IDENTIFICATION OF SELF-CONDENSATION AND CROSS-CONDENSATION PRODUCTS IN ORGANICALLY MODIFIED SILICA SOLS BY SI-29 AND O-17 NMR-SPECTROSCOPY

High resolution Si-29 and O-17 NMR spectroscopy has been used to ident ify self- and cross-condensation products in sols prepared from tetrae thoxysilane (TEOS) and organically modified triethoxysilanes (RTES, wh ere R is a methyl, ethyl or phenyl group). The sols were prepared by t he acid catalyzed hydrolysis of TEOS and RTES with H2O/Si mole ratios of 0.15, 0.3 or 0.5, Resonance assignments were made by comparing the positions and intensities of peaks in the spectra of single and multic omponent systems as a function of reaction time. Both Si-29 and O-17 N MR spectroscopy exhibit resonances which are uniquely attributed to sp ecies formed by cross-condensation reactions between TEOS and RTES. Ap proaches to improve the resolution of O-17 NMR spectra were only moder ately successful because the resonance envelopes have substantial cont ributions from inhomogeneous components.