DISPERSION COPOLYMERIZATION OF POLYOXYETHYLENE MACROMONOMER AND STYRENE .3. MOLECULAR CHARACTERIZATION OF POLYSTYRENE-GRAFT-POLYOXYETHYLENECOPOLYMERS

Graft copolymers (polystyrene-graft-polyoxyethylene) (PS-graft-PEO) we re prepared by the dispersion copolymerization of methacryloyl-termina ted polyoxyethylene macromonomer and styrene initiated by an oil-solub le initiator (dibenzoyl peroxide, DBP). The apparent molecular weights of graft copolymers measured by size exclusion chromatography in tetr ahydrofuran were found to be proportional to the -0.8th power of DBP c oncentration. This reaction order supports the termination of growing radicals by a first order radical loss process. The molecular weight d istribution estimated from the size exclusion chromatography (SEC) dat a was found to decrease slightly with DBP concentration and to drop ra pidly with macromonomer concentration. This was attributed to chain tr ansfer events and to the increase of particle number: the higher the p article number the lower the monomer concentration in the particles. T he bulkiness of the macromonomer molecules and the high segment densit y around the propagating reaction loci hinder the incorporation of mac romonomer molecules into a copolymer growing chain.