Polymerization reactions in methyltriethoxysilane studied through 29Si NMR with polarization transfer

Si-29 nuclear magnetic resonance (NMR) spectroscopy was used to identify and characterize the alkoxysilane polymers formed in the early stages of the hydrolysis and condensation reactions of methyltriethoxysilane (MTES) dissolved in ethanol. The distortionless enhancement by polarization transfer (DEFT) experiments were tuned for optimum sensitivity, quantitative information and also used as editing methods for Si-29 spectra of various oligomers. The structures of polymers were identified, including various linear oligomers up to tetramers and cyclic species with three and four silicon atoms. The proportion of cyclics and cagelike structures is more important with an excess of water. It is shown that the hydrolysis ratio and the pH affect the hydrolysis rate of the species formed. (C) 1998 Elsevier Science B.V. All rights reserved.