Anionic Graft Copolymerization of Epoxides and Cyclic Acid Anhydrides Initiated by Surface-Functionalized Silica Gel Prepared by Sol-Gel Process

Abstract

The preparation of silica gel powder having functional groups by sol-gel process and the grafting of polyesters onto the silica gel surface were investigated. Silica gel having carboxyl groups was prepared by copolycondensation of tetraethoxysilane with 4-trimethoxysilyltetrahydrophthalic anhydride. The silica gel was ground into a powder : The average diameter determined by SEM and carboxyl group content of the powder were 4 μm and 1.07 mmol/g, respectively. Then the carboxyl groups on the surface were converted into potassium carboxylate groups by the neutralization with dilute aqueous solution of potassium carbonate. It was found that the anionic alternating copolymerization of epoxides with cyclic acid anhydrides was successfully initiated by potassium carboxylate groups on the silica gel surface. In the copolymerization, the corresponding polyester was grafted onto the silica gel based on the propagation of the polymer from the surface : The percentage of polyester grafting onto silica gel obtained from the copolymerization of styrene oxide with phthalic anhydride and chloromethyloxirane with succinic anhydride was determined to be 37.1% and 42.2%, respectively. The copolymerization rate and percentage of polyester grafting increased with an increase in the polymerization temperature. The stability of silica gel dispersion in organic solvent was found to be remarkably improved by the grafting of polyesters onto the surface.