Effect of Zinc Chloride on the Velocity Coefficients in the Polymerization of Methyl Methacrylate

Abstract

IT is well known that the reactivity of the propagating species in ionic polymerization is greatly influenced by the proximity and character of the gegenions and by complex formation. As a rule, free radical reactions are comparatively insensitive to the nature of their environment, although there are references in the literature to changes in the rate of free-radical polymerizations, and the nature of the polymers formed, which have been attributed to the participation of radicals in complexed forms. The investigation of the structure and reactivity of radical complexes in polymerization is a field which has not been surveyed systematically, but which, nevertheless, may contain interesting features. We have embarked on an investigation of the absolute rate coefficients in the free-radical polymerization of vinyl monomers in the presence of possible complexing agents and report here some results for the methyl methacrylate–zinc chloride system. The only measurements of a similar type recorded in the literature appear to be those of Bamford, Jenkins and Johnston¹, on acrylonitrile in NN-dimethylformamide solution in the presence of lithium salts. Kargin, Kabanov and Zubov² considered that the presence of zinc chloride during the polymerization of methyl methacrylate affects the microstructure of the polymer, but this finding was not confirmed by Bovey³. More recently, Imoto, Otsu and Harada⁴ have investigated the steady-state polymerization of methyl methacrylate in the presence of zinc chloride and have shown that at 60° C the rate of the reaction initiated by azo-bis-isobutyronitrile is increased by addition of zinc chloride, the ratio k_p/√(k_t) also being increased (k_p, k_t are the velocity coefficients for propagation and total bimolecular termination, respectively).