineering I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. Wallace S. Brey, Jr. Professor of Chemistry

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I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. George B~. Butler Professor of Chemistry I certify that I have read this study and that in my opinion it conforms to acceptable standards of scholarly presentation and is fully adequate, in scope and quality, as a dissertation for the degree of Doctor of Philosophy. William M. Jo"hes Professor of Chemfstpy This dissertation was submitted to the Graduate Faculty of the Department of Chemistry in the College of Liberal Arts and Sciences and to the Graduate School, and was accepted for partial fulfillment of the requirements of the degree of Doctor of Philosophy. December 1Q84 Dean for Gradua te Studies uecember 1984 and R esearch

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UNIVERSITY OF FLORIDA HlllilllllllWllllllllii 3 1262 08554 8617


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