SILYLATION OF A TUBULAR ALUMINOSILICATE POLYMER (IMOGOLITE) BY REACTION WITH HYDROLYZED (GAMMA-AMINOPROPYL)TRIETHOXYSILANE

The reaction between imogolite, a novel tubular aluminosilicate with an outer molecular diameter of ~23 A and an inner diameter of ~8.2 A, and (γ-aminopropyl)triethoxysilane (APS) in aqueous acetic acid (pH 3.6) has been investigated by FTIR and 29Si MAS NMR spectroscopy. For products formed over the formal APS:A1 range 2.5:1 to 0.5:1, the imogolite tube structure is retained, and the surface-bound APS is in the form of a protonated siloxane polymer. Little or no change in 29Si NMR chemical shift is observed for the silylated products, suggesting that the APS binds mainly at the external Al-OH surface of the tube wall, not at the internal Si-OH surface. Both partially cross-linked RSiOH(OSi)2 and fully cross-linked RSi(OSi)3 sites are observed for the APS-functionalized imogolite. The degree of APS cross-linking is lower in the surface-bound state than in the pure polymer, but the APS-functionalized imogolite is more stable toward hydrolysis than the pure polymer when dialyzed against distilled water. Nevertheless, nearly complete loss of APS from the imogolite surface occurs after only 3 days of dialysis time, indicating that the APS-imogolite interface is quite labile. © 1990, American Chemical Society. All rights reserved.