Synthesis and properties of polyimide ionomers containing 1H-1,2,4-triazole groups

A series of sulfonated polyimide copolymers containing 1H-1,2,4-triazole groups in the main chains were synthesized as proton-conducting membranes for fuel cell applications. Polycondensation of triazolecontaining dianiline, acid-functionalized benzidine, and naphthalenetetracarboxylic dianhydride gave the title polyimide ionomers. The ionomers were high molecular weight (M _w > 100 kDa, M_n > 20 kDa) to give tough and flexible membranes by solution casting. The ion exchange capacity (IEC) of the membranes ranged from 1.10 to 2.68 mequiv/g as confirmed by ¹H NMR analyses and titration. Comparison with the other polyimide ionomer membranes revealed that introducing triazole groups caused better thermal stability (decomposition temperature of ca. 200°C), comparable hydrolytic and oxidative stability, and better mechanical properties. Although NH groups did not function as ion exchange sites, the triazole-containing membranes showed slightly higher proton conductivity. The highest proton conductivity (0.3 S/cm at 88% RH) was obtained for the high IEC (2.68 mequiv/g) ionomer membrane. The ionomer membranes showed low hydrogen and oxygen permeability under dry and wet conditions.