Gas permeability and permselectivity of photochemically crosslinked copolyimides

Abstract

A series of copolyimides were prepared from 2,4,6-trimethyl-1,3-phenylenediamines (3MPDA), 3,3′,4,4′-benzophenone tetracarboxyl dianhydride (BTDA), and pyromellitic dianhydride (PMDA). Modification of the copolyimides by ultraviolet irradiation were carried out. Gas permeabilities of H2, O2, and N2 through the copolyimides and photochemically crosslinked copolyimides were measured at temperatures from 30 to 90°C. The relationships between gas permeabilities and temperature are in agreement with the Arrhenius equation. The structure of photochemically crosslinked copolyimides were characterized by Fourier transform infrared and gel measurement methods. Linear relationships between both log P and Ep and the volume fraction of PMDA–3MPDA exist. Photochemically crosslinking modification result in a decrease in gas permeability and an increase in Ep and α(H2/N2) for all the copolyimides. For H2/N2 separation, photochemically crosslinked copolyimides are of higher gas permeabilities and permselectivities simultaneously than normal polyimides. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 521–526, 1999