ALKYLENE-BRIDGED POLYSILSESQUIOXANE AEROGELS - HIGHLY POROUS HYBRID ORGANIC-INORGANIC MATERIALS

Alkylene-bridged polysilsesquioxane gels were prepared by sol-gel poly merizations of alpha, omega-bis(triethoxysilyl)alkanes 1-5. The gels w ere extracted with supercritical carbon dioxide to afford a novel clas s of hybrid organic-inorganic aerogels. The effect of the length of th e alkylene bridging group and catalyst (HCl and NaOH) on the structure was examined. The molecular structure was characterized by solid-stat e C-13 and Si-29 cross polarization magic angle spinning nuclear magne tic resonance spectroscopy. The alkylene bridging groups survived sol- gel polymerization to give materials with average degrees of condensat ion of 79 and 90% for the acid- and base-catalyzed aerogels, respectiv ely. Scanning electron microscopy was used to examine the macroscopic structure of the gels and nitrogen sorption porosimetry was used to me asure their surface areas and pore structures. Most of the alkylene-br idged aerogels were mesoporous, high-surface-area materials. As with a lkylene-bridged polysilsesquioxane xerogels, the surface area decrease d with increasing alkylene bridging group length. Only the base-cataly zed tetradecylene-bridged aerogel was found to be non-porous.