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 m ethoxylation of the silicon chloride end groups. Dendrimers with respe ctively 12 [first generation (1G)] and 36 [second generation (2G)] met hoxysilane groups and arborols with octadecyl and phenyl group of firs t and second generation have been prepared. They were characterized by elemental analyses and H-1, C-13 and Si-29 NMR spectroscopy. Polycond ensation by a sol-gel process yields the hybrid materials. 2G; dendrim ers formed porous materials while nonporous materials were obtained fr om 2G arborols containing the octadecyl group. The precursor of the se cond generation containing the phenyl group formed different gels depe nding on the solvent used for the polycondensation process. Neverthele ss, no gel was obtained for dendrimers and arborols of the first gener ation. The solid-state 29Si NMR spectroscopy was used to evaluate the integrity of the material and to determine the degree of polycondensat ion in the network material. Oxidative thermal treatment was performed in order to remove the organic part of the hybrids. The texture of th e 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.