GAS SEPARATION PROPERTIES OF AROMATIC POLYETHERIMIDES FROM 1,4-BIS(3,4-DICARBOXYPHENOXY)BENZENE DIANHYDRIDE AND 3,5-DIAMINOBENZIC ACID OR ITS ESTERS

The gas transport properties of a series polyetherimides, which were p repared from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) with 1,3-phenylenediamine or 3,5-diaminobenzic acid (DBA) or its ester s are reported. The effects of carboxylic group (-COOH) and carboxylic ether groups (-COOR), at five positions of 1,3-phenylenediamine moiet y, on H-2, CO2, O-2, and N-2 permeability, diffusivity, and solubility of the polyetherimides were investigated. The gas permeability, diffu sion, and solubility coefficients of the polyetherimides containing CO OR are bigger than those of HQDPA-PDA, but the ideal separation factor s and ideal diffusivity selectivity factors are much smaller than that of HQDPA-PDA because COOR decreases chain segmental packing efficienc y and increases chain segmental mobility. The permeability coefficient s of HQDPA-DBA to H-2, CO2, and O-2 are bigger than those of HQDPA-PDA ; the ideal separation factors for gas pairs H-2/N-2, CO2/N-2, and O-2 /N-2 are also much bigger than those of HQDPA-PDA. Both the diffusion coefficients of CO2 and O-2 and the ideal diffusivity selectivity fact ors for CO2/N-2 and O-2/N-2 are bigger than those of HQDPA-PDA because COOH decreases both chain segmental packing efficiency and chain segm ental mobility. The copolyimides, which were prepared from 3,5-diamino benzic acid and 3,5-diaminobenzic esters, have both high permeability and high permselectivity. (C) 1997 John Wiley & Sons, Inc.