Radical Graft Polymerization of Vinyl Monomers onto Barium Sulfate Initiated by Azo Groups Introduced onto the Surface

Abstract

To modify the surface of barium sulfate, the radical graft polymerization of vinyl monomers initiated by azo groups introduced onto the surface was investigated. The introduction of azo groups onto the surface was achieved by the direct condensation of carboxyl group of 4,4'-azobis(4-cyanopentanoic acid) with 12-hydroxystearate groups on modified barium sulfate using N,N'-dicyclohexylcarbodiimide as a condensing agent. It was found that the radical polymerizations of methyl methacrylate (MMA), styrene, and N-vinylcarbazole were initiated by the azo groups introduced onto the surface, and the corresponding polymers were grafted onto the surface based on the propagation of grafted polymer from the surface : the percentage of PMMA grafting onto the surface reached 25.3% at 70°C after 1.5 hours and the grafting efficiency was 21.4%. The polymerization rate (R p ) of styrene initiated by the surface azo groups was given by R p = k[styrene][BaSO 4 -Azo] where k is a constant, [styrene] is the styrene concentration, and [BaSO 4 -Azo] is the concentration of barium sulfate having azo groups. The result suggests that in such an initiating system the unimolecular termination of growing polymer radicals from the surface proceeds preferentially at the initial stage of the polymerization.