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Sol‐gel polycondensation kinetic modeling: Methylethoxysilanes
Author(s) -
Rankin Stephen E.,
Macosko Christopher W.,
McCormick Alon V.
Publication year - 1998
Publication title -
aiche journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.958
H-Index - 167
eISSN - 1547-5905
pISSN - 0001-1541
DOI - 10.1002/aic.690440512
Subject(s) - condensation polymer , kinetic energy , substitution (logic) , condensation , hydrolysis , chemistry , polymer , kinetics , polymer chemistry , silicon , computational chemistry , thermodynamics , organic chemistry , physics , quantum mechanics , computer science , programming language
Abstract Quantitative kinetic modeling of the condensation of methylethoxysilanes {(CH 3 ) 4‐ f Si(OC 2 H 5 ) f } of varying functionality ( f ) is needed to engineer inorganic polymers, resins, and ceramics. To that end, a kinetic model that accounts for hydrolysis pseudoequilibrium, nearest‐neighbor substitution effects, and unimolecular cyclization reactions in homogeneous ethoxysilane polycondensation is presented. Condensation rate parameters are determined by fitting to 29 Si NMR transients. Several important features become evident: (1) the success of the hydrolysis pseudoequilibrium 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. The first three observations are consistent with previous findings for ethylethoxysilanes, but the last two are strikingly different.