Proton conductive polyimide Lonomer membranes: Effect of NH, OH, and COOH groups

A new series of sulfonated polyimide (SPI) copolymers containing NH, OH, or COOH groups were synthesized by the polycondensation of 1,4,5,8- naphthalnetetracarboxylic dianhydride, 3,3′-bis(sulfopropoxy)-4,4′- diaminobiphenyl, and 3-(4-aminophenyl)-5-(3-aminophenyl)-1H-1,2,4-triazole (SPI-8m), 3,5-bis(4-aminophenyl)-1H-1,2,4-triazole (SPI-8-p), 3,6-diaminocarbazole (SPI-9), 3,5-diamino-1H-1,2,4-triazole (SPI-10), bis(3-aminopropyl)-amine (SPI-11), 2,6-diaminopurine (SPI-12), 2,4-diamino-6-hydroxyprymidine (SPI-13), or 3,5-bis(4-aminophenoxy)benzoic acid (SPI-14). The obtained SPIs were soluble in polar organic solvents and gave tough and flexible mem-branes by solution casting. The SPI membranes having NH and COOH groups showed high thermal (decomposition temperature ≈200 °C) and mechanical (maximum stress >22 MPa) stability. Introducing NH groups, especially triazole and carbazole groups, was effective in improving proton conductive properties of SPI membranes at low humidity.