Kinetics of emulsion polymerization of methyl methacrylate

The kinetics of the emulsion polymerization of methyl methacrylate at 50 degree C have been studied in seeded systems using both chemical initiation and gamma -radiolysis initiation. The data are quantitatively interpreted using a generalized Smith-Ewart-Harkins model, allowing for free radical entry, exit, bimolecular termination within the latex particles, and aqueous phase hetero-termination and re-entry. From this treatment, there results (i) the dependence of the termination rate coefficient (k//t) on the weight fraction of polymer (w//p), (ii) lower bounds for the dependence of the entry rate coefficient on initiator concentration, and (iii) the conclusion that most exited free radicals undergo subsequent reentry into particles rather than hetero-termination. The results for k//t(w//p) are consistent with diffusion control at temperatures below the glass transition point. Comparisons are presented of the behavior of methyl methacrylate, butyl methacrylate, and styrene in emulsion polymerization systems.