Gas separation properties of aromatic polyetherimides from 1,4‐bis(3,4‐dicarboxyphenoxy)benzene dianhydride and 3,5‐diaminobenzic acid or its esters

Abstract

The gas transport properties of a series polyetherimides, which were prepared from 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) with 1,3-phenylenediamine or 3,5-diaminobenzic acid (DBA) or its esters are reported. The effects of carboxylic group (—COOH) and carboxylic ether groups (—COOR), at five positions of 1,3-phenylenediamine moiety, on H2 CO2, O2, and N2 permeability, diffusivity, and solubility of the polyetherimides were investigated. The gas permeability, diffusion, and solubility coefficients of the polyetherimides containing COOR are bigger than those of HQDPA-PDA, but the ideal separation factors and ideal diffusivity selectivity factors are much smaller than that of HQDPA-PDA because COOR decreases chain segmental packing efficiency and increases chain segmental mobility. The permeability coefficients of HQDPA-DBA to H2, CO2, and O2 are bigger than those of HQDPA-PDA; the ideal separation factors for gas pairs H2/N2, CO2/N2, and O2/N2 are also much bigger than those of HQDPA-PDA. Both the diffusion coefficients of CO2 and O2 and the ideal diffusivity selectivity factors for CO2/N2 and O2/N2 are bigger than those of HQDPA-PDA because COOH decreases both chain segmental packing efficiency and chain segmental mobility. The copolyimides, which were prepared from 3,5-diaminobenzic acid and 3,5-diaminobenzic esters, have both high permeability and high permselectivity. © 1997 John Wiley & Sons, Inc.