| Abstract: | 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?CMeCO2(CH2)3Si(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 surfacegrafted 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 HSiMe2-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. |
