Hybrid organic-inorganic membranes

The gas separation performance of a series of hybrid polyimide-silica membranes has been compared to Robeson's upper bound for various gas pairs. Exceptional gas separation was achieved primarily with crosslinked polyimides and with hybrid systems subjected to annealing treatments at elevated temperatures. The hybrid materials were prepared by carrying out sol-gel reactions of various alkoxysilanes in the presence of fully imidized polyimides, whose chain ends and backbone have been functionalized to different degrees with triethoxysilane groups. The alkoxysilanes employed included phenyltrimethoxysilane (PTMOS), methyltrimethoxysilane (MTMOS), tetramethylorthosilicate (TMOS), and tetraethylorthosilicate (TEOS). The presence of additional covalent linkage points along the polyimide backbone served to improve both, gas selectivity and gas permeability, primarily in the case of MTMOS-based hybrid materials. While TEOS and TMOS-based hybrid materials exhibited highly homogenous morphologies, the presence of alkyl groups in the PTMOS and MTMOS-based hybrid systems lead to morphologies of various degrees of phase separation. (C) 2001 Elsevier Science B.V. All rights reserved.