POLYMERISATION of SOME CYCLIC ETHERS and ALLYL COMPOUNDS at Higf PRESSURES

POLYMERISATION OF SOME CYCLIC ETHERS AND ALLYL COMPOUNDS AT HIGf PRESSURES.

THESIS SUBMITTED FOR THE DEGREE OF

DOCTOR OF PHILOSOPHY

IN THE FACULTY OF SCIENCE UNIVERSITY OF LONDON

MUSTAFIZUR RAHMAN.

DEPARTMENT OF CHEMICAL ENGINEERING AND CHEMICAL TECHNOLOGY, IMPERIAL COLLEGE OF SCIENCE AND TECHNOLOGY, LONDON, S.W.7. SEPTEMBER, 1967. ABSTRACT.

The polymerizations of seven cyclic ethers and two allyl compounds have been studied at high pressures (up to 12,000 atm.). BF3.(C2H5)20 was usually used as catalyst to polymerize the ethers, except for 1,4-epoxycyclohexane with wilich the co-catalyst epichlorohydrin was employed. Benzoyl peroxide and azo-isobutyronitrile were used to polymerize the allyl compounds. The polymerizations of 1,4-epoxycyclohexane and tetrahydrofuran (THF) have been studied most extensively. From the lag rate vs. pressure graphs, "overall volumes of activation" Air*pol were calculated and compared with those for vinyl compounds. Conductances of solutions of BP3.(C2H5)20 in tetrahydropyran were measured and the results discussed in relation to the kinetic measurements. The variation of the polymerization ceiling temperature of THF with pressure was determined between 1 and 2500 atm. The polymerizations of cyclohexene oxide, styrene cxide, cyclooctene oxide, tetrahydropyran, triallyl phosphate, triallyl phosphite and the co-polymerization of triallyl phosphate and styrene, have been studied briefly. The results, wherever possible, have been explained in terms of existing ideas. 3.

Polymers from viscous liquid to insoluble solids were obtained during this investigation and the molecular weights were determined, where possible. 4

ACKNOWLEDGEBENTS.

The author wishes to express his gratitude to Dr. K.E.Weale for his kind supervision, valuane guidance and constant encouragement during the course of this study.

The author would also like to thank Pakistan Council of Scientific and Industrial Research (Karachi) and Valika Trust (Karachi) for the financial support during the period of this investigation.

Thanks are also due to the Departmental Workshop staff for their help in maintaining the high pressure equipment and especially for making a new steel reaction tube. 5. COITIENTS. Page Section I. INTRODUCTION. 8 1, General Theory of Polymerization. 8 A. Free Radical polymerization. 8 B. Kinetics of free radical polymerisation. 10 C. Chain Transfer Reaction. 12 D. Inhibitors and Retarders. 13 E. Determination of Velocity Constants of the Component Remotions. 14 F. Cationic Polymerization. 15 G. Anionic Polymerization. 18 H. Living Polymers. 20 I. Co-ordination Polymerization. 21 J. Polymerization-Depolymerization Equilibrium. 22 2(1) Theory of Chemical Reaction. 23 A. Collision Theory. 23 B. Transition Rate Theory. 24 C.Effects of pressure on Rates of Polymerization. 31 2(2) Polymerization at High Pressure. 31 2(3) Effects of Pressure on Ceiling Temperature. 34 2(4) Effect of Pressure on Ionic Equilibrium. 35 3. Review of Polymerization of Cyclic Ethers. 36

A. At Atmospheric Pressure. 36 B. At High Pressures. 39 C. Review of Polymerization of Triallyl Phosphate. 41 4. Scope of this work. 41

6. Page Section II. EQUIPMENT, MATERIALS AND PROCEDURE. 43 1. Equipment. 43 A. High Pressure Equipment. 43 B. Reaction Tubes and Holders. 48 C. Atmospheric Pressure Equipment. 51 D. Equipment for Conductivity Measurement at High Pressure. 51 2. Materials. 55 A. Monomers. 55 Be Catalysts and co-catalysts. 57 C. Solvents. 58 3. Procedure. 59 A. PrepataTion of Reaction Mixture. 59 B. Technique of Polymerization. 59 C. Separation of the Polymers. 60 D. Molecular Weight Determination. 61

Section III. RESULTS AND DISCUSSION. 64

1. The Polymerization of 1,4-epoxycyclohexane. 64 2. The Polymerization of Tetrahydrofuran. 79 3. The Variation of Polymerization Ceiling Temperature of Tetrahydrofuran with Pressure. 100. r, •

Page

4. The polymerization of cylcohexene oxide. 109 5. The polymerization of styrene oxide. 114 6. The polymerisation of cyclooctene oxide. 116 7. The polymerization of tetrahydropyran. 118 8. The polymerization of triallyl phosphate and triallyi phosphite. 119. Section IV. GENERAL DISCUSSION. 26

REFERENCES. 130

SECTION I.

INTRODUCTION.

1.1. General Theory of Polymerization.

Staudinger 1 proposed first in 1920 that addition polymerizations are chain reactions which show the stages of initiation, propagation and of termination in which polymer chain-carriers are either destroyed or rendered inactive. Depending on whether the chain-carrier is a free radical, cation or an anion, addition polymerization reactions are classified into three main types : (a) Free radical polymerizations; (b) Cationic polymerizations; and (c) anionic polymerizations.

A. Free Radical Polymerization.

The first step in radical polymerization is usually the decomposition of the initiators such as organic peroxides, azo- and diazo-compounds, under photochemical or thermal influence to give radicals. Two reactions often used to produce free radicals in addition polymerization are the decomposition of benzoyl peroxide (Bz202)

e + 2C0 (C6H3C00)2 206H5COO' = 2C65H 2 and of azobisisobutyronitrile (AIBN) 0 = 2(0113) -C + N (CH3)2 - C - N = N - C - (CH3)2 2 2 CN CN CN 0

Such reactions can be represented generally by l = 2 X* The addition of a free radical to the double bond of an ethylenic compound; with regeneration of a free radical, leads to propagation of a growing polymer chain

CH2 = X* + CH2 = C'= X - CH2 - R, X - CH2 - C(RR')-CH2-d(RR) R' R' etc.

At each addition, one electron of the double bond pairs with that of the free radical, and the second electron of the double bond regenerates a radical which repeats the process. The chain can thus be propagated by the addition of a large number of monomers. Evidence for this mechanism comes not only from the acceleration of such polymerization by free radicals but also from the fact that polymers formed have been shown to contain fragments of the initiating radicals. The growing polymer chains can be terminated in at least two ways. Two growing chains may combine, the activity of the two free radicals being mutually satisfied (Termination by coupling or combination) :

X - [CH2-C(RRI)]m, + X - [CH2-C(RR')]n = X - [CH2-C(RR')]mill - X. Alternatively, two growing chains may undergo a procass of disproportionation; this involves the transfer of a hydrogen atom from one growing chain to the other with the formation of an unsaturated end group on the chain which 1c-es the 10. hydrogen atom : R "00H2-C(RR, ) +-w,C1-12-C(RR') =e-CFI2 - CH + (RR') Jr.= CHP40 R' The wavy lines denote the bulk of polymer chains. Each type of termination is known: polystyrene chains terminate mainly by combination, polymethyl methacrylate chains terminate entirely by disproportionation at temperature: above 6000. B. Kinetics of Free Radical Polymerization.

The initiation of free radical chains may be regarded as occurring in two steps; (a) the decomposition of the initiator, I, with a velocity constant kd kd I la: 2 X' and (b) addition of monomer, denoted by M, to form a radical,

M.1 ' with a velocity constant ka : ka X' + M Mi

The propagation steps,

M' + M = Id' ; M' + M = M' 1 2 2 3 etc. can be represented generally by

M' + M = M'2+1 and are assumed to have the same velocity constant k , i.e. the radical reactivity is assumed to be independent of the chain length. The termination step may occur by either 11. combination or disproportionation. A single velocity constant kt can be assumed to cover both mechanisms. The rates of the three steps can be expressed in terms of the molar concentration (C) of the substances involved and the appropriate velocity constants. The rate of initiation Vi is given by

Vi = (dCm(dt) = 2f kd CI (1) where f is the efficiency of the initiator i.e. the fraction of the radicals formed from I which initiate chains. The value of f is usually less than unity because a fraction of the radicals (X) formed in pair from the initiator recombine by a "cage effect" before escaping from each other's proximity. The rate of termination Vt is given by

Vt = (-dCm/dt) = 2kt Cm2 (2)

It is assumed that in the process of polymerization, 0 will become constant very eazly in the reaction, as radicals are formed and destroyed at identical rates.

In such a steady-state condition Vi = Vt and ,? 2f kd CI = 2ktCm (3) from which 0 = (fkdykt)2 (4)

The rate of propagation V is essentially the same as the overall rate of disappearance of the monomer, that is, of polymerization, since if the chains are long the number 12. of monomers concerned in the reaction X' = M°1 must be small compared with those used in propagation, Hence,

Vp = (—dCH/dt) = ki)C14Cm = yfkd Cl/lied' Cm (5)

The overall rate of polymerization in the early stages of the reaction should thus be proportional to the square root of the initiator concentration, and if f is independent of Cm, to the first power of monomer concentration. This is true if initiator efficiency is high. With very low efficiencies f may be proportional to Cm, making Vp 3/2 proportional to 0,.7 • The proportionality of the overall rate to the square root of initiator concentration has been confirmed experimentally in a large number of cases.

C. Chain Transfer Reaction.

The kinetic chRin lengthli is defined as the number of monomer units eonsumee7, per active centre. If no reaction takes place other t:lan those already discussed * the kinetic chain. length should he related to the number average degree of polymerization Y : for termination by combination fn = 2`ti and for disproportionation n=1) . This is found to be precisely true for some systems, but for others wide deviations are noted in. the direction of more polymer molecules than active centres. The deviations are the results of chain transfer reactions, as pointed out by Flory 2 in 1937. 13.

M' + XP MxX + P' P' + M --4 Mi etc.

A common mechanism of chain transfer is the removal by a growing chain of a hydrogen or other labile atom from the transfer agent, which may be a molecule of solvent, initiator, monomer or polymer. Chain transfer to polymer produces branching in polymers. Chain transfer usually reduces the polymer molecular weight but not the rate of polymerization. Active chain transfer agents are sometimes used as "modifiers" in polymerizations to control the molecular weight of the polymers. If the new radical(P') produced from the transfer agent is too much stabilized by resonance, then it is incapable of further propagation. Bartlett 3 has termed such reactions "degradative" chain transfer, and in the case of allyl acetate it can be formulated. Thus,

-4 PH + CH2 = CH -- CHOOC CH P' + CH, CH. • 000C .CH3 3 CH - CH = CHOOC CH 2 3 DeEradative chain transfer reduces both the rate and the decree of polymerization.

D. Inhibitors and Retarders.

The rate and degree of polymerization may both be controlled by the use of inhibitors and retarders. These are substances which react with free radicals to form products 1/1r. incapable of adding monomer. Tnhibitors react with radicals as soon as they are formed, and polymerization cannot occur until all the inhibitor has been used up. In the presence of inhibitors, polymerization will be preceded by an induction period, the length of which depends on the amount of inhibitor present in the system. Retarders are less reactive and compete with the monomer for free radicals, thus reducing both rate and degree of polymerization. The distinction between inhibitors and retarders is one of degree. Benzoquinone is an inhibitor for polymerization of styrene, nitrobenzene is a retarder.

B. Determination of the Velocity Constant9 of the Com,.:onent Reactions.

TherateofinitiationV.is given by

V. = 2f kd I (1) sothatifV.is found, and the initiator effi,3iency f and concentration of the initiator are known, kd can be calculated. By combining equations (1) and (5) we have

2 (6) kp 2 /fit = 2 Vp /V. C2 2 30 that if V., Vp and Cm are known the ratio kp /11t can be k found. Either Y. or t must now be determined in order to obtain the value of the other. The mean life-time T of the free radicals is related thus 15. C T P M (7) s 2k V t /3 Melville 4 devised a method called the "rotating sector" method which is applicable to photochemically induced polymerization. In this periods of illumination of the reactants alternate rapidly with periods of darkness and the results enable one to determine Ts. The values of Ts, Cm, and the overall polymerization rate, Vp, suffice to calculate kp/lt. With the ratio kp2/kt obtained from other data, the individual rate constants may be evaluated.

F. Cationic Polymerization.

Certain ethylenic derivatives and cyclic monomers readily polymerize in the presence of Friedel-Craft catalysts such as A1C13, AlBr3, BF3' H2SO4 and other strong acceptors and the monomer may be regarded as being basic. Most of the initiators require a co-catalyst to initiate the polymerization. Unlike free radical polymerizations, such polymerizations proceed best at temperatures well below 0°C and often as low as -120°C. Polymerization may occur so rapidly that uniform reaction conditions are unobtainable. The polymerization of isobutylene by A1013 or BF3 takes place within a few seconds at -100°C, producing a polymer of molecular weight up to several millions. In order to prevent an excessive rise in temperature, a liquid (e.g. ethylene, propane or butane) at itsiboilLng point may be used as an 'internal refrigerant', the heat of polymerization is thus dissipated in vaporising a portion of the diluent. The most satisfactory explanation of the mechanism of the cationic polymerization of vinyl compounds in the presence of Friedel-Crafts catalysts involves carbonium ions and may be illustrated by reference to the polymerization of isobutylene in the presence of TiC14. The first step is believed to be the reaction of the catalyst with the co-catalyst represented by RH, to form a complex acid:

TiC1 + RH H+RTiC1 4 4 Water may serve as a co-catalyst and its reaction with TiC1 4 is represented by + TiC14 + H2 O H Tin OH - 4 The complex acid then donates a proton to the isobutylene molecule to form a carbonium ion or cation

HMTi01 (0H3)20 = 0112 = (CH3)3(1../ + + 4 RT1O1 This cation then reacts with monomer, with the reformation of carbonium ions at the end of each step

+ ( CH ) c + = CH - [(CH )0- - CH21 -C(H ' 3 3 3 3 2 ' 312

Since the reaction is in general carr:i.ed out in a liquid of relatively low dielectric contant, the counterion RTiC17 cannot be greatly separated from the growing cationic end; rather they form an ion-pair. 17.

The termination reaction can take place by the rearrangement of the ion-pair to yield a polymer molecule with terminal unsaturation, plus the original complex acid

CH - [(CH3)2C - CH 3 2]n - C (CH3)2 + RTiC14 ,,CH0 CH -[(CH3)2C-CH2]n C' + H+ 3 RTICI4 3 Alternatively, the cation and anion may react in such a way that R combines with the cation, liberating the catalyst. :

CH - [(0 3)20 CH2]n - C(CH ) + RTiC1 3 3 2 4 CH3 4, CH3 - [(CH3)20 - CH2]n C - R + TiC1 4 CH3 Infra-red absorption studies suggest that the first of these termination processes is more probable. In the polymerizations of cyclic ethers by cationic catalysts, the chain carrier is an oxonium ion. For the polymerization of 1,4 epoxycyclohexane with FeC1 and SOC1 3 2 as co-catalyst, Wittbecker et al 5 postulated the following mechanism: + 01-S-0 Peal4 * - Initiation : + SOC1Fe014 i-4-

0 If Propagation: 01-S-0 Cl-S-ONFeClA t 0 lit"J

18.

Termination : 4 ... ---- .FeC1 Fe01 4 3 Cl

In cationic polymerization chain transfer to 6 monomer and to impurities such as water (e.g. in the polymerization of tetrahydrofuran by BF3(02H5 )2 0 and epichlorohydrin 7), may take place. Chain transfer to polymer8 is also known and leads to branched polymers.

G. Anionic Polymerization.

Ethylenic monomers with electronegative substituents, such as acrylonitrile, methyl methacrylate and styrene, and monomers which polymerize by ring—scission, are susceptible to a type of polymerization which OCCU2S readily in the presence of reagents capable of providing negative ions. Typical catalysts for such polymerization include alkali metals; alkali metal alkyls, such compounds as sodium naphthalene and triphenyl methyl sodium, and Grignard reagents. Like cationic polymerizations, anionic polymerizaticns often proceed best at low temperature but differ in the nature of the catalyst involved and in the intense colours produced. Addition of methyl methacrylate to a solution of sodium in liquid ammonia at —7500 results in immediate formation of high molecular weight polymer 9. Early production of elastometers in Germany and Russia from 19.

butadiene, catalysed by sodium and potassium; was based on this type of reaction. Higginson and Wooding 10 studied the polymerization of styrene catalysed by poyassium in liquid ammonia. The rate of reaction was observed to be proportional to amide ion concentration and to the square of the monomer concentration. The degree of polymerization (ranging from 5 to 35) increased approximately as the styrene concentration, but was independent of the concentration of amide ions. These observations together with presence of approximately one nitrogen atom per molecule, and the absence of unsaturation, offer strong support for a mechanism consisting of the following steps:

KNH2 K + NH2

NH7 + M ---> NH2 NH2 M; + MNH2 M;4.1

NH2-M.141 + NH3 NH2 - Mn+/F + NH2

(The gegen ion K+ has been omitted from the scheme because of the comparatively high dielectric constant of the liquid ammonia medium). These reaction steps correspond to those g-r-esa-i-t-t- cationic polymerization except that termination is essentially a chain transfer with solvent. The mechanism of termination of sodium catalysed polymerization of butadiene in the 20.

presence of toluene involves the transfer of a proton from the solvent to the gro7ing chains

Y----CH2 - CH= OH-Uff2 + Na+ + 06H5CH3 =,-0112 - CH = CH •-OH3 + Na + C6H5 CH2 The mechanism of the ring-opening polymerization of ethylene oxide bi methoxidc ion may be described as follows:

Initiation; CH 6 + - CH CH..0 CH - CH .0 3 2 5 2 2

2 Propagations CF.-5OCH2 CH2 d" + n CH -CH %-0 CH30(CH2 -- CH2 - 0)n - CH2 - 01120-

Termination:

• -• GH30(cH2 - OH2 0), -0112 - 01120 + 01130H

CH30(CH2 --CH2 --0)n+1 H + CH30-

H. "Living Polymers".

Since the termination step usually involves '6ransfer from some species not essential to the reaction, anionic polymerization with carefully purified reagents may to systems in which termination is lacking. The resulting species were called "living polymers" by Swaro 11, who prepared an example by polymerizing styrene w:lth sodium 21. naphthalene. Kinetic analysis 12 shows that these polymers can have an extremely narrow distribution of molocilar weight and for all practical purposes be essentially monodisperse, this has been confirmed by ultracentrifugation in some cases. The polymer can be "killed" by addition of terminating agent eoF. water, at the end of the reaction,

I. Co—ordination Polymerization,

For many years polyethylene was only produced by a free radical reaction at high pressure; the resulting polymer is branched. In 1955, Ziegler 13 polymerized ethylene to high molecular weight linear polymers at normal temperature and pressure by use of catalysts involving aluminium and other metal alkyls; in combination with metallIe halj.des capable of reduction to a lower valency state. SLR oh Ziegler catalysts consist generally of (a) a reducing compound, often an alkyl of an element in Groups I, II and III of the periodic table, and (b) a halide of a transition metal compound. Trialkyl aluminium and Ti01 form a 4 pFxticularly active catalyst. Aluminium alkyls are realising agents; and Eat-6a and co—workers 14 in 1955 showed that the initial product of reduction TiC13, 71_n combination with the alkyl, was a very powerful catalyst z cyr the production of stereospecific polymers of substituted olefins, diolefins and other monomers Stereospecific polymers are those in which repeating units of the chain aal possess the 22. same stereochemical configuration - isotactic polymers - o5? a regular alternation of stereochemical configurations along the chain - syndiotactic polymers. These polymers contrast with "atactic" polymers, formed by other polymerization mechanisms, in which the stereochemical configuration of ifie repeating unit varies randomly along the chains. The mechanism of co-ordination polymerization is not well. established. Probably the polymerization takes place on the surface of the solid catalyst, which in some way induces a particular stereochemical configuration.

J. Polymeriza4-ion Depslymerizatio/1 Equilibrium.

Some polymers decompose by step-wise loss of monomer in a reaction which is essentially the reverse of Polymerization. The depolymerization reaction can be incorporated into the kinetic scheme for chain polymerization. At ordinary temperatures the scheme is not much changed because the rate constant for depolymerization is small. The activation of depolymerization is very high (10-26 Kcal./ mole), compared to that of propagation. However, at some elevated temperature the rate of polymerization will eoual that of depolymerization. This temperature is the "ceiling temperature" above which polymer chain carriers, in the 'Presence of monomer at 1 atm., depolymerize rather then grow. This temperature is akin to the sharp temperatures which 23,

characterise physical aggregation processes, e.g. melting point or Curie point. The term "ceiling temperature" was first used in 1938 by Snow and Frey 15 who also found the temperature to be independent of the catalyst 1JJ3ed. But a satisfactory explanation of ceiling temperature was first advanced by Dainton and Ivin 16.

1.2. (1) Theory of Chemical Renotion Evt High Pres2=e,

Fre-3sure is a very effective variable in chemical reactions, The effect of pressure on gas-phase rr:-.1etions is mainly' due to changes in the c6moentration of tho reactants, Since the compressibility of liquids is far less than trot cf gases, the mass law effects cannot account for the influence of prssuro on the rates of liquid reactions. The effect of pressure on liquid phase reactions is explained by two main theoreies of reaction rates, namely, the %i-a.C4t collision theory and the active. com1Dlex theory. In a sense the two theories are equvalent but their methods of approaching the problems of ki,.letics are ouite different.

Theory.

The classical collision theory expresses the rate constant k for a bimolecular reaction in the form k pz e-E/RT where Z is the frequency of collision of the 24 • reacting molecules in a unit volume at unit concentration and P is the probability factor (often less than unity) which takes account of the fact that molecules may also need a particular orientation before they can react. The attempts to apply this equation to reactions under pressure have to explain why both the quantities PZ and E are changed. Pressure changes k to a small extent in bimolecular "normal" reactions i.e. reactions in which P has a value close to unity. In such reactions the magnitude of PZ is not greatly affected by pressure and the increase in rate is due to a decrease in E. In the so-called "slow" reactions where P has a small value, pressure usually causes a large increase in the numerical value of PZ. This more than compensates for an increase in E and the net effect is a large increase in the rate of reaction. ?Wale 17 has tabled the effects of pressure on the numerical values of PZ(A) and E in the Arrhenius expression for the rate constants of some reactions.

B. Transition State Theory.

The effect of pressure on liquid phase reactions is best explained by the transition-state theory. The derivation of an expression showing the effect of pressure 17 on the reaction rate constant k has been described by Weale and Hamann 18. The derivation involves contribution of the effect of pressure on the equilibrium between reactants and transition state. or

(i) Effect of pressure on equilibrium constEnt.

Let us consider a homogeneous liquid phase system in which the following equilibrium exists,

aA + bB + ove•A 1M MM • t• • • e • (1)

Here a, b 6666,. 1, m denote the stoichiometric number of the molecules of the type A,B ...se L, M 60.04 taking part in the reaction. Now, the chemical potential of a compound i in any state is given by,

u. = u.o + RT lnai. (2) whereui.o is the chemical potential of the component in its standard state, R the gas constant, T the absolute temperatureanda.its activity. At equilibrium,

+ L 30,1 auA + buB + = luL + muM (3) From eqn. (2),

(am)m. o o RT ln = auA + buB +-6 lu+ L nu m . (4) (aA)a (aB)b....

By defining equilibrium constant K by

L)1 (am)m.... K = (a (aA)a (aB)b 0 • • • and from the equation, bu.o ( ) - V.° (P T

where .° is the molar volume of the component i in its standard state, the relation between K and P is

( S RT In K 1V.„. 0 0 /T = aV ° + 1V ° + *000 mVm P A = - A 7.° (5) where V° is the excess of molar volumes of th,,, products over those of the reactants all in their standard states. In a liquid mixture in which all of the components in their pure states are liquids at the temperature and pressure under consideration, and are present in comparable amounts, the standard state is chosen to be the pure components (mole fraction xi = 1). Eqn. (2) can be rewritten as u. = u. + RT ' x. (6) which defines activity coefficient Y • and the choice of the standard state requires that

1 as xi ..) 1. With this definition the activity equilibrium product, Kd' is given by

(x)1 (xM)m x ?,)1 (VM)m t • • • "a (xA )a (xB )b.... (7) ('A )aYB)b • • • • and equation (5) applies.

However, it is easier to measure Kx the mole 27. fraction equilibrium product, which is given by

(xL )1 (xM/ 1111 "" x (8) (xA )a (xB )b Since the variation of the activity coefficients with pressure is given by the relation of the type

SRT 1n),I. ( —T7-- )T = Vi - Vi ° (10) where Vi = (I V./i gn) the partial molar volume of the component i, it follows from equation (5)

ART In K ( r x 1 / T = - 4, V (10) where V is the excess of the partial molar volumes of the produ is over those of the reactants, in the equilibrium mixture, For a solution of a solid or a gas in a liquid the solute activity coefficient is taken to approach unity at infinite dilution i.e. for solutes

u. = u.° + RT In x.)e i and --4 1 as 0

For a chemical equilibrium between solute species this definition leads to an expression for the pressure dependence of the activity equilibrium, which is

RT in K d 'T — AeNV4 (12) 28.

The quantity 44 V is the excess of the partial molar volumes, at infinite dilution, of the products over those of the reactants If for experimental convenience, we again define a mole fraction equilibrium product (eqn. 8) then, as before

( CNRT ln K V (13) P X )T D° This equation was derived by Planck 19 in 1887. When we express the concentration in molality mi and volume concentration c (molarity) we get the molal equilibrium constant Km and molar equilibrium constant K which are related to the Kx in the following ways: ( Cs,RT In Km .CRT in Kx )T = ( P ) T -A r6 (14)

( ART ln Kc RT In K, P )T ( p ) T + (l+m a-b ...) RTX6

or = -stOrc + (l+m - a -b ...) RTJ% (15) where K is the compressibility coefficient of the solvent given by k Cln V C Ps T) (16)

It thus follows that variously defined equilibrium constants all depend on pressure according to equations of the form, ERT In K (17) P - fSV except when the molarity concentration is used. 29.

(ii) Effect of pressure on rate constant.

According to transition state theory a chemical reaction proceeds via a transition state X*. Thus bimolecular reaction which yields two products may be written

A+ B X* C D where the activated complex X* is in equilibrium with the reactants. So following equations (14) and (15) ,

.37;132 In Km* fyliT In K * ( x ) V* )T (18) RT In K * gRT In K * and ( p )T p x + (l+m... a -b...)RTI%

=-0V* + -a-b RTlcs (19) where AV* = Vx* - VA - VB , and Kc* is the molar, Kx* the mole fraction and Km* the molal equilibrium constants expressed by - fx*1 K* - LA] LB] (20) Now the rate constant k is related to the equilibrium constant K* 20

12h1 [ k T rive]K * (21) where k is the Boltzmann constant, h is Planck's constant andt is the transmission coefficient assumed to be close to unity, which defines the probability that the transition state X* will decompose into the products rather than revert to the original species.

30,

Assuming N: to be independent of pressure

k _ Zln T (22) 6ff1 p Therefore,.at constant temperature,

g k (Sin IC* •-Sr — •T 6P 'T (23) RT In. &RT In kx So ‘11. V* ( GIs )T —( P )T (24)

( 6RT in RT In kx k ,_T ) k p )T RTIc

- V* - RTk. (25)

For first order reactions,

RT In 6RT In k tRT In k ) = )T A e T P c)- P It is oommoa practice to discuss experimental data on the basis of an assumed relationship

(6 RT ln —7TM — — v* (27)

where L'‘V*, x*=- VA - VB and is called the "volume of activation". is a small difference between the quantity A V* and th-, true volume change for activation. Equation (27) was first suggested by Evans and Polanyi 21 • From theoretic'l considerations Evans and Polanyi split "V* into e"-V1.* and Z-1 V2* : -4=tV1* is the change in 31. volume of the reacting molecules when they form the transition

state and Li V2* is the accompanying change in volume of the surrounding liquid arising principally from changes in electrostriction. 4. 1T2* is usually the dominant factor in reactions which produce or destroy ionic charges.

C. Effects of Pressure on Rates of Polymerization.

Kinetic data for monomers other than styrene are limited to overall rates of polymerization under pressure.

pol* calculated from these is a composite quantity given by 1:11rpot ='-1Vp d t* (from eqn. (5) of Smetion 1.1) where 4.,N -Vp*, ZAVd* and oLvt* are the volumes of activation for propagation, initiation and termination respectively.

I.1.(2) Polymerization at High Pressure.

Early studies on polymerization at high pressure were made by Conant and his collaborators 22 and Starkweather23 They subjected a large number of olefins, dienes and higher aldehyde to pressures of 3000 - 12,000 atm. and found that some which formed no polymer or small amounts at 1 atm. gave substantial yields at high pressures. Sapiro, Linstead and Newitt 24 studied the polymerization of a few more olefins and found methyl styrene to be most responsive to pressure. A great many workers have since investigated the 32. polymerizations at high pressures. Weale17'25 has described the developments of polymerizations at high pressures. Merrett and Norrish 26 investigated the polymerizations of styrene at 6000 (with benzoyl peroxide) at pressures up to 5,000 atm. They found the logarithm of the overall rate to be approximately a linear function of pressure over a considerable range. The polymer molecular wei:ht is nearly tripled between 1 and 3,000 atm. but increases only slightly at higher pressures. The reaction order with respect to initiator concentration is 0.5 at 1 eta. but • ... decreases a little with increasing pressure. They explained their results in terms of the effect of pressure on the component steps of the polymerization process. The initiating radicals are produced by the decomposition of benzoyl peroxide in which the transition state is pre6uced by bond-stretching so that AlTd* is likely to be positive. The rate of this bond-breaking step was therefore assumed to be somewhat decreased at high pressure. Since propagation is a bimolecular reaction which involves the formation of new bonds, 4'.V.3* should be negative, and propagation should be accelerated by pressure. For termination by combination,

t* should be negative and therefore termination should be accelerated by pressure. But Merrett and Norrish assumed that this reaction between two large radicals is diffusion- controlled, and is therefore retarded at high pressure because 33. of the increased viscosity of the medium. The acceleration of polymerization is then ascribed to an increase in the rate of chain propagation and a decrease in the rate of termination of the kinetic chains, which together outweigh the accompanying decrease in the rate of radical production. This also explains the increase in molecular weight with increase in pressure. The levelling off of polymer molecular weight is due to an alteration in the balance between the termination and transfer reactions, the rate of which is also increased by pressure. This explanation of the effects of pressure on the rate of polymerization and the molecular weight has been substantially confirmed by later work. Nicholson and Norrish 27 studied the photochemically initiated polymerization of styrene by the rotating-sector method. They also determined the effect of pressure on the rate of unimolecular decomposition of benzoyl peroxide. As predicted, they found the rate of chain growth to increase considerably with pressure, and both the rates of radical production and mutual termination of polymer radicals to decrease with pressure. The effect of pressure on chain transfer constants, monomer reactivity ratios in co-polymerization, the tacticity of the polymers obtained and on many other aspects of polymerizations have been studied 28-31 34 .

I.1(3) Effects of Pressure on Ceiling Temperatures.

The ceiling temperature effect in addition polymerization has been extensively investigated at ordinary pressure and the results are reviewed by Dainton and Ivin 32 and Ivin 33 The equilibrium between monomer and polymer at equilibrium obeys the thermodynamic relation

,e1G = 411 To N S in which H and S are enthalpy and entropy changes per monomer unit under the prevailing conditions. For the formation of long chains, these are identical with the heat and entropy changes of the propagation reaction. At equilibrium, = 0, so that ► Tc = H/4 S For most addition polymerizations H, 4% S and V are negative and Tc can be raised by increases in the :monomer cr.ncentration air the external pressure, both of which cause a decrease in the numerical value of,a S. The effect is potentially important in the polymerization of substances which do not react' at ordinary pressure. There is qualitative evidence for the existence of pressure effects on the polymerization ceiling temperature of various aldehydes; but only two systems have been studied quantitativelf, and Neale 34 studied the effect of 35. pressure on the ceiling temperature of 04-methyl styrene. T0 increases from 61°C at 1 atm. to 170°C at 6480 atm.; and does so in accordance with the 01apeylibn equation,

d Tc m LXV d P =

Later Busfield and Whalley 35 studied the equilibrium between chloral (in pyridine solution) and insoluble crystalline polychloral up to 1,500 atm. For 0.1M chloral in pyridine at 1 atm. Tc is 12.5°C. They found the pressure coefficient of ceiling temperature to be 19°C per kilobar. Their results are similar to those for a-methyl styrene.

1.1(4) Effect of Pressure on Ionic Equilibrium.

Usually the dissociation of electrolytes is accompanied by a contraction in volume because of the increased solvation of ions. The ionization of acetic acid involves a contraction of — 10 cm3/mole 36. So pressure is likely to shift the equilibrium more towards ionization and greater conductivity. High pressure measurements of the conductance of weak electrolytes in non—aqueous solvents show clearly that the increase in ionization due to pressure is quite appreciable 37,58. 36. I. 3. Review of the Polymerizations of Spme Cyclic Ethers.

A. Polymerization of qyclic Ethers at 1 atm.

Many cyclic ethers undergo ring-scission and propagation reactions, under the influence of either anionic or cationic catalysts, to give polymers ranging from low molecular weight oils to high molecular weight solids. Cationic polymerization is, however, more general and often yields polymers at a very fast rate 39.

1. Tetrqhydroflaran (T.H.F,)

Tetrahydrofuran is the most extensively studied of the cyclic ethers. Meerwein et al 40 used oxonium salts to polymerize tetrahydrofuran. They produced the oxonium salts by the reaction of diethyl ether additLan moriapo%Indei,with boron, antimony , ferric or aluminium halides and an epoxide such as epichlorohydrin (ECH). They also reported thc'.t derivatives of boron and antimony halide etherate were more effective than the others. Hamann 41 reported that SbC1 and PC1 alone could 5 5 initiate the polymerization. M eerwein et al 42 and Hachihema 43 Rad Shono found a mixture of perchloric acid and acetic anhydride to be a very effective catalyst system. More recently a great deal of work has been done to determine the polymerization ceiling temperature of tetrahydrofuran at 1 atm. Bavm and his co-workers 44 found the ceiling 37. temperature to be between 60 and 70°C using a triphenyl methyl carbonium ion as the catalyst. Rosenberg et al 7 used BF3(C2H5)02 and epichlorohydrin to polymerize tetrahydrofuran to a solid polymer. They claimed to have obtained "living polymers" and suggested that the chain carriers are the oxonium ions. The value estimated for the ceiling temperature was 73°C. Sims 45 found the ceiling temperature to be 83°C using FF5 as the catalyst. Sims 46 observed the effect of small quantities of water on the system and found that the rate of polymerization goes through a maximum as the concentration of water is increased. The reaction rate increased with time and at the beginning was dependent on [M], [PF5], and [ECH] when used as co-catalyst. From a consideration of the results of Bawn and his co-workers, Rosenberg et al. and Sims, Ivin and Leonard 47 re-estimatedthe ceiling temperature and concluded it to be 80 + 3°C. Dreyfus and Dreyfus 48 further studied the polymerization of THE in great detail using opl,osioLcvte_ p-chlorophenyl diazonium hexafluomds as catalyst. They found the ceiling temperature to be 84°C.

2. 1,4 epoxycyclohexane.

Wittbecker, Hall, Emerson and Campbell 5 obtained high melting (450°C) polyether from 1,4 epoxycyclohexane using syncatalysts such as BP3 and ECH; FeC13 and S0C12; SbC1 and ECH (or succinic anhydride or propylene oxide). 3 38.

The combination of Feel and SOC1 was found to be the most 3 2 effective. The molecular weight of the polymer obtained was in the range 5,000 to 10,000. The polymer was soluble only in a mixture of 100 parts phenol and 66 parts tetrachloroethane. The molecular weight was not a function of time, which indicates a chain reaction mechanism.

3. 1,2 epoxycyclohexane.

Bacskai 49 obtained a yield of 82% poly-1,2 epoxycyclohexane in 25 minutes at -78°C using triethyl aluminium as the catalyst. The polymer had the limiting viscosity number of 2.28 in benzene at 30°C. Aluminium diethyl chloride yielded 86% in five minutes. Lenzi et al 50 reported the radiation induced polymerization of 1,2 epoxycyclohexane. The values of the molecular weights of a few polymer samples, determined by a vapour pressure method, were in the range 10,000 - 20,000. They also observed that addition of water drastically reduced the rate of polymerization and the molecular weight of the polymer obtained.

4. 1,2 epoNycyclooctane.

Bacskai 49 used triethyl aluminium as initiator to polymerize 1,2 epoxycyclooctane and found only some viscous polymer which dissolved in methanol.

5. Styrene Oxide. Bartleson 51 obtained a viscous oil and semi-solid 39.

polymer of molecular weight 400-700 in pentane soli)tion at 52 -29°C using BF3 as initiator. Blanchette produced a polymer having a molecular weight of about 3,000 with FcC13- styrene oxide complex. Low molecular weight polymer was also obtained by the use of A1C13, SbC13, BeC13, SnC14, Ti014 and 53 54 measured the heat of 7,1012- ' ' Dainton et al. polymerization of styrene oxide initiated by BFe.(C2H5)20. 6. Tetrahydropyran.

Polymerization of tetrahydropyran has not yet been reported.

B. Polymerization of Cyclic Ethers at High Pressure,

Conant and Peterson 55 first observed that ring opening polymerization is facilitated by pressure. They obtained a hard, stable transparent polymer when cyclohexene oxide was kept at 12,000 atm. for one week with 2% benzoyl peroxide. Mehdi 56 studied the kinetics of polymerization of propylene oxide, THF, 113,5-trioxane, cyclohexene oxide, styrene oxide, 3:3-ois(chloromethyl) cyclobutane and 1,2- epcxy-4-vinyl cyclohexane. No polymerization of cyclohexene oxide occurred between 5000 and 7000 atm, at 60°C with benzoyi peroxide initiator, but a solid polymer was obtained at pressures between 8400 and 12,500 atm. The rate of polymerization increased 7.5 times between these pressures a:id the molecular 40. weight went up from 1850 to 6700. Benzoic acid at 6850 in 67 hrs. produced a polymer (3.8% yield) of molecular weight 750. Thermal polymerization at 10,000 atm. gave a yield of 0.45% per hour. AIBN failed to polymerize this monomer even at 11,300 atm. Boron trifluoride diethyl etherate was not used to polymerize this monomer at high pressure. With 2% Bz202 at 1000 atm. in 6hrs. styrene oxide yielded a polymer of molecular weight 1350. With the styrene oxide-ferric chloride complex as initiator a polymer having a molecular weight of 1710 was obtained at 4100 atm. The rate of polymerization was twice as fast as the rate at 1 atm. BF3.(C2H5)20 was not used to polymerize this monomer at high pressure. Mchdi found that the rate of polymerization of tetrahydrofuran (with BF3.(C2H5)20 as initiator) went up from 0.17% yield per hour at 1750 atm. to 9.3% yield per hour at 5400 atm. The limiting viscosity number of the polymers went up from 0.1 to 2.2 in this pressure range. He also observed that the rate increased with the concentration of the initiators from 1% (V/V) to 3% (V/V) and the polymer obtained with 2% initiator had the highest molecular weight. The

"overall volume of activation" Vpo1* for pressures between 2000 and 5400 atm. was estimated to be -30 mm/mole, and the difference between the apparent molar volumes of monomer and polymer in solution in monomer at 1 atm. was -17.1 cm/mole. Apart from these no other polymerizations of cyclic ethers at high pressure have been reported. 41.

C. Review of Polymerization of Triellylphosphate.

Kennedy and his collaborators 57 reported the polymerization of triallyl phosphate with Bz202 at 98-100°C. In 6 hrs. the yield was 50%, No solid polymer was obtained from triallyl phosphite. Toy and Cooper 58 found triallyl phosphite to be an inhibitor in the polymerization of allyl esters of phosphonic acid with Bz202 and AIBN. No work on the polymerization of these monomers at high pressure has been reported.

1.4. Scope of this work.

A considerable amount of research in.s been carried out on the polymerizations of cyclic ethers at normal pressure but there has been little work on their polymerizations at high pressure. Some preliminary studies were carried out by Mehdi, in this laboratory, as described in his thesis. The present work was undertaken to continue the study of the effect of pressure up to 12,000 atm. on the reaction rates and on the molecular weight of the polymers obtained from cyclic ethers. In the first part of the work measurements of the effect of pressure on the yield of polymer andthe type of polymer obtained were made for the monomers 1,2-epoxy cyclohexane, tetrahydrofuran, styrene oxide and 1,4-epoxycyclohexane. Except for the last named the catalyst generally used was the addition compound of boron trifluoride with diethyl 42.

ether. More detailed measurements wore then made of the rates of polymerizations of tetrahydrofuran and of 1,4-epoxycyclohexane in order to obtain volumes of activation from the pressure coefficients of the rates. During these measurements it became apparent that the ceiling temperature for polymerizations of tetrahydrofuran was considerably changed by pressure and a detailed investigation of this effect, between 1 and 2500 atm, was carried out. Attempts were also made to polymerize tetrahydro- 9ran and 1,2-epoxycyclohexane. Six-membered ring systems such as tetrahydropyran are often thermodynamically stable with respect to chain polymers at ordinary pressures, but it is possible that at high pressure this situation may change. The failure to obtain solid polymers from 1,2-epoxycyclooctane has been ascribed to steric hindrance, but there are indications in the literature that pressure accelerates some sterically hindered reactions very considerably. Some measurements on the conductivity of solutions of BF3.(C2H5)20 at various pressures have also been carried out in order to find whether this catalyst is appreciably dissociated under the conditions used. As well as the work outlined above Nome experiments on the high pressure polymerizations of triallyl phosphate and triallyl phosphite, and on the polymerization of triallyl phosphate with styrene were also carried out, and are described in Section III. 43.

SECTION II.

EQUIPMENT, MATERIALS AND PROCEDURE.

II 1. Equipment.

A. High Pressure Equipment.

The design and construction of high pressure 59-62 equipment are described by many authors . The equipment used. in 1;2= pl'csont stlIdy :Lac bak7,11 dco(;:ciucd prevIousiy in detail 63-66 but a brief outline of the high pressure equipment is given here. During the course of this work three vessels were used and they were capable of containing pressures of 15,000 atm. (Vessel No.1), 5,000 atm. (Vessel No.2) and 4,000 atm. (Vessel No.3) respectively. The method of operating all three vessels may be seen by reference to Fig.II.1. The pressure was generated by a twc-stage hand operated pump, F. The reservoir, R, connected through the valve A contained the pressure transmitting fluid which was liquid paraffin B.F. In all the three vessels the moderate pressure delivered by the pump is increased to high pressure in the reaction chamber V by use of a pressure intensifier D. Low pressure is applied to a large-diameter piston of area 'A' which in turn drives a small piston of area 'a'. Thus, neglecting the friction, the low pressure is stepped up by a FIG-II.1 AN OUTLINE OF HIGH PRESSURE EQUIPMENT • factor A/a. This ratio is approximately 15, 5 and 10 for vessels 1, 2 and 3 respectively. The intensifier in vessel No.3, unlike the other two, is separated from the vessel. There is a pressure gauge, G, in between the low pressure side of the intensifier and the pump, which are connected through valve B and there is a by—pass around the intensifier, through valve C so that the reaction chamber can be primed to pressure Soo between 5Te€Per and 1,000 atm by direct action from the pump, the other two valves being shut. In this way the maximum pressure may be attained (because of the limited travel of the intensifier piston). The tubing connecting the intensifier and the vessel to the pump was made of stainless steel of 3/8" o.d. and 1/8" i.d. The vessels No 1 and 2 were surrounded by electric jacket J while the vessel No.3 was immersed in an oil bath heated by a 1400 watt electric heater. H in Fig,II.1 indicates the electrical connection for the heating jacket. A conventional Sunvic switch relay operating through a mercury contact thermoregulator T inserted between the vessel and the heater provides on—off temperature control witLth The pressure was measured on the low pi-essure side of the intensifier by a Bourdon tube gauge which was calibrated against a standard free piston gauge. The low pressure and high pressure were found to be related by the following expressions 67 46.

Vessel No.1. H.P. = 14.84 L.P. - 520 Vessel No.2. H.P. = 4.74 L.P. 170 Vessel N0.3 H.P. = 9.24 L.P. - 200

The vessel No.1 is sketched in Fig.II.2. The upper part is the pressure vessel proper. It consists of an autofrettaged cylindrical monobloc of "Vibrac V.45" steel, six inches in diameter. The reaction chamber is centrally located and has a diameter of 0.6 inch. The steel plug is screwed down on a steel mushroom head, which holds a Poulter packing against the pressure in the reaction chamber. The side inlet allows the reaction chamber to be filled with oil and be primed to the initial pressure from the pump. _It the bottom of the reaction chamber below the level of the side inlet is another Poulter packing which automatically seals the side inlet when it is forcod hols,- by the advancement of the high pressure piston. The lower part of the sketch is the intensifier of the same dimension as the reaction vessel. Oil is pumped through the low pressure inlet against the Bridgman packing of the low pressure piston (dia. 2.5 inches). A thrust block containing a seat of soft metal ensures the high pressure piston is always aligned with the low pressure piston and the reaction chamber. The high pressure piston has a clearance of 0.001 inch in the reaction chamber. The upper and lower COD PLuc

Tv MUSHROOM HEAD POULTER PACKING

REACTION CHAMBER

SIDE I NLET • PouLTER PACKING I

H.P. PISTON THRUST BLOCK ki AL kL.'P. PISTON l BRIDGMAN PACKING

6\\ L.P. INLET

VESSELN014 INTENSIFIER cylinders are joined with steel sleeve, The voluime of the reaction chnmber is such that only small samples, from 3 to 5 mis. can be accommodated. Vessels No.2 and 3 are each constructed of two cylinders of "Vibrac V 45" steel shrunk together. The vessel No.2 was sealed on the top with a rubber 0—ring and vessel No.3 with a Poulter packing and a screw plug. The intensifier pistons and thrust blocks in all cases are made from hardened C.R.C. quality race steel bar.

B. Reaction Tubes and Holders.

For reactions up to 2,000 atm., a pyrex glass tube of 15 cm. in length and 0.8 cm. i.d. was used. It was sealed at the top with a ground glass stopper and had a 3 mm. wide hole at the bottom, through which pressure equalizt:tion was effected. To prevent any contamination of the reaction mixture by the surrounding liquid paraffin, about 3/4" of the reaction tube (Fig.II.3) at the bottom was filled with mercury and it floated on mercury contained in the bu,Aot which held it. For reactions above 2,000 atm., a PT,F.E. (Teflon) tube about 10 cm. long, 8.5 mm. o.d. and 6 mm. i.d. was used. It was stoppered at both ends by plugs machined from Teflon rod and had copper rings at the ends to prevent any extrusion of the tube (Fig,II.3). The pressure was transmitted through the collapsible walls of the tube. The tube was then put in a A-GLASS TUBE &BUCKET ; "B-TEFLON TUBE

C - HOLDER FOR'31 ; D- STEEL TUBE.

FIG-Ii.3 REACTION TUBES 84 HOLDERS, 50. perforated steel bucket having retaining steel plugs at both ends. The plug at the top end was fitted with a hook so that the bucket could be removed from the reaction chamber. There was sufficient clearance between the tube and the bucket wall to allow rapid transmission of pressure and a bowed steel spring was soldered to the side of the bucket to hold it in any desired position in the reaction chamber. For the polymerization of tetrahydrofuran (b.p. 65°C), above 8000 the Teflon tube proved inadequate because the monomer vapour leaked past the Teflon plugs. So a steel reaction tube (Fig.II.3) was de-rised for this purpose. The tube was 5 inches long, 0.54" o.d. and 0.375" i.d.. On the top, the tube was machined to an angle of 300 wheiza green spot rubber 0-ring (7/16" o,,d. and 5/16" i.d.) supplied by Dowty Seals was placed. The top end was then sealed by a screw plug provided with a hook. The screw plug at the bottom had a 5 mm, wide hole in the centre. Just above the plug was a steel piston of 0.375" diameter and 0.45" in length with a groove round its periphery in which a 'green spot rubber 0-ring of 1/4" i,d. and 3/8" o.d. was fitted. The pressure equalization was achieved by sliding of the piston inside the tube. L bowed steel spring was soldered to the side to hold it in the desired position in the reaction chamber and so no holder was necessary for this reaction tube. This reaction tube was satisfactory for polymerization of THE up to 130°C. 51.

C., Atmospheric Pressure Equipment.

Reactions at atmospheric pressure were carried out in a well—stirred oil bath heated by a 150 watt electric bulb and controlled by a mercury—toluene regulator operating in conjunction with a Sunvic relay. The temperature control was better than + 0.05oC. Sealed amber glass ampoules of 5 or 10 ml. capacity wore used for such reactions.

D. Equipment for Conductivity Measurement at High Pressure.

A vessel plug with two insulated electrodes to which a high pressure conductivity cell could be connected was used in the measurement of conductance at high pressure. The plug (Fig.II.4) was machined from a "Vibrac V 30" steel and the electrodes mounted on 1/2" centres. The electrodes were insulated from the plug by hollow ebonite cones machined to a thickness of about 1/16", forced against the plug by silver steel cones. The screw plug and electrodes withstood pressures up to 3,000 atmc (4000 with no leakage or electric shorting. The high pressure conductivity cell (Fig.II.5) was made from standard B.10 Quickfit cone and socket glass connectors. The electrodes were made from 0.006" thick platinum foil cut into rectangles approximately 0.6 cm. x 0.6 cm. and welded to 0.03" diameter platinum wire through the top 52,

EBONITE INSuLATOR L

STEEL ROD

asm.

EBONITE CONE STEEL CONE

ELECTRICAL LEADS

FIG-B.4 VESSEL ?LUG WITH ELECTRICAL LEADS. 53

FIG 1I.5 HIGH PRESSURE CONDUCTIVITY CELL .54. of the cell into slomt glass walls which contained mercury to make contact with the wires from the plug. The cell capacity was about 8 mis, Spring connectors held the cell firmly together. The pressure oqulization was effected through holes cut in the upper portion of the glass bucket which had mercury to isolate the solutions from the liquid paraffin. The whole cell was suspended in a brass holder attached to the plug. To platinize the electrodes, they were immersed in a solution of 0.3% chloroplatinic acid, 0.025% lead acetate and 0.025N hydrochloric acid and a current of about 10 mh./cm2 was passed for 15 minutes reversing the direction every 10 68 seconds Conductances were measured with a Wayne—Kerr B.221 Universal Bridge, operating at 1592 c.p.s. (10,000 -ratio/sec,), —1 -8 The bridge measured conductances from 10 to 10 mhos with an accuracy of better than + 0.2%. Balancing was effected by two 'magic eyes' of different senEitivities. Capacitance decades could be adjusted to balance out any reactive term associated with the unknown conductance. 55.

II. 2. Materials.

...A Monomers.

(i) 1,4-epoxycyclohexane: its preparation and dryin.

An equimolar mixture of 1,4-cyclohexanediol supplied by Koch-Light Ltd. and freshly roasted alumina was heated to 250-300°C under a 30 cm. Vigreux column until the distillation ceased. This usually took 8-10 hours. The distillate thus obtained consisted of two layers and the lower aqueous layer was extracted with ether several times. The combined oil layer and ether extracts were dried over anhydrous magnesium sulphate, filtered, subjected to preliminary vacuum distillation, and finally fractionated through a 60 cm. Fenske column to give the main fraction of the epoxide, b.p. 116-118, np6 1.4457 (lit. bnp. 117-118, 20 nD 1.4477). This method of preparation of 1,4-epoxycyclohexane was described by ?7ittbecker et al. 5 and Olberg cat al69. Since calcium hydride is a more effective drying; agent 39, it was used in subsequent drying instead of anhydrous magnesium sulphate and the product was fractionated as above. The monomer obtained by drying with calcium hydride and subsequent fractionation boiled at 116-118°C and had a refracti7e index of 1.4461 at 26°C. Two sets of results were obtained as shown in Section III,1. In one set monomer dried v:Lth 56, anhydrous magnesium sulphate was used and for the other the monomer was dried with calcium hydride.

(ii) Tetrahydrofuran.

Tetrahydrofuran supplied by B.D.H. was first dried with calcium hydride from 16-18 hrs., the mixture being constantly stirred by a magnetic stirrer. The mixture was then filtered and the filtrate was refluxed for at least four hours with lithium aluminium hydride. The clean liquid from the top was then decanted off and fractionated using a Vigraux column. The middle fraction boiling at 65°0 was collected (lit. 70 bop. 64-65oo . The monomer was dried before every run was carried out.

(iii) 112-epoxIaplehemane.

1,2-epoxycyclohexane supplied by K. K L1boratories Ltd., Inc. New York, was fractionated and the fraction boiling at 131°0 was collected (lit. 70 b.p.

(iv) Styrene Oxide.

Styrene oxide (L.Light and 0o.) was distilled under vr..cuum and the fraction boiling at 84-5°0/15 mm. Hg was collected.

(v) Tetrahydropyran.

Tetrahydropyran (Koch-Light and Co.) was dried over calcium hydride for 16-18 hrs. and distilled. The fraction 57.

boiling at 88°C was collected.

(vi) Cyclo-octene Oxide.

Cyclooctene oxide supplied by B.D.H. was used without further purification.

(vii) Triallyl phosphate and Triallyl phosphite.

Triallyl phosphate and triallyl phosphite mere used as supplied by Allbright and Wilson Ltd., London.

(viii) Styrene,

Styrene as supplied by B.D.H. contained tert,butyl catechel as an inhibitor. Before using the monomer the inhibitor was removed by shaking with coustic soda solution in a separating funnel. The alkali contamination was removed by successive washfmg with distilled water. The styrene was Bien dried over anhydrous sodium sulphate in the dark under vacuum for 24 hours. The monomer after filtration, was distlled under reduced pressure in an atmosphere cf oxygen- free nitrogen gas and the middle fraction distilling at 32°C mme Hg) was collected. The monomer was stored at 0°C an,J was used within 24 hours.

B. Cataluts and Co-catalysts.

(±) Benzoyl peroxide (Bz202).

A saturated solution of Bz202 was prepared in 58. chloroform and solid crystalline benzoyl peroxide was precipitated by adding cold methanol. The recrystallized material was dried under vacuum and was kept in the dark in a vacuum desiccator. Fresh materials were prepared every few days. (ii) Azo-bis isobutytonitrile (AIBN).

AIBN was recrystallized from a saturated solution in ether, dried and stored in vacuum.

(iii) Boron trifluoride diethyl etherate [BFriC„die 5)„0].e

an initiator BF3.(C2H )20 (BDH)was used as supplied. For measurements of conductance Bk3°(02H5)20 was distilled and the fraction boiling at 125°C was collected 71

(iv) Epichlorohydrin (BCH).

Epichlorohydrin was used as co-catalyst with

BF3'(02H5)20 without further purification. C. Solvents.

Solvents used such as methanol, absolute alcohol, benzene, phenol, tetrachloroethane, toluene, etc. were used without further purification. Tetrahydropyran was dried and distilled in the same way as for reaction experiments, Benzene used for viscosity and cryoscopic measurements was of "Molecular Weight determination" grade, 59.

II. 3. Procedure.

A. Preparation of Reaction mixture.

All the materials used during the present study were liquids except cyclooctene oxide, Bz202 and AIBN, which are solids. In the case of liquid, monomer, initiator or solvent, a known volume was pipetted out into a stoppered conical flask. Solid materials were weighed out in exact amounts into the flask. The conical flask was slowly shaken to ensure uniform mixing or complete dissolution of the reactants. While adding BF3.(C2H5)20 to styrene oxide, cyclohexene oxide, and to toluene solution of cyclooctene oxide, the reaction mixture became very hot. So the flask was cooled in iced water while the initiator was added to the monomer or monomer solution. :liter reaction mixture was prepared, it was poured into the reaction tube through a glass tube with a capillary end. Any air bubbles were carefully eliminated from the reaction tube filled with the reactants.

B. Technique of Polymerization.

The reaction tube, contained in a holder if necessary, was placed in the vessel, kept at the desired reaction temperature. The Poulter packing w-s then f.-sei'ted. in the top of the reaction chamber by a brass tool (previously heated to the temperature of the vessel), keeping 60, valves C (H.P.) and A (Rosrvoir) open. Finally the vessel was closed with the screw plug (Fig,II.2) which had also been preheated to the temperature of the vessel. Valve A was then shut and the reaction chamber was primed to the initial pressure. Valve C was then closed and valve B (L.P.) was opened. After the desired pressure was developed, Rs indicated by the gauge, valve B was closed. The reaction chamber was thus isolated from the rest of the system. After a certain period of reaction, the pressure was released. Keeping valve A open, valve B was slowly opened. 'Men the pre:Jsure was a few hundred atmospheres, valve B was shut and valve C opened so that the intensifier travelled back to its original position. The screw plug was then removed and the rubber bung was pushed out by pumping oil from the reservoir through the valve C, The reaction tube was then removed from the vessel by a hook. The period during which the vessel was under the desired pressure was take_i. to be the reaetion time. For reactions with BF3.(C2H5)20, the reaction tubes were quenched in ether or acetone immediately after it was takm out to stop any further polymerization.

C. Separation of the pglymers.

154 epoxycycaohexane and triallyl phosphate yielded insoluble polymers. So they were simply washed several times by methanol and absolute F2.1cohol to remove the unreacted 61, monomer. To separate the polymers of tetrahydrofuran, the monomer was pumped off the reaction product and the polymer finally washed with methanol and dried under vacuum. The copolymer of styrene and triallyl phosphate 'MO precipitated by methanol from a solution of the reaction product in benzene. For precipitation of polyyclohexene oxide, the reaction product was dissolved in absolute alcohol. Distilled water was then added to cause the precipitation of the polymer. In some cases, a polymer fraction of slightly higher molecular weight precipitated out on adding the alcohol. Low molecular weight polymers of styrene oxide were precipitated in two fractions. The first fraction was obtained by adding methanol to the reaction prol,,Ict. After the first fraction was removed, water was added to the methanol soluble part of the reaction product and the second faction precipitated out.

D. bbl ocular. Weight Duterminaticr.

Molecular weights up to 49000 were determined cryoscopically in benzene. This gave the nurT,cr average molecular weight Fi. The apparatus used for this purpose consisted cf an inner freezing tube fitted with a Beckmann thermometer and a stirrer, an air—jacket surrounding the inner tube to ensure 62. slower and more uniform cooling of the liquid and a Thermos flask, with a stirrer, containing melting ice. A weighed amount of pure benzene was placed in the inner tube and the Beckmann thermometer reading was noted at its freezing. Then a weighed amount of polymer was added to the benzene in the tube and the Beckmann reading at the freezing of the polymer solution was noted. The difference in the Leckmann readings gave the depression (AT) of the freezing point of benzene for a known polymer concentration which was adjusted in such a way thata T was more than 0.2°C but less than 0,5°C. The molecular weight was then calculated from the equation:

= 1000xKxw 4).T x W where w = weight of the polymer, W = weight of solvent (benzene) and K = the molar depression for 1000 gms. of the solvent (benzene) The value of K was taken from literature 72 to be 5.12, For polymers of higher molecular weight viscometry was employed, An M.2 Oetwald viscometer was suspended in a thermostatted water bath maintained at a comtant temperature within + 0.05°C. A lens was used to observe the failing liquid levels and the viscometer etch marks, to avoid any parallax. A stop-watch graduated in 0.1 second intervals 63. was used to measure the time of flow. If to is the flow time for pure solvent and is for a solution of a particular concentration specific viscosity [isp] is defined as (ts-to)/to. The limiting viscosity number or intrinsic viscosity [11] is given by the equation,

[T1] = lim (lsp/c) c 0 where c is the polymer concentration usually given in g/100 mis. The limiting viscosity number was determined by plotting lsp/c against c for three or more values of c and extrapolating the straight line thus obtained to zero concentration. The intercept on the ('sp/c) axis gave the value of [''1 ]. The viscosity average molecular weight 1171v of co-polymer of styrene and triallyl phosphate was calculated from the formula [it] = K In the absence of any knowledge about the values of K and 4k, , only [Y] was determined. This was, however, s,:ifficient to show the change in molecular weight with change in pressure or temperature or time. SECTION-III. RESULTS AND DISCUSSION. 64

III, 1. Polymerization of 114-epoxycyclohexans at high Pressure.

(a) Free Radical Polymerization.

No polymerization of 1,4-epoxycyclohexane by means of free radical initiators has been reported. To investigate whether the reaction would occur under pressure benzoyl peroxide and AIBN (2% w/w) were used with 1,4-epoxycyclohexane at 60°C under 3,000 atm. for 24 hours; but no polymerization could be observed with these initiators. Attempts were then made to polymerize this monomer with ionic catalysts.

(b) Ionic Polymerization.

The addition compound of boron trifluoride and diethyl ether is known to catalyse the polymerization of tetrahydrofuran 56 at high pressure. This initiator (2% mole) was therefore used with 1,4-epoxycyclohexane at 60°C under 3,000 atm. for 24 hours; but the monomer again failed to polymerize. When the initiator concentration was increased to 4% mole, a yield of 6.6% of polymer was obtained under 3825 atm. at 60°C in 5 hours. The addition of 0.1% mole of epichlorohydrin as co-catalyst to 4% mole of the catalyst, however, yielded 34.2% polymer under identical conditions. Epichlorohydrin is therefore a very effective co-catalyst for the polymerization of this monomer with BF3.(C2H5)20. The catalyst concentration was then reduced to 2% mole, but only 0.83% conversion was obtained at 60°C under 58fl5 atm. for 5 hrs., even with 0.1% mole of the co-catalyst„ As a result, higher concentrations of the catalyst, with e, chlorohydrin 60------.,

A- ~1. \'\'\.0 It e..x~ . so B ... At'l. ""crt.. c~. .., C-'3,/- m~~.

i~.v,,~_ &0·<:..

T~ ! ~ ~ouM"

7' 10

1,000 2.,000 1,000 ".000 f"f'~(~) t't\~..£Aw ~ ~ ~ xcvn.~ Pia'DL ,· f? ./J I J S, '-1' 01:J e eLo h ..,.. It B ~3' ~c~ uS") 0 ~ ~l.oytoh.:J ~Y'I'Y\. 2- ( '"0'll0"YY\.,., 01 ,.,'w ..n.It. ~ 4\"'oMM rn...,,,....:- ~)

. .

66, as co-catalyst, were always used in the subsequent polymerizations. The results of these polymerizations are shown in tables 1,2 and 3, and graphically represented in Fig.III.1.

Table 1. Polymerization of 124-epoxycyclohexane (Monomer dried with anhydrous magnesium sulphate).

Catalyst: BF3.(02H5)20 4% mole per cent. Co-catalyst: Epichlorohydrin 0.1 mole per cent. Temperature : 60°C; Time : 5 hours. Pressure (atm.) Yield of Polymer (wt. percent) 1 0.26 1950 2.67 2500 8.69 3240 19.9 3825 34.2

Table 2. Polymerization of 1,4-epoxycyclohexane (Monomer dried with anhydrous magnesium sulphate). Catalyst: BF3,(C2H5)20 5 mole per cent. Co-catalyst: Epichlorohydrin 0.1 mole per cent. Temperature : 6000. Time : 5 hours. Pressure (atm,) Yield of Polymer(wt. per cent) 1475 6.6 1710 11.6 1920 28.2

67.

Table 3. Polymerization of 1,4-epoxycyclohexane (Monomer dried with anbIdraus magnesium sulphate).

Catalyst : BF3°(C2H5)20 3 mole per cent. Co-catalyst : Epichlorohydrin 0.1 mole percent' Temperature : 60°C. Time : 5 hours.

Pressure (atm.) Yield of Polymer (wt. percent) 3120 4%7 3875 9.5 After two runs with 3% mole initiator (table 3) were carried out, a fresh batch of monomer was prepared. This time calcium hydride was used as a drying agent as mentioned in Section 11.2 and experiments were carried out with 3% mole initiator. The yield of polymer was found to be much higher for the monomer dried with calcium hydride than for the monomer dried with anhydrous magnesium sulphate. Similar experiments were carried out with 5% mole of catalyst at 60°C and 3% mole of catalyst at 20°C under high pressures, with monomer dried by means of calcium hydride. The results are shown in tables 4, 5 and 6 respectively and are graphically represented in Fig.III.2 and Fig.III.3. '0.---...;,------

':) Fo u 20

',000 2,000 3,000 1,.000 'Pn.~wu-( o.:.t....w) (.'.',.m.2 Po'.1 hl~~ 0) ',1lf ~ OIJ C.)f:(oJ,.~o...l)"

IN' H. B f i .~~ Hr) '10 ~ Xe, If . 49

Igo l eo

170 cio 16o Ito

•... 130

'2,000 3,000 ktbo en.(44Amg, ( aityr) etwxy cyelohumme. 4013 sTo Isy trazr' 73F5. (Cti4)20 Givud. E CH . 70.

Table 4. Polymerization of 1,4-ePoxYcyclohexane (Monomer dried with calcium hydride). Catalyst : BF3.(C2H5)20 3 mole percent. Co-catalyst : Epichlorohydrin 0.1 mole percent. Temperature : 60°C. Time : 5 hours. Pressure (atm.) Yield of Polymer (wt. percent) 1 0.27 725 5.1 1025 6.5 1500 10.2 1950 16.2 2575 24.6 3200 36.3

Table 5. Polymerization of 1,4-epoxycyclohexane Caiwcesiey, gfkclus)2.0 -C‘a.-4pt- o.i (Monomer dried with calcium hydride) t sue. - Pressure (atm.) Yield of Polymer(wt. percent) 1 0.46 900 10.5 1200 18.8 1500 32.3 1700 47.5 71„

Table 6. Polymerization of 1,4—epoycyclohexane (Monomer dried with calcium hydride)

Catalyst : BF3.(C2H5)20 3 mole percent. Co—catalyst : Epichlorohydrin 0.1 mole percent. Temperature : 20°C, Time : 5 hours, Pressure (atm,) Yield of Polymer (wt. percent) 2525 8.7 2950 11.8 3300 14.0

The polymer separated out of the reaction mixture and was not soluble in any of the single organic solvents tried. In agreement with Wittbecker et al. it was found to be soluble in a mixture of 100 parts phenol and 66 pa:: is tetrachloroethane. Because of the insoluble nature of the polymer no attempt was made to determine the molecular weight of the polymer; but as an indication of the effect of pressure, tc1.rature- and initiator concentration on molecular weight, the limiting viscosity number was determined at 40C, the solvent being a mixture of 100 parts phenol and 6&; parts tetrachloroethane, The results are shown in table 7, 72.

Table 7. Limiting Viscosity Number [] of poly-1,4,-epoxycyclohexare at 40°C.

Pressure Catalyst Temperature (atm.) Concentration (00 (mole percent)

900 5 60 0.183 1700 5 60 0.187 1500 3 60 04162 2575 3 60 0.167 2525 3 20 0.247

Finally the molar volume difference (.11.0) between the monomer and the polymer in solution was determined by simple density measurements. A 10 ml. measuring flask was used for this purpose. 4'11T0 was calculated to be -4.1 cc/mole. The calculations are shown in table 8.

Table 8. The difference between the molar volume of 1,4-epoxycyclohexane monor.er (M01.,Wt. 981) and apparent molar volume of ycJ,T71121-: epoxycyclohexane in a solution of a mixture of 100 parts phenol and 66 parts TOE.

Density of the solvent at 20°C = 1.235 g./cc. Now 0„5 g. of the polymer was dissolved in 11.7248 g. of the solvent, the total volume of the solution being 10 mis. 73.

•• a The volume of 0.5 g. of polymer = (10-11.7248/1.235) cc. = (10 - 9.501) cc. 0.499 cc. 0.5 g. of the monomer was then dissolved in 11,6992 g. of the solvent, the total volume of the solution being 10 mlsa

. • . The volume of 0.5 g. of monomer = (10-11.6992/13235) cc. = (10 - 9.480) cc. 0,520 cc.

.*. The volume difference between o.5 g. of polymer and 0.5 g. of monomer = (0.499 - 0,520) cc. = -0.021 cc. The negative sign indicates the smaller molar volume of the polymer.

• . a The molar -volume difference = - 0,021 x 98.1

-1-.41cc/mole. 74. Discussion.

The difference in the rate of polymerization of 1,4-epoxycyclohexane dried with anhydrous magnesium sulphate (tables 1,2 and 3) and 1,4-epoxycyclohexane dried with calcium hydride (tables 4,5 and 6) is probably due to the difference in the moisture contents of the monomer samples. No attempt was made to estimate the water contents of the monomer dried with the two different agents, but the monomer dried with calcium hydride was almost certainly drier. Water thus appears to be retarder in the polymerization of 1,4-epoxycyclohexane with boron trifluoride diethyl etherate and epichlorohydrin. The present discussion will be confined to results shown in tables 4 to 8 as they are obtained with monomer samples which from the above considerations are more dry and pure.

The Effect of Pressure on the Rate.

As figure 111.3 shows the logarithm of the percent yield in a fixed time is a linear function of pressure to a good approximation. Merrett and Norrish -96 observed a similar type of pressure-dependence for the rate of polymerization of styrene with benzoyl peroxide at 6000 between 1 and 3,000 atm., and the same kind of behaviour has been found in a number of other polymerizing systems. There is virtually no polymerization at 1 atm. 75.

even with 5 mole percent of BF3.(C2H5)20 and 0.1 mole percent epichlorohydrin. For this reason the increase in rate at high pressure cannot be calculated relative to the rate at 1 atm. With 3 mole percent of catalyst at 600C the yield per hour is 4.9 and 7.2 percent at 2575 atm. and 3200 atm. respectively. Thus the reaction rate increases nearly 1.5 times over the pressure range. The increase in rate between 725 atm. and 3200 atm. is 7-fold. At the higher initiator concentrations of 5 mole percent, the rate is 9.5 percent per hour at 600C and 1700 atm.; and the increase in rate between 900 and 1700 atm. is 4.5 times, The rate of polymerization of 1,4-epoxycyclohexane with BF3.(C2H5)20 and epichlorohydrin is thus very dependent on pressure. Since the relationship between log (overall rate) and pressure is approximately linear (Fig3.III.3) it is possible to express the pressure coefficient of the rate in terms of 11overall volume of activation" (in.V*pol ) calculated from the equation

(ln pol) ,_ AV ol dP RT In the radical initiated polymerizations of vinyl 25, monomers V*olp is usually in the range -16 to -20 cm /mole V*olp is a composite quantity and a function of the volumes of activation for the component processes of chain initiation, propagation and termination (4NIT*d' V* and INVt- ), which T,. have been soparately evaluateC- X01- -ulii oystem styrene— beneoyl peroxide.

The values of 4iV*pol_ calculated for 1 4—epoxy— cyclohexane (data of Fig.III.3) are shown below :

Temperature Catalyst Epichlorohydrin a v* (00) mole percent mole percent poi cm mole 20 3 0.1 —16 60 3 0.1 —22 60 5 0.1 —48

The value of4V*pol is seen to depend on the catalyst concentration and when this is 5 mole percent pol is unusually high, so that the reaction is very pressure dependent. No detailed interpretation of this finding can as yet be made. It may be noted that the density measurements indicate a fairly small difference (0w4 cm3/mole) between the molar volumes of the monomer and the polymer chain unit in ccaution. From this it can be inferred that, if the reaction were carried out in a solvent for the polymers the chain propagation reaction itself would not be greatly accelerated by pressure. However, under the conditions used, polymer separates as a solid and the unusual pressure sensitivity of the rate of reaction may be connected with this. Alternativel the complex catalyst system of BF3.(C2H5)20 and epichlorohydrin may be considerably influenced by pressure 77.

changes. Conductance measurements of solution of BF3(C2H5)20 alone in tetrahydropyran show a significant rise in conductivity with pressure at 40°C. A much more extensive study of the system would be necessary to explore these factors.

The effect of catalyst concentration on the rate.

The effect of concentration of catalyst on the polymerization rate may be seen by comparing the rates at 1500 atm. pressure. By increasing the catalyst concentration from 3 mole percent to 5 mole percent the rate is increased from 2.04 to 6.4 percent yield per hour. The catalyst concentration thus greatly influences the rate of polymerization,

211221LesialLIpaperature on the rate.

The rate of polymerization also goes up with increased temperature at high pressure. Thus with 3 mole percent of catalyst the yield per hour at 20°C is 1.7 at 2525 atm. as compared to 4.9 at 60°C and 2575 atm. pressure. A similar effect of temperature on the polymerization rate was also observed by Wittbecker and his co-workers 5 at 1 atm. With Fen and S0C1 as catalysts, they found the 3 2 rate of polymerization of 1,4-epoxycyclohexane at 0°C. to be 1,2 percent yield per hour while they obtained at 21°C a 75.8 percent yield of polymer in half an hour. 780

The effect oLp:_L=Ixe, catalyst concentration and tem?erature on the molecular weight of the polymer.

It is clear from table 7 that press-Lre or catalyst concentration has little effect on the molecular weight of the polymer. With 5 mole percent of the catalyst, the limiting viscosity number [n] increases from 0.185 to 0.137 in going from 900 - c) 1700 Temperature seems to have a larger effect on the molecular weight of the polymer. Thus DI] for the polyme:.? obtained at 6000 with 3 mole percent of catalyst under 2575 atm, is 0.167 while that at 20°C under 2525 F.tm, pressure is 0,247. The last value of [T1] corresponds well with that obtained by Wittbeker et al. 5. They found the value of [Ytj to be 0.23 fcr polymer pxepared with Peal. and 50012 at 210 3 0

Mechanism: The mechanism of the polymerization catalysed by BF3„(C2H5)90 with epichlorohydria as co-clyst remains obscure. Rozenberg et al rl have studied the polymerization of tetrahydrofuran by this catalyst system and one of the initiation mechanisms suggested by them is as follows lir 4 / BP (C H ) 0 + 3 + (C2H5)20

BF30 - CH - CH2 „„--0 CH, CH2Cl 79.

Similarly initiation for poiymn7rizatcn 1,4-epoxycyclohexane by this catalyst system may proceed by the following mechanism: F 3B (a) BF .(C H )0 (02H5)20 3 2 5 2 L/N 7 3 BO \> + CH -CH F BO - CH - CH - ON_ (b) 2 2 3 (k4 a ,0 CH C1 2 2 .1\1 C, H 2 '

Pressure is likely to aid the formation of I, the chain carrier, as the development of the ionic charges will involve some contraction in the surrounding syritem. Pressure may thus enhance the rate of polymerization by increasing the rate of initiation.

III. 2. The rite of polymerization of tetmhy(112ofur3n(THP).

Mehdi 56 investigated the polymeirza-r,ion of tetrahydrofuran at 60°C with the catalyst BF3.(C2H5)20„ He found that there was no aprreciable polymerization at 1 atm_ but he obtained a yield of 31.1 percent polymer in 6 hrs. at 5400 atm. with 2% of the initiator. The polytetrahydrofuran he obtained in the last-mentioned experiment had a limiting viscosity number [NI] of 2.2. The selected temp3rature of 60°C was considered to be probably close to the ceiling- temperature of tetrahydrofuran at 1 atm. and it was thought 80. that this might account for the failure ofTEF to polymerize at 1 atm. Initiator concentration from 0.5% (V/V) to 5%(V/V) were tried and, taking into acco@nt the balance between the rate of polymerization and the molecular weight of the polymer, 2% (V/V) was chosen by Mehdi as the best initiator concentration for a preliminary study of the polymerization of

THE with BF3°(02H5)20. In the present investigation, polymerizations of THE were first carried out at 40°C with 2% (V/V) BF3.(e2H5)2C at pressures up to 5400 atm. At 1 atm. no polymer was obtained from THE at 40°0 with 2% initiator in 24 hrs. At 1000 atm. and 40°C, with 2% initiator, the percent yield of polymer was 1.8 in 24 hrs. In order to obtain a good rate of polymerization, pressures above 3,000 atm. were needed. The results are presented in table 9 and shown graphically in Fig.III.4 and Fig.III.5. The "overall rate of activation"Z> V* for polymerization of THE at 40°C with 2% (V/V) BF3.(C2H5)20 was calculated from the pressure coefficient of the logarithm of the rate (Fig.III.5) and was found to be - 29.5 cm3/mole between pressures of 3,000 and 5,000 atm. 81

43 4.

0 i . o eo 2,000 3,000 'f, 0 ocs 54000 r, ; 0 • G° To 4/1444ni. ( atnw )

ci3,111.1.1 G,'0-tAr.-1/441),•Liirk. v 9: t szt..0.47tA.otwtow4 . xi, 6P3. (to s-)2o ; if 0.0 . 8/

2.1

0.0 Is 0 0 0 2,000 3,0 0 0 410 0 0 Sp 0 0 5) 40 0 IfiRe (44AARA. caeftv) qua. &iv 100-471.11 twtm.412.0W/5-wkAvvy ( IN F

/. 6 F5. ; o°t. 83,

Table 9. Polymerization of Tetrahydrofuran at 40°C. Initiator : BP (C H ) 0! 24 (V/ V)

Time 6 hours.

Pressure Conversion Rate Percent [11]* (atm.) (wt. percent) Conversion/hr.

2600 1.0 0.15 11•••

3200 2.5 0.41 ONO 4000 9.7 1.61 1.30 4660 17.3 2.88 1.80 5400 30.1 5.02 2.22

* [IL] determined in benzene at 25°C.

Mesaurements of the rate of polymerization of tetrahydrofuran were also carried out at 80°C. Curves of the yield of the polymer vs. time were obtained at this temperature and at two (constant) pressures. The results are shown in table 10 and the results at 4,000 atm. and 2,500 atm. are plotted in Fig.III.6 and Fig.III.7 respectively.

The "overall volume of activation" A V*pol for polymerization of THE at 80°C was determined from the log Rate vs. pressure graph (Fig.III.8) and found to be - 28 cm3/mole. 211

0 10 it 2.0 fr‘.fte, ( twit) Fia.11. 6 fotrrt THF. 2 500 ikkerov. sec. SE

0 2 3 it S. 6 Ti Cho)

P1.111.7 Poly tn cri- THE

ti 000 asietril g O e C . 200 ISO

~ -o

3) 000 It,ooo 5',000 ~'f'~(~)

l="i~.m.8 (Pol)~~ Of THF "j: 80·' 87.

Table 10. Polymerization of Tetrahydrofuran at 80°C.

Initiator : BF3.(C2H5)2); 2% (V/V).

Pressure Time Conversion Rate Conversion 01]* (atm) (hr) (wt. percent) percent/hr.

1 72 None ••• 1000 24 1.5

2500 4 6.4 1.6 S=. 2500 8 11.8 2500 16 17.1 0.23**

4000 1 8.7 8.7 00•11 4000 2 16.2 0.34 4000 4 23.5 4000 6 28.3 0.43

5400 1 23.5 23.5 am•P

determined in benzene at 25°C. ** Molecular weight determined cryoscopically in benzene and found to be 3900.1

In order to check Mehdi's results for the polymerization of THE at 600C, two runs were carried out at 5400 atm. The results are shown in table 11. 88.

Table 11. Polymerization of Tetrahydrofuran at 60°C.

Pressure : 5400 atm. Initiator: BF_ 3 .,_(C2H 5 )2_0 ; 2% (V/V)

Time Conversion* Conversion (hr) (wt.percent) (wt.percent) 2 18.56 22.4 4 27.50 30.1 * Results obtained by Mehdi.

Finally a run was carried out to polymerize THE at 20°C and 5400 atm. with 2% (V/V) BF3(C2H5)20. The yield in 6 hrs. was 0.8 percent. To compare the rates of polymerizations of THE at different temperatures, the results obtained at 5400 atm. with 2% (V/V) BF3.(C2H5)20 are shown in table 12.

Table 12. Rates of polymerization of THE at 5400 atm. and different temperatures.

Temperature Time Conversion Rate (00) (hr) (wt.percent) Percent Conversion /hr. 20 6 0.8 0.13 40 6 30.1 5.02 60 2 22.4 112 80 1 23.5 23.5 89.

Moisture and Reaction Rates.

Moisture was found to affect the polymerization of tetrahydrofuran with BF3.(C2H5)20 catalyst. If the drying was incomplete, the monomer boiled at 65.5 - 66°C and the polymerization rates were reduced to a great extent. So special care was taken to dry the monomer until the monomer boiled at 65°C. The results shown in tables 9 to 12 were obtained from tetrahydrofuran extensively dried and collected at 65°C.

The decomposition of yolytetrahydrofuran at 1 atm.

The solid polytetrahydrofuran of high molecular weight ( rn,] = 2e22) obtained at 5400 atm. with 20 (V/V) BF3.(C2H5)20, at 40°C, was found to undergo decomposition when left at 1 atm, and room temperature in a desiccator, until the limiting viscosity number attained a limiting value of 0.38. The decomposition is shown by the change in limiting viscosity number with time, (below) :

Change in UR] with time for aattImiag.n1LIzi.m.

Freshly prepared polymer. After After After 6 weeks 12 weeks 18 weeks

[n. 2.22 - 0.43 0,38 0.38

The molar volume difference (AV°) between tetrahydrofuran.and polytetrahydrofuran in THP solution was determined at 26°C and found to be - 9,5 - cc/Mole. The 90. results are described in table 13.

Table 13. Molar volume difference between tetrsbydrofuran and polytetrehydrofuran in THE at 26°C.

Density of tetrahydrofuran at 26°C = 0.8766 g/ml.

Wt, of m - flask : 14.6613 g. m.flask + polymer : 16.1684 g.

-°. wt. of polymer: 1.5071 g.

Flask + polymer (1,5071 g) + THE (the total volume = 10 ml.) = 23.8017 g.

.*. 1.5071 g of polymer was dissolved in 7.6333 g. of THF.

The volume of 7.6333 g. of THE = -7787.6333 7 = 8.479 cc.

••. Volume of 1.5071 g of polymer = (10 - 8.479)cc = 1.521 cc. 1.521 _ • • • Volume of 1 g of polymer : 1.5071 - 1,008 cc.

Now 1 g of THE occupies a volume of 1 cc i.e. 1.140 cc. 0.81-66

.• . Volume difference between 1 g of monomer and 1 g of polymer = (1,140 - 1,008) cc. = 0.132 cc.

0 O 4 Molar volume difference = 0.132 x 72.11 = -9,5 cc/mole

Effect of pressure on the conductivity of BF3 (C2 H5 )2 0--- in tetrahydrofuran at 40°0.

In order to get some indication of possible effects of pressure on the ionic equilibrium of the catalyst the 91. conductance of solution of BF-) * (C 2 H5 )2 0 in tetrahydropyran was measured up to 3,000 atm. Tetrahydropyran was chosen as solvent because it is a cyclic ether, resembling tetrahydrofuran, which does not polymerize even at pressures as high as 12,000 atm. (Section 111.7). A freshly prepared solution of BF3.(02115)20 in tetrahydropyran was used for measurement of conductance at each concentration of BF3°(C2H5)2O. In order to determine the specific conductivity, the cell constant was determined from measurements of the conductance of 0.1 Demal KC1 solution in de-ionized water which is known to have the specific conductivity of 0.012856 mho cm 1 at 25°C. 72'73. The cell constant was found to be 0.6871 cm 1. The extremely small effect of presdure on the cell constant and the concentration change due to compressibility, were neglected. The conductances for various concentrations

of BF3.(02H5)2.0 at a number of pressures are given in table 14 and plotted against pressure in Fig.III.10 and Fig.III.11.

isso

600

6"50 L

Soot

450 6000 2,000 3,000 P" ,t. ( &toy)

. 'M.. 9 C es..41.4.a.4.tawc.A. I a a Fa.lic Hs-)20 z", i4stivet ci.A.4)ist) '114 04W 93

S"~O ------, Mot~ .c~QIWU "s. f.,,~. 0.0 I matt. A F~{C.'1~~-) 0 ~""'- Ubu. G) TH'P '1 r . T~ ~""ooe

~ o ~ '100

',000 2~OOO s,ooo f.,.~(~)

~ la· m.IO l'~~ o:f t)r~·l(2Hs_)'l0 * THP o-:t ~ ~V'~. 9

600 . Mo ojt. 0-191,.CLU.R.i0JVvt.A. v 0.16 w.oLt F3•(C2H5),1)f o (2..tut. - clec

O Itto

/too

350 1,000 9.,000 oo o erv444.4ta aketr,)

Fla. El .11 CriftcLuelAdamicA. cr-1 nf 3.r2 H5 i;v4 TN P itoy. . 95.

Table 14. Molar conductance of BF3.(C2H5)20 in tetrahydropyran at 4000.

Units : mhos cm2 mole-1

Concentration 0.02 0.04 0.08 0.16 (moles/litre) Pressure(atm.) 1 790.0 463.7 377.8 369.3 500 890.0 532.5 429.3 407.9 1000 961.5 566.7 463.7 425.1 2000 996.0 618.2 489.5 438.1 3000 996.0 618.2 489.5 438.1 Percent increase in molar conductance between 1 and 3000 atm. 26.7 33.3 29.6 18.6

Discussion.

The polymerization of THE with BF3.(C2H5)20 is very dependent on both pressure and temperature. The monomer did not polymerize at 1 atm. with this catalyst at 40°C (for 24 hrs) or at 80°C (for 72 hrs). The polymerization at 1000 atm. is also not very appreciable. There appears to be a minimum pressure above which the rate is reasonably fast. At 40°C this pressure is around 3000 atm. (table 9). Once the minimum pressure is exceeded, the rate of polymerization increases exponentially with pressure (Fig.III.4). Thus at 96.

40°C the rate at 3200 atm, is 0.41 percent yield per hour. The molecular weight of the polymer also goes up with the pressure of polymeirzation. The limiting viscosity number of polymer obtained at 40°C increases from 1.30 to 2.22 in going from 4000 to 5400 atm. As table 10 shows, the rate of polymerization at 80°C falls off gradually with time at a particular pressure. Thus the yield for 1 hr., at 4000 atm. is 8.7 whereas the yield in 6 hrs is 28.3 percent. The molecular weight, however, increases slightly with time. Thus at 4000 atm., the polymer obtained in 2 hrs. has the [TI] value of 0.34 and that obtained in 6 hrs. has the limiting viscosity number of 0.43. This is unlike free radical polymerizations in which the molecular weight is not a function of time. Although polymerization of THr proceeds by a chain mechanism, it appears to have some characteristics of step-wise condensation polymerizations in which the molecular chain length may be extended to any desired value by controlling the reaction time. The molecular weight also increases with pressure at 80°C.

Thus nu4 increases from 0.34 at 4000 atm. to 0.73 at 5400 atm. Temperature seems to have a large efect on the polymerization of THE a4- high pressures with BP3 (C2H5)20. Thus at 20°C there is not any appreciable polymerization even under 5400 atm. while at 40°C the rate is reasonably fast at around 3000 atm. The reason why there is not any 97. appreciable polymerization at 800C and 1000 atm. is the occurrence of the coiling—temperature phenomenon. As table 12 shows at 5400 atm. The polymerization rate is more than doubled in going from 40 to 600C and the rate at 80°0 is nearly 5 times the rate atn40°C. As table 11 shows, in thetwo runs carried out at 600C and 5400 atm., the rates are found to be somewhat faster than the rates of polymerizations observed by Mehdi. This is probably due to incomplete drying of the THE used by Mehdi, which boiled at 65.5 — 65.70C. That moisture is a retarder in the polymerization of THE with BF,.).(C2 H5 )2 0 may indicate a cationic and not a pseudo—cationic mechanism 74, because polymerization by the latter type of mechanism is relatively insensitive to water in amounts even 10 times the concentration of catalyst. In polymerizations catalysed by boron trifluorid water in quantities double or more the concentration of catalyst, forms a stable hydrate 7576 so causing a retardaton in the polymerization. In the case of catalysis by BP3.(02H5)20 it is not known how water retards the reaction. Emelius et al 77, from conductance nnasurements of pure BP3.(C2H5)20, suggested that the etherate exists in the + — form of the ion—pair 02115BP3 C2H50 (ethyl ethloxy trifluoroborate) at atmospheric pressure. The results in

98. table 14 shows a significant increase in the conductance of

solutions of BF3'(02H5)20 in tetrahydropyran with pressure at 4000. The increase in conductivity may arise from the dissociation of the ion-pair into free ions, C2H5+ and

BF3-.0 2 H5 O. A more precise interpretation is not possible since the nature of the species, formed when BF3.(C2H5)20 is in solution of cyclic ethers such as tetrahydropyran, tetrahydrofuran, etc., is unkknown. In a solvent of low dielectric constant associated ions (ion-pairs, ion-triplets, etc.) are likely to be present in significant concentrations. BF3.(C2H5)20 may thus be thought to initiate the polymerization of tetrahydrofuran in the following way: + BF3.(C2H5)20 C H O 2 5 C2H5OBF3

The "overall volume of activation"il V*pol for polymerization of THE with BF3.(C2H5)20 changes very little with temperature as the table below shows. av*pol for polymerization of THE at different temperaturen o Temperature C. eNv*pol (cc/mole) 40 —29.5 60 —30.0* 80 —28.0

*AV*pol obtained by Mehdi. 990

Typical values ofAV*pol for free radical polymerizations of vinyl compounds are (a) Styrene at 600C - 18 cc/mole, (b) Methyl methacrylate at 600C - 19 cc/mole, and (a) Allyl acetate at 800C - 14 cc/mole. "Volumes of activation" INV*pol for THE are much higher than those for free radical polymerizations. There is

also a large difference betweenV*pol for THE and the molar volume difference between THE monomer and polymer in monomer solution (-66 V° = -9.5 cc/mole). From conductance measurements of tetrahydropyran solution of BF3.(C2H5)20 at high pressures (table 14), it appears likely that the effect of pressure on the rate of polymerization of THE may be partly due to its influence on a pre-equilibrium involving catalytically-active ionized species, and possibly also on the rate constant for initiator. Such effects would contribute volume terms to eNvie , THE pol and could account for higher values ofe V*pol for than those for free radical polymerizations of vinyl compounds, . In the absence of such effects the difference between 4.V*pol and 4vV° for THE would not possibly be so large. To establish definitely the mechanism of the polymerization of THE by Bi3.(02H5)20 is very difficult because the reaction does not appear to proceed at 1 atm. with this catalyst to more than a small extent. Attempts to determine the mechanism from kinetic measurements at high pressures would be very laborious because the reaction could 100. not be followed continuously. The reaction is further complicated by the occurrence of the polymerization ceiling— temperature and its variation with pressure. In view of the difficulties of developing kinetic studies any further attention was turned to the pressure dependence of the ceiling—temperature.

III. 3. Determination of the variation of the polymerization ceiling7temperature of tetrahydrofuran with pressure.

A. Results at Atmospheric Pressure.

Bawn et al 44 investigated the ceiling—temperature of tetrahydrofuran at 1 atm. using triphenylcarbonium — hexachloroantimoniate as catalyst. They plotted the concentration of polymer in equilibrium with the monomer against the temperature at which the equilibrium was established. This curve was then extrapolated to zero conversion of polymer in equilibrium with the monomers and the point at which this curve cut the temperature axis was taken as the ceiling temperature, which was estimated to be between 60 and 70°C. In order to verify that true equilibrium was

IMO established they used the equation 32 ln[M] e = T R —R) according to which In [M] vs. 1y should be a straight line having a slope equal to 4s.11x/R. They found this graph to be a straight line and determined AHx from the slope to be 101.

- 5„3 + 1Kcal/mole-1. This was in good agreement with the value (-.5.2 kcal/Mole) of 4SHx for the hypothetical polymerization of cyclopentane, calculated by Dainton from thermodynamic data. Using PF5 as catalyst, Sims 45 found the ceiling temperature to be 83°C and 4611x to be -4.3 kcal/ mole. Rozenberg et al 7 had also determined the limiting temperature for polymerization of THE in bulk to be 73°C. They used Bk3(02H5)20 as catalyst and epichlorohydrin as co—catalyst to polymerize THF. All these authors approached the eauilibrium from monomer. - c-uc.2.s.s.ock Ivin and Leonard 4-7 then maaoulacd the experimental findings of these authors. They pointed out that the 1 (IsHx LsSx. expression In [THF]eq R ) applies to conditions in which the solution of polymer in monomer is an ideal one. But at the conversion of polymer obtained in the experiments ideal conditions were not maintained and in fact there is a great deal of interaction between the monomer and the polymer at such concentrations. They plotted the equilibrium volume fraction of the polymer against temperature and extrapolated the curve to zero volume fraction of the polymer. They estimated Te for THE to be 80 + 3°C, at 1 atm. Following the methods of Bawn et al and Sims, Dreyfus and Dreyfus 48 (who do not refer to Ivin and Leonard's measurement of the results previously reported), who used 102

90 100 110 120 130 Ttnmo .w....imh.t.° C . ria.m.12. t 1~1,04NA...two. ivf T to t 11 r4A4.4.00.05 . 103

1,000 2,000 31000 ervAdiyukt (atm) pia.x.13 Soa Tc (19 I IsP44/14An.ut. 104. p-chlorophenyl diazonium hexafluorophosphate as catalyst, determined the ceiling temperature to be 84°C and 4613x to be -4.58 kcal/Mole. These authors approached the equilibrium from monomer or equilibriated the polymer-monomer mixtures at higher or lower temperatures.

B. Results at High Pressure.

From the results in table 10 (III.2) it appeared that pressure raises the polymerization ceiling temperature,

Tc, of THF. To confirm this polymerizations of tetrahydrofuran were carried out at 1500 atm. for a fixed time and at temperatures up to 110°C. The percent yield of polymer was plotted against temperature. The curve passed through a maximum and when extrapolated to zero conversion, it cut the temperature axis at 109°C. Similar series of experiments were carried out at 2000 atm. and 2500 atm. and T0 was found to be 119°C and 129°C at these pressures respectively. The results are presented in tables 15, 16 and 17, and shown graphically in Fig.III.12. Following Ivin and Leonard, the ceiling temperature at 1 atm. was taken to be 80°C and the plot of the logarithm of ceiling temperature (°K) against pressure (Fig.III.13) was found to be a straight line. The pressure coefficient of the polymerization ceiling temperature was found to be 19.6°C/1000 atm. between 1 atm. (Te = 80°C) and 2500 atm. (Te = 129°C).

105.

Table 15. Polymerization of Tetrahydrofuran.

Pressure : 1500 atm. Time : 18 hours.

Initiator : BF3 (C2 H5 )20 ; 2% (V/V). Temperature (00) Percent yield. 80 4.5 90 6.3 100 6.7 105 4.4 108 1.1 110 None

Table 16. Polymerization of Tetrahydrofuran. Pressure : 2000 atm. Time : 10 hours. Initiator : BF3(C2H5)20 9 2% (V/V) Temperature (°C) Percent yield 90 8.5 95 9.8 100 10.7 105 11.3 110 10.0 115 6,9 118 3.1 120 106.

Table 17a olymeri of Tetrahydrof=n. Pressure : 2600 atm. Time : 6 hours.

Initiator : BF3 (C2 H5 )20 '• 2% (V/V). Temperature (°C) Percent yield 90 9.5 100 11.4 110 13,6 115 12.5 120 11,0 125 7.6 127 4.5 130 None

For these determinations of the ceiling temperatures the monomer was rigorously dried because moist THF yielded a liquid methanol—insoluble polymer of low molecular weight (430) at higher temperatures. This was presumably due to chain transfer with water as Rozenberg et al.7 showed that there is chain transfer with water in the polymerisation of THF even when the catalyst/water ratio is less than 1 jn the reaction mixture. When the monomer was properly dried, THF yielded only solid methanol—insoluble polymer and no liquid polymer, The results shown in tables 15, 16 and 17 aro based on yields of solid methanol—insoluble polytetra— hydrofuran. 107. No attempt was made to determine the ceiling temperatures at pressures above 2500 atm. as that would have involved experiments at temperatures higher than 130°0. As described in Section II.11 a steel reaction tube was devised for the determination of the polymeriation ceiling temperature of THF. The reaction tube described was the final and most satisfactory form reached after many modifications and improvements, but above 130o0 the rubber 0-ring did not prevent leakage of the monomer vapour.

Discussion.

The logarithm of To is a linear function of pressure in accordance with Clapeyronts equation, d ln To so that the pressure-dependence of To is like that of the melting point of a pure substance.

The pressure coefficient of Tc for THE is 19.6°C per 1000 atm. between 1 and 2500 atm. Kilroe and Weale 34 found dTc/dP for if-methyl styrene to be 16.8c0/1000 atm. between 1 and 6480 atm.; and Busfield and Whal]ey 35 found dTc/dP for 0,1 M chloral in equilibrium with soii.1 polymer in pyridine to be 19ce/kirobar. The pressure coefficient dTo/dP for the polymerization of THE is thus quite similar to those for d:-methyl styrene and chloral. 108.

The molar volume difference (t11.°) between the monomer and the polymer was found, from density measurements, to be -9.5 cc/mole (Section 111.2). LNV° may be calculated from the present measurements by means of the Clapeyron equation, if the value of LSH, the heat of polymerization, is known or estimated.

Now, Tc at 1 atm. = 353°K and at 2500 atm. = 402°K.

.°. For 4sP = 2500 atm. i.e. 2500 x 1.013 x 106 dynes/cm2

ZS1nTc = 2.303 x 0.0564 If (Section 111.3A, above) the value of AH is taken to be 4.6 kcal/mole, that is 4,6 x 103 x 4.185 x 107 ergs, then from Clapeyron's equation, 3 7 A v = -2.303 x 0.0564 x 4.6 x 10 x 4,105 x 10 2500 x 1.013 x 106 - 9.9 cc/mole. If the value of Hx is taken to be -4.3 kcal/mole: es.v° comes out to be -9.2 cc/mole. Agreement with the measurement of (,7.0 at 1 aLm. appears good but results should be treated with caution. Huglin 78 has found that eV.° varies appreciably with concentration for solutions of polytetrahydrofuran in monomer. gYV° will probably vary appreciably with pressure ( -AV° is likely to be smaller with increasing pressure) and the pressure-dependence of Ail is unknown. 109-u

III. 4. Polymerization of Cyclohexene Oxide.

Cyclohexene oxide was found to polymerize (with benzoyl peroxide initiator) by Conant and :Peterson 55 at 12,500 atm., and the kinetics of this polymerization have been studied by Mehdi 56 at pressures between 8000 and 12,500 atm, In the present investigation attempts were made to polymerize this monomer by the cationic catalyst BF32(C-11 5 )2 0 (2% and 1% V/V) at 60° and 21°C. Polymerizations were carried out both in bulk and in solutions of the monomer in toluene (1:1% at 1 atm., and at pressures up to 2850 atm. The results for the polymerization of cyclohexene oxide with (V/V) catalyst at 1 atm, are shown in table 18.

Table 18. Polymerization of Cyclohexene oxide with 2 0 1YLY) Boron trifluoride dietgyletherate at 1 atm.

Temperature Time Method of polymeri,zation Yield (00) (hr) (wt.percent) 60 24 Bulk 40.5 60 24 Solution 40.1 21 24 Bulk 43,2 21 24 Solution 41.0 c-n 1 5 Bulk 21,3 21 5 Solution 20,5 21 0.75 Bulk 12,8 110.

One run was carried out with 2cr'0! BF 3 (C2 H5 )2 0 at 2100 and 2850 atm. in bulk. The yield was 45.1 percent in 3 hrs. All the polymers obtained by 2% catalyst were precipitated by water from a solution of the reaction product in ethanol. Attempts were then made to polymerize cyolohexene oxide in bulk at 21°C and 1 atm. with 1% (V/V) BF3.(C2H)20. two fractions of polymers were obtained: (1) one precipitated from the reaction product by ethanol, and (2) the other precipitated out of the filtrate from the first fraction by water. The results are shown in table 19.

Table 19. Polymerization of Cyclohexene oxide with 174 catalyet at 1 atm. Initiator : BF30(C2H5)20 9 1% (V/V). Temperature : 21°C. Time (hr) Yield - of fraction (i) Yield - of fraction (2) (wt,percent) (wt.percent) 6 4.3 16,2 9 5.9 15.9 24 10.4 13.2

With 1% (V/V) catalyst two runs were carried out at 21°C and high 13ressures, one at 1000 atm. for 3 hrs, and the other at 2700 atm. for 9 hrs. There was no water-soluble fraction and the yields of the polymer, precipitated by ethanol from the reaction mixture, were 13.3 and 73.2 wt. 1114 percent respectively. During the addition of the catalyst to the monomer at room temperature the reaction mixture became hot; so the catalyst was added to ice-cooled monomer or to its solution slowly by means of a micro-burette. The molecular weights of polycyclohexene oxide were determined cryoscopically in benzene and the results are shown in table 20.

Table 20, Molecular weights of polycyclohexne oxide.

Pressure Initiator Time Molecular Weight (atm) Concentration (hr) percent V/V. 2850 2 3 620 1 1 9 812 ** 2700 1 9 983 **

* polymer insoluble in water but soluble in ethanol. ** polymer insoluble in ethanol.

An infra-red spectrograph of a chloroform solution of the polymer which had a molecular weight of 988, was obtained. This showed very strong absorption at 1080 - 1100 -1 cm (attributed to the saturated ether group) but no absorption at 1240 - 1260 cm-1 (epoxy group). 79 112,

Discussion.

With 20 (V/V) BF3.(C2H5)20, cyclohexene oxide yields a solid polymer, insoluble only in water, both at 1 atm. and high pressures; and the average degree of polymerization (Table 20) is probably not higher than 6. The rate of polymerization, however, increases appreciably with pressure. Thus the yields in 3 hrs. at 2850 atm. is 45.1 wt. percent and that at 1 atm. in 5 hrs. is 21.3 percent at 21°C with 2% catalyst. At 21°C and 1 atm. the increase in yield with time diminishes rapidly. Thus the yield of polymer in 0.75 hr. is 12.8 wt.percent while that in 24 hrs. is 43.2 wt. percent (Table 18). With 1610 catalyst (Table 19) at 1 atm. two fractions of the polymer are obtained, one insoluble in water and the other insoluble in ethanol. At high pressures, however, all the polymers obtained were ethanol—insoluble. As Table 20 shows the ethanol—insoluble polymer is of slightly higher molecular weight than the water•-insoluble polymer. The molecular weight of the polymer goes up slightly with decreased initiator concentration; and with 1% catalyst the polymer obtained under pressure has a slightly hither molecular weight than that obtained at 1 atm. The rate of polymerization rises with increased 113. initiator concentration. Thus the total yield of polymer in 24 hrs. with 1% catalyst is 23.6 percent, as compared to 43.2 percent with 2% catalyst; both the reactions being carried out at 21°C. With 1% catalyst the rate of polymerization increases with pressure. Thus the total yield of polymer in 9 hrs. is 21.8 percent at 1 atm. while that at 2700 atm. in 9 hrs. is 73.2. Although the rate of polymerization of cyclohexene oxide both at 1 atm. and higher pressures is quite fast, the molecular weight of the polymer obtained is very low, the highest being 988 ( decamer). This suggests that chain transfer reactions are important in the polymerizations of cyclohexene oxide with BP3 A(C2H5)20 catalyst, and that this is little affected by pressure. The infra-red analysis indicates the absence of epoxy linkages and the presence of ether linkages in the product, which presumably has the polyethor structure shown below. 114,

III, 5. Polymerization of Styrene Oxide with BF3.(02H5)20.

Mehdi 56 polymerized styrene oxide at 10,000 atm. with benzoyl peroxide, and at 1 and 4100 atm. with the styrene oxide - ferric chloride complex as catalyst. The polymer obtained with the latter catalyst had the highest molecular weight (1730). In the present won: BF3.(C2H5)20 was use3 as catalyst to polymerize styrene oxide at 60 and 21°C both at 1 atm. and high pressure. Reactions at 60°C. yielded tacky polymer insoluble in water only and those at 21°C yielded two fractions of low molecular weight polymer; one fraction being insol'Able in methanol and the other fraction being insoluble in water. As with cyclohexene oxide, the reaction mixture beoame very hot when the catalyst was added to the monomer, so the monomer was ice-cooled and the catalyst added slowly from a micro-burette. The results of Polymerization of styrene oxide are shown in table 21. The molecular weight of the polymer was determined cryoscopically in benzene The fraction insoluble in methanol had a molecular weight of 640, and that of the polymer insoluble in water was 378 (Mol.wt of monomer, 120). 115. Table 21. Polymerization of Styrene Oxide with BF3'(02H5)2O. Catalyst Temperature Pressure Time Yield Concentration (oc) (atm.) (hr) (wt.percent) (V/V) 2 60 2400 1.8 35.5 1 60 2500 1.8 26.8 1 21 1 70 0;67 * 29.0 1 21 6150 70 15:9 * 55.6 1 21 7200 24 6.9 * 23.4 0.25 21 7500 24 7;5 * 18.4 0.1 21 7500 24 0.9 17.5 * polymer insoluble in methanol. Others insoluble in water.

Discussion.

The rate of polymerization of styrene oxide with BF3.(C2H5)20 is quite appreciable even at 1 atm. pressure. Pressure accelerates the rate further. Thus at 21°C, the rate at 6150 atm. is 2.5 times faster than the rate at 1 atm. Pressure also slightly increases the molecular weight of the polymer. Thus at 21°C the yield of methanol—insoluble polymer at 6150 atm in 70 hrs. is 15.9 percent as compared to 0.67 percent at 1 atm. in 70 hrs. Styrene oxide does not yield any polymer of higher molecular weight even with 116.

0.25% or 0.1%(V/V) of the catalyst at pressures up to 7500 atm. With 0.25% catalyst the total yield of polymer is 25.9 percent at 21°C and 7500 atm. in 24 hours. The low molecular weight of the polymer, even when the total conversion is 71.5 percent, suggests that chain transfer reactions are important in the polymerization of styrene oxide with boron trifluoride diethyl etherate.

Polymerization of Cyclooctene Oxide.

Attempts to polymerize cyclooctene oxide were made in toluene solution, the monomer/solvent ratio being 1. Both a free radical initiator (benzoyl peroxide) and the cationic catalyst BF3.(C2H5)20 were used.

(a) Free Radical Polymerization.

With a 2 mole percent benzoyl peroxide the toluene solution of cyclooctene oxide was kept at 60°C and 12,000 atm. for 48 hours. No polymerization of this monomer occurred under these conditions.

(b) Cationic Polymerization.

2% (V/V) BF3.(C2H5)20 was used to polymerize cyclooctene oxide at 60°C, and at 1 atm. and 3000 atm. pressure. A methanol insoluble viscous liquid polymer was obtained. The yield in 6 hours was 25.5 and 28.4 percent 117. at 1 and 3000 atm, respectively. As with cyclohexene oxide and styrene oxide, toluene solutions of cyclooctene oxide became very hot when ) BF3'(02H5 20 was added, so the monomer solution was kept ice—cooled while initiator was added slowly from a micro— burette.

Discussion.

Unlike cyclohexene oxide benzoyl peroxide is ineffective as an initiator to polymerize cyclooctene oxide, even at pressures as high as 12,000 atm. Cyclooctene oxide, with BF3'(C2H5)20 as catalyst, yields a viscous liquid polymer at the rate of nearly 4.5 percent polymer per hour, at 60°C and 1 atm. The rate at 60°C and 3000 atm. is 4.7 Percent per hour with this catalyst. The polymer obtained was the same sort of viscous liquid as was obtained at 1 atm., so that pressure has little effect either on the molecular weight of the polymer or on the rate of polymerization of cyclooctene oxide with BF3.(C2H5)20.

Bacskai 49 , whilepolymerizing 1,2—epoxides of 5 to 8 membered ring compounds with triethyl aluminium, observed the rate of polymerization (Vp) to be in the following order: V q> V V 1) V 8. The polymer P P . P he obtained from cyclooctene oxide had the limiting viscosity number of 2.28 in benzene at 3000 as compared to 0.04 for methanol soluble polycyclooctene oxide prepared at 125°C in 118.

960 minutes. The low rate of polymerization and low molecular weight of the polymer of cyclooctene oxide were attributed to greater steric hindrance in this monomer.

III. 7. Polymerization of Tetrahydropyran.

Polymerizations of tetrahydropyran were tried with 2% (V/V) BF3.(C2H5)201 2 mole percent benzoyl peroxide and 2 mole percent AIBN at 60°C and 12,000 atm. Each run was carried out for 48 hours; but no polymer was obtained even under such drastic conditions.

Discussion.

From theoretical considerations, Dainton, Devlin and Small 80 calculated the difference in free energy contents (ON G) between ring and chain configurations for cyclic hydrocarbons and the corresponding straight-chain hydrocarbons. They plotted &G- against the number of atoms in the ring and found NG to be positive and a maximum for the six-membered ring, the chain configuration having the higher free energy. Small 81 later calculated CSG for the ring and chain configurations of cyclic ethers and the corresponding straight- chain compounds. The relation between AG and the number of atoms in the ring was very similar to that for the hydrocarbons, AG for the six-membered cyclic ethers being positive. Small therefore concluded that six-membered 119; cyclic ethers such as tetrahydropyran and 1,4-dioxan are unlikely to polymerize at 1 atm. The failure of tetrahydropyran to polymerize, even at 12,000 atm., possibly indicates that this situation is not altered by pressure.

8. Polymerization of triallyl phosphate and triallyl phosphite.

A. Polymerization of Triallyl phosphate.

Polymerization of triallyl phosphate was carried out at 60°C, and 1 atm., and at pressures up to 3000 atm., with 1 mole percent benzoyl peroxide as initiator. No polymerization occurred at 1 atm. in 6 hours, but at higher pressures a solid insoluble polymer was obtained which swelled in solvents such as methanol and benzene. The yields of polymer at different pressures are shown in table 22 and log yield is plotted against pressure in Fig.III,14.

Table 22. Polymerization of Triallyl Phosphate. Initiator : Benzoyl peroxide, 1 mole percent. Temperature : 60°C. Time : 4.5 hrs. Pressure (atm.) Conversion (wt.percent) 1000 2000 12.7 2250 18.8 2500 25.4 3000 30.6 120

3000

1000

1'0 • 1.1 11 165 1.5 troa yiad

Fi8.11.111 °I.,`)"1"-ilf°4-" I ITA? Pdt . Avg. I IA 0 tiy. 131202. ; 4.5 12'

oll.o.----f---.L---.L.--...l.---L--...J--...... J ~ 3 " 5 , '7 TLwu. ("'tt') Fia·m.·,r ?ol~M~ DjTAP ~ '30~O~. I moL .. ~~ B:z'102,; ~o c.

122.

In order to see the effect of time on polymer yield$ polymerizations of triallyl phosphate were carried out at 3000 atm. with benzoyl peroxide for different reaction periods. The results are presented in table 23 and the yield vs. time graph is given in Fig.III.15.

Table 23. Effect of time on polymerization of TAP. Pressure : 3000 atm. Temperature : 60°C. Initiator : Benzoyl peroxide 1 mole percent.

Time (hrs.) Conversion (wt.percent)

3.0 17.3

4.5 30.6

6.0 45.1

A run was carried out with 1 mole percent AIBN as initiator at 60°C and 3000 atm. The yield in 4.5 hours was 32.7 percent.

B. popolarmerization of Triallyl phosphate and Styrene.

An equimolar mixture of triallyl phosphate and styrene was subjected to a pressure of 3000 atm. at 60°C in the presence of 1 mole percent benzoyl peroxide. A 24.1 percent yield of polymer was obtained in 3 hrs, The polymer was soluble in the reaction mixture and was precipitated by methanol from a benzene solution of the reaction products. The polymer was also soluble in carbon tetrachloride and 123.

chloroform, and melted at 188 - 192°C. The carbon and hydrogen contents of the polymer were found to be 87.08 and 7.57 wt. percent respectively. The limiting viscosity number FL] in benzene at 25°C was 0.334. Taking the values of K andlL as 4.37 x 10-4 and 0.66 respectively, the molecular weight was calculated from the equation, [TL] = K M and found to be 23,400.

C. Polymerization of Triallyl phosphite.

Polymerizations of triallyl phosphite were tried with 2 mole percent of benzoyl peroxide and AIBN, and 2% (V/V) BF3.(C2H5)20 at 60°C and 3000 atm. for 24 hours; but no polymerization of this monomer occurred under these conditions.

Discussion.

Kennedy et al.57 polymerized triallyl phosphate with 1.5 wt. percent ( 1.4 mole percent) benzoyl peroxide at 98 - 100°C. The yield in 6 hrs. was 50 wt.percent. In the present investigation no polymer was obtained at 60°C with 1 mole perecnt Bz202 in 6 hrs. at 1 atm. This indicates that the rate of polymerization of TAP with Bz202 at 1 atm. depends strongly on temperature or initiator concentration, or both. 124.

Table 22 indicates that below a certain minimum pressure the polymerization of triallyl phosphate at 60°C with 1 mole percent Bz202 proceeds very slowly if at all. This minimum pressure seems to be just below 2000 atm. (Fig.III.14). Above this pressure, the log of yield of polymer in a fixed time is not a linear function of pressure but curves towards the pressure axis. This deviation may be due to complications arising from the separation of the polymer from the reaction mixture, and to the relatively high conversion at 3000 atm. The yield vs. time graph shows some curvature in the early period of the reaction so that the results of table 23 cannot be used to calculate accurate initial rates. From 3 hrs. to 6 hrs., the yield increases linearly with time. The rate of polymerization is almost the same with benzoyl peroxide and AIBN. Thus at 60°C and 3000 atm. the yield in 4.5 hrs. is 30.6 and 32.7 with 1 mole percent

Bz202 and AIBN, respectively. The swelling of the polymer in solvents indicates a cross—linked structure. The carbon and hydrogen contents together account for 94.65 wt.percent of the elements present in the polymer obtained from triallyl phosphate and styrene in the presence of benzoyl peroxide. The deficit of 5.35 percent must then be due to oxygen and phosphorus. The polymer is soluble in the reaction mixture, unlike the homopolymer of triallyl 125. phosphate, and its melting point (188 - 192°C) is much higher than that of polystyrene, which softens slightly above 100°C. In all probability, it is a copolymer of styrene and triallyl phosphate which (from its analysis and estimated molecular weight) contains on average 198 styrene units and 13 phosphate units per chain. Triallyl phosphite did not polymerize under pressure in the presence of either the free radical initiators, benzoyl peroxide and AIBN, or the cationic catalyst BP3.02H5)20. Kennedy et al. also observed that triallyl phosphite did not polymerize with benzoyl peroxide at 1 atm. They advanced no explanation for this but refer to results of Toy and Cooper 58 who found triallyl phosphite to be an inhibitor in the polymerization of allyl esters of phospho is acid with free radical initiators. 126.

SECTION IV.

GENERAL DISCUSSION.

A separate discussion of the results of the polymerizations has been given for each monomer, but the main fegtures of the results are summarised here to provide a general outline. Tetr•ahydrofuran and 1,4-epoxycyclohexane do not polymerize at 1 atm. in presence of the catalyst BF3.(C2H5)20 or of the syncatalysts BF3.(C2H5)20 plus epichlorohydrin, respectively. At high pressure they yield solid polymers at a fast rate with these catalysts. The logarithm of the rate of polymerization increases linearly with pressure as in the free radical polymerization of styrene at high pressure 26. The molecular weight of polytetrahydrofuran increases greatly with increase in pressure, and also increases slightly with time of reaction. The molecular weight of poly 1,4-epoxycyclohexane is not a function of reaction time. The polymerization of 1,4-epcxy- cyclohexane is complicated by the fact that polymer separates out of the reaction mixture. The rate of polymerization increases with temperature for both the monomers and the rate of polymerization of 1,4-epoxycyclohexane, in particular, increases appreciably with increase in catalyst concentration. Water seems to retard the polymerization of these monomers in the presence of BF3.(C2H5)20. 127.

The pressure-dependence of the polymerizations of THF and 1,4-epoxycyclohexane are reflected in their respective "volumes of activation" AV*For THF /....* 20° -.22c4,..3/44.11-. pol' pol &Hoc' is -291cm3/mole'. These values agree well with that of

2LNs.vpol at 6000 obtained by Mehdi 56 so that >\V*pol appears to be independent of temperature for this monomer-catalyst system. z.NV*pol for 1,4-epoxycyclohexane seems to be dependent on both reaction temperature and the concentration of the catalyst used. Thus ZSV*pol at 21oC with 3 mole percent catalyst is -16 cm3/mole as compared to -22 cm3/mole

at 60°C. With 5 mole percent catalyst at 60°C, ',YU**pol is -48 cm3/mole. The molar volume difference (A V°) between the monomer and one unit of polymer chain is -9.5 cm3/mole for THF and -4 cm3/mole for 1,4-epoxycyclohexane. This implies that the "volume of activation" for propagation step, LSVt, is not numerically as large ash.V13-01. The higher values of ZSV*pol may be due to pressure effects on the ionic equlibrium of the catalyst systems which contribute to the "overall volume of activation" Conductance measurements of solution of BF3'(C2H5)20 in tetrahydropyran show an increase of about 30 percent in the molar conductance between 1 and 3000 atm. The logarithm of the polymerization ceiling temperature, Te, of THF increases linearly with pressure in 128. accordnace with Clapeyron's equation. This shows that the pressure-dependence of Tc is like that of the melting point of a pure substance. The pressure coefficient of the ceiling temperature (dTc/dP) of THE is 19.6°C/1000 atm. This value is similar to those fort)C-methyl styrene 34 and 35 chloral . Cyclohexene oxide and styrene oxide yield low molecular weight polymers. The highest molecular weight of polycyclohexene oxide is 988 and that of polystyrene oxide is 640. The rate of polymerization is greatly increased by pressure, but there is little increase in the molecular weight of the polymer. This probably indicates that chain transfer reactions dominate the polymerizations of these monomers with BP3.(C2H5)20. Cyclooctene oxide does not polymerize even at 12,000 atm. and 60°C in the presence of benzoyl peroxide (2 mole percent). Cyclooctene oxide, however, yields a methanol-insoluble liquid polymer with BP3.(C2H5)20 at 1 atm. Pressure (3000 atm.) does not increase the rate appreciably, neither does it increase the molecular weight of the polymer. Bacskai 49 has attributed this behaviour of eyclooctene oxide to steric hindrance. Tetrahydropyran has not yet been polymerized at 1 atm. According to Small 81. this monomer is unlikely to 129. polymerize at 1 atm. because the free energy of polymerization (AG) is positive. Pressure as high as 12,000 atm. does not change this situation. Triallyl phosphate does not polymerize at 1 atm. and 60°C with 1 mole percent Bz202' At 3000 atm. triallyl phosphate yields 30.6 percent of an insoluble polymer in 4.5 hours. The swelling of the polymer in methanol and benzene and its insoluble nature indicate a cross-linked structure. Triallyl phosphite on the other hand, does not polymerize even under pressure. Toy and Cooper 58 found triallyl phosphite to be an inhibitor in the free radical polymerizations of allyl esters of phosphoric acid. Triallyl phosphate copolymerizes with styrene at 60°C and 3000 atm.'with 1 mole percent benzoyl peroxide. On average one molecule (23,400) of the copolymer appears to contain 198 units of styrene and 13 units of triallyl phosphate, approximately.

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