Understanding Hydrolysis and Condensation Kinetics of γ-Glycidoxypropyltrimethoxysilane

Abstract

Monitoring the kinetics of hydrolysis and condensation of γ-glycidoxypropyltrimethoxy-silane (γ-GPS) was carried out by NMR spectroscopy (29Si–, 13C–, and 1H–). The course of these reactions was followed in 2 wt% aqueous dilution conditions (26% D2O/74% H2O), pH 5.4, and temperatures of 26, 50, and 70°C. At ambient temperature, hydrolysis and condensation proceed at very different time scales: a few hours for the hydrolysis versus several weeks for the condensation. Distortionless Enhancement by Polarization Transfer (DEPT) sequences by 29Si– and 13C–NMR spectroscopy were optimized for determining the complete spectral assignment for each hydrolysis step, i.e., RSi(OMe)3–n(OH)n (with R = (C H 2 OCH)C H 2 OC H 2 C H 2 C H 2–;and n = 1, 2, 3). A pseudo-first order rate constant for the first hydrolysis step, T0(OMe)3 + H 2 O → T0(OMe)2OH + MeOH, was calculated to be 0.026 min−1. Simultaneously to the condensation reactions, we have observed epoxy ring opening of the glycidyl- group. All three processes (hydrolysis, condensation, and epoxy ring opening) are dramatically accelerated with temperature increases from 26 to 70°C. The activation energy of the epoxy ring opening leading to the formation of a diol structure at the extremity of the glycidoxypropyl- chain was estimated to be 68.4 kJ/mol.