Intracrystalline grafting on layer silicic acids

Abstract

Silanol groups (Si–OH) present at the surface of amorphous silica and microcrystalline silicates can react with organosilicon compounds to form stable organic derivatives1–3. The grafting reaction always occurs at the external surfaces of these materials. The present work considers the intracrystalline grafting on internal Si–OH groups in certain layer silicic acids. For the reaction to occur, the silicic acid must have been expanded by the intercalation of appropriate organic polar molecules such as dimethylsulphoxide; in this way, the individual layers of the silicic acid can be separated and the internal Si–OH groups become accessible to the grafting reagents. The resulting grafted products are organosilicic compounds which retain the lamellar structure of the starting silicic acids, but with the interlamellar surfaces covered by organic groups homogeneously distributed. These materials can be thought of as planar silicones.