Synthesis and characterization of polyhedral silsesquioxanes bearing bulky functionalized substituents

A simple route to synthesize polyhedral silsesquioxanes, (RSiO1.5)(n), by the hydrolytic condensation of modified aminosilanes, is reported. The starting material was N-(beta-aminoethyl)-gamma-aminopropyltrimethoxysilane, a trifunctional aminosilane. It was reacted with a stoichiometric amount of phenylglycidyl ether in sealed ampules at 50 degrees C for 24 h, leading to the trisubstituted product plus a series of oligomers arising from the intermolecular reaction between methoxysilane groups and the secondary hydroxyls generated by the epoxy-amine reaction. When this product was subjected to hydrolytic condensation using a variety of catalysts (HCl, NaOH, HCOOH) and a thermal cycle attaining 150 degrees C, polyhedral silsesquioxanes (SSQO) were obtained. Their molar mass was independent of reaction conditions as revealed by size exclusion chromatography. Characterization by H-1, C-13, and Si-29 NMR suggested that the main product was a mixture of polyhedral SSQO with n = 8 and 10; i.e., T-8 and T-10. Due to the high OH functionality, i.e., 24 OH groups in T-8 and 30 OH groups in T-10 polyhedra, the synthesized product may be used as a cross-linking unit of very high functionality or as a modifier for several polymeric materials.