Surface Alkoxylation of Silicas by Mild Reactions with Alcohols

Abstract

Abstract The surface alkoxylation reaction of silicas was investigated under mild reaction conditions with some low-molecular-weight saturated aliphatic alcohols. Silica gels and porous silica glass were treated with liquid alcohols using a Soxhlet extractor below their boiling points. The number of formed alkoxyl groups was examined by both thermal analyses and infrared spectra. It was shown that some of the surface hydroxyl groups were easily esterified to alkoxyl groups, even by contact with the alcohols under mild reaction conditions. The degree of alkoxylation was higher for the silica gels than for porous silica glass. The adsorption isotherms of methanol vapor at room temperature were measured on silica gel samples which were previously activated at various temperatures. The adsorption equilibrium strongly depends on the pretreated temperature. The surface methoxylation reaction took place not only on the surface hydroxyl groups, but also on the siloxane bridges, even at room temperature.