Polysiloxane–silica hybrids from novel precursors by the sol–gel process

Abstract

1,1,1,7-Tetramethoxy-3,3,5,5,7,7-hexamethyl-1,3,5,7-tetrasiloxane {TMOS-D₃} and 1,1,1,7-tetramethoxy-3,5,7-trimethyl-3,5,7-trivinyl-1,3,5,7-tetrasiloxane {TMOS-V₃} were made, respectively, by cationic telomerisation of hexamethylcyclotrisiloxane (D₃) or 2,4,6-trimethyl-2,4,6-trivinylcyclotrisiloxane (V₃) with tetramethoxysilane (TMOS). These compounds were used as precursors of siloxane–silica materials. Their structure resulted in the generation of short trisiloxane segments which were well dispersed in the formed hybrid framework. These precursors or their mixtures with TMOS were subjected to sol–gel polycondensation in dispersions or in bulk catalysed by NaOH. Siloxane–silica hybrid materials were obtained either in the form of precipitated particles (1–80 µm) of various regular or irregular shapes or in the form of a monolithic material disintegrated on drying. In the sol–gel dispersion process, which was performed in the presence of a surfactant, cetyltrimethylammonium bromide, almost all methyl groups were converted to oxygen bridging two silicon atoms while in the bulk process a small fraction of unreacted alkoxyl and hydroxyl groups remained in the gel. Materials obtained from pure {TMOS-D₃} and {TMOS-V₃} showed a very low porosity and surface area. In contrast, particles having a high surface area can be obtained from mixtures of these new precursors and TMOS. Gels prepared from {TMOS-V₃} and its mixture with TMOS were subjected to hydrosilylation with HMe₂SiCl and the silylated particles were used for grafting of a living polysiloxane polymer.