FREE-RADICAL GRAFT-POLYMERIZATION OF VINYLPYRROLIDONE ONTO SILICA

The free-radical graft polymerization of vinylpyrrolidone onto silica was studied in an aqueous slurry batch reactor. The graft polymerization process consisted of first activating the silica surface with vinyltriethoxysilane followed by a free-radical-polymerization step. The progress of the homo-polymerization and graft polymerization reactions was followed by UV and thermogravimetric analyses, respectively. In order to determine the molecular weight of the grafted poly(vinyl-pyrrolidone) (PVP) chains, the surface-grafted polymer was cleaved from the silica substrate by acid hydrolysis with hydrofluoric acid, and the polymer molecular weight was determined by size exclusion chromatography (SEC). The study revealed that the polymer graft yield and monomer conversion increased with increasing initial monomer concentration and reaction temperature, and that the rate of graft polymer formation is correlated to the rate of monomer consumption. The weight-average molecular weight of the surface-grafted polymer was shown to be higher than that of the homopolymer for the graft polymerization reations performed at low values of the initial monomer concentration and low reaction temperatures. In contrast, for graft polymerization reactions performed at high initial monomer concentration and temperature, the weight-average molecular weight of the grafted polymer was as much as 60% lower than that of the corresponding homopolymer.