NMR studies on hydrolysis and condensation reactions of alkoxysilanes containing Si-H bonds

Hydrolysis and condensation reactions of four organically modified alkoxides, used for the preparation of silicon oxycarbide gel precursors, have been followed by Si-29 NMR. Triethoxysilane (HSi(OEt)(3)) and methyldiethoxysilane (MeHSi(OEt)(2)) react extremely fast compared to methyltriethoxysilane (MeSi(OEt)(3)) and tetraethoxysilane (Si(OEt)(4)). Co-hydrolysis reactions between different pairs of precursors - MeSi(OEt)(3)/Si(OEt)(4); MeSi(OEt)(3)/HSi(OEt)(3); MeHSi(OEt)(2)/Si(OEt)(4); and MeHSi(OEt)(2)/HSi(OEt)(3) -were investigated by solution state Si-29 and O-17 NMR. Despite significantly different reactivities between precursors, evidence for co-condensation reactions has been found for each system. Finally, two-dimensional Si-29-H-1 heteronuclear correlation MASNMR spectroscopy was used to probe the local environments of the various Si sites in the product hybrid networks.