Termination‐rate coefficients in methyl methacrylate polymerizations

Abstract

It is shown that, by observing the kinetics of the seeded emulsion polymerization of methyl methacrylate with and without added chain‐transfer agent, and using γ‐radiolytic initiation, it is possible to examine separately the effects of the length of the growing chain and of the weight fraction of polymer on the termination rate coefficient. Studies using this technique confirm predictions that chain entanglement causes translational diffusion to be the rate‐determining termination event for growing chains of lower molecular weight, while the rate‐determining termination event for growing chains of higher molecular weight is “residual,” the annihilation encounter being caused by excess chain end mobility of two growing chains in a viscous medium. The data show unambiguously that free‐volume theories which do not incorporate the molecular weight of the growing chain are inapplicable to this system.