Acid-free synthesis of poly-organo-siloxane spherical particles using a W/O emulsion

Abstract

Poly-organo-siloxane spherical particles were synthesized by a sol–gel method from methyltrimethoxysilane (MTMS) using a W/O emulsion comprising of sorbitantrioleate (SPAN85), n-octane, and H₂O. MTMS was hydrolyzed and condensed without acid and/or basic catalysts in this W/O emulsion at room temperature. The size of the spherical silica particle depends on both the composition of the emulsion and the reaction time, ranging from 1 to 80 µm in diameter. A W/O emulsion comprising 10 wt% SPAN85, 60 wt% n-octane, and 30 wt% H₂O was appropriate for the uniformity and reproducibility of spherical particles. The particle size increased with increasing reaction time. It is considered that the formation mechanism of poly-organo-siloxane spherical particles consists of three steps. The first step is that MTMS is hydrolyzed at the interface between oil and water phases. The second step is that spherical pre-polymers are synthesized by condensation of silanol. The third step is particle growth by condensation of spherical pre-polymers and silanol.