GAS PERMEATION OF AROMATIC POLYIMIDES .2. INFLUENCE OF CHEMICAL-STRUCTURE

The permeability Of C02 and CH4 in 17 different types of polyimides membranes has been determined at 25-degrees-C and at an applied pressure of 4.87 atm. The relationship between structures of polyimides and their gas permeability was studied. Polyimides containing an -0- group in the dianhydride part of the polymer chain showed low permselectivity and low permeability. Polyimides with an -SO2- group in the dianhydride exhibited high permselectivity but low permeability. On the other hand, a -C (CF3)2- groUP in the dianhydride showed both high permselectivity and high permeability. The effects of the diamine part of 6FDA polyimides on gas permeability were studied. Aromatic diamines with meta-connections in the polymer chain showed a higher permselectivity and lower permeability compared with para-connected polyimides. Polyimides with longer diamine chains with -0- linkages show decreased permselectivity and permeability. PolYimides having -C (CF3)2- groups both in the dianhydride part and the diamine part showed both high permeability and high permselectivity.