STERICALLY STABILIZED SILICA COLLOIDS - RADICAL GRAFTING OF POLY(METHYL METHACRYLATE) AND HYDROSILYLATIVE GRAFTING OF SILICONES TO FUNCTIONALIZED SILICA

Colloidal silica sols having a narrow dispersity, prepared by the ammonia-catalyzed hydrolysis of Si(OEt)(4), were functionalized by reaction with vinyltrimethoxysilane (H2C=CHSi(OMe)(3)) or methacryloxypropyltri-methoxysilane (H2C=CMeCO(2)(CH2)(3)Si(OMe)(3). The electrostatically stabilized colloids were stable in acetone and dimethylformamide. Radical polymerization of methyl methacrylate in the presence of either type of functionalized particle led to particles with surface-grafted poly(methyl methacrylate) (PMMA). The efficiency of polymer grafting was shown to be related to the nature of the functional groups. The PMMA-modified, sterically stabilized particles were colloidally stable in solvents ranging from acetone to toluene but unstable in water or hexane. The vinyl functionalized silica was alternatively reacted with HSiMe(2)-terminated silicones in a platinum-catalyzed hydrosilylation. The resultant sterically stabilized particles were stable in hexane. It was thus possible to convert the unmodified silica to organo-functionalized silica and finally to polymer-grafted silica while maintaining colloidal stability. During the course of these modifications, the mechanism for colloidal stability changed from electrostatic to steric stabilization.