Hybrid organic-inorganic membranes

The gas separation performance of a series of hybrid polyimide-silica membr anes has been compared to Robeson's upper bound for various gas pairs. Exce ptional gas separation was achieved primarily with crosslinked polyimides a nd with hybrid systems subjected to annealing treatments at elevated temper atures. The hybrid materials were prepared by carrying out sol-gel reaction s of various alkoxysilanes in the presence of fully imidized polyimides, wh ose chain ends and backbone have been functionalized to different degrees w ith triethoxysilane groups. The alkoxysilanes employed included phenyltrime thoxysilane (PTMOS), methyltrimethoxysilane (MTMOS), tetramethylorthosilica te (TMOS), and tetraethylorthosilicate (TEOS). The presence of additional c ovalent 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 hig hly 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.