Relationship of temperature to composition of copolymers of α-methylstyrene and maleic anhydride

Relationship of temperature to composition of copolymers of ( -methylstyrene and maleic anhydride Raymond B. Seymour and David P. Garner Department of Chemistry, University of Houston, Houston, Texas 77004, USA (Received 19 August 1975; revised 16 September 1975) Alternating copolymers of e-methylstyrene and maleic anhydride were prepared in good yields in a decalin solution at temperatures below 80°C. Random copolymers with large percentages of (xmethylstyrene were obtained in good yields at higher temperatures. These results were in accord with the charge transfer complex which was characterized by n.m.r, and u.v. spectrophotometry and shown to exist below 80°C. The copolymers were characterized by pyrolysis/gas chromatography and differential scanning calorimetry. The glass transition temperature of poly(a-methylstyrene) and the random copolymer of this monomer and maleic anhydride were approximately 450 and 458 K respectively.

INTRODUCTION Polymers of ~-methylstyrene 1 and maleic anhydride 2 as well as alternating copolymers of these two monomers 3 have been described. Likewise, the alternating copolymer of styrene and maleic anhydride was one of the first recognizable copolymers4. Both block copolymers and random copolymers of this system have also been described s'6. The formation of block copolymers is the result of the addition of excess styrene monomer to styrene-maleic anhydride macroradicals 7. The formation of random copolymers has been attributed to the decomposition of the charge transfer complex at elevated temperatures s. It is assumed that this complex is formed when the electronpoor maleic anhydride accepts a charge from the electron rich styrene 9. Absorbance bands attributable to this complex and not characteristic of either monomer species have been observed in the u.v. spectra of a solution of these monomers 1°. The presence of this complex has also been demonstrated by n.m.r, techniques H.

solution of the maleic anhydride/~-methylstyrene complex in carbon tetrachloride using a Varian T-60 spectrophotometer. The d.s.c, data were obtained on a Perkin-Elmer Differential Scanning Calorimeter lB. Pyrolysis/g.c. data were obtained from small samples of copolymers which were thermally decomposed by a current of 8 A for 6 sec in a Varian Aerograph A-25 pyrolysis unit. Helium at a flow rate of 60ml/min was used as the carrier gas for the decomposition products in a Varian Aerograph A 100 C Gas Chromatograph.

RESULTS

Charge transfer complex of c~-methylstyrene and maleic anhydride Since c~-methylstyrene is a better electron donor than styrene, it forms a stronger charge transfer complex with maleic anhydride as shown below: O

EXPERIMENTAL Copolymers of c~-methylstyrene and maleic anhydride were prepared from freshly distilled c~-methylstyrene and maleic anhydride, which had been crystallized from benzene. Mixtures of these monomers as a 10% w/w solution in purified decalin were polymerized in oxygen-free sealed containers at specified temperatures. Azobisisobutyronitrile (AIBN) was used as the initiator. The decalin was washed with concentrated sulphuric acid, washed with water, dried over sodium and freshly distilled. Yields of better than 90% w/w of alternating copolymers were obtained in the presence of 2.5% w/w AIBN. However, it was necessary to increase this concentration to 10% w/w in order to obtain comparable yields of random copolymers at higher temperatures. U.v. absorbance data were obtained from 0.001 M solutions of the monomeric mixtures in decalin using a Carey Model 14 spectrophotometer. N.m.r. data were obtained from solvent free c~-methylstyrene, 10% w/w solution of maleic anhydride in carbon tetrachloride, and 10% w/w

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As shown in Figure 3, the n.m.r, absorbance for maleic anhydride has shifted from 7.1 6 (Figure 1) to 5.9 6 in the mixture of this monomer and ~-methylstyrene. The n.m.r. absorbance for the latter is shown in Figure 2.

Effect of temperature on the charge transfer complex Since the effect of temperature on the charge transfer complex is not readily determined by n.m.r, techniques, u.v. spectrophotometry was used to investigate this effect. The change in the absorbance band at 291 nm in the u.v. spectrum was followed with the change in temperature. As shown in Figure 4, the intensity of this absorbance decreased as the temperature was increased. Extrapolation of these

POLYMER, 1976, Vol 17, January

21

Relationship of temperature to composition of copolymers: R. B. Seymour and D. P. Garner

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Copolymers of a-methylstyrene and maleic anhydride As shown in Table 1, good yields of decalin insoluble alternating copolymers were obtained when 10% solution of equimolar ratios of a-methylstyrene and maleic anhydride in decalin were heated at temperatures below 80°C for 72 h in the presence of 2.5% AIBN. These compositions were determined by pyrolysis/gas chromatography. Typical pyrograms are shown in Figure 5. As shown in Table 2, the composition of the copolymer was independent of the monomer ratio in the feed at temperatures below 80°C. However, random copolymers with large proportions of a-methylstyrene were obtained at 100°C

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data showed zero absorbance at temperatures above 85~C. Since the formation of an alternating copolymer is dependent on the presence of a charge transfer complex, the composition of the copolymer is independent of compositions at temperatures below 85°C.

The d.s.c, thermograms, shown in Figure 6, indicate that the copolymers prepared at 100°C were random copolymers while those prepared at temperatures less than 80°C (B) were alternating copolymers. Scan A for poly(amethylstyrene) shows a glass transition temperature of approximately 450 K, which corresponds well with the previously obtained range of 446-453 K 12. Table I Effect of temperature (60°--80°C) on composition of copolymers of e-methylstyrene (e-MS) and maleic anhydride (MA) Temperatu re (oC)

Feed ratio (e-MS/MA)

Polymer composition (e-MS/MA)

60 70 80

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P O L Y M E R , 1976, Vol 17, January

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Relationship of temperature to composition of copolymers: R. B. Seymour and D. P. Garner

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Tab/e2 Effect of temperature (60°-100°C) on composition of copolymers of (x-methylstyrene ((x-MS) and maleic anhydride (MA) Temperature (°C) 60 70 80 100 100

Feed ratio ((X-MS/MA)

Polymer composition ((~-MS/MA)

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REFERENCES 1 2 3 4 5 6 7

No transition at ~ 4 5 0 K was observed for the alternating copolymer (B), which melted at about 480K. Scan C for the copolymer produced at 100°C resembles scan A. However, since a-methylstyrene does not form a homopolymer at temperatures above 61 °C, and g.c. pyrograms showed the presence of two monomers in a 7:2 ratio, this scan is for a random copolymer.

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Kilroe, J. G. and Weale, K. E. J. Chem. Soc. 1960, p3849 Lang,J. L., Pavelich, W. A. and Clarey, H. D. J. Polym. Sci. {A) 1963, 1, 1123 Oshima,K. Kogyo Kagaku Zasshi 1964, 67, 2159 Wagner-Jauregg,T. BerDtsch Chem. Ges. 1930, 63, 3213 Seymour, R. B., Tsang, H. S., Jones, E. E., Kincaid, P. D. and Patel, A. K. Adv. Chem. Ser. 1971, 99,418 Muskat, I. E. U.S.Pat. 3 388 106 (1.6.68) Seymour, R. B., Kincaid, P. D. and Owen, D. R. J. Paint Technol., 1973, 45, 33 Seymour, R. B. and Garner, D. P. J. Paint TechnoL in press Bartlett, P. D. and Nazaki, K. J. Chem. Soc. 1946, 68, 1495 Andrews, L. J. and Keefer, R. M. J. Chem. Soc. 1953, 75, 3776 Tsuchida, E., Tomono, T. and Sono, H. J. Macromol. Sci. (A) 1972, 6,151,295 Cowie,J. M. G. and Toporowski, P. M. J. Macromol. Sci. (B) 1969, 3, 81