Journal of Sol-Gel Science and Technology 26, 73–76, 2003 c  2003 Kluwer Academic Publishers. Manufactured in The Netherlands. Novel Siloxane-Silica Nanocomposite Aerogels and Xerogels N. H ¨ USING ∗ , J. BAUER, G. KALSS, G. GARNWEITNER AND G. KICKELBICK Institut für Material Chemie, Technische Universit¨ at Wien Getreidemarkt 9, A-1060 Wien, Austria nhuesing@mail.zserv.tuwien.ac.at Abstract. Novel covalently bonded silicone-silica nanocomposite network materials have been synthesized from a single component molecular precursor. A novel polymeric sol-gel precursor was prepared by hydrosilation of oligo(methylvinylsiloxane) with triethoxysilane and it was applied in sol-gel processing for the synthesis of silicone- silica based gel networks. Acid/base catalyzed hydrolysis and condensation reactions were performed from solutions of the pure macro precursor as well as from mixtures of this precursor with tetraalkoxysilanes followed by either supercritical drying with liquid carbon dioxide or drying at ambient conditions. In both cases monolithic gels as well as powders were obtained and properties such as porosity, surface area and thermal stability have been investigated. Solid state (CP MAS) 29 Si-NMR were used to evaluate the chemical composition and extent of condensation of the gels. Keywords: silicone-silica, aerogels, solid state NMR, macro precursor, nanocomposite Introduction The sol-gel process has been employed extensively for the synthesis of hybrid inorganic-organic and nanocomposite materials, and different types of pre- cursors have been employed such as monomeric organoalkoxysilanes, bistrialkoxysilylalkyl or -aryl precursors, polyhedral silsesquioxanes etc. [1]. In ad- dition, polymers have been incorporated into silica gels to improve the mechanical properties of the result- ing gels [2], e.g. silanol-terminated polydimethylsilox- anes (PDMS) were co-condensed with tetraethoxysi- lane (TEOS) [3]. The idea behind our studies was to create a poly- functional macromolecular building block in which part of the chemical connections is already predeter- mined in the precursor molecule. The new precursor not only contains difunctional (D) and trifunctional (T) units in a given structural arrangement, but the D units are already precondensed to form a linear oligomeric structure (Fig. 1). In the new precursor, a controlled micro phase sepa- ration is expected due to the chemical incompatibility ∗ To whom all correspondence should be addressed. of the silicone-like and the silsesquioxane part of the molecule. We hope to achieve a better control on the micro architecture of the resulting nanocomposite ma- terial due to the preorganisation of di- and tri-functional units. In addition, the presence of up to 120 reactive alkoxy sites per molecule should lead to unusual rates and pat- terns of reactivity, a different relative tendency for the precursors to undergo intra- vs intermolecular conden- sation reactions and a different percolation threshold for gel formation is expected. Small amounts of this macro precursor can also substantially influence the sol-gel behavior in more conventional systems (mix- tures with tetraalkoxysilanes). Experimental Synthesis of Oligo Methyl(2-Triethoxysilyl)Ethyl Siloxane Oligomeric methylvinylsiloxane (Wacker) was char- acterized by SEC (size exclusion chromatogra- phy), NMR and thermal analysis. For the different batches, the molecular weight ranged from 8770 to 10189 g mol −1 . An amount of repeating units