Gas-sorption properties of 6FDA-durene/1,4-phenylenediamine (pPDA) and 6FDA-durene/1,3-phenylenediamine (mPDA) copolyimides

We investigated the sorption isotherms of O-2, N-2, CH4, and CO2 gases in 6FDA-durene, 6FDA-1,4-phenylenediamine (6FDA-pPDA), and 6FDA-1,3-phenylenediamine (6FDA-mPDA) homopolymers and 6FDA-durene/pPDA and 6FDA-durene/mPDA copolyimides. The solubilities decrease in the order of the inherent condensabilities of the penetrant gases, namely, CO2, CH4, O-2, and N2. The chemical structures of the polymer, as well as the chain packing, determine the sorption properties of these homopolymers and copolymers. The FDA-durene hemopolymer has the highest solubility for all gases because of its high specific free volume and fractional free volume. The solubilities of the copolymers increase with an increasing 6FDA-durene content, while the solubility selectivities of the copolymers only vary slightly. The values of KD (Henry's law constant) and C-H' (Langmuir site capacity) of these copolyimides decrease with a decreasing 6FDA-durene content. To our surprise, contradictory to the previous known fact that the meta-connected materials tend to have denser molecular packing than that of the para-linked materials for homopolymers, the 6FDA-durene / mPDA 80 / 20 copolymer has higher gas solubilities than those of the 6FDA-durene/ pPDA 80/20 copolymer. The random moiety sequence within the copolymer may be the main cause for the abnormal phenomenon. (C) 2003 Wiley Periodicals, Inc.