A series of novel fluorinated copolyimides were synthesised with various diamine compositions by chemical imidisation in a two-pot procedure. The gas permeation behaviour of 2,2´-bis(3,4´-dicarboxyphenyl) hexafluoropropane dianhydride(6FDA)-2,4-diamine toluene(DAT)/1,3- phenylenediamine(mPDA) polyimides was investigated. The gas permeatility coefficients decreased with increasing mPDA content; however, the permselectivity of gas pairs such as H2/N2, O2/N2 and CO2/CH4 was enhanced with the incorporation of mPDA moiety. The permeability coefficients of H2, O2, N2, CO2 and CH4 were found to decrease with the increasing order of kinetic diameters of the penetrant gases. Moreover, all of the copolyimides studied in this work exhibited performance near, lying on or above the existing upper bound trade-off line between permselectivity and permeability.
Keywords: 6FDA, fluorinated copolyimides, gas permeation, gas separation, global warming