Sol-gel kinetics III. Test of the statistical reaction model

Abstract

The distribution of functional groups, -OCH 3, -OH, -OSi, about a silicon atom, undergoing concurrent hydrolysis and condensation in an acid catalyzed Si(OH 3) 4:CH 3OH:H 2O sol-gel, were measured by 29Si NMR. These NMR results were compared to predictions based on a statistical reaction model which assumes that all the hydrolysis and condensation rate constant depend only on the functional group reactivity and not on the local silicon environment. The hydrolysis and condesation reactions of monomeric species were successfully predicted by the model. The greater than predicted population of silicon species bonded to one other silicon via an SiOSi bond and the less than expected population of silicon species bonded to two other silicons via SiOSi bonds indicates that the condensation of partially condensed species is slower than the condensation of monomeric species.