The Effect of Conversion on the Mechanism of Vinyl Polymerization. II. Methyl Methacrylate

The usual photochemical method and the rotating sector technique have been used to study the effect of conversion on the termination mechanism in the polymerization of methyl methacrylate. The strong rate acceleration, the extreme increase in kinetic chain lifetime and some decreases in the overall activation energy and the reaction order of chain termination have been detected with increasing conversion of the reaction system. These results are in good agreement with those reported on styrene in the first paper of this series and with the available data on this polymerization. These results have been discussed under several assumptions and confirmed to be due to a large change in the termination mechanism, i. e., from the activation-controlled termination of polymer radicals in the initial stages to the predominant diffusion-controlled termination in the later stages.