A quantitative description of the low temperature radical post-polymerization in the system butyl methacrylate-zinc chloride

A study has been made of the low temperature radical post-polymerization by a “living chains” mechanism in the system butyl methacrylate (BMA)ZnCl2 and in BMA without additives. A theoretical analysis of kinetic regularities of the polymerization process has been carried out for the system BMAZnCl2 (mole fraction of ZnCl2 = 0·37). According to the kinetic model presented in the paper, the process may be subdivided into two stages. In the first stage of the process, i.e. from the onset of defrosting to the establishment of a constant concentration of propagation radicals in the system, account was taken of the lower diffusion controlled bimolecular termination rate constant, when the length of the radicals is increased. It is proposed that during the second stage of the process, when bimolecular termination of radicals does not occur at all, a major role is played by monomolecular termination (“disappearance” of radicals) whereby some of the radicals are “lost” at high degrees of conversion. In terms of the model, good agreement is obtainable between theoretically calculated and experimentally determined molecular weights and polydispersity coefficients Pw/P̄n for polybutylmethacrylate obtained in the polymerization process. Theoretical proof of the widening of MWD of the polymer observed at high degrees of conversion has been obtained. On the basis of the proposed model one can explain a possible “survival” of varying amounts of propagation radicals at the start of the second stage of the process, the amount depending on the rate of heating of the system, as was found on a previous occasion in a study of the post polymerization of pure (wtihout any additives) butyl methacrylate.