Trimethylethoxysilane Liquid-Phase Hydrolysis Equilibrium and Dimerization Kinetics: Catalyst, Nonideal Mixing, and the Condensation Route

Stephen E. Rankin, Ján Šefčík, Alon V McCormick

Research output: Contribution to journalArticlepeer-review

22 Scopus citations

Abstract

Although the kinetics of organoethoxysilane hydrolytic (poly)condensation have been studied under kinetically simplified conditions, materials are actually synthesized from nonideal mixtures with high monomer and catalyst concentrations. Using 29Si nuclear magnetic resonance, we study the hydrolysis of trimethylethoxysilane and the dimerization of the resulting silanol in aqueous ethanol at monomer and catalyst concentrations typical of organically modified silicate synthesis. Under acidic conditions, we find that when (and only when) the effects of solvent composition on catalyst activity are considered, it becomes clear that water-producing condensation is the dominant dimerization route. Under basic conditions, the extent of deprotonation of the weakly acidic silanol passes through a minimum during reaction, thereby producing an anomolous trend in reaction rate. This necessitates a kinetic model which is first order in both silanol and deprotonated silanol and which accounts for changing deprotonation.

Original languageEnglish (US)
Pages (from-to)4233-4241
Number of pages9
JournalJournal of Physical Chemistry A
Volume103
Issue number21
DOIs
StatePublished - May 27 1999

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