Synthesis of new copolyimides containing pyridine and morpholine groups for gas separation through molecular design and simulation

Through one-step copolymerization of 4-(4-[1-morpholinyl]phenyl)-2,6-bis(4-aminophenyl)pyridine (MPAP), 9,9-bis(4-aminophenyl)fluorene (BAFL), and (4,4′-hexafluoroisopropylidene)diphthalic anhydride (6FDA), a series of polyimides containing morpholine group, pyridine ring, fluorene “cardo” pendant and hexafluoroisopropyl group are obtained. The synthesized polyimides have good thermal stability, high transparency, outstanding hydrophobicity and excellent solubility in not only high-boiling solvents but also low boiling-point solvents. Furthermore, polyimide films have large molecular chain spacing, which is consistent with the free volume calculated by molecular simulation. Consequently, polyimide membranes display better gas permeability values of CO 2 (up to 24.47 Barrer) and He (up to 45.04 Barrer), and good ideal gas selectivity values of CO 2 /N 2 (up to 15.33 Barrer) and He/N 2 (up to 23.89 Barrer), which also shows potential application of polyimide matrix materials in gas separation.