Thermal elimination of poly(phenylvinylsulfoxide) and its styrene block copolymers

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Thermal elimination of poly(phenylvinylsulfoxide) and its styrene block copolymers
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ix, 135 leaves : ill. ; 28 cm.
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Kanga, Rustom Sam
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Polyacetylenes   ( lcsh )
Styrene   ( lcsh )
Polymers   ( lcsh )
Polymerization   ( lcsh )
Chemistry thesis Ph. D
Dissertations, Academic -- Chemistry -- UF
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Thesis:
Thesis (Ph. D.)--University of Florida, 1988.
Bibliography:
Includes bibliographical references.
Statement of Responsibility:
by Rustom Sam Kanga.
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Typescript.
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Vita.

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THERMAL ELIMINATION OF POLY(PHENYLVINYLSULFOXIDE)
AND ITS STYRENE BLOCK COPOLYMERS



















RUSTOM SAM KANGA








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

1988


























Dedicated


to

my parents

Sam and Gool Kanga


and to my mentor

the late Mr. J. Elavia

















ACKNOWLEDGMENTS

I wish to thank all the members of my supervisory committee: Dr.

George Butler, Dr. Kenneth Wagener, Dr. Merle Battiste, Dr. Russel Drago, Dr.

Christopher Batich and Dr. James Boncella.

Special thanks are given to Dr. Batich for his help and advice in XPS,

to Mr. Richard Crockett for running the XPS spectra of my polymers and to

Dr. King for running the pyrolysis-MS.

I thank Dr. Wagener for his support, encouragement and sagacious

advice, both chemical and non-chemical.

I am gratefully indebted to Dr. Thieo Hogen-Esch for his direction,

guidance, encouragement and best of all patience. He taught me a lesson I

will never forget: avoid mediocrity!

Thanks are offered to Lorraine Williams for her ready smile and

readier help. Thanks and cheers are expressed to all the people on the

polymer floor for having enriched my existence.

Words cannot express my gratitude nor my indebtedness to Pauline

Schneider for her help in preparing this manuscript and for being there at

the most critical point in my life!















TABLE OF CONTENTS


Page

ACKNO W LEDG M ENTS ..................................... ......................................................................... iii

KEY TO ABBREVIATIONS.................................................................... vii

ABSTRACT ................................................... viii

CHAPTER

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

Polyacetylene (PA) ...................... ................................................................... 3

Precursor Routes to Polyacetylene.......................................................... 5

2 EXPERIM ENTAL ......................................................................................................... 11

High Vacuum Anionic Polymerization Techniques.......................... 11

Purification of Solvents, Monomers and Reagents............................. 12

Purification of Phenylvinylsulfoxide and Ethylphenylsulfoxide.. 12

Purification of Styrene and 1,1-Diphenylethylene......................... 13

Purification of t-Butyllithium ..................................... 1 6

Preparation of Initiators .......... ................................................ 1 6

Lithium Naphthalide........................................................................ 16

Triphenylmethyllithium (TPML)....................................................... 18

1,1 Diphenylhexyllithium (DPHL).......................................................... 20

Triphenylmethylpotassium (TPMK).......................................................... 20

1 -Lithio-1 -(Phenylsulfinyl) Ethane (EPSL) .................................... 20

Determination of Concentration of Carbanions................ 22

Titration with Fluorene........ ....................................................................... 22









Determination of Concentration by UVNisible Spectroscopy......23

Polymerization of Phenylvinylsulfoxide................. ..... .............. 24

Copolymerization of Styrene and Phenylvinylsulfoxide................. 28

A -B C opolym ers ................................................................................................. 28

A-B-A Triblock Copolymers .......................................... ............................ 33

Monomer Conversion Study....... ........................................ .............................. 34

T herm al E lim ination................... ......................................................................... 36

Instrumental Methods................. .................................................................. 38

Size Exclusion Chromatography (SEC)................................. ....... 38

Capillary Gas Chromatography (GC) ....................................................... 39

Nuclear Magnetic Resonance Spectroscopy (NMR)........................... 39

Infrared Spectroscopy (IR) ............................................... 40

UV/Visible Spectroscopy..... .......................................... ............................ 41

Polarim etry................................ ................................................................... 4 1

Pyrolysis-Mass Spectrometry ....................................... ........................... 41

Thermogravimetric Analysis (TGA) ....................................................... 42

X-Ray Photoelectron Spectroscopy (XPS)................................... 42

Contact Angle of PPVS Homo- and Copolymers........................... 44

3 HOMOPOLYMERIZATION AND COPOLYMERIZATION OF PVS......... 45

Homopolymerization................... .................................................................. 45

Initiators.................................... ................................................................... 47

Nature of the Propagating Carbanion............................... ......... 48

Effect of Temperature......................................................................................... 52

Effect of Temperature on Initiation of PVS ..................................... 54

Effect of Temperature on Polymerization........................... ...... 59

Conversion of () PVS With Time ................................................................ 65

Polymerization and Studies of (+)-PVS..................................................... 67









Copolymerization of Styrene and PVS .................................... .... 67

A-B Copolymers ................................................................................................. 67

A-B-A Copolymers.................. ......................................................................... 76

Proof of Dianion Formation in the Lithium Naphthalide Initiated
Polystyryllithium............... ........................................ .............................. 79

4 THERMAL ELIMINATION STUDIES................................................................... 85

Mechanism of Sulfoxide Elimination ............................................................. 85

Use of Sulfoxides as Acetylene Synthons........................................ 88

Michael Addition-Elimination ................................................................. 88

Alkylation-Elimination......... ......................................................................... 88

Sulfenylation-Dehydrosulfenylation................................................... 91

Diels-Alder Cycloadditions and Elimination..................................... 91

1,3 Dipolar Cycloaddition and Elimination .................................... 91

Elimination of PPVS and PS-PPVS Copolymers........................... 91

Fate of Phenyl Sulfenic Acid........................................................................ 94

Thermal Methods for Study of Elimination.............. ....... 98

Thermogravimetric Analysis (TGA) ....................................................... 98

Pyrolysis-Mass Spectrometry ....................................... 106

Studies of the Elimination of PPVS by Spectroscopic Methods .......112

X-Ray Photoelectron Spectroscopy (XPS)................................ 1 12

Nuclear Magnetic Resonance (NMR).......................................................1 16

Infrared (IR) ............................... ........................................ 125

REFERENCES.................................................... ................................................................... 129

BIOGRAPHICAL SKETCH............................... ........................................................................ 1 35
















KEY TO ABBREVIATIONS

PVS..................................... phenylvinylsulfoxide

PPVS...................................... poly(phenylvinylsulfoxide)

PPVO................................. poly(phenylvinylsulfone)

PA ..................................... polyacetylene

PS............ polystyrene

EPS....................................... ethy lphenylsulfoxide

TPML ...................... ....... tripheny lm ethyllithium

1,1-DPE................................... 1,1-diphenylethylene

GC................................... gas chromatography

SEC ...................................... size exclusion chromatography

M W................................ molecular weight

Mn........................................... number average molecular weight

Mw............................................ weight average molecular weight

Mp ............................................. peak molecular weight from SEC

XPS ..................................... X-ray photoelectron spectroscopy















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

THERMAL ELIMINATION OF POLY(PHENYLVINYLSULFOXIDE)
AND ITS STYRENE BLOCK COPOLYMERS

By

Rustom Sam Kanga

December 1988

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

The polymerization of phenyl vinyl sulfoxide (PVS) was carried out
in THF at -780C using various anionic initiators. It was found that

delocalized carbanion initiators such as triphenylmethyllithium are
effective initiators as are methyllithium and the dipole stablilized

1-lithio-1-(phenylsulfinyl) ethane. There was excellent correlation

between the measured molecular weight and the calculated molecular

weight. The molecular weight distribution was found to be narrow (<1.4).

The polymerization reaction was found to be extremely rapid with a half

life time of about 4 seconds. A side reaction at higher temperatures was

observed leading to broadening of the molecular weight distribution. The

effect of counter ion, solvent polarity and temperature on the

polymerization reaction was investigated.

Both A-B and A-B-A block copolymerization were carried out. The

A-B diblock copolymerization was carried out by vapor-phase


viii









polymerization of styrene in THF at -78oC using t-butyllithium initiator

followed by capping with 1,1-diphenylethylene. The capped

polystyryllithium was used for initiation of the PVS block. The A-B-A

triblock copolymerization was carried out by reacting two-ended

polystyrene prepared by using lithium naphthalide as initiator with 1,1-

DPE to give a capped stable living dianion of polystyryllithium which

initiated PVS at both ends to give an A-B-A triblock copolymer,

polystyrene being the inner block. The molecular weight distributions of

the block copolymers were, in general, narrower than the homopolymers.

The thermal elimination of the homo and copolymers was studied by

TGA and pyrolysis-MS. The TGA of homopolymers typically show two

degradation stages: one at lower temperatures corresponding to

elimination of phenyl sulfenic acid and one at higher temperatures

corresponding to polyacetylene degradation. Pyrolysis-MS was used for

elucidating the fate of phenyl sulfenic acid formed upon elimination. XPS

was used to monitor the elimination reaction with temperature. Proton

NMR was also used to characterize the elimination process and shows

formation of cis and trans polyenes at high temperatures (>100oC). A

change in IR spectra with temperature was observed but gave no useful

information about the polyenes formed.

Preliminary studies carried out elsewhere show a relatively short

conjugation length in the polyacetylene formed. Preliminary conductivity

measurements are in progress.














CHAPTER 1
INTRODUCTION

In the course of previous investigations on the mechanism of anionic

oligomerization and polymerization of phenyl vinyl sulfoxide (PVS) [1, 2] it
was discovered that poly(phenylvinylsulfoxide) (PPVS) upon standing,
either in the solution or the solid state, at room temperature changed color
from white to yellow within 24 hours. The polymer then became red and
finally black within one week. The color change occurred in dark or in the

presence of light. It occurred in air, under vacuum or under an argon

atmosphere. The color change, indicating decomposition of some type, was
suppressed to some extent by storage at freezer temperatures.
These color changes were also observed while warming in a melting

point apparatus and were essentially immediate upon heating the polymer
above 100-150oC. Interestingly when PPVS was oxidized to

poly(phenylvinylsulfone) the above color changes were not observed upon
heating. The color changes were consistent with the formation of

polyacetylene through a concerted, cyclic, sigmatropic thermal elimination
of phenyl sulfenic acid from PPVS illustrated in Figure 1-1. The sulfoxide

elimination was first proposed by Kingsbury and Cram [3] and later used as

an acetylene equivalent in a Michael addition-elimination [4-9], and a
Diels-Alder cycloaddition-elimination [10] for introduction of a vinyl group

in organic syntheses. Thus PPVS could be regarded as a soluble

polyacetylene precursor.














CH2- CH Ph

II


Phenyl vinyl sulfoxide


2000C


H H


Poly(phenylvinylsulfoxide)


S O S O
Ph Ph

Poly(phenylvinylsu lfoxide)


Polyacetylene




Ph-S-O-H


Figure 1-1. Scheme for the elimination of phenyl sulfenic acid from
PPVS.


R-Li
-780C
THF









Polyacetylene (PA)
Polymers with conjugated n-electron backbones are currently of

intense research interest worldwide [11-20]. This is because this class of
polymers displays unusual electronic properties such as low energy optical
transitions and low ionization potentials. As a result they can be oxidized
or reduced more readily and reversibly than conventional polymers without
conjugation [11]. Therefore an insulating polymer could be converted into
conducting polymers with near metallic conductivity in many cases.
Polyacetylene, the simplest conjugated polymer has become a prototype in
the conducting polymers field and has been the most widely studied of the
conducting polymers.
The main impetus for the study of conducting polymers was provided
when Shirakawa [12] successfully synthesized PA as a coherent free
standing film. They used an unusually high concentration of a Ziegler-type
catalyst system. When acetylene gas was introduced into a vessel
containing Ti(OC4H9)4 / AI(C2H5)3 (AI:Ti::4:1) in toluene (0.1-0.2 M in Ti)

at -78OC, a lustrous film formed at the gas-liquid surface. This polymer
referred as "Shirakawa polyacetylene" had a lustrous, golden appearance
and predominantly cis-geometry and was an insulator. The cis-PA
isomerized to trans at higher temperatures (>1500C) or upon doping with
electron acceptors such as iodine or AsF5 (called p-doping) or with

electron donors like sodium or potassium naphthalide (called n-doping). In
the pristine form cis-PA is an insulator (a = 10-9 S/cm) whereas trans-PA
is a semi-conductor ( = 10-5 S/cm). Upon doping, however, conductivities

as high as 103 have been obtained [13]. Recently Naarman in W. Germany
[14] report an improved synthesis of PA with fewer SP3 defects having

conductivity in the range of 1.5 x 105 which is about one-fourth the









conductivity of copper by volume and twice the conductivity of copper by

weight!

The doping of conjugated polymers results in high conductivities

primarily by increasing the carrier concentration. The description of this

process as doping is a misnomer since dopant concentrations are

exceptionally high compared to the conventional doping of inorganic semi-

conductors. In some cases the dopant constitutes about 50% of the final

weight of the conducting polymer [11]. Thus the system would be more

appropriately described as a conducting charge-transfer complex rather
than a doped polymer. Conductivity in doped polymers may be due to

electron transport through the chain (intramolecular), between chains

(interchain transport) and also through interparticle contact [11].

PA is an inconvenient material for fabrication. It is insoluble in all

solvents and cannot be melt processed. Intractability is the major hurdle

for large scale commercial application of PA. Also PA as synthesized can

undergo oxidation in air fairly readily resulting in a severe drop in

conductivity [13].

Another problem is contamination of the PA sample with catalyst

residues which may influence the detailed outcome of the individual

measurements of conductivities which varies with the details of

preparation, recovery, and the washing technique. PA has a fibrullar mat

morphology in which only one third of the space available is occupied by

the PA fibrils. Generation of alternate morphologies has resulted in little

success. The necessity of producing the film at the interface between a

catalyst solution and acetylene gas limits the physical form in which PA

can be produced and this restricts the utility and applicability of direct

synthesis. Considerations of this kind lead to the conclusion that a two









step precursor route to synthesis of PA would be advantageous in
circumventing one or more of the above problems. Thus a soluble precursor

could be generated which on further chemical reaction would yield PA in
the second step.
Precursor Routes to Polvacetylene

Precursor routes to PA are not unknown [16-20]. Marvel et al. were

the first to consider dehydrohalogenation of polyvinylhalides to from PA

[15]. Unfortunately they found that under the extreme reaction conditions
used (high temperatures in presence of high local concentrations of HX) the
nascent polyene formed undergoes further reactions.
Precursor routes for PA syntheses have been extensively studied by

Feast in Durham, U.K. Their approach is outlined in Figure 1-2 and 1-3. The
precursor polymers are synthesized by a metathesis ring-opening
polymerization of monomers like 7,8-bis(trifluoromethyl) tricyclo
{4.2.2.02,5} deca-3,7,9-triene (Figure 1-2) [17, 18]. These precursor

polymers are obtained as colorless soluble materials by conventional
reprecipitation and films or fibres could be spun from solution. A

1,2-disubstituted benzene is thermally eliminated from the precursor

polymer in a symmetry allowed step to yield PA. Cis-PA is initially
formed which isomerizes to trans-PA at higher temperatures. Under
increasingly applied stress ordered films of PA can be produced. This two

step approach allows a whole range of new morphologies to be prepared and

investigated [16,17].

Recently Grubbs [20] found that ring opening metathesis
polymerization (ROMP) of benzvalene yields poly(benzvalene) which is a

polyacetylene precursor. ROMP of benzvalene was achieved using well-
defined non-Lewis acid tungsten alkylidene metathesis catalysts like













CF3


CF3,


WCI6

Me4Sn


7,8-bis(trifluromethyl)
tricyclo-[4.2.2.02'5]
deca-3,7,9-triene


CF3


A



j CF3


Trans-polyacetylene
Cis-polyacetylene

Figure 1-2. Precursor route -1- to "Durham Polyacetylene."













CF3


CF3,


WCI6

Me4Sn


3,6-bis(trifluo romethyl)pentacyclo
[6.2.0.02,4.03,6.0,7 ]dec-9-ene


CF3 CF3



+


nn


Trans-polyacetylene


Cis-polyacetylene


Figure 1-3. Precursor route -2- to "Durham polyacetylene."









Schrock's catalyst {(RO)2W(N(2,6-(iPr)2Ph))CHC(Me)3} [Figure 1-4].

Poly(benzvalene) isomerizes to PA by the action of transition metal
catalysts like HgC12, HgBr2, and Ag* salts in THF. The thermal and

photochemical isomerizations were unsuccessful.

The SEC studies of poly(benzvalene) reveals a very broad molecular

weight distribution ranging from 1000 to 600,000 with average molecular

weight approximately 20,000 (relative to polystyrene standards). The

conductivities of the doped PA was 1 S/Cm [20] which was comparable to

Durham PA but is much lower than Shirakawa and Narmann PAs. This may

be due to the amorphous morphology formed during the isomerization.

The synthesis of PA from PPVS in our case has potential advantages.

Firstly the polymerizations of PVS proceeds through stable carbanions

(Chapter 3) so that the molecular weight distribution is expected to be

narrow (unlike those of the Durham and Grubb precursors). Moreover the

control of molecular weight through the ratio of monomer to initiator is

quite good and thus formation of high molecular weight PPVS is possible.

As a result a series of monodisperse PAs of known molecular weights is

possible. Unlike the previous precursor routes which use exotic and

difficult chemistry, the anionic polymerization of PVS is simple and uses

readily available reagents and well-known techniques.

A second advantage of the sulfoxide precursor route to PA is the

formation of A-B and A-B-A type copolymers with monomers like styrene,

butadiene, isoprene etc which are accessible through living anionic

polymerizations. These may then be subjected to elimination to form block

copolymers of styrene (or other monomers) and PA. Previous attempts to

make block copolymers of PA have been known [21-24]. There have been

two different approaches to make PA block copolymers. Aldissi [21-22]















ROMP


(tBuO)2W(N(2,6-(iPr)2Ph))C HC(Me)3


Benzvalene


Polybenzvalene


HgCI2, HgBr2
or Ag+


Polyacetylene


Figure 1-4. Ring opening metathesis polymerization of benzvalene
to polybenzvalene, a polyacetylene precursor.









had proposed an "anionic to Ziegler-Natta catalyst" approach wherein the

styrene, isoprene etc have been polymerized anionically followed by
addition to a Ziegler-Natta catalyst like Ti(OBu)4 which exchanges one of

the ligands with the anionically growing polymer chain. Acetylene gas was

then introduced to make the soluble block copolymer. Baker and Bates have

used a similar approach to make both block and graft copolymers [23].

Stowell et al. [24] on the other hand used the "anionic to metathesis

catalyst" approach to make block copolymers of PA. They react the growing
polystyryllithium with a co-ordination catalyst like WC16 and polymerize

acetylene with the WCI6/polystyryllithium catalyst. Our approach to make

block copolymers would be one using the traditional anionic block

copolymerization technique where styrene is first polymerized using

alkyllithium initiator followed by capping with 1,1-diphenylethylene and

the capped polystyryllithium would be used to polymerize PVS. The

copolymer could then be subjected to thermolysis to make the

poly(styrene-b-acetylene).
Thus the purpose of the present study was twofold: (i) to synthesize

and characterize PVS homopolymers and its block copolymers with styrene

(both A-B and A-B-A) and (ii) to demonstrate the thermal elimination of

phenyl sulfenic acid from the homo- and copolymers to form PA and its


block copolymers.














CHAPTER 2
EXPERIMENTAL

High Vacuum Anionic Polymerization Techniques

Anionic polymerizations are extremely sensitive to trace amounts of

electrophilic impurities. Thus rigorous techniques for purification of

reagents and solvents were found to be necessary. Also most of the

reagents, solvent transfers, etc. were carried out under high vacuum (10-6

Torr).

High vacuum line techniques have been well known for decades

[25,26,27] and routinely used in our group. The vacuum system consists of

a rotary oil pump in conjunction with a mercury or oil diffusion pump. The

vacuum line was custom made in our glass shop, constructed entirely of

pyrex glass. High vacuum pyrex ground glass joints (Eck & Krebs) were

used at various junctions in the line to permit evacuation of reaction

vessels and distillation of solvents from one part to another. A mercury

McCleod gage attached to the manifold was used to monitor the pressure in

the system.

The reaction vessels used in most of the reactions were made from

pyrex and were self built by use of a hand-held gas and oxygen torch. The

manipulations required for various reactions like addition, transfer of

reagents etc. were performed in vacuo using the breakseal technique

[25,26]. The glassware used was scrupulously cleaned using in order: KOH

/ isopropanol (15% W/V), 1% HF, rinsed with water and acetone and dried

before attaching it to the line. Once attached to the line the whole system









was evacuated and flamed thoroughly with a torch to remove traces of

adsorbed water vapor and oxygen from the surface of the glass. The system

was then checked for the presence of pinholes using a Tesla coil. Reactions

were carried out only after confirming "sticking vacuum" (10-6 Torr) as

registered on the McCleod gage.

Purification of Solvents. Monomers and Reagents

All polymerizations and other reactions were carried out under high

vacuum in THF. Since anionic polymerizations involve reactive

intermediates, it was found necessary to use highly purified and dry

reagents and solvents. THF was purified by refluxing over a

sodium/potassium alloy for 24 hrs., followed by distillation onto fresh

alloy in a round bottom flask which was then flushed with argon and

connected to a vacuum line equipped with a water-jacketed condenser. A

small amount of benzophenone was added as an indicator. The THF was

evacuated and degassed several times. The color turned purple which

indicates formation of the benzophenone dianion and absence of protic

impurities and oxygen.

Purification of Phenylvinylsulfoxide and Ethylphenylsulfoxide

Phenylvinylsulfoxide (Aldrich) in the crude form is a dark brown high

boiling liquid. The crude phenylvinylsulfoxide was stirred over calcium

hydride for 24 hrs., followed by distillation in a Vigreux distillation

apparatus at 100-1100C / 0 mm Hg onto fresh calcium hydride. This

procedure was repeated thrice. The colorless distillate from the last

distillation was collected in a break-seal equipped ampule and further

divided as needed. Care was taken while sealing to make sure that none of

the high boiling monomer remains at the site being sealed and which might

degrade forming undesirable impurities.









Other purifying agents were tried but did not work. The monomer
became black within minutes when stirred over potassium mirror. McGrath

[28-29] has advocated the use of triethylaluminum for the purification of
acrylate and methacrylate monomers. The trialkylaluminum forms a
colored charge-transfer complex with the carbonyls of the monomer and
hence is self-indicating in the titration. We tried using triethylaluminum
once with disastrous results! There was a strong exothermic reaction
between PVS and triethylaluminum and ultimately an explosion!
The monomer was characterized by GC (>99% pure) and by proton and
carbon-13 NMR.
1H NMR (CDC13, 200 MHz, a in PPM): d at 5.85 (1H), d at 6.15 (1H), d

of d at 6.6-6.8 (1H), 7.45 (3H),7.6 (2H)
13C NMR (CDCI3, 50 MHz, i in PPM): 121 (vinyl methylene), 125

(ortho aromatic carbons), 131.5 (para carbon), 143 (vinyl methine), 143.5

(substituted quarternary aromatic).
(+) Poly(phenylvinylsulfoxide) was synthesized by M. Buese [2]. It
was purified by distilling twice over calcium hydride. The optical
rotation, [a]D20, was found to be 358.50.

Ethylphenylsulfoxide (ICN Pharmaceuticals, INC.) was purified in a
similar manner.
1H NMR (CDC13, 200 MHz, a in PPM): t at 1.1 (3H), q at 2.75 (2H), m at

7.6 (5H).
13C NMR (CDC13, 50 MHz, a in PPM): 10 (methyl), 52 (methylene),
126,131,132,147(aromatics).
Purification of Styrene and 1.1-Diphenylethylene

Styrene (Fisher) was purified by stirring over calcium hydride for 24
hrs. followed by fractional distillation under vacuum (7500C / 95 mm Hg).









The middle fraction was collected in an ampule. The ampule was further

attached to an apparatus shown in Figure 2-1 and evacuated. The side arm
contained freshly cut potassium metal which was heated gently with a
torch to form a shiny mirror in the main container. Styrene was then added
onto the mirror and allowed to stir gently for 30 minutes. After degassing
it was distilled into the side flask provided with a break-seal and
carefully sealed off from the main apparatus. The extremely pure and dry
styrene was stored in the freezer and used as needed. Styrene-d8 (Aldrich)
was purified by distilling twice over calcium hydride in vacuo.
Styrene: 1H NMR (CDCI3, 200 MHz,a in PPM): d at 5.11 (1H), d at 5.59

(1H), d of d at 6.59 (1H), 7-7.5 (5H)
Styrene: 13C NMR (CDCI3, 50 MHz, a in PPM): 113 (vinyl methylene),

126 (ortho aromatics), 127.8 (para aromatic), 128.5 (meta), 137 (vinyl
methine), 138 (substituted quarternary). Styrene-d8: 1H NMR (neat with
TMS, 200 MHz, a in PPM): t at 5.0 (1H), t at 5.5 (1H), d at 6.5 (1H), s at 7.0
(para 1H), s at 7.1 (meta 2H), s at 7.25 (ortho 2H).
13C NMR (neat with 1% CDCI3, 50 MHz, a in PPM): pentet at 112.5
(vinyl methylene CD2), t at 125.6 (aromatic ortho CD), t at 126.9 (aromatic

para CD), t at 127.7 (aromatic meta CD), t at 136.2 (vinyl methine CD), s at
137.1 (substituted aromatic quarternary C). All assignments made from
non-deuterated styrene in Sadtler.
1,1-Diphenylethylene was purified in a similar manner. 1H (200 MHz,
CDCI3, a in PPM): s at 5.4 (2H), m at 7.2 (10H)
13C (50 MHz, CDCI3, a in PPM): 114 (=CH2), 127.5 (ortho aromatic),

128.1 (m and p aromatic), 141.5 (ipso aromatic), 150 (>C=).





































potassium
mirror


Apparatus used for purification of styrene.


Figure 2-1.










Purification of t-Butyllithium

It was found that the crude t-butyllithium (Aldrich) contained

undesirable impurities like lithium t-butoxide, lithium hydroxide etc. It

was thus found desirable to further purify t-butyllithium by sublimation of

the crude product [30]. The apparatus shown in Figure 2-2 was used.

Crude t-butyllithium was introduced in "a" under a constant flow of

argon. The solvent was pumped off into the trap and the side arm sealed.

Crushed dry ice was put in the cork ring on the flask "b" to trap the

subliming t-butyllithium. The lower part of the apparatus was immersed

in a hot water bath (850C) and the combination of heat and dynamic vacuum

was used to sublime highly pure t-butyllithium which was trapped in "b"

while the impurities remained unaffected in "a." The flask containing the

t-butyllithium was sealed off from "a" at the constriction "S1" and from

the line at "S2." Extreme care was taken to see that none of the

t-butyllithium remained at the sites "S1" and "S2" which might form

undesirable decomposition products and might also create pinholes. The

shiny white solid t-butyllithium was then dissolved in Na/K dried hexane

and further subdivided as needed.

Preparation of Initiators

Lithium Naphthalide

Lithium wire (Mallinckrodt) was cleaned by dipping successively in

methanol, hexane, and finally THF. A THF solution of naphthalene (Aldrich,

Gold label) was prepared in vacuo in a break-seal equipped ampule. An

excess of naphthalene was used to avoid formation of the naphthalene

dianion [31, 32]. The lithium metal was introduced in the reaction vessel

under a constant flow of argon. After evacuation more THF was distilled

in. The naphthalene solution was then added in. A noticeable color change

















































Figure 2-2. Apparatus used for purification of t-butyllithium by
sublimation.










was observed upon reaction of naphthalene with lithium metal. The

reaction was allowed to proceed at 250C for 12 hrs. At the end of 12 hrs. a

dark green solution was obtained which was filtered through a course frit

into various ampules. The concentration of the initiator was determined as

described later.

Triphenylmethilithium (TPML)

TPML was made as described in reference 33. A THF solution of

triphenylmethane (TPM) was prepared in vacuo and attached to an apparatus

illustrated in Figure 2-3. The apparatus was attached to the line,

evacuated and flame degassed. Argon was then charged into it and

n-butyllithium was injected through the serum cap. Both argon and the

solvent were removed by distillation into the cold 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.

THF was then distilled into the n-butyllithium and the TPM solution was

added from the ampule through the breakseal. The solution started turning

red almost immediately and was allowed to stir at room temperature for

8-10 hrs. THF was then distilled from the solution into the trap leaving

behind the dark red TPML. The apparatus was then cooled to -78oC and

dried hexane was distilled into the flask (THF:Hexane approximately 1:15).

The apparatus was sealed from the line and the recrystallized TPML was

washed with the hexane. This was accomplished by pouring the hexane

from the main body of the apparatus into the wash ampule and distilling

back into the main body. After repeating this procedure several times the

hexane was removed from the main body in the wash ampule.

The apparatus was reattached to the line and THF was distilled in to

dissolve the TPML salt. The TPML solution was poured into a separate


















































Figure 2-3. Apparatus used for the preparation of TPML.









ampule and sealed off from the main body. The initiator was stored at

-20oC and was further divided as needed. The concentration of the

initiator was determined as described later.

1.1 Diphenvlhexyllithium (DPHL)

DPHL [33] was prepared by reaction of equimolar amounts of

1,1-diphenylethylene and n-butyllithium in THF at room temperature for 12

hrs. The reddish orange salt was purified by washing with hexane as

described for TPML. The THF solution of DPHL was stored at -20oC and

divided as needed. The concentration of the initiator was determined as

described later.

Triphenylmethylpotassium (TPMK)

TPMK was synthesized by reaction of a 1.1-molar excess of a

solution of TPM in THF with a solution of oligomeric dianions of
a-methylstyrylpotassium (aMSK) in THF prepared by reaction of

alphamethylstyrene in THF with potassium metal for 24 hrs at 250C [34].

A THF solution of TPM was prepared in vacuo in a breakseal equipped

ampule. The red solution was filtered through a frit and divided into
ampules. The THF solutions of TPM and aMSK were reacted with each other

in vacuo at room temperature for 2 hrs. After the reaction the TPMK

solution was sealed from the line and divided into various ampules. The

concentration of the TPMK solution was measured as described later.

1-Lithio-1-(Phenvlsulfinvl) Ethane (EPSL)

EPSL [1, 2] was synthesized by a reaction of a 1.1 excess of

ethylphenylsulfoxide with methyllithium in THF at -780C. The apparatus

used for the synthesis is illustrated in Figure 2-4. The apparatus was

attached to the line and evacuated. Argon was then charged into it through

the line and methyllithium was injected through the serum cap. The
















































Figure 2-4. Apparatus used for the synthesis of EPSL.









solvent was carefully removed by distillation into the trap as the solution

tended to bump in the apparatus. The serum cap was sealed off and THF

was distilled to make a solution of methyllithium. The solution was then

cooled to -78oC and ethylphenylsulfoxide was added from the ampule

through the breakseal. The solution started becoming yellowish as the

methyllithium reacted with ethylphenylsulfoxide to form the carbanion.

The solution was degassed several times to remove the methane gas and

was stirred at -78oC until no more methane gas evolved (as evidenced by

the bubbling of the solution upon degassing and the characteristic pump

noise). The yellowish-green solution was sealed from the line and poured

into a side ampule which was sealed off. The initiator was stored at -20oC

and divided as needed. The concentration of the initiator was determined

as described below.

Determination of Concentration of Carbanions

For polymerization reactions concentration determination of metal

alkyls and the delocalized carbanion salts was necessary. Thus, for anionic

polymerizations in the absence of terminating impurities the number

average molecular weight can in principle be predicted if the accurate

concentration of the initiator is known. Also for two-ended carbanions the

accurate determination of the concentration was imperative in order to

prove the "two-endedness" of the system. Two methods were used for

determination of concentration of initiators. The agreement between the

two methods was found to be excellent (5%).

Titration with Fluorene

The fluorene (Aldrich) used in titrations of the carbanion solutions

was purified by crystallization from ethyl alcohol and pumped on the









vacuum line for several days to get rid of the traces of alcohol. Purity was

better than 99% by GC.

The carbanion solutions in THF are reacted with a known excess of

fluorene in THF at -78oC. In most cases the reaction of the carbanions

with fluorene was instantaneous as seen by an immediate color change of

the solution to yellowish-orange, the characteristic color of
fluorenyllithium. The fluorenyllithium was then reacted with an excess of

methyl iodide to form 9-methylfluorene and the ratio of fluorene to

9-methylfluorene was determined by capillary GC.

Determination of Concentration by UV/Visible Spectroscopy

UVNis was found to be an excellent method for concentration

determination since most delocalized carbanions have distinct and strong

absorptions in the visible region.

All of the absorbance measurements were carried out under high

vacuum using an apparatus equipped with a UV cell. The absorbance of the

unknown carbanion was measured followed by a reaction with an excess of

fluorene. The absorbance of the fluorenyl carbanion thus formed was

measured. Comparison of the two absorbances and the molar absorptivity

of the fluorenyl carbanion from the literature [35, 36, 37] provided the

molar absorptivity and hence the concentration of the unknown carbanion

solution. This technique was found to be most convenient for solutions of

living polystyryllithium capped with 1,1-diphenylethylene. The capped

solutions are quite stable at room temperature during the time of

spectroscopic determination and it also avoids the problem associated

with the entrapment of fluorene and 9-methylfluorene in the polymer

matrix during precipitation of the polystyrene in methanol (Method I).










The ampule containing the carbanion solution was attached to an

apparatus which was provided with a quartz cell having a 2 mm path

length, in conjunction with a 1.9 mm spacer. The whole system was

attached to the line, evacuated, flamed and sealed off the line. The

carbanion solution was introduced in the cell from the ampule through the

breakseal and scanned in the visible and near UV regions. The fluorene was

then introduced. A change in color was noted as the carbanion reacted with

the fluorene to form fluorenyllithium. After all the carbanion reacted the

fluorenyllithium was scanned in the UV region.

Assuming Beer's law to be applicable to both the carbanion solutions

[25] one can write the following equations:
Ax = ex Cx I................ ...................................................................................................2 1

Ay = ey Cy I.................................................... 2 2

Cy -A y ex Cx / Ax y....................................................................................................... 2 3

where x refers to the unknown carbanion solution and y to the
fluorenyllithium, A = absorbance, e = molar absorptivity, C = concentration

of the absorbing species, I = path length, determined using a known
standard solution of Potassium Chromate (e372nm = 4815) [37].

Since Cx = Cy (assuming no inadvertent protonation of the carbanion during

the reaction) we get ex = Ax/Ay ey. Knowing ex one can calculate the molar

concentration of the unknown carbanion solution using the equation 2-3.

Polymerization of Phenylvinylsulfoxide

The homopolymerization of phenylvinylsulfoxide (PVS) was carried

out using the apparatus illustrated in Figure 2-5. The system consists of

two round bottom flasks "a" and "b" (100 ccs and 50 ccs respectively)

joined together. The ampules containing the initiator (TPML, methyl

lithium, DPHL etc) and the terminating agent (usually methanol) were













MeOH
Initiator

pVS































Figure 2-5 Apparatus used for the homo- and copolymerization of
PVS.









attached to "a" along with a ground glass joint to hook it to the vacuum
line. The monomer ampule is attached to the smaller flask ("b").

The apparatus was hooked to the vacuum line, evacuated and flamed

thoroughly. The initiator solution was introduced into flask "a" through the

break seal. The ampule was "washed" with the solvent using a cold cotton
dauber in order to remove all of the initiator solution. Dried THF was then

distilled in "a" to dilute the carbanion solution and the carbanion solution

was thoroughly cooled to -78oC. The apparatus was then carefully sealed
from the line at S1. The monomer breakseal was then broken and the
monomer was introduced in the flask "b." THF was distilled into "b" from

the carbanion solution. Care was taken to see that the initiator solution

did not bump during the distillation. After sufficient dilution of the

monomer both the initiator and the monomer solutions were cooled to

-78OC as was the tube connecting the two flasks. The solutions were then

rapidly mixed by pouring "b" into "a." An immediate change in color is

usually seen, in the case of TPML from dark red to yellowish-green. This

indicated that the initiation of PVS is quite rapid. After a few minutes

more monomer is added. This procedure is repeated several times until all

the monomer is consumed. The time of polymerization varied from 15

minutes to 12 hours. The yellowish-green color of the living
a-phenylsulfinyl carbanion persists throughout the polymerization. The

chain terminating electrophile (usually methanol) was then added to the

polymerizing solution resulting in an immediate discharge of the

yellowish-green color.

The solvent from the polymerization reaction was rotovaped down

and the polymer was precipitated by pouring into a ten times excess

diethylether solvent. The yield of poly(phenylvinylsulfoxide) (PPVS) was









determined by weighing and the polymer was characterized further by NMR,
SEC etc. The PPVS was found to be thermally unstable and starts becoming
yellow within a matter of days. It was thus found necessary to store the
polymer in the freezer under argon.
Poly(phenylvinylsulfoxide): 1H NMR (CDC13, 200 MHz, Z in PPM):
1.1-2.1 (2H), 2.5-3.5 (1H), 7.2-8 (5H)
Poly(phenylvinylsulfoxide): 13C NMR (CDCI3, 50 MHz, 9 in PPM): 26-
32 (methylene in the chain), 56-60 (methine), 123-126, 128-130, 131,
140-142 (aromatic carbons)
(+) Poly(phenylvinylsulfoxide) [alpha]D20= 408: 1H NMR (CDC13, 200

MHz, a in PPM): 1.3-2.3 (2H), 2.7-3.6 (1H), 6.7-7.7 (5H)
(+) Poly(phenylvinylsulfoxide): 13C NMR (CDC13, 50 MHz, a in PPM):
55-57 (methylene), 23-26 (methine), 123-126 (aromatic meta carbons),
128-130 (aromatic ortho carbon), 130-132 (aromatic para carbon), 140
(substituted aromatic quarternary carbon).
PPVS upon oxidation to poly(phenylvinylsulfone) (PPVO) becomes
stable to air (or thermal) degradation. PPVS was oxidized to PPVO by
hydrogen peroxide [1, 2, 38]. The polymer was dissolved in glacial acetic
acid. An excess of 30% hydrogen peroxide was added. The polymer solution
was allowed to stir at room temperature for 12 hrs. A bright white ppt
was formed upon completion of the oxidation. The resulting PPVO was
found to be insoluble in most solvents and partially soluble in chloroform
and THF. Oxidation of the sulfoxide to the sulfone was seen to be
quantitative by IR measurements and also by XPS (see Chapter 4).









Copolvmerization of Styrene and Phenylvinvlsulfoxide

A-B Copolvmers

A-B copolymerization of styrene and PVS was carried out in two

steps: (a) Polymerization of styrene was first carried out at -78oC in THF

initiated by t-butyllithium [25] followed by capping with

1,1-diphenylethylene (1,1-DPE) followed by division of the capped living

polystyryllithium into various ampules. (b) Polymerization of various

amounts of phenyl vinyl sulfoxide was then carried out by using the capped

living polystyryllithium as the initiator.

Polymerization of styrene was carried out in an apparatus

illustrated in Figure 2-6. Once again the basic apparatus consists of 2

round bottom flasks "a" and "b" (500 ml and 50 ml respectively). The

ampules containing the initiator (t-butyllithium) and the capping agent

(1,1-DPE) are attached to flask "a." The monomer (styrene) ampule is

attached to flask "b." The flask "b" is connected to "a" with a tube which

extends into "a" at the top forming a lip. Additionally there are 2 ampules

Al and A2 equipped with breakseals having volumes 10 ml and 100 ml

respectively.

Once the apparatus was assembled it was attached to the vacuum

line through the ground glass joint, evacuated, checked for pinholes and

flamed. The initiator was added from the ampule through the breakseal

into flask "a" and washed down using a cold dauber. THF was then distilled

into the initiator solution by cooling flask "a." The color of t-butyllithium

turned yellow upon distillation of THF. This was probably due to

deaggregation of the t-butyllithium in going from hexane to THF. It is also

known that t- butyllithium reacts with THF at 250C to form various

alkoxides [25]. However the yellow color observed was probably not due to


















Initiator


Styrene


Figure 2-6. Apparatus used for the polymerization of styrene.









this reaction since the solution was kept at -78oC at all times. Several

precautions were taken before styrene was distilled in; the level of the

isopropanol/dry ice bath was kept below the level of the initiator and the

path between the flasks "a" and "b" was kept warm using an air dryer.

These precautions were warranted to make sure of a uniform vapor phase

distillation of styrene into the rapidly stirring initiator solution and to

avoid any local concentration of the monomer which is undesirable. The

excellent molecular weight distributions bear testimony to the correctness

of this technique (see Chapter 3). The breakseal of the styrene ampule was

broken and styrene was slowly distilled from the flask "b" which was

cooled to -20oC. The color of the t-butyllithium solution turned cherry red

instantaneously. After all the styrene was distilled into "a" the solution

was further stirred for 10 to 15 minutes. 1,1-DPE was then added to the

living polystyryllithium solution. The cherry red solution turned dark red

upon reaction. The apparatus was sealed off the line at S1. The solution

was allowed to warm up and was then carefully poured into the side

ampules. The constrictions S2 and S3 were washed using a cold dauber and

the ampules were sealed off the main body.

Ampule Al was used for the detection of the concentration of the

living carbanions by UVNisible spectroscopy and terminated by an

electrophile like fluorene or methanol. The polystyrene was precipitated in

an excess of methanol nonsolvent and characterized using SEC and NMR.

1H NMR (CDCI3, 200 MHz, a in PPM): 0.6 (d, t-butyl), 1.2-1.8 (2H),

1.6-2.3 (1H), 6.3-6.9 (2H), 6.8-7.3 (3H).
13C NMR (CDCI3, 50 MHz, a in PPM): 40-41 (methylene), 42-48

(methine), 125.8 (para aromatic), 127 (ortho aromatic), 128 (meta

aromatic), 145 (substituted quarternary).









Ampule A2 was further attached to a divider (Figure 2-7), thoroughly

evacuated, flame degassed and sealed from the line. The carbanion solution
was introduced into the apparatus and was carefully divided into the

various ampules. After washing the constriction of each ampule the
divider was cooled in a large dewar to -780C and each arm was carefully
sealed off.

The polymerization of phenylvinylsulfoxide initiated by the living
DPE capped polystyryllithium was carried out as described before for

homopolymerization. The length of the styrene block was kept constant

whereas the length of the poly(phenylvinylsulfoxide) was varied. The

composition of the block copolymer was calculated from the moles of
styrene and PVS used for each polymerization. The mole ratio of phenyl
vinyl sulfoxide / styrene was varied between 0.26 to 8.0. The apparatus

was the same as that for the homopolymerization of PVS (Figure 2-5).

Once again a color change from dark red to yellowish-green was noticed
upon addition of the monomer to the initiator and the living copolymer

turned colorless upon termination with methanol. The copolymer was
purified by precipitation in a solvent system comprised of ethyl ether and
methanol (75/25 v/v).

1H NMR (CDC13, 200 MHz, a in PPM): 0.6 (t-butyl), 1.2-1.8 (methylene

of both polystyrene and poly(phenylvinylsulfoxide) blocks), 1.5-2.4

(methine of polystyrene block), 2.5-3.5 (methine of

poly(phenylvinylsulfoxide) block), 6.3-6.9 (2H, ortho aromatic of
polystyrene block), 6.7-7.5 (3H, meta and para aromatic of polystyrene

block), 7-8 (5H, poly(phenylvinylsulfoxide) block)

The copolymer was stored in the freezer and characterized by SEC
and by NMR. Conditions for oxidation of the copolymer were the same as















































Figure 2-7. Apparatus employed for division of a carbanion solution
into several smaller ampules.









that for the homopolymer using an excess of 30% hydrogen peroxide for 24

hrs, yielding the thermally stable poly(styrene-b-phenylvinylsulfone).
A-B-A Triblock Copolymers

The A-B-A copolymers of styrene and phenylvinylsulfoxide like the

AB copolymers were prepared in two steps: (a) formation of living two-

ended polystyryllithium using lithium naphthalide initiator [39] followed

by capping with 1,1-DPE and division of the capped living polystyryllithium
into various ampules and (b) polymerization of various amounts of PVS

using DPE capped two-ended polystyryllithium.

Living two-ended polystyryllithium was prepared in a manner similar

to the polymerization of styrene using t-butyllithium described before.

Lithium naphthalide was employed as the initiator. After assembling the

apparatus (Figure 2-6) it was attached to the vacuum line, evacuated,

checked for pinholes and flame degassed. The initiator solution was

introduced into "b" and cooled to -20OC. The usual precautions were taken

during distillation of styrene in the polymerization solution as described

before. An immediate color change from dark green to cherry red was seen

upon addition of styrene. After all of the styrene was distilled the

solution was further stirred at -78OC for 15 minutes. 1,1-DPE was then

added to the living polystyryllithium. The cherry red color changed to dark

red upon reaction with 1,1-DPE. The apparatus was sealed from the line

and the solution was divided into two ampules as described earlier. The

determination of concentration and workup were similar to that of the
one-ended system.

The second step in the triblock copolymerization was identical to the

diblock. Once again the styrene block length was kept constant whereas

the phenylvinylsulfoxide block length was varied depending on the moles of









styrene used and the ratio of phenylvinylsulfoxide to styrene desired.

Workup of the triblock copolymer was same as that of the diblock.

Monomer Conversion Study

It was found necessary to roughly determine the conversion of

monomer with time, so as to have a rough idea of the kinetics of the

polymerization reaction. Since aliquots of the polymerization mixture

were withdrawn at various times during the polymerization, the

polymerization had to be carried out under rigorously dried argon.

Naphthalene was employed as an internal standard in order to
monitor the consumption of monomer with time. Several factors were

considered for using naphthalene as an internal standard. Naphthalene and

PVS have retention times in GC which are quite different and measurable.

A calibration curve of ratio of moles of phenylvinylsulfoxide to

naphthalene versus the GC ratio of the areas of PVS to naphthalene (Table

2-1) gave a straight line with an excellent correlation coefficient (Figure

2-8). Also naphthalene is inert in presence of living the PPVS carbanions.

The apparatus used during the above polymerization was similar to

Figure 2-5 and consisted of 2 bulbs "a" and "b" joined together. The
initiator ampule was attached to "a" along with a high vacuum stop-cock.

To the flask "b" was attached a monomer ampule and a short outlet with a

rubber septum for aliquot withdrawals. The apparatus was attached to the

vacuum line and the absence of pinholes was checked. Purified argon was

charged to the apparatus and a known amount of naphthalene was added to
flask "b" which was then evacuated again. Care was taken to see that none

of the naphthalene sublimed to the trap under the high vacuum. The

initiator was introduced in flask "a" and the contents of the ampule were

washed down. Additional THF was distilled into the initiator solution











. Calibration for the determination of
of naphthalene as an internal standard.


phenylvinylsulfoxide in the


0 1 2
Area PVS/Area NPH


Figure 2-8. Graph of ratio of moles of PVS to Naphthalene versus ratio of
areas (in GC) of PVS to Naphthalene.


Table 2-1
presence


mol PVS mol NPH mol PVS/mol NPH A PVS/A NPH
x 104 x 104

6.1 1.7 3.6 2.56
5.7 4.3 1.3 0.96
7.7 7.7 1.0 0.68
5.9 9.7 0.61 0.39
5.7 12.2 0.47 0.33
6.5 15.3 0.42 0.31









through the vacuum line. The monomer was then introduced into "b", and

diluted with THF by distillation from the initiator. Both "a" and "b" were

cooled to -78oC. Argon was charged into the apparatus, through the line.

The argon had to be rigorously dried, which was accomplished by using a

solid KOH and drierite traps followed by a cold (-78OC) trap. The stopcock

S between the line and the apparatus was closed off and the apparatus

detached from the line Both the flasks were then cooled to -78oC. The

initiator solution was introduced into flask "b" by tilting the apparatus.

Aliquots of the polymerization solution were withdrawn at various times

during the polymerization through the rubber septum using a syringe and

were quenched in methanol. The quenched solution was added to an excess

of diethyl ether to precipitate the polymer, which was filtered and the

filtrate was rotovaped and analyzed by GC so that the change in

concentration of monomer with time could be determined. The polymer was

dissolved in THF and analyzed by SEC for the change in polymer molecular

weight with time.

Thermal Elimination

Thermal elimination of the homo- and copolymers in the solid state

was carried out using a Thermolyne tube furnace with a suitably equipped

pyrolysis tube (Figure 2-9). The polymer was dissolved in a minimum
amount of THF or chloroform. The solution of the polymer was introduced

into the section "a" using a pipette. The tube was attached to a rotovap in a

horizontal position and was evaporated with a gradual application of

vacuum. The application of vacuum and slow rotation ensured a thin

uniform film surface in the section "a." The tube was then inserted into

the Thermolyne furnace and hooked to the vacuum line. A cold (-78oC) trap

was used between the line and the tube to trap any condensables.




















a





















Figure 2-9. Pyrolysis tube used for the thermal eliminations of the
homo- and copolymers in the Thermolyne tube furnace.









Elimination was carried out by gradually increasing the temperature to

180-2000C and under high vacuum (10-6 torr) for 1.5 hrs. The polymer

after heating became dark black and shiny and was handled under argon

(glove bag) at all times. The eliminated products obtained from the side of

the tube outside the furnace were analyzed by MS, GC, and NMR.
Instrumental Methods

Size Exclusion Chromatograohy (SEC)

SEC was carried out on a Waters 6000-A liquid chromatograph
Phenomenex (Rancho Palos Verdes, CA) TSK Gel G-3000H and G-5000H

columns were employed in series (column dimensions: 75mm x 30cm). The

columns were packed with spherical, crosslinked poly(styrene divinyl

benzene) particles having pore sizes 103 A and 105 A for G3000H and

G5000H respectively. The molecular weight limits for G3000H were 600

to 60,000 and that for G5000H were 10,000 to 106. Polystyrene standards

were supplied by Scientific Polymer Products, Polysciences INC., Pressure

Chemical Co. and Waters Associates. The standards ranged from a

molecular weight of 2000 to 2,00,000. All polymer solutions injected in

the columns were filtered through a 0.5 g PTFE filter ("Alltech", II.).

The eluting solvent was HPLC grade THF filtered through a 0.5 gi

filter. The flow rate was usually 1 ml/minute. The model 6000A solvent

delivery system by "Waters Associate" was utilized. Injection into the

column was achieved by a Waters Associate Model U6K universal liquid

chromatograph injector which allowed loading and injecting samples at a

pressure of up to 600 psi without interruption of the solvent flow. A
Perkin-Elmer LC-75 spectrophotometric UV detector set at 254 nm was

used for detection of the eluting polymer. The detector was interfaced

with a Zenith PC-100 personal computer equipped with a MS-DOS Dascon-1









data collecting program operating at a rate of 1 Hz. The Basic programs

used for data acquisition, molecular weight calibration, computation of

molecular weight averages and distributions were written by W. Toreki in

our group [40]. The Basic program for the conversion of the data into a high

resolution graphics display was written by the author with help from Dr.

Gardiner Myers. Explanations of these Basic programs and the relevant

analytical chemistry involved with it are described elsewhere [40].
A calibration curve was created by injecting various polystyrene

standards and using a correction factor to account for band broadening. The

retention volume of PPVS was then compared to the calibration curve and

an apparent molecular weight for our system was determined. In the

absence of suitable PPVS standards this method was found to be quite

accurate for determination of apparent molecular weight and molecular

weight distribution of PPVS homopolymers and its copolymers with

styrene.

Capillary Gas Chromatography (GC)

Routine analyses of monomers and reagents were done by GC. A

Hewlett-Packard 5880A gas chromatograph was used for this purpose. The

system consisted of a 50 meter (G. E. Co. SE-54) fused silica capillary

column (0.2mm ID) coated with a 0.11 gM film of silicone gum, a

microprocessor capable of automation, a temperature programmable oven

and a flame ionization detector. Helium was used as the carrier gas. A

stepwise gradient temperature program was used so that the oven

temperature increased at a controlled rate for higher resolution.

Nuclear Magnetic Resonance Spectroscoov (NMR)

Proton and Carbon-13 NMR spectroscopy was used as an extensive

tool for structure determination, determination of purity of reagents, for






40


characterizing the microstructure in the copolymers and also for

monitoring the change in the structures of the homo- and copolymers upon

heating. Most of the NMR spectra were recorded on a Varian FT-NMR XL 200

spectrometer featuring distributed microcomputer control and a flexible,

high-storage-capacity memory capable of high resolution Fourier

transform. Deuterated chloroform was used as a solvent in most monomer

and polymer studies. The chemical shifts were reported in PPM using TMS

as a reference.

High temperature NMR was done on a Varian XL-300 NMR

spectrometer featuring the same software as the XL-200. Acetic acid-D4

was used as a solvent. A heavy-walled 5 mm tube was employed and the

polymer solution was sealed under a partial pressure under argon. The

spectra were recorded at room temperature and the temperature was

increased in steps of 200C. A nitrogen atmosphere was used in the probe.

Spectra were recorded at 60, 80, 100, 120, 140, and 1500C.

Infrared Spectroscopy (IR)

Infrared spectroscopy was used for additional structure

determination of the polymers, determination of oxidation of sulfoxide to

sulfone and monitoring of the thermal degradation of PPVS. Routine

measurements were carried out using a Perkin-Elmer 281 IR

spectrophotometer using a pressed KCI pellet or a NaCI window coated with

the polymer. Spectra were also recorded on a Nicolet 5DXB FT-IR

spectrophotometer using NaCI windows under a nitrogen atmosphere. High

temperature IR runs were carried out by Ms. Jennifer Lin in the materials

science department. Spectra were recorded on a Nicolet 60SX FT-IR

spectrophotometer equipped with an "Omega" temperature controller. The

polymer was mixed in diamond powder, mounted and heated under nitrogen









atmosphere. The temperature was increased to 2000C over a period of time

at a heating rate of 50C/min and the spectra were recorded continuously.
UV/Visible Spectroscopv

UV/VIS spectroscopy was used for determination of concentration of

carbanions. A Perkin-Elmer Lambda-9 UVNIS/NIR spectrophotometer was

employed. Quartz cells having a 2 mm path length were used in conjunction

with a quartz spacer. The path length was calibrated using a known

standard solution of potassium chromate. The cells were usually attached

to the reaction vessel and the spectra recorded under high vacuum. A

special spectrometer cover was made by the chemistry department
machine shop designed to prevent extraneous light to interfere with the

measurement. The spectra were usually scanned from 700 nm to 300nm.
THF was the solvent in most cases. The response time was 1 second, scan

speed 120 nm/min, peak threshold 0.02 A, cycles/time 1/0.05 min, using an

automatic lamp.

Polarimetry

The optical activity of the optically active monomer and polymer

was measured using a Rudolph Research Autopol Ill automatic polarimeter.

Pvrolysis-Mass Spectrometry

Pyrolysis-MS was used as a technique for characterizing the thermal
elimination on the homo- and copolymers. It was carried out by Dr. King in

the mass spectrometry laboratory. The mass spectrometer used for this

purpose was the AEI MS-30.

The polymer was inserted using a direct insertion probe. A gradient

temperature from 100 to 5000C was employed. Spectra were recorded

continuously at various temperatures and processed by a "Kratos" data

system.









Thermogravimetric Analysis (TGA)

TGA was carried out on a Perkin-Elmer TGA7 thermogravimetric

system. The system consists of the TGA7 thermogravimetric analyzer

controlled by the TAC7 thermal analysis instrument controller. The
analyzer permits the measurement of weight changes in a sample material

resulting from chemical reactions, decomposition, eliminations etc as a
function of either temperature or time.

The heart of the thermal analysis system is the 32 bit PE-7500

professional microcomputer which allows for totally computerized control

of the TGA7 analyzer. Thus the TGA7 can be programmed to scan a

temperature range by changing at a linear rate over several temperature

ramps or it can analyze data at isothermal temperatures to measure weight

loss/gain with time.
The TGA7 analyzer is made up of 2 major components: a sensitive

ultramicrobalance and a furnace element. Other components of the system

include the GSA-7 gas selector accessory and the graphics plotter.

Before each session the analyzer balance and the furnace were

calibrated over the temperature range used. A curie point temperature

calibration was also carried out using 2 standards: Alumel (1630C) and

Perkalloy (596oC). The polymers were usually scanned under a nitrogen

sample purge (50 ml/min) from 50oC to 900oC at a heating rate 10oC/min.
X-Ray Photoelectron Soectroscopy (XPS)

XPS (also known as Electron Spectroscopy for Chemical Analysis or
ESCA) was used for the determination of the surface composition of the

homo- and copolymers, the determination of oxidation of sulfoxide to

sulfone, and the observation of changes on the surface of the polymers upon

thermal treatment. A Kratos XSM-800 x-ray photoelectron









spectrophotometer was employed for the measurements. All the
measurements were done by Mr. Richard Crockett in the material science
department. The instrument consisted of 2 chambers: (i) sample
treatment chamber and (ii) sample analysis chamber.

The sample was mounted as a film on a 10-sample carousel.
Automation allowed analysis of 10 consecutive samples during a run. Once
the sample is mounted the sample treatment chamber is evacuated. A

rotary oil pump in conjunction with a turbomechanical pump and a cold trap
makes it possible to attain vacuum in the order of 10-8 Torr routinely. The

sample is transferred into the sample analysis chamber only after a
vacuum of 10-8 Torr is attained in both of the chambers.

The sample is irradiated with a low energy Mg K-alpha (1253.6 eV)

X-ray photoelectrons. The kinetic energy of the electron emitted due to the
interaction of the X-rays with the atomic orbital electron is measured and

the binding energy of the electron is calculated. The binding energies of
the various elements are standardized using the Cls peak (285 eV) as the

reference. The instrument is occasionally calibrated using a thin silver
foil (Ag3s 368 eV).

High temperature XPS was carried out using a fast insertion
stainless steel probe mounted on a copper block. The polymer was mounted
on the copper block, introduced in the sample treatment chamber and

evacuated. The sample was scanned at room temperature and heated in the
sample treatment chamber to 100oC for 0.5 hrs. The thermocouple was

standardized to the sample temperature (500C differential). After all the

condensables were removed as registered by the vacuum in the chamber
(10-7 to 10-8 Torr) the sample was introduced in the analysis chamber and

scanned. A similar procedure was followed at 2000C and 3000C.









Contact Angle of PPVS Homo- and Copolymers

Contact angle is a measure of the surface free energy of PPVS homo-

and copolymers. Measurement of the contact angle was carried out by the

captive air bubble method. The polymer was dissolved in chloroform,

coated on a glass slide and was thoroughly pumped in the vacuum oven to

get rid of residual solvent. The coated slide was immersed in water and
constant volume air bubbles were delivered between the polymer film and
the water surface using a 5 p1 syringe. The contact angle of the air bubble

between the polymer film and the water surface was measured after 30 s.
A number of observations were made and the mean of the values was taken.

The contact angle is inversely proportional to the surface free energy.

Thus the higher the contact angle the lower is the surface free energy.













CHAPTER 3
HOMOPOLYMERIZATION AND COPOLYMERIZATION OF PVS
Homopolymerization

The polymerization of phenylvinylsulfoxide (PVS) was investigated.
Most of the polymerization studies were carried out on the racemic
monomer. However the optically active monomer was also investigated

albeit not as thoroughly.
Attempts were made by Mulvaney and Ottaviani to polymerize R-(+)-

isopropenyl p-tolyl sulfoxide using various anionic and radical initiators
which were unsuccessful [41]. Homopolymerization of R-(+)-p-
tolylvinylsulfoxide was also attempted using initiators such as benzoyl

peroxide, azobisisobutyronitrile, n-butyllithium and boron trifluoride
etherate. Once again their attempts failed. n-Butyllithium most likely
attacked the sulfur displacing the aryl group [42] and thus failed to

polymerize the monomer. Kunieda et al. [43,44] tried polymerization of

optically active p-tolylvinylsulfoxide using n-butylmagnesium bromide as

initiator. This gave an optically active polymer of a molecular weight of

2400. However they obtained very poor yields (10%). The successful

polymerization of PVS has recently been carried out using methyllithium as

initiator in THF at -78OC [2].

In the present work the polymerization of PVS was carried out by
mixing a solution of the initiator and monomer in THF in vacuo at -78oC.

Various initiators were tried initially for the polymerization and are

summarized in Table 3-1.









Table 3-1. Homopolymerization of PVS Using Various Anionic Initiators in
THF at -780C.



Initiator Apparent Molecular Mn Mw / Mn Yield

Weights (Exptl)a Calcdb (%)
Mw Mn


TPML






TPMLC

TPMK

DPHL

Methyl-

lithium






EPSL


LiNph


2679

2747

5945

33100

4502

8060

1240

3025

10309

11261

17811

18384

9751

14418

18982


2066

2469

4219

24600

3310

6063

1171

2605

7423

7698

12349

15515

7497

11982

14594


1979

3200

5328


3970

12500

6089

6241

7537

6729

12177

19976

11873

11720

15222d


1.33

1.11

1.41

1.34

1.36

1.33

1.1

1.16

1.39

1.46

1.44

1.18

1.3

1.2

1.3


95

60

92

90

90

95

>70

94

95

90

84

75

70

86

90


a. From GPC using polystyrene standards
b. Mn Calcd. = [monomer] converted/[initiator] x Mmonomer
c. solvent system 1:1::THF:toluene
d. Mn Calcd. = [monomer]/[initiator] x 2 x Mmonomer











Initiators
It is seen from the Table 3-1 that the delocalized carbanions viz
triphenylmethyllithium (TPML), triphenylmethylpotassium (TPMK) and
diphenylhexyllithium (DPHL) are excellent initiators. TPML was, in fact,
the initiator of choice and most of the studies of the polymerization of
PVS (kinetics, temperature effects, etc.) were carried out using this
initiator. There were several reasons for the choice. TPML is very easy to

synthesize (Chapter 2) from a quantitative reaction of triphenylmethane
(which itself is a solid and easy to purify and handle) with n-butyllithium.

The carbanion salt is extremely stable even at R.T. in vacuo (although we

always stored it in the freezer). The solutions of TPML have an intense
absorption in the visible region (e at 500 nm = 31,000) so that their

concentrations can be accurately measured by UV/VIS spectrometry. The

intense color also helps in monitoring visually the initiation process since

a dramatic change in color is seen in going from the TPML carbanion to the
a-lithiosulfinyl carbanion (dark red to yellowish green). Also TPML is not

nucleophilic enough to attack the sulfur atom in the monomer causing side
reactions (at least at -780C).
Methyllithium was the only alkyllithium successfully employed as
the initiator [1, 2]. n-Butyl and t-butyllithium, interestingly, attack the
sulfur atom causing an SN2 displacement of the aryl group [42, 45-48].

This has also been documented [44, 47] in alkyl aryl sulfoxides where the

alkyllithiums other than methyllithium prefer nucleophilic attack on the

sulfur of the sulfinyl rather than proton abstraction.

Electron transfer initiators like lithium naphthalide were also

employed for initiation. A two-ended polymerization of PVS was thus









achieved similar to conventional monomers like styrene [25]. Thus the
initiation of polymerization of PVS appears to be similar to the

conventional anionic polymerization for instance of styrene.
The dipole stabilized initiator 1-lithio-1-(phenylsulfinyl) ethane

(EPSL) which is a carbanion analogous to that of the growing chain was

also found to be an effective initiator giving polymers of controlled

molecular weight and narrow molecular weight distribution. As will be
discussed later polymeric initiators, both one-ended and two-ended can
also be used as initiators to give block copolymers.
The initiation of PVS is instantaneous as seen from an immediate

change in color from dark red (for the delocalized carbanion) to yellowish-
green color of the growing a-lithiosulfoxide carbanion (Figure 3-1).

Nature of the Propagating Carbanion
The living a-sufinyl carbanion has been shown to be a dipole

stabilized ion pair in THF [2]. For instance the U.V. spectrum of

ethylphenylsulfoxide (EPS) and the carbanion derived from it show almost

no difference in the absorption maxima [2]. Also the 13C NMR signals for

the carbanion are almost the same as those of the parent hydrocarbon.

Since delocalization of the negative charge into the aromatic ring would
generally result in an upfield shift of the para carbon due to shielding [49-

51], there appears to be little or no delocalization of the negative charge

into the aromatic ring. Also the IR spectra of the carbanion of EPS and the

parent hydrocarbon exhibit the same absorption wavelength for the S=O

stretch [2]. All of these observations indicate the absence of

delocalization of the negative charge into the S=O bond.

The bond moment of the S-0 bond has been determined to be 4.76 D

[51]. From the x-ray structure the S-0 bond length in EPS was found to be












C(Ph)3Li
(Red) I


+ CH2= CH S Ph

0


-78"C,
THF


Initiation


C(Ph)3- CH2- --CH Li

s=0o

Ph
(Yellowish-Green)

n CH2- CH S Ph
II
0


C(Ph)3-


(CH2- CH CH2- CH Li+
I I


Propagation


MeOH


C(Ph)3- (CH2- CH-)-
Ic


CHg- CH2

s=0


Termination


(colorless)


Homopolymerization of PVS.


Figure 3-1.








1.47 A [2]. Using the equation: p = e d, where is the dipole moment in

debye, e is the magnitude of charge in ESU and d is the bond length. The
magnitude of the apparent charges on oxygen and sulfur was thus found to
be 0.67 electrons. Thus the S-O bond can be best described as a bond with
substantial ionic character.
Elegant 13C NMR studies by Marquet et al. [49-51] reveal that the

AlJC-H in the a-lithio sulfoxide shows a large increase (+16.5 Hz) in 13C
NMR upon metalation of the a-carbon of methyl phenyl sulfoxide. Thus the

carbon bearing the negative charge was shown to have a high sp2 character
similar to that found in Ph2CHLi. In methyl phenyl sulfoxide it was found

that the 13C-1H coupling constant decreases in the cryptated potassium

salt as compared to the uncryptated complex. Thus the carbanion becomes
more pyramidal (or the sp3 character increases) upon cryptation. This

suggests that the planar sp2 configuration is stabilized by interaction with
the cation. It is therefore reasonable to assume a chelated structure
(Figure 3-2) possible because of the high charge density present on the
oxygen in the S-0 bond. This internal chelate interaction is strong even for
very polar solvents and is disrupted only upon using a very powerful
chelating agent such as a cryptand [51].
The chelated structure is possible even for potassium which is
expected to have a looser interaction with the anion. The a-potassio
sulfoxide would be expected to have similar properties as the a-lithio

sulfoxide. This is in fact what we find by using TPMK as initiator (Table
3-1). The molecular weight distribution which is a good indication of the
efficiency of the initiation is similar to that for TPML. The effect of
decreasing the solvent polarity from 100% THF to 1:1 THF: toluene would be
expected to increase the anion-cation interaction. However we see little


















- Li*
i

I


Figure 3-2. Chelated ion pair structure of a-sulfinyl carbanions with
lithium as counter ion.









change in the SEC of the polymerization product in going to a less polar

medium (Table 3-1).

Effect of Temperature

The effect of temperature in both the initiation and in the

propagation reaction was found to be dramatic. A series of experiments
were performed to explore the effect of temperature on the initiation and

polymerization. The results of these experiments are summarized in Table

3-2.

In runs 1 and 2 two parallel polymerizations were carried out having

similar concentrations of initiator and monomer. One of the

polymerizations was initiated at -850C and was allowed to propagate at

-85oC using a mixture of dry ice and ethylether. The other was initiated at

-250C and kept at -25oC using a mixture of dry ice and carbon

tetrachloride. Runs 3 and 4 were carried out by initiation and propagation

at -780C and 250C (room temperature) respectively.

Run 5 was carried out in an apparatus which was provided with a

side bulb connected through a high vacuum teflon stopcock. The reaction

was initiated at 250C and the solution was then immediately divided into

two portions by pouring half of the reaction mixture in the side bulb

through the high vacuum teflon stopcock. The stopcock was then closed off

and the solution in the side bulb was quickly cooled to -78oC. The solution

in the main body, however, was kept at 250C. In this way one can see the

effect of initiation at 250C and propagation at -780C and 25oC

respectively.

Run #6 was similarly initiated at -780C and divided into two

portions; one was allowed to proceed at -780C while the other was warmed

up to 250C. Run #7 was simply a repeat of run #6.












Table 3-2. Effect of Temperature on Polymerization of PVS. Initiated by
TPML in THF.



Run # Ti a Tp b Mw HM Mn Mw/Mn Distribution

oC oC CalcdC


1 -85 -85 10810 7595 19025 1.42 unimodal

2 -25 -25 11012 7127 19025 1.55 unimodal

3 -78 -78 5945 4219 5328 1.41 unimodal
4 25 25 8495 3751 4892 2.26 bimodal

5 25 -78 9178 3671 4033 2.5 bimodal

25 25 8805 3108 4033 2.83 bimodal

6 -78 -78 6947 4533 4652 1.53 unimodal

-78 25 6829 3949 4652 1.73 unimodal

7 -78 -78 4795 3138 4567 1.53 unimodal

_ -78 25 4907 2392 4567 2.05 unimodal


a. Temperature of initiation.
b. Temperature of polymerization.
c. Mn Calcd. =[monomer]/[initiator] x Mmonomer











Effect of Temperature of Initiation of PVS

It was seen that during initiation of PVS at 25oC the color changed
from dark red (TPML) to yellowish-green, characteristic of the a-sulfinyl

carbanion, and then once again to red within minutes. The color

progressively became darker with time and did not discharge when the
carbanion solution was reacted with methanol. An attempt made to
monitor the formation of the colored side products using UV/VIS
spectroscopy failed. Only a tail was seen in the visible region which gave

no useful information as to the identity of the colored products.

The effect of temperature during initiation by TPML was of interest.

It was seen that initiation at low temperatures (<-250C) led to a unimodal
distribution in the SEC chromatogram. However, initiation at 25oC gave

rise to a bimodal distribution (Figure 3-3) even when the solution is cooled

down to -780C immediately after initiation (Figure 3-4).

This leads us to believe that at low temperatures the initiation

process forms only one propagating species. However, at higher

temperatures two distinct propagating or initiating species may be

present: a major giving rise to the high molecular weight peak in SEC with

a minor giving rise to the low molecular weight peak (Figures 3-3 and 3-4).

Obviously the high molecular weight (major) initiating species propagates
or initiates faster than the low molecular weight (minor) one.

It is seen from Table 3-1 that there is excellent agreement between
the calculated and experimental Mn in most runs. This indicates that the

"living" nature of the polymerization is similar to that of a conventional

anionic polymerization for instance of styrene.
































13









Figure 3-3.
polymerized


IW I I I I I I I


14 15 1U 17 1









SEC chromatogram of PPVS initiated by
at 250C in THF. Eluting solvent: THF.


I 1 26


TPML at 250C and
Flow rate: 1 ml/min.

















































Figure 3-4. SEC chromatogram of PPVS initiated by TPML at 250C and
polymerized at -780C in THF. Eluting solvent: THF. Flow rate: 1 ml/min.











Reactions of alkyllithium with sulfoxides having an a-proton have

been well-studied [44-47]. Methyllithium and LDA mainly abstract the
a-proton. n-Butyllithium and t-butyllithium, on the other hand, attack the

sulfur causing a ligand exchange on the sulfoxide. Jacobus and Mislow [44]
report the racemization and cleavage of optically active aryl methyl
sulfoxides with methyl and phenyllithium. According to their mechanism
racemization of the sulfoxide and exchange of the alkyl group takes place
via a sulfine intermediate (Figure 3-5). They also proposed a sulfurane
adduct to account for the exchange of the aryl group (Figure 3-6).
Durst et al. [47] have disagreed with the above mechanisms. They
found two competing reactions when various sulfoxides were reacted with
alkyllithiums: a) abstraction of an a-hydrogen to give a-lithio sulfoxide

and b) carbon-sulfur bond cleavage according to the equation
0 0
II II
R1-S-R2 + R3-Li---- R--S-R3 + R2-Li


They propose a simple SN2 displacement at sulfur and considered the

sulfurane as a transition state not an intermediate. In our system

displacement of the phenyl group by TPML at -78oC is unlikely because
TPML is less basic and more sterically hindered compared with

alkyllithium. The nature of the side reaction is possibly associated with
the presence of chelated stereoisomers some of which propagates faster
than others. A true side reaction, therefore may not be present.
We found the polymerization of PVS to be extremely rapid even at
-780C. Thus at 250C the polymerization is expected to be even more rapid.
The two initiating or propagating species (slow and rapid) that are seen








0
II
S
R'I CH3


CH3Li


RLi


0

R CH2Li


RLi + [CH2=S=O]
s Ifine

I CH3Li


O O
S S
R SCHLi CH3 SCH2- Li
racemization ligand exchange

Figure 3-5. Sulfine intermediate formed during racemization of
sulfoxides.


0

IIh
Ph*'f CH3


+ PhLi -_-_


Ph* C OLi
S -CH3

Ph
rSulfuranel


Ph 0 CH3 + Ph*Li

Figure 3-6. Sulfurane intermediate formed during ligand
exchange in phenylmethylsulfoxide.









would be expected to form and propagate in the first few seconds of the

polymerization. Thus cooling the reaction mixture after initiation at 250C

does not have much effect on the distribution and we still see the bimodal

nature of the chromatogram (Figure 3-4) (Run 5 in Table 3-2).
The total absence of bimodal distributions for the samples initiated
at -780C suggests that at -78oC we form only one initiating species which

propagates further. Warming the solution up to 250C after initiating at
-78oC does not give rise to bimodal distribution (Runs 6 and 7 in Table

3-2). However, the molecular weight distribution of the sample was
considerably broadened when it was warmed up to 250C. This indicates a
different effect of temperature on the polymerization as compared to the

initiation (see below).
Also from Table 3-2 it is seen that lower the polymerization

temperature narrower the MW distribution. The difference in molecular
weight distributions observed at the same temperature (-78oC) for
different runs (Tables 3-1 and 3-2) for the same initiator is probably due

to the difference in the purity of monomer from batch to batch. Also this
small variation may be due to changes in the SEC conditions. Although all

the SEC runs were carried out as much as possible under identical

conditions and although the calibration curves were recalibrated from

month to month there would still be the some experimental error involved
with the system (i.e. change in flow rate due to wear and tear of the pump,

leakage in the system, difference in the injection conditions, difference in

the concentration of the solution injected, etc.).
Effect of Temperature on Polymerization

It was noticed that warming the polymerization mixture to 2500C

resulted in a change in color from yellowish-green to red which









progressively became darker with time. The dark red color did not
discharge when terminated with methanol. Furthermore the molecular

weight distributions of the polymers were found to broaden considerably at
higher temperatures (Table 3-2). This was an indication that

polymerization side reactions played an important role at ambient

temperatures. As mentioned before efforts to determine the colored side

products by UVNIS spectometry failed due to the strong absorption of the
sulfoxide group in UV (Xmax 253 nm).

The side reactions are seen to be present even at -78oC. Thus a

tailing effect in the SEC chromatograms were usually observed (Figure

3-7), which was always in the low molecular weight region. The tailing

and consequent worsening of the molecular weight distribution was more
prominent for longer reaction times. Even at -78oC, after termination,

there was usually a yellowish tinge in the solution which was not due to

the living carbanions.

During the initial stages of our investigation of this system we

attributed the tailing due to our inability to completely purify PVS to

anionic polymerization standards. As mentioned in Chapter 2 the

importance of rigorous purification of solvents and reagents during anionic

polymerization cannot be overemphasized. The presence of parts per
million of electrophilic impurities could be disastrous especially for the

preparation of high molecular weight polymers [25, 26]. Sulfoxides are
known to form strong hydrogen bonds so that hydrogen bonds may have

formed with electrophiles such as water. PVS is probably synthesized

from a Grignard reaction of vinyl magnesium bromide with

ethylbenzenesulfinate [2]. It is conceivable that some of the reactants may

















































Figure 3-7. SEC chromatogram of PPVS initiated by TPML in THF at -780C
and polymerized at -780C for 33 hours. Eluting solvent: THF. Flow rate: 1
ml/min.









have been left behind which may have very close boiling points and thus

cannot be completely removed through distillation.

Another possibility is the decomposition of the monomer during

distillation at high temperatures. Mislow did extensive studies on the

thermal racemization of alkyl aryl sulfoxides [52, 53]. They estimated the

bond dissociation energy of cleavage of C-S bonds in alkyls and aryls to be
about 56-69 kcals/mole whereas the activation energy of the pyramidal
inversion was estimated to be about 36 kcal/mole [52]. Thus they

discounted the homolytic cleavage-recombination mechanism for

racemization except in case of benzyl p-tolylsulfoxide which gives rise to
benzyl and p-toluenesulfinyl radicals upon cleavage of the benzylic C-S

bond [53]. Another possibility is a five-center pyrolytic cis-elimination
mechanism for sulfoxides having a P-hydrogen (Figure 3-8) [3, 54]. A

detailed discussion of this elimination will be given in Chapter 4.

The absence of detectable impurities in GC leads us to believe that
the tailing effect in the low molecular weight side in polymerizations

carried out at -78oC may be due to factors other than impurities in the

monomer. It was noticed that the side reactions were more prominent in

polymerizations with long reaction times so that the growing polymer
chain is somehow deactivated during the polymerization. Several
explanations are possible since we have a number of sites in the polymer
chain which could be attacked by a carbanion leading to various side

products. Apparently these side reactions are strongly temperature

dependent and lead to broad molecular weight distribution (Table 3-2).

Probable deactivation reactions could be
i. E2 elimination of phenyl sulfenic acid in the polymer chain by a growing

carbanion [55, 56] to form polyene linkages in the chain












S + CH CH CH2 --CH

Phr S So
Ph Ph


ii. Deprotonation of an a proton in the chain to form a dipole stabilized
carbanion [44-48]





v'^^^ C CH2- C- CH2 -CH


Ph/ Ph/ Ph/

iii. Attack on the sulfinyl of a polymer chain by the growing a-lithio
sulfoxide [47]



d, .CH -i CH- CH2 CH
I ~+ I +
SPh =O S S=o

Ph/ Ph Ph

The pKa of LDA [57] is very similar to that of the a-lithio sulfinyl
carbanions [48]. Thus it was decided to investigate the effect of LDA on
PPVS. LDA was prepared in vacuo by a reaction of diisopropyl amine and
























S H

0'


a /S-O-H


A .


H C C-H


Figure 3-8. Possible elimination reaction in phenylvinylsulfoxide at high
temperatures.









methyllithium. The ratio of LDA:sulfoxide was about 1:1. The THF solution
of PPVS was then added to the THF solution of LDA at -78oC. It was seen

that the polymer solution turned dark red (similar to that of the solution of

polymerization at 250C ). After about 15 minutes methanol was added to
quench any LDA left behind and the polymer was purified by precipitation in

ether. The polymer was not completely soluble in THF. The SEC of the

soluble polymer showed a decrease in molecular weight as compared to the

starting polymer. Thus a cleavage of chains by LDA at -78oC may have

occurred. The change in color upon reaction of LDA with PPVS may be due
to the formation of low MW polyenes in the polymer due to a 0 elimination

of phenyl sulfenic acid as discussed above.

Conversion of () PVS With Time

A rough idea of the conversion of monomer with time and the
kinetics was highly desirable. This would give us the half life of the

polymerization reaction and would help us decide when to terminate the

polymerization so as to obtain reasonable yields without the side reactions

associated with long reaction times.

A polymerization reaction was carried out at -780C under rigorously

dried argon and aliquots of the polymerizing solution were withdrawn by

syringe at various times. Naphthalene was employed as an internal

standard to monitor the concentration of the monomer at various times

during polymerization (Chapter 2). The polymer was also characterized by

SEC. The results of one of the runs are summarized in Table 3-3.

Surprisingly the variation in molecular weight was negligible from 5

minutes to 3 hours. Also no detectable monomer was found by GC even

after just a few minutes of reaction. This indicated that the

polymerization of PVS was extremely rapid even at -780C.










Table 3-3. SEC Results of the Conversion of Monomer with Time. Initiated
by TPML in THF at -78oC under Argon.

TIME Mpa Mw Mnb Mw/Mn
minutes SEC

5 5859 6559 3772 1.74
15 6215 7209 4096 1.76
60 6691 7852 4708 1.67
120 6790 7515 4001 1.88
180 6891 7907 4053 1.95

a. With reference to polystyrene standards.
b. Mn Calculated = 2854.



Since stop-flow techniques were not available, an experiment was

devised wherein the polymerization reaction was terminated at incomplete

conversion. The time of reaction was 21 seconds after which the

polymerizing solution was quenched with methanol. The polymer was

precipitated as usual in excess of ether and the concentration of monomer

in the filtrate was determined by GC.

The rate constant for the pseudo-1st order polymerization reaction

(at a concentration of living polymer chains of approximately 10-3 M)

determined in this way was found to be 0.17 sec-1 with a half life of 4.1

seconds. Thus the polymerization reaction is seen to be extremely rapid.

Several factors must be considered before accepting the above value

of the rate constant. There could be errors involved in the determination of

the time of polymerization. Also the rate of polymerization may not

necessarily be pseudo-1st order (i.e., the assumption that the

concentration of the living ends is constant may not be true).









Polymerization and Studies of (+)-PVS
Optically active (+)-PVS {[a]d20 = 358.50) was polymerized using a

procedure similar to that used for the racemic monomer using TPML in THF
at -78oC. The polymer shows some unique properties.
It was found that the optically active monomer does not lose its
optical activity upon polymerization. This is expected since sulfoxide
sulfur does not epimerize under the polymerization conditions [1, 2]. As
seen from the 13C NMR (Figure 3-9) all of the signals from the optically
active polymer are considerably sharper than the corresponding ones of the
racemic PPVS (Figure 3-10). This suggests a highly stereoregular
structure of (+)-PPVS as compared to the racemic polymer. The (+)-PPVS
would be expected to be isotactic as suggested by the broad methylene
absorption in 1H NMR and by the stereochemistry of the dimers and trimers
studied extensively by Buese and Hogen-Esch [1, 2]. The polymer was found
to be only partially soluble in THF and chloroform both of which are
excellent solvents for racemic PPVS. The polymer is soluble in glacial
acetic acid. The decrease in solubility of (+)-PPVS also points to a more
regular structure. The polymer was found to be monodisperse (Mn = 1359,

Mn Calculated = 2920, Mw/Mn = 1.19).
Copolymerization of Stvyrene and PVS
Both A-B and A-B-A type of copolymers were synthesized as
described in the experimental section.
A-B Copolymers
Figure 3-11 illustrates the various steps in A-B block
copolymerization and Table 3-4 summarizes the SEC data of various A-B
copolymerizations.






68






































I 'i -i'r71 'w,7-


Figure 3-9. 50 MHz 13C NMR of (+)-PPVS in CDCI3 at room temperature.


















































Figure 3-10. 50 MHz 13C NMR of racemic PPVS in CDC13 at room
temperature.
















C/) CM 00 CM Lv 1r- CM

L o, CM qt (D r-o P- It




7T 0o) o t







o art O a


om o / o

Do D 3 pr c\j in 't CM







0 > D0 C6t4 i uiJvT CM
2 Q < x Ti-C Ti-C



CLn (D nnfCD /) f I
o Io C4 )C4C.O .
2Q x coooooo

Fn2 i



CV CO CV C O CO co -


\ a\ CM C4 C4 C4 ( C6

Cm Co C i C M Ci r r u c(7
0. 1 7q o Y- D ^- (D c












ao ^ o o Cu oo o
2 x 000 00










c


L- Cto00l 00D>
E CM nooocna.
4-








a T m cococm co


a) <

a
0
a,



C
0-
0.


c






o
C





0 -
a-

A :



a ^o
a'
CY -
CL






4 -

Cc $--
0. V4-'













a 0


> o M



E 0 C EE0

%, -1 o n=






= M i nto
(n > ..5 0 -
o E-o s. E c
E Eo




e)0 c

CO C c E

e to g t








(CH3)3C-Li


+ nCH, = CH-Ph


-780C/THF


(CH3)3 C- CH2 CH (CH2 CH)n Li+
I I
Ph Ph
living polystyryllithium (cherry- red)


NPh


(CH3)3 C- (CH2 CH)n- CH2- C(Ph)2Li
Ph
capped living polystyryllithium (dark red)


mCH2= CH- -S- Ph
II
0 0

(CH3)3 C- (CH2- CH)n- CH2- C(Ph)2- (CH2- CH)mLi
I I
Ph S-0
(yellowish green) Ph

I MeOH
(CH3)3 C- (CH2- CH)n- CH2- C(Ph)2- (CH2- CH) H
Ph S=0O
(colorless) Ph

Figure 3-11. A-B copolymerization of styrene and PVS.










Styrene was polymerized by a slow vapor phase addition of the

monomer onto a rapidly stirred initiator solution at -780C in vacuo [25,

26]. Several initiators like methyllithium, s-butyllithium, etc. were tried.

However we found purified t-butyllithium to be the most efficient. This
initiator gave polymers with reproducible molecular weights and narrow

molecular weight distributions.
As can be seen from Table 3-4 the Mn calculated from the

concentrations of monomer and initiator (determined by UV) was quite

close to the one determined by SEC. Also the molecular weight distribution

for the styrene block was narrow (<1.1) which indicates negligible killing

of the growing polystyryllithium chains. Thus the DPE capped

polystyryllithium was seen to be an excellent initiator for PVS. The
molecular weight distributions were also better than for homopolymers of

PVS which is expected since we start out with polymeric initiators of
narrow molecular weight distribution. However at high PVS concentrations

considerable termination during polymerization was observed as seen from

the worsening molecular weight distribution and lower yields (entries 4

and 5 in Table 3-4).

Figure 3-12 shows a typical SEC chromatogram of the polystyrene

homopolymer (i) and styrene-PVS copolymer (ii). The PPVS content in the

copolymer was calculated from the 1H aromatic absorptions of the

polystyrene phenyls (a = 7.0 PPM {meta and para} and a = 6.5 PPM (ortho))

and the sulfoxide phenyls (a = 7.5 PPM). Figure 3-13 is a 200 MHz 1H NMR

of a styrene-PVS A-B diblock copolymer and Figure 3-14 is the

corresponding 200 MHz 1H NMR of poly(phenylvinylsulfoxide) initiated by

TPML in THF at -78oC. The ortho protons in polystyrene are seen to be


















18 1
0

I .1 *
*
8 1 *









15 i 16 17 18 19 28








Figure 3-12. SEC chromatograms of i) Polystyrene homopolymer (Mp =
8200, Mw/Mn = 1.09) and ii) A-B copolymer of styrene and PVS (Mp =
13,120, Mw/Mn = 1.09). Eluting solvent: THF at 1 ml/min.






74












G
H A 3 C 0 E
(CH3)3C-(cH2-CH2C) -(CH2-a)-H







U 2I

F


C




























Figure 3-13. 200 MHz 1H NMR of poly(styrene-b-PVS) copolymer in CDC13
at room temperature.





75






























II I I # I I '- v r P p 'I-* 'Ti- i-rTR T- T1 .. ... 1 1 ,. 1 I i











Figure 3-14. 200 MHz 1H NMR of PPVS (initiated by TPML in THF at -780C)
in CDC13 at room temperature.









shifted upfield relative to the meta and para. This is due to the shielding
of the ortho protons being in the anisotropic field of the 7c-electron current

of the neighboring ring [58].
In the runs 1-5 the polystyrene block was kept constant (Mp SEC =

2,713) whereas the sulfoxide content was varied. There was a good

correlation between the sulfoxide content calculated (from the ratio of

moles of styrene to moles of PVS) (21%, 53% and 66%) and that observed

from 1H NMR (21%, 47% and 67% respectively) for the first three runs.

However, a large variation was seen for runs 4 and 5 (85% and 90%

calculated and 75% and 78% observed). This also indicates substantial

killing during runs 4 and 5, where the concentration of PVS was high.

Run 7 was carried out using styrene-d8 and the corresponding

copolymer was used for the structure determination of the thermal

elimination product.

A-B-A CoDolymers

Figure 3-15 illustrates the various steps in the A-B-A block

copolymerization and Table 3-5 summarizes the SEC data of the A-B-A

runs.

Lithium naphthalide was employed as the initiator for the two-ended

polymerization of styrene [39]. As is well known [25, 26] lithium

naphthalide initiates polymerization of styrene by electron transfer to

form the radical anion of the monomer which then immediately couples and

forms the dimer with two anions on either end. This dimer can further

propagate in both directions to give a two-ended polystyryllithium.
Excellent results were obtained when lithium naphthalide was

prepared using excess of naphthalene (Table 3-5) (Figure 3-16). However,

when lithium naphthalide was prepared by using an excess of lithium metal










COI-Li+ +
(dark green)



Li-CH- CH2 CH2

Ph i


CH2= CH -Ph

-780C/THF



-0- Li+

Ph
mCHo= CH -Ph


Li'CH CH2) -

Ph

(dark red)


CH- CH2 CH2
I


Ph


+ 2n


-CH --(CH2- CH)mLi
I I


CH2=-CH -S-Ph
II
0


Li'(CH CH2) ----- (CH2- CH)nLi'
I I


s-0


s=o


(yellowish-green)
^ MeCH
PPVS-PS-PPVS triblock copolymer
(colorless)


A-B-A copolymerization of styrene and PVS.


Figure 3-15.
















C)
> co 0)0 C
CL o r ^- qt i n
CL 5 e0 ini cri o ui


oW 1 CDC( CM C 0


N) CD UV) IT) 0) 0) a

Cmmm

it CV) M- C1 0 a

0)O COnC) o

-0 0C 'C r- 0 00


Si 00 C) T0 CM 0 0

^a_-.01-- -.



oo coE or- CVo M-
-0 0a CDO C)oo C c)






aU TOOOTCvc
)r wmmNco
a 't coovocvoo v







-0 C



S000 00 00
7 C (6 ammoi oC n co






C



S0,000000

CQ) C ) C) C)o U)
V) m M sco m' J


o -o CDcoCWC)o )
0" Mo 0))0) aOO
a. 0 (Ot0- T- <00<0 0




o o o aooo?

7 >, v_ (CoC6 ui Cm (7i Lei m
o
2 CO x co C/ 0

co 000)O0 IM
) <<<<00 E <<<<<<<
0 _<<<<<<


0


_>
a)


a
0

c
C



ci ai
>0



g wc
( -0 N


v2a 0






EC g2
x C
o 0 + o:

xZ cc


S o(


0-o
-=s 00

S2S- o Lc


E 0Eo a

0 Q D 0
7 0 0 0 ( %
oC (D CL



onQ B.C>g-r a0
E o C13
S) o> c0
C ec U, Co) C




no go CL 2=
(0 D

75 i3 E t
0d (D .- 0
E 0 OM ~EsrC,
E CL -o-d ~ci









we ended up with a bimodal distribution in the SEC chromatogram (Figure
3-17). When lithium naphthalide is prepared using excess of lithium metal

one also gets the formation of naphthalene dianion alongwith the radical

anion [31]. The dianion itself may initiate styrene and a naphthalene group

may thus be incorporated in the middle of the chain [59]. In absence of
more extensive experimental evidence we will not attempt to interpret in
detail these anomalous results.

Table 3-5 once again shows that the dianion of polystyryllithium is

an excellent initiator for PVS. Again the molecular weight distribution of
the copolymer increases with increasing content of sulfoxide. This
indicates some termination when larger amounts of PVS are used.

Proof of Dianion Formation in the Lithium Naphthalide Initiated
Polystyrvllithium

The "two-endedness" of the DPE capped living polystyryllithium
initiated by lithium naphthalide was proved in the following manner.

Styrene was independently initiated by lithium naphthalide in THF at -780C

and capped with 1,1-DPE. The concentration of the carbanions was

measured using UVNIS spectrometry (Table 3-6). The carbanion solution

was attached to an apparatus equipped with a quartz cell and a quartz
spacer. An excess of fluorene in a break-seal was also attached to the

apparatus. This was then evacuated and the carbanion solution was poured
in the cell through the break-seal and the absorbance of the red carbanion
solution was measured at its .max (500 nm, Table 3-6). The living

carbanion was then reacted with fluorene. An immediate change in the
color of the solution was noticed on formation of the fluorenyllithium from

dark red to yellow. The absorbance of the solution of fluorenyllithium was
measured at its Xmax (373 nm) (Table 3-6). The extinction coefficient of













ii i






1 :1
*. *
# #
0* *#

**
*0 *

0 **
i t
0 o







l1 13 14 15 1 17 19






Figure 3-16. SEC chromatograms of i) Polystyrene homopolymer (Mp =
10,553, Mw/Mn = 1.08) and ii) A-B-A copolymer of styrene and PVS (Mp =
14,921, Mw/Mn = 1.1). Polystyrene block initiated by lithium naphthalide
prepared by using an excess of naphthalene. Eluting solvent: THF at 1
ml/min.












Mi
o 0

*000
0 ** 0
00,
0

0000
00 0
** .
0*90
.. *


? I1

// V O
000
0O 0,0
.. **




rI~




13 4I 131 I I~









Figure 3-17. SEC chromatograms of i) Polystyrene homopolymer and ii)
A-B-A copolymer of styrene and PVS. Polystyrene block initiated by
lithium naphthalide prepared by using an excess of lithium metal. Eluting
solvent: THF at 1 mi/min.

















Table 3-6. UV/Visible data for various carbanion initiators in THF at 250C.

CARBANIONS 4MAX MOLAR
nm EXTINCTION
_________________________~__COEFFICIENT ()
TPML 500 30,980
TPMK 486 26,420
Lithium Naphthalide 367 10,263
326 22,350
292 32,550
aMS-22Li+ 342 19,700
Polystyryllithium capped with 501 56,000
1,1-DPE, dianion
Fluorenyllithiuma 373 9,600
Fluorenylpotassiumb 362 11,500
Potassium Chromatea 372 4815

a. From references 35-37.
b. Estimated from e of fluorenylsodium (Xmax 356 nm) =10,800 and
fluorenylcesium (Xmax 364 nm) = 12,000 [37].









the carbanion was thus calculated (e at Xmax = 28,000) from that of
fluorenyllithium which is well-known (e at X max = 9,600) [35-37]. Hence

the concentration of the dianion of diphenyl polystyryllithium was
determined (moles of the carbanion solution = 3.03 x 10-6).
The terminated polystyrene was purified by precipitation in excess
of methanol and injected in SEC (Mw = 9199, Mn = 8633, Mw/Mn = 1.07, Mn

calculated = 9591). The polymer was weighed and hence the number of
moles of polymer was calculated from Mn (Moles of polymer = 1.48 x 10-4

moles.). Thus the ratio of moles of carbanion / moles of polymer was found

to be 2.05. This confirms that there are two moles of carbanion for every
mole of the polymer (i.e., two carbanions per growing polymer chain).
In conclusion, it is seen that homo- and copolymerization of PVS can
be carried out using conventional anionic polymerization techniques. A
variety of initiators could be employed but it was seen that delocalized
carbanions like TPML are excellent initiators. Electron transfer initiators

could also be employed to achieve two ended polymerization of PVS. There
was an excellent correlation between the calculated Mn and the
experimental Mn determined by SEC and 1H NMR. The molecular weight

distribution in most homopolymers was found to be narrow (<1.4). The

effect of temperature on initiation and propagation was seen to be

dramatic. In general lower temperatures resulted in well-defined and

narrow molecular weight distribution polymers. Initiation at -78oC led to

unimodal distribution indicating one initiating species whereas initiation

at 250C led to a bimodal distribution due to the possible presence of two
initiating species. The polymerization of ()-PVS was seen to be

extremely rapid with a pseudo-first order rate constant of 0.17 sec-1 and








a half-life of 4.1 seconds. Optically active (+)-PVS was also polymerized

and the resulting polymer was found to be stereoregular in structure.

Both A-B and A-B-A block copolymers of styrene and PVS were

synthesized. The A-B diblock copolymerization was carried out by vapor-

phase polymerization of styrene in THF at -78OC using t-butyllithium as
initiator followed by capping with 1,1-DPE. The capped polystyryllithium

was used for initiation of the PVS block. The A-B-A triblock
copolymerization was carried out by reacting two-ended polystyrene
prepared by using lithium naphthalide as initiator with 1,1-DPE to give a

capped stable living dianion of polystyryllithium which initiated PVS at

both ends to give an A-B-A triblock copolymer, polystyrene being the inner

block. The molecular weight distributions of the block copolymers were, in

general, narrower than the homopolymers.













CHAPTER 4
THERMAL ELIMINATION STUDIES

The thermal instability of sulfoxides has been recognized for more

than a century [60]. However, the synthetic utility of sulfoxides in organic

chemistry and the detailed mechanism of elimination of sulfoxides was

pioneered by Kingsbury and Cram [3]. They demonstrated the facile
elimination of phenyl sulfenic acid from 1,2-diphenyl-1-

phenylsulfinylpropane to give the isomeric 1,2-diphenylpropene. The

mechanism they proposed involved a stereospecific cis elimination similar
to the Ei Cope elimination in amine oxides [61] and elimination in

selenoxides [62].

Mechanism of Sulfoxide Elimination

The mechanism of sulfoxide elimination proposed by Kingsbury and

Cram [3] is accepted even today. The mechanism they proposed is similar

to the classical mechanism for the internal elimination reaction. The
leaving group (Ph-S-O) abstracts a hydrogen from the P-carbon (Figure 4-

1). The elimination is stereospecific; the erythro (1R, 2R or 1S, 2S)

sulfoxide gives trans-i 1,2-diphenylpropene whereas the threo (1S, 2R or 1R,

2S) gives cis-1,2-diphenylpropene at least at low temperatures.

At higher temperatures the reaction is less stereospecific. Thus at

higher temperatures a C-S homolytic bond cleavage was proposed to form a

sulfinyl and a benzyl radical pair without the radicals ever leaving the

solvent cage [3] (Figure 4-2). Other workers in this field [7, 65, 66, 67]

have accepted the above mechanism with some changes. Block [77]













H Ph

OH C C H
CH "II+


Ph/


(1R, 2S)-1,2-diphenyl
propane


S-0 -


1-phenylsulfinyl


I I I

CH3' C"C H

Ph Ph
Ph


/


CH> H

Ph Ph
Cis 1,2-diphenylpropene


Figure 4-1. Thermal eliminations in (1R, 2S)-1,2 -diphenyl
1-phenylsulfinyl propane at low temperatures.

















CHC


Ph


A
low


S O


Ph


**


(1 R, 2S)-1,2-diphenyl-l phenylsulfinyl
propane






CH3 Ph --
> C=C < Ph
Ph H
Trans1 ,2-diphenylpropene


0 v-n



CH3 CC C H
Ph Ph




Ut


Ph

S- .


CH, -C C '*" Ph
Ph' H
Ph


Figure 4-2.


Thermal eliminations in (1R, 2S)-1,2-diphenyl
1-phenylsulfinylpropane at high temperatures.









considered the sulfoxide elimination analogous to that of the amine oxides,

involving a five-membered six-electron transition state (4 electrons from

the C-S and C-H o bonds and 2 electrons as a lone pair on oxygen) and

termed it as a o2s + o2s +o
Kwart et al. [54] carried out a detailed comparison of the sulfoxide

and amine oxide thermolysis. A temperature dependence of the kinetic

deuterium isotope effect was found for the deuterated sulfoxides. This

result was apparently in keeping with what has been established for a

planar, concerted, pericyclic transition state. In contrast the amine oxide

elimination was indicative of a bent, cyclic transition state.

Use of Sulfoxides as Acetylene Synthons

Vinyl sulfoxides have been extensively used in synthetic organic

chemistry as acetylene equivalents. It would serve us well to know a little

about the synthetic value of sulfoxides to introduce a vinyl group in a

molecule.

Michael Addition-Elimination.

Vinyl sulfoxides react with certain nucleophiles to give Michael-type

addition [4-9]. This Michael-adduct could then be subjected to thermolysis

to introduce a vinyl group. Thus vinyl sulfoxides were shown to be

acetylene synthons in Michael addition. This is illustrated in Figure 4-3 [4,

5] and Figure 4-4 [6]. The Michael adduct could also be subjected to

reductive desulfurization [9].

Alkylation-Elimination.

Trost [63, 69] carried out a series of synthetic reactions involving
the alkylation of a-sulfinyl carbanions and eliminations of the resulting

sulfoxides to give a-3 unsaturated olefins (Figure 4-5).





89



Base/THF
+ CH2= CH- S- Ar -
II
0


X-CH2-CH--S-Ar
II


X- CH- CH2


Ar-S-O-H ---


X- CH- CH2 S A Ar

0


Figure 4-3.


Michael addition-elimination of vinyl sulfoxides.


0

,C-0-CH2-CH3


+ CH2=CH-S -Ph


1)NaH/THF
2) H+


O
C-O-CH2-CH3

CH2-CH2-S-Ph
11


(60%)


(50%)


PVS as a vinyl synthon.


X- H


0
II
C-O-CH2

SCH=CH2


Figure 4-4.











Ph- -CH,-Ph
0


1) LiNR2/DME
2) Ph-CH2-Br


Ph
Ph-W-CH-CH2-Ph


IA


Ph-CH=CH-Ph
Trans-stilbene (79%)


Alkylative eliminations.


R1 CH2 CH2- C R
0


/CH2
R


1) Base -R
2) R2-S-S-R2


S-R2

[01


0
II
R,-CH=CH-C-R


/ CH2
R1 /-


-R2SOH


O= S-R2


Figure 4-6.


Sulfenylation-dehydrosulfenylation route to unsaturated
ketones and esters.


Figure 4-5.


0
II
C








Sulfenylation-Dehvydrosu Ifenylation.

Trost [64-65] utilized the facile elimination of R-S-OH from
sulfoxides to introduce unsaturation a,p to a carbonyl group. A general

scheme for their approach of sulfenylation of ester and ketone enolates and
the oxidation and thermal elimination of the resulting sulfides is shown in

Figure 4-6.
Diels-Alder Cycloadditions and Elimination

Paquette et al. [10] used PVS as an acetylene equivalent in Diels-
Alder cycloadditions. They utilized the dienophilicity of PVS and the in

situ thermal extrusion of phenyl sulfenic acid to give a one-pot reaction

giving the product of an acetylene-like Diels-Alder cycloaddition (Figure

4-7).

1.3 Dipolar Cycloaddition and Elimination

Matsumoto et al. [68] used the above Diels-Alder reaction in 1,3
dipolar cycloadditions of PVS to dicyanomethylids. Thermal elimination of

the adducts gave 3-cyanoindolizines in moderate to good yields (Figure

4-8) indicating the use of PVS as an acetylene synthon in 1,3-dipolar

cycloadditions.

Elimination of PPVS and PS-PPVS Copolymers

Thermal elimination of the homo- and copolymers was carried out in

the solid state as described in Chapter 2. The polymer was dissolved in
chloroform or THF and a thin film of the polymer was cast in the pyrolysis

tube by a combination of vacuum and slow rotation on the rotovap. The tube

was then inserted in the furnace and the elimination carried out at 190-

2000C under high vacuum (10-6 Torr) for 1.5 to 2.0 hours. The yellowish-

white polymer became shiny black upon elimination and was handled under

argon at all times.