Hydrolysis pseudoequilibrium: Challenges and opportunities to sol-gel silicate kinetics

We quantitatively model the kinetics of acid-catalyzed hydrolytic condensation of trimethylethoxysilane, a representative monomer for 'sol-gel' inorganic polymerization chemistry. Sol-gel processing is of interest as a flexible route to new ceramic gels, silicone resins, inorganic/organic hybrids, and micro- or meso- porous catalysts such as zeolites. Using principal component analysis of the sensitivity matrix for this model, we quantitatively demonstrate that hydrolysis pseudoequilibrium is not only appropriate but also demanded if unique rate coefficients are to be determined. While this provides a challenge in the sense that hydrolysis kinetics may be difficult to measure, it also provides the opportunity to model alkoxysilane polymerization using only condensation kinetics. Parametric sensitivities are not directly observable however, so we also present an experimentally observable phase portrait signature of hydrolysis pseudoequilibrium. Finally, we discuss why, under hydrolysis pseudoequilibrium, the condensation route (water producing or alcohol producing) is virtually impossible to distinguish from a single batch experiment. (C) 2000 Elsevier Science Ltd. All rights reserved.