THE REACTIVITY OF MONOMERIC SILANOL INTERMEDIATES IN THE HYDROLYTIC POLYCONDENSATION OF TETRAETHOXYSILANE IN ACIDIC MEDIA

Trimethylsilylation-gas-liquid chromatography techniques combined with computer simulation were used to study the acid catalyzed hydrolytic polycondensation of tetraethoxysilane (TEOS) in dioxane solution. The kinetics of the initial period of this process, in which the reactions of Q0 species, i.e. monomer and hydroxysilanes derived from the monomer, predominate, were investigated. Rate constants of some individual component reactions of the Q0 intermediates were estimated. The reactivity in all three reactions of compounds of (EtO)4 - nSi(OH)n series, i.e. hydrolysis ethanolysis and condensation, strongly increases with the number of hydroxyl groups n. It was also demonstrated that the ethanolysis reactions play an important role in the overall process since they control concentration of hydroxyl-substituted silane intermediates. © 1990.