GRAFT-POLYMERIZATION OF VINYL MONOMERS BY PEROXYESTER GROUPS INTRODUCED ONTO THE SURFACE OF INORGANIC ULTRAFINE PARTICLES

The radical graft polymerization of vinyl monomers from inorganic ultrafine particles, such as silica, titanium oxide, and ferrite, initiated by peroxyester groups introduced onto their surfaces was investigated. The introduction of peroxyester groups onto the ultrafine particles was achieved by reactions of hydroperoxide with acid anhydride groups, introduced by the reaction of hydroxyl groups on the surface with 4-trimethoxysilyltetrahydrophthalic anhydride. The amounts of diisopropylbenzene peroxyester groups introduced onto ultrafine silica, titanium oxide, and ferrite were determined to be 0.11, 0.07, and 0.05 mmol g-1, respectively. The polymerization of vinyl monomers, such as methyl methacrylate (MMA) and styrene, or copolymerization of divinyl ether with maleic anhydride was initiated by peroxyester groups introduced onto ultrafine particles. During the polymerization, the corresponding polymer was effectively grafted onto these surfaces through the propagation of the polymer from the surface radicals formed by decomposition of the peroxyester groups; the percentage of grafting was 45-50%. Furthermore, the rate of the polymerization was found to be accelerated by the addition of reducing agents to the polymerization system. Polymer-grafted ultrafine particles gave a stable colloidal dispersion in organic solvent for grafted polymer.