On the nature of chemical binding of organic silanes to water-free silica surfaces: a high-resolution solid-state NMR spectroscopic study

Methoxytrimethylsilane (A), dimethoxydimethysilane (B), and trimethoxymethylsilane (C) were used to silylate porous silica gel, which was very thoroughly dried with thionylchloride. Products were characterized with elemental analysis and by CP / MAS NMR (29Si and 13C). Under these conditions monofunctional silane A yields monodentate silane-to-surface links (trimethylsiloxysilanes) plus some esterification of silanol sites by methanol, resulting from the main reaction. Bifunctional silane B yields mono- and bidentate silane-to-surface links under the described reaction conditions. Trifunctional silane C also yields mono- and bidentate links. Cross-linked tridentate groups are formed only after exposure to air or reaction with water.