Structure/permeability and permselectivity relationship of polyetherimides from 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride. I

Gas permeability coefficients of a series of aromatic polyetherimides, which were prepared from 1,4-bis(3,4-dicarboxyphenoxy) benzene dianhydride (HQDPA) and various aromatic diamines, to H₂, CO₂, O₂, N₂ and CH₄ have been measured under 7 atm pressure and over the temperature range 30–150°C. A significant change in permeability and permselectivity, which resulted from a systematic variation in chemical structure of the polyetherimides, was found. Generally, increases in permeability of the polyetherimides are accompanied by decreases in permselectivity. The order of decrease of the permeability coefficients is as follows: HQDPA–IPDA > HQDPA–DDS > HQDPA–MDA > HQDPA–ODA > HQDPA–DABP > HQDPA–BZD. However, HQDPA–DMoBZD and HQDPA–DMoMDA, with bulky methoxy side-groups on the aromatic rings of the diamine residue, display both high permeability coefficients and high permselectivity. The favourable gas separation property, excellent thermal and chemical stability, and high mechanical strength make HQDPA–DMoBZD and HQDPA–DMoMDA promising candidates for membrane-based gas separation applications.