KINETICS AND MECHANISM OF MICROEMULSION POLYMERIZATION OF HEXYL METHACRYLATE

A kinetic analysis of the microemulsion polymerization of hexyl methac rylate in mixed dodecyltrimethylammonium bromide/didodecyldimethylammo nium bromide cationic microemulsions is developed and used to test mec hanistic assumptions. In the limit of no bimolecular termination and f ast radical capture, analytical expressions are derived for the conver sion and reaction rate as a function of time and for the dependence up on the initiator concentration of the maximum reaction rate and the ti me at which it occurs. The conversion at which the rate maximum occurs is predicted to be constant at 39%. The theoretical results are in ex cellent agreement with experimental data through to 100% conversion fo r reactions initiated by azobis(amidinopropane) hydrochloride (V-50) a nd by buffered potassium persulfate, but not for unbuffered persulfate reactions. The discrepancy is argued to be a consequence of initiator hydrolysis in the unbuffered systems, and the importance of buffering persulfate reactions in mechanistic studies is emphasized. Some of th e earlier studies of microemulsion polymerization are reviewed in ligh t of this finding.