Bifunctionalized Intrinsically Microporous Polyimides with Simultaneously Enhanced Gas Permeability and Selectivity

Two novel intrinsically microporous copolyimides synthesized by condensation reaction of 4,4'-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 3,3,3',3'-tetramethyl-1,1'-spirobisindane-5,5'-diamino-6,6'-diol, and 3,5-diaminobenzoic acid with diamine ratios of 80/20 (Co-80/20) and 50/50 (Co-50/50) are reported. Unexpectedly, the Co-80/20 not only demonstrates higher microporosity (300 m(2) g(-1) ) than the PIM-6FDA-OH homopolymer (190 m(2) g(-1) ) but also exhibits simultaneously enhanced CO2 permeability (from 119 to 171 Barrer) and CO2 /CH4 selectivity (from 35 to 41) after thermal annealing at 250 °C. This higher permeability originates from enhanced diffusivity (D CO2 ) and the higher selectivity results from its increased diffusion selectivity (D CO2 /D CH4 ). After crosslinking at 300 °C, the Co-80/20 exhibits an even higher CO2 permeability (261 Barrer) and almost unchanged CO2 /CH4 selectivity.