Hybrid xerogels from dendrimers and arborols

Dendrimers and arborols with a carbosilane core have been prepared by a divergent hydrosilylation/vinylation reaction sequence followed by methoxylation of the silicon chloride end groups. Dendrimers with respectively 12 [first generation (1G)] and 36 [second generation (2G)] methoxysilane groups and arborols with octadecyl and phenyl group of first and second generation have been prepared. They were characterized by elemental analyses and H-1, C-13 and Si-29 NMR spectroscopy. Polycondensation by a sol-gel process yields the hybrid materials. 2G; dendrimers formed porous materials while nonporous materials were obtained from 2G arborols containing the octadecyl group. The precursor of the second generation containing the phenyl group formed different gels depending on the solvent used for the polycondensation process. Nevertheless, no gel was obtained for dendrimers and arborols of the first generation. The solid-state 29Si NMR spectroscopy was used to evaluate the integrity of the material and to determine the degree of polycondensation in the network material. Oxidative thermal treatment was performed in order to remove the organic part of the hybrids. The texture of the solid was determined by BET measurement for xerogel before and after oxidation. Porous silica were obtained with similar porosity and pore size diameter from all the precursors.