THE HOMOGENEOUS PHOTOPOLYMERIZATION OF METHYL-METHACRYLATE BY COLLOIDAL CADMIUM-SULFIDE

A completely new method of initiating the homogeneous radical polymeri zation of methyl methacrylate in bulk or in solution via the photogene ration of an electron hole pair in colloidal cadmium sulfide is presen ted. A polymerization mechanism involving an excited cadmium sulfide p article in both the initiation and termination steps is proposed. In t he initiation a methyl methacrylate molecule is oxidized by a positive hole photogenerated in a CdS particle, which results in a novel chain -end structure of the poly(methyl methacrylate) (PMMA). Degradative ch ain transfer to reduced excited cadmium sulfide particles is responsib le for chain termination. Thus, for the first time, a detailed polymer ization mechanism in which all states of the polymerization, i. e., in itiation, propagation, chain transfer and termination, is presented fo r the polymerization of vinyl monomers initiated by semiconductors. Th ermogravimetry (TG) showed that the newly synthesized PMMA has greatly enhanced thermal stability when compared to normal radically prepared PMMA. In fact, the thermal stability approaches that of anionically p repared PMMA but is experimentally much easier to prepare. This techni que enables the homogeneous embedding of CdS particles in a polymer ma trix.