Polycondensation behavior of methyltrimethoxysilane studied by NMR spectroscopy

Silicate gels are most often synthesized by hydrolyzing monomeric alkoxide precursors employing acid or base catalysts. The properties of final products are determined by the pathway of the reactions, which includes hydrolysis, condensation, and solvent exchange reaction. We analyzed a system with methyltrimethoxysilane as monomer and ethanol as solvent by using 1H, 13C, and 2D heteronuclear correlated nuclear magnetic resonance (NMR) spectroscopy. Complete assignments of the proton and the 13C-NMR bands were established, which rendered the kinetic study feasible. An understanding of the behavior of the system was also attempted, especially at earlier stages. The results showed that hydrolysis and solvent exchange reactions occurred at early stage whereas condensation occurred slowly. © 1996 John Wiley & Sons, Inc.