Synthesis of polysiloxane-modified silica hybrid particles by a high temperature water technology

Polysiloxane-modified silica hybrid particles were synthesized by hydrolysis and subsequent polycondensation of phenyltrimethoxysilane in the presence of colloidal silica at above 220 °C. The process variables include pH of the colloid, [silica]/[phenyltrimethoxysilane] molar ratio, reaction temperature, and reaction time. The products were characterized by solvent extraction, TGA, GPC, TEM, and 29Si NMR. The degree of surface modification (DOM) ranged between 5 and 35 wt.% by tuning the process variables when a neutral colloid was used. On the other hand, the DOM proved to be strongly dependent on temperature and becomes essentially zero when the synthesis was conducted with an acidic colloid at temperatures as high as 350 °C. TEM analysis suggested that each silica particle was surface modified resulting in minimal aggregation of the particles. The hybridization mechanism was studied by the DOM and the molecular weight of ungrafted polysiloxane.