Sulfonated poly(arylene ether nitrile)s containing cross-linkable nitrile groups for proton exchange membranes

In order to solve the problem of high methanol crossover for direct methanol fuel cells, a series of cross-linkable sulfonated poly(arylene ether nitrile)s with pendent nitrile groups as cross-linkable groups have been synthesized through direct condensation polymerization. As far as we know, there are no detailed reports connected with nitrile groups being used as cross-linkable groups. The chemical structures of the sulfonated poly(arylene ether nitrile)s were confirmed by Fourier transform infrared (FT-IR) spectroscopy. The introduction of cross linking network structure caused significant enhancement in thermal property and dimensional stability. Meanwhile, methanol permeability, swelling ratio and water uptake of the membranes substantially decreased after cross-linking. For instance, the water uptake and swelling ratio of SPEN-CN-70 are 1985.3% and 157% at 80 degrees C, while those of CSPEN-CN-70 decrease to 64.9% and 16.9%, respectively. The SPEN-CN membranes showed the methanol permeability range from 0.838 x 10 (-7) to 8.24 x 10 (-7) cm(2) s (-1), while the CSPEN-CN membranes showed the lower permeability range from 0.156 x 10 (-7) to 1.64 x 10 (-7) cm(2) s (-1), respectively. Most importantly, after cross-linking, CSPEN-CN-60 showed the highest selectivity of 5.37 x 105 S s cm(-3), which was 11.9 times higher than that of Nafion 117. Although the conductivity of the CSPEN-CN was lower than that of the SPEN-CN, the higher selectivity makes the CSPEN-CN as potential candidate for applications in fuel cells.