Soluble High Polymers from Allyl Methacrylate

JOURNAL OF POLYMER SCIENCE: PART A-1 VOL. 6, 3007-3013 (1968) Soluble High Polymers from Allyl Methacrylate J. P. J. HIGGINS and K. E. WEALE, Department of Chemical Engineering and Chemical Technology, Imperial College of Science and Technology, London, England synopsis Allyl methacrylate has been polymerized by free-radical methods and found to yield a soluble polymer in carbon tetrachloride, dioxane, and diallyl ether solutions. The l,s. overall rate equation in diallyl ether is R , = k [ln]o.7[M] It is suggested that propagation and cyclization reactions proceed only via addition to the methacrylyl groups of the monomer. Some degradative chain transfer occurs with the allyl groups, and it is considered that the solvents may ensure the production of soluble polymers by reactions in which allyl-radical side chains are terminated without crosslinking. INTRODUCTION It has been shown‘ that 1,6-dienes can, under certain conditions, yield soluble polymers by an alternating inter-intramolecular mechanism. Previous attempts to obtain a soluble polymer from the monomer allyl metha ~ r y l a t ehave, however, not been successful. Kawai3has attributed this ~,~ to the predominance of the intermolecular reaction and to degradative chain transfer . Allyl methacrylate (I), which is an unsymmetrical 1,6-diene, has now been found to produce soluble polymers up to high conversions in solutions of carbon tetrachloride (CClJ, dioxane, and diallyl ether. Examination of the polymers so produced shows that they are true homopolymers and that in diallyl ether little or no copolymerization occurs with the solvent. The cyclopolymerization reactions may be represented as : CHs CHz CHFC I \CH I I R + R-CHz-b. CHa CHz \CH I I Inter- CH, molecular O=C I O=C Intramolecular CHa CHz RCHZC/ I \cH. I I I1 ‘’ 0 CH, 0 ‘ ’ O=C CHz ‘/ O where R ‘ is an initiator or polymer radical. Normal propagation can take place by the addition of monomer to either structure I1 or structure 111. For reasons which are discussed below and in a forthcoming paper on the kinetics, the alternative reactions through the allyl group as shown in eq. (2) are considered unlikely. 3007 3008 J. P. J. HIGGINS AND K. E. WEALE IV V EXPERIMENTAL The monomer and all of the solvents were obtained from standard commercial sources and were distilled under vacuum before use. Benzoyl peroxide (Bz202) was recrystallized from chloroform solution. Polymerizations were carried out in sealed glass ampules in an oil bath at 6O"C, and the rate of polymerization R, was determined gravimetrically. Monomer and diallyl ether which were exposed to air for a few days turned yellow, presumably through absorption of oxygen, and these samples gave relatively low yields when used in polymerizations. However, a few samples prepared by the high vacuum filling technique gave results similar to those obtained from freshly distilled monomer and solvent, but with no special precautions to exclude air. Infrared absorption spectra of the monomer and polymer were obtained on a Hilger H-800 spectrometer with an NaCl prism. RESULTS Ally1 methacrylate (M) was polymerized in bulk and in solution in toluene, benzene, acetone, CCL, isopropyl ether, epoxypropane, dioxane, and diallyl ether, with benzoyl peroxide initiator. With the reactions in bulk, and in the solvents toluene, benzene, acetone, isopropyl ether, and epoxypropane, gelation occurred at very low conversions. The polymers were insoluble in the common organic solvents, in the monomer, and in dimethyl sulfoxide. I n CC1, solution, at low concentrations, conversions of up to 40% soluble polymer were obtained before gelation occurred. Autoacceleration was also observed and careful purification techniques and the exclusion of oxygen did not prevent its occurrence. I n dioxane solutions, a t concentrations of up to 2.2 mole/l monomer, high yields of soluble polymer were obtained. I n diallyl ether solution very high yields of soluble polymer were also obtained. The gel point occurred at lower conversions as the concentration of the monomer was increased. At very low monomer concentrations almost 100% soluble polymer was obtained. Figure 1 shows the results for the polymerization in three solvents a t fixed monomer and initiator concentrations. In various attempts to homopolymerize dioxane and diallyl ether by free-radical methods4a t temperatures from 30°C to 100°C and a t pressures from 1 to loo00 atm. it was found that these substances would not polymerize, (diallyl ether is, however, polymerized by cationic catalysts such as boron trifluoride diethyl etherate). Elemental analyses of the polymers SOLUBLE HIGH POLYMERS 3009 60 50 1 20 10 I 0 1 2 3 I 4 5 I 1 7 6 a TIME (hrs) Fig. 1. Polymerization of allyl methacrylate in three solvents at 60°C: (a) dioxane; ( b ) diallylether; (c) CC14. [BzzOz] = 1.1 X 10+ mole/l; [MI = 1 mole/l. of allyl methacrylate formed in dioxane and diallyl ether solutions confirmed that little or no copolymerization had occurred and that the allyl methacrylate had formed homopolymers. Table I shows the effect on the rate of polymerization of allyl methacrylate in diallyl ether solution as the initiator concentration is varied at constant monomer concentration. TABLE I Polymerization of Ally1 Methacrylate at 60°Ca No. [BzzOZ] lo3 X molefl X 106, moleflaec R p ~ 1 2 3 4 5 1.03 5.80 16.80 27.20 45.20 1.01 3.04 5.16 8.49 12.40 * Solvent: diallyl ether; [MI : 2.2 mole/l. The plot of log R , versus log [Bzz02Jis linear and has a slope of 0.7. Table I1 shows the effect on the rate of polymerization of allyl methacrylate in diallyl ether solution as the monomer concentration is varied at constant initiator concentration. The plot of log R , versus log [M J is linear and has a slope of 1.6. Thus the rate of polymerization of allyl methacrylate in diallyl ether solution at G0"C in the range of concentrations studied is given by: R , = k[B~202]O.'[M]~.' (3) J. P. J. HIGGINS AND K. E. WEALE 3010 TABLE I1 Polymerization of Ally1 Methacrylate at 60°C.a RP X 10: [MI, mole/l mole/l-sec 1.1 1.8 2.2 3.3 3.6 4.4 6.1 No. 27.7 57.6 84.9 172.7 176.9 282.2 580.1 * Solvent: diallyl ether; [Bz201] 1.1 x : lo-* mole/l. where k is a constant. Such irregular orders with respect to initiator and monomer concentrations are common for allylic and substituted allylic monomers. Characterization of Polymer Intrinsic viscosity was measured in an Ubbelohde viscometer a t 25°C in toluene solution. The intrinsic viscosity [v] varied from 0.1 to 0.5. Because of residual unsaturation the intrinsic viscosity varied with the amount of time the polymer had been exposed to air, and all polymer samples so exposed eventually became insoluble due to crosslinking. Using freeze-dried polymer samples which were immediately dissolved in toluene it was possible to obtain an intrinsic viscosity-molecular weight relationship by comparing intrinsic viscosity results with osmometrically determined molecular weights for the same samples. The Mark-HouwinkSakurada equation for poly(ally1 methacrylate) in toluene at 25°C was found to be: = 2.4 x 10-4AT~0.65 (4) kfnis the number-average molecular weight. In the case of poly(ally1 methacrylate), formed in diallyl ether solution a t 60°C using BzzOz as the initiator, the molecular weight varied from 70000 to 1 O O . OOO Infrared Spectra The infrared spectra of the monomer and the polymer are given in Figure 2. In the spectrum of the monomer the carbonyl stretch frequency absorption exhibits a peak a t 1725 cm-' but in the polymer this peak is broadened and shifted towards 1740 cm-'. This indicates the presence of Glactone units (six-membered rings) in the polymer. The spectrum of the polymer also shows a small absorption at 1775 cm-l. This is attributed to the presence of a small proportion of -y-lactone units (five-membered rings) which may be formed as shown in eq. (5). SOLUBLE HIGH POLYMERS F R4Hz ‘ I O=C 3011 CHs CH=CHz I + RCHzC-CH-CHz’ o=b CHz I \’ O I1 (5) &HZ \’ O VI The presence of two types of lactone ring in the polymer is supported by the absorptions a t 1230 and 1275 cm-’. These are probably due to the -COstretching frequencies in the 6- and y-lactone rings. WAVE NUHBW (--I) Fig. 2. Infrared spectra of (-) allyl methacrylate and (- -) poly(ally1 methacrylate) at 8W1800 em-’. DISCUSSION It has long been known that allylic monomers undergo degradative chain transfer (DCT) reactions.6.’ In these reactions, which compete with normal propagation, a hydrogen atom is extracted from the monomer by an active radical. In the case of allyl acetate: R- + C H ~ C H C H ~ O C C H RH + CH~=CHCHOCCH~ ~ -+ II 0 It (6) 0 The resulting acetoxyallyl radical is resonance-stabilized and does not readily add monomer, although it may terminate by bimolecular combination. If DCT predominates the rate of polymerization varies approximately as the first power of the initiator concentration6 rather than the 0.5 power found with normal monomers such as styrene and methyl methacrylate. The results for allyl methacrylate show that R , varies as the 0.7 power of the initiator concentration. This result may be explained if the methacrylyl groups can add to chains and undergo cyclizationwith the allyl groups as shown in eq. (l), while the allyl groups preferentially undergo f DCT rather than the reactions shown in eq. (2). I the allyl group is 3012 J. P. J. HIGGINS AND K. E. WEALE pendant on a polymer or radical chain, which is denoted by X, the DCT reaction is: The pendant resonance-stabilized allyl radicals do not propagate further with monomer but may terminate by bimolecular combination in two ways : 2 VII * CH-CH4H-X AH* I VIII CH AH I X‘ 2 VII + X-CH=CHCHzCHzCH=CH-X’ IX (9) When there are many pendant resonance-stabilized allyl radicals these reactions would quickly lead to crosslinked gel polymers and may account for the formation of insoluble polymers in polymerization in bulk and in the solvents toluene, benzene, acetone, isopropyl ether, and epoxypropane. The formation of soluble polymers in the other solvents suggests that in these the resonance-stabilized allyl radicals are preferentially terminated by a process which does not lead to crosslinking. Carbon tetrachloride is an active chain-transfer agent in some polymerizations8~9 and ethers and dioxane are known to cause rapid induced decomposition of benzoyl peroxide.lOpll The allyl groups of the solvent diallyl ether can also take part in DCT reactions. Radical-solvent and radical-initiator reactions wl produce small rapidly diffusing radicals which would be expected to i l react with pendant resonance-stabilized allyl radicals much more rapidly than the latter can combine mutually. The differences between the polymer obtained in the two groups of solvents may thus be explicable in terms of the differing abilities of the solvents to bring about termination of radical side chains before they can react. It has been shown that methacrylyl groups are much more reactive than allyl groups in the polymerizations of the methacrylic ester of 2-allylphenol12 and allyl methacrylate.la The polymerization proceeds via the methacrylyl groups to give high molecular weight polymer. That fraction of the allyl groups not included in cyclization reactions via the methacrylyl groups are left pendant on the growing chains. On the view that the allyl group does not enter into chain addition reactions it is possible to make some simplifications in the kinetic equations for the polymerization of allyl methacrylate, and these are discussed in a forthcoming paper. SOLUBLE HIGH POLYMERS 3013 References 1. G. B. Butler and R. J. Angelo, J. Amer. Chem. SOC., 79,3128 (1957). 2. S. G. Cohen, B. E. Ostberg, and D. B. Sparrow, J. Polym. Sci.,3,264 (1948). 3. W. Kawai, J. Polym. Sn'. A-l,4,1191 (1961). 4. J. P. J. Higgins and K. E. Weale, unpublished results. 5. P. D. Bartlett and R. Altachul, J. Amer. Chem. SOC., 67,812,816 (1945). 6. R. Hart and G. Smets, J. Polym. Sci., 5,55 (1950). 7. P. D. Bartlett and F. A. Tate, J. Amer. Chem. SOC., 75.91 (1953). 8. R. A. Gregg and F. R. Mayo, J. Amer. Chem. SOC., 70,2373 (1948). 9. S. Palit and S. K. Das, Proc. Roy. SOC. (London), A226.82 (1954). 10. P. D. Bartlett and K. Nozaki, J . Amer. Chem. SOC., 69,2299 (1947). 11. W. E. Cass, J . A m . Chem. SOC., 69,500 (1947). 12. 0. F. Solomon, M. G. Corviovei, and V. Tarareacu, J. Appl. Polym. Sn'., 11,1631 (1967). 13. S. Cohen, B. E. Ostberg, D. B. Sparrow, and E. R. Blount, J. Polym. Sn'., 3,264 (1948). 14. J. P. J. Higgins and K. E. Weale, to be published. Received January 4,1968 Revised March 19, 1968