Sol-gel polycondensation kinetic modeling: methylethoxysilanes

Stephen E. Rankin, Christopher W. Macosko, Alon V. McCormick

Research output: Contribution to journalArticle

52 Scopus citations

Abstract

Quantitative kinetic modeling of the condensation of methylethoxysilanes {(CH3)4-fSi(OC2H5)f} of varying functionality (f) is needed to engineer inorganic polymers, resins, and ceramics. To that end, a kinetic model that accounts for hydrolysis pseudoequilibriiim, nearest-neighbor substitution effects, and unimolecular cyclization reactions in homogeneous ethoxysilane polycondensation is presented. Condensation rate parameters are determined by fitting to 29Si NMR transients. Several important features become evident: (1) the success of the hydrolysis pseudoeqidlibriiim approximation; (2) strong negative substitution effects with unusual dependence on connectivity; (3) a strong kinetic tendency for ring formation, growing with methyl substitution; (4) acceleration of condensation upon methyl substitution; and (5) destabilization of three silicon rings by methyl substitution. Tlie first three observations are consistent with previous findings for ethylethoxysilanes, but the last two are strikingly different.

Original languageEnglish (US)
Pages (from-to)1141-1156
Number of pages16
JournalAIChE Journal
Volume44
Issue number5
DOIs
StatePublished - Jan 1 1998

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