Microemulsion Polymerization of Styrene Using Surface-Active Peresters as Photoinitiators

Abstract

Three surface-active organic peroxides have been evaluated as initiators (INISURFs) in the microemulsion polymerization of styrene. Two of the three are cationic surfactants, [4-(4‘-tert-butyldioxycarbonylbenzoyl)benzyl]trimethylammonium chloride (1) and {6-[4-(4‘-tert-butyldioxycarbonylbenzoyl)phenyl]hexanyl}trimethylammonium chloride (2). The third is a nonionic surfactant, isohexadecyl icosaoxyethylene 4-(4‘-tert-butyldioxycarbonylbenzoyl)benzoate (3). It is found that the interfacial activity of the initiator has a direct impact on the polymerization kinetics and characteristics of the resulting polymer latex. More specifically, the molecular weight and particle size of polystyrene initiated by an ionic peroxide (1 or 2) are more sensitive to the nature of the surfactant (cationic, anionic, or nonionic) that makes up the miroemulsion. The surfactant makeup of a microemulsion has much less impact on the characteristics of the polymer latex obtained from a nonionic surfactant peroxide (3). In addition, while heat-activated decomposition of cationic peresters 1 and 2 in an aqueous solution leads mainly to heterolytic cleavage of the dioxy bond and a low radical-generation efficiency, their photochemical decomposition gives predominately homolytic cleavage and a much higher radical efficiency. The radical efficiency, in turn, has a profound influence on the profile of the resulting polymer latex.