Sol-gel polycondensation kinetic modeling: Methylethoxysilanes

摘要: Quantitative kinetic modeling of the condensation methylethoxysilanes ~(CHJj.+$i(OCz H5)f 1 varying functionality fl is needed to engineer inorganic polymers, resins, and ceramics. To that end, a model accounts for hydrolysis pseudoequilibrium, nearest-neighbor substitution eflects, unimolecular cyclization reactions in homogeneous ethoxysilane polycondensation presented. Condensation rate parameters are determined by fitting 29Si NMR transients. Several important features become evident: (1) success pseudoequilibrium approximation; (2) strong negative effects with unusual dependence on connectivity; (3) tendency ring formation, growing methyl substitution; (4) acceleration upon (5) destabilization three silicon rings substitution. The first observations consistent previous findings ethylethoqsilanes, but last two strikingly diflerent.