Molecular weight distributions of poly(methyl methacrylate) produced at high viscosities

Abstract

AbstractThe molecular weight distribution of poly(methyl methacrylate), which is produced by the free‐radical polymerisation of methyl methacrylate, is influenced by the presence of poly(methyl methacrylate) which is dissolved in the monomer prior to the polymerisation. An experimental technique has been devised which permits a distinction to be made between polymer which is present at the start of the reaction and the polymer which is formed by the reaction. Mathematical analyses of alternative reaction schemes have been made. These predicted changes that would occur in the molecular weight distribution of the new polymer when the solution viscosity increased. Comparison with experimental measurements of molecular weights makes possible the distinction between the alternative reaction schemes. The results are compatible with a reaction mechanism in which the mobilities of the growing radicals are not influenced equally by the solution viscosity. The results are not those which would be expected by the simple inclusion of primary radical termination in the reaction scheme. In some cases, analysis by gel permeation chromatography showed that the molecular weight distribution of the poly(methyl methacrylate) formed by the reaction is bimodal. This is consistent with predictions from the mathematical analysis.