Cross-linked sulfonated poly(arylene ether nitrile)s with high selectivity for proton exchange membranes

For the purpose of prepare a high performance proton exchange membrane with low methanol permeability and high proton conductivity, a sulfonated poly(arylene ether nitrile)s (SPEN) with carboxyl groups were synthesized. Then the cross-linked membranes were prepared by simply thermal curing in which the polymer network structures were covalent cross-linked. The chemical structures of the cross-linked membranes were characterized by Fourier transform infrared analysis. The resulting cross-linked membranes can effectively reduce water uptake, swelling ratio and methanol permeability. Among the cross-linked membranes, CSPEN-70 exhibits low water uptake, low swelling ratio (135.4% and 23.8% at 80 °C, respectively) and low methanol permeability coefficient (3.23 × 10− 7 cm2·s− 1), while maintaining proton conductivity of 0.148 S·cm− 1. More importantly, the selectivity of cross-linked CSPEN-70 is about 5 times higher than that of Nafion117. All the data prove that the cross-linked membranes may be potential proton exchange membrane for the direct methanol fuel cells (DMFCs) application.