EFFECT OF FLUOROALKYL SUBSTITUENTS ON THE REACTION OF ALKYLCHLOROSILANES WITH SILICA SURFACES

We have investigated the reaction of (fluoroalkyl)chlorosilanes with silica at the solid/gas interface by infrared spectroscopy. In the absence of surface water, the (fluoroalkly)chlorosilanes react at room temperature to form a surface Si-O-Si bond. Under these same conditions, alkylchlorosilanes do not react with the silica surface. This difference in reactivity is explained by an inductive effect of the fluoroalkyl groups on the gamma-carbon atom (gamma-C). The effect of surface water and adsorbed amines on the surface chemistry has also been examined. Surface water reacts with the (fluoroalkyl) chlorosilanes to form silanols which then undergo a condensation reaction with the surface hydroxyl groups. Nitrogen-containing bases promote the reaction of the (fluoroalkyl)chlorosilanes with the surface and yield surface species that are identical to those obtained by direct reaction.