Copolymerization of methacrylic anhydride with vinyl monomers

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Abstract
Copolymerizations of methacrylic anhydride and a variety of common types of vinyl monomers were conducted in bulk and in solution at 60–80° with benzoyl peroxide catalyst. The copolymers were characterized by conversion, solubility in hot dimethyl sulfoxide, elementary analysis, and infrared spectroscopy. A copolymer composition equation was derived for a special divinyl–vinyl system in which the divinyl monomer would cyclize extensively during polymerization and give rise to soluble, although perhaps branched, copolymers. The results showed that both soluble and insoluble copolymers were obtained, depending on the comonomer used and experimental conditions under which the copolymerization was carried out. In general, soluble copolymers were formed under the following conditions: (a) the less reactive the comonomer in free radical copolymerizations; (b) the greater the dilution; (c) the greater the difference in the moles of the two components in charge; and (d) the lower the conversion. According to reactivity ratio determinations and a comparison with published data, the anhydride ring radical behaved like a methyl methacrylate radical. The key step which led to gelation was believed to be “ring interruption” by the comonomer (CH2 = CHR): The question why methacrylic anhydride does not gel in homopolymerization, however, still remains unresolved.