Hydrophobic aerogels from SiOMe4/MeSiOMe3 mixtures

Gels prepared from mixtures of Si(OMe)4 and MeSi(OMe)3 under basic conditions were supercritically dried by the methanol process. In aerogels prepared from only Si(OMe)4, 30 percent of the silicon atoms still contain an OMe substituent. When Si(OMe)4/MeSi(OMe)3 mixtures are employed, most of the residual methoxy substituents are replaced by methyl substituents. Thus, a permanent hydrophobicity is provided to the aerogels without affecting the average degree of condensation per silicon atom. The use of 40 percent or more MeTMOS in the preparation of the aerogels lowers the degree of condensation.beyond that of pure 'SiO2' aerogels.