Catalytic effect of chemically modified metal alkoxides on hydrolysis and condensation reactions of methyl- and phenyi-ethoxysilanes

The catalytic effect of chemically modified metal alkoxides on the hydrolysis and condensation reactions of methylethoxysilanes and phenylethoxysilanes was investigated by Si-29 nuclear magnetic resonance spectroscopy and gel permeation chromatography. Metal alkoxides such as Al (O-sec-C4H9)(3), Ti (O-iso-C3H7)(4) and Nb (OC2H5)(5) modified with ethyl acetoacetate accelerated not only the condensation reactions but also the hydrolysis reactions of methyl- and phenyl-alkoxysilanes. The catalytic effect of these metal alkoxides was found to be different between methyl- and phenyl-alkoxysilanes. The catalytic activity increases in the order of Nb < Al < Ti alkoxides in the case of methyl-ethoxysilanes, whereas in the case of phenyl-ethoxysilanes it increases in the order of Nb < Ti < Al alkoxides. The difference in catalytic activity was discussed on the basis of the partial charge of M in metal alkoxide, the difference in electronegativity between M and Si and the difference between the coordination number and valence of M.