Metal Oxide Trialkylsilyloxide Polymers. Part VI. Aluminum Oxide Trimethylsilyloxides

Abstract

Tris(trimethylsilyloxy)aluminum, [Al(OSiMe3)3]2, was hydrolyzed under controlled conditions in dioxane at 25 °C. The soluble initial products [AlOx(OH)z(OSiMe3)3−2x−z]n, with x = 0.03–0.65, underwent disproportionation when heated at 120–150 °C under vacuum to give final products with x = 0.8–1.1. Molecular weights were determined by cryoscopy in cyclohexane, and the linear dependence of 1/n on x was combined with an extension of the theory of regular polymer series to show that the number of OH groups, z, was small compared to the number of bridging oxygen atoms, x, per Al atom. The initial products consist of dimeric units, each linked to an adjacent unit by one or two oxygen bridges between aluminum atoms. The degree of polymerization is 1 to 4, based on the dimer unit. The final products have much higher degrees of polymerization (10–40, based on the dimer), and appear to contain a higher proportion of Al—O—Al bridges.