SYNOPSISThe photografting of polymers onto ultrafine inorganic particles, such as silica and titanium oxide, initiated by azo groups introduced onto these surfaces was investigated. The introduction of azo groups onto the particles was achieved by the reaction of 4,4'-azobis (4cyanopentanoic acid) with surface isocyanate groups, which were introduced by the treatment with tolylene 2,4-diisocyanate. It was found that the photopolymerization of vinyl monomers, such as methyl methacrylate (MMA), styrene, and N-vinylcarbazole, is initiated by ultrafine particles having azo groups. The corresponding polymers were effectively grafted onto these surfaces through the propagation of the polymer from the surface radicals formed by the photodecomposition of the azo groups: e.g., the percentage of grafting of PMMA and polystyrene onto silica was reached to 112 and 176%, respectively. The percentage of grafting onto silica in the graft polymerization initiated by photodecomposition of surface azo groups was much larger than that initiated by thermal decomposition. Polymer-grafted ultrafine particles thus obtained gave a stable colloidal dispersion in good solvents for the grafted chain.

ABSTRACT:The cationic postgraft polymerization of several monomers initiated by pendant acylium perchlorate groups of polymer chains previously grafted onto a surface of ultrafine silica was investigated. The introduction of pendant acylium perchlorate groups to the grafted polymer chains on the silica surface was achieved by the reactions of silver perchlorate with pendant acyl chloride groups prepared by the radical graft copolymerization of styrene with acryloyl chloride using the ultrafine silica having azo groups onto the surface as an initiator. The pendant acylium perchlorate groups of the grafted copolymer chains on the silica surface were able to initiate the cationic postgraft polymerization of styrene, and polystyrene was effectively postgrafted from these grafted copolymer chains with a higher percentage of grafting to give branched polymer-grafted silica. The percentage of postgrafting of polystyrene and that of total polymer grafted onto silica, i.e., overall grafting, reached about 80 and 120%, respectively. The cationic ring-opening polymerization of e-caprolactone was also initiated by pendant acylium perchlorate groups of the grafted copolymer chains to give polyester-postgrafted silica. Postgrafting of polystyrene was remarkably affected by the composition of the copolymer previously grafted. The percentage of postgrafting increased with the solubility of these copolymer chains in the polymerization system. The polystyrene-postgrafted silica gave a stable colloidal dispersion in a good solvent for the grafted polymer.

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