Copolymerization of isobutylene and styrene at low temperatures in the presence of friedel‐crafts catalysts

Isobutylene and styrene were copolymerized at low temperatures, in methyl chloride solution, in the presence of aluminum chloride. The temperature was varied from −30 to −94°C., and the monomer/solvent ratio, the ratio of monomers, and the catalyst concentration were varied over a considerable range. The copolymerization equation was found to be applicable to the data, and the reactivity ratios were determined for various experimental conditions. For an “open” system in which the volume steadily increases during the course of polymerization, it is shown that the copolymerization equation is formally identical to that of Mayo and Lewis, except that concentrations are replaced by amounts of the reacting species. The temperature coefficients of the reactivity ratios in the present system are compared with those for free‐radical systems; some important differences are noted. The reactivity ratios of isobutylene and styrene in the present system are greatly increased under conditions of turbulent agitation. A procedure for the compositional fractionation of the copolymers is described. The results are interpreted in terms of the copolymer chain structure; they appear to admit the postulate that the reactivity ratios and corresponding propagation rate constants are functions of chain length.