Effect of molecular separation on the hydrolytic polycondensation of Si(OC 2H 5) 4

Abstract

The course of network forming reactions during the hydrolytic polycondensation of alkoxysilanes and metal alkoxides is determined primarily by chemical encounter rates and the diffusion process. The host liquid and the molecular separation of the interacting species in the host liquid play a fundamental role in shaping the molecular structure and molecular size distribution in these cases. In this work, the molecular separation concept is discussed, and the effect of molecular separation during the hydrolytic polycondensation of Si(OC 2H 5) 4 in ethanol on the molecular make-up of the resultant organosiloxane polymers is presented. The effect of the concentration of the reacting species, i.e., Si(OC 2H 5) 4 and H 2O in the solutions is distinguished from the effect of concentrating the solution. The concentration of water-rich siloxane solutions leads to significant molecular size expansion by oxide network formation. No similar polymer size growth occurs during the concentration of alcohol based solutions. This differences in the polymeric activities can be related to the difference in the terminal bonds under the two different conditions.