Research the effect of crosslinking degree on the overall performance of novel proton exchange membranes

As we all know, introducing crosslinking groups into the polymer chain can effectively improve the overall performance of proton exchange membranes, which are for the formation of intermolecular three-dimensional network. In this work, side-chain nitrile-based cross-linked sulfonated poly(arylene ether nitrile) (SPEN) membrane is expected to be an ideal material for preparing proton exchange membranes (PEMs). A series of SPEN-60-COOH-x with different carboxyl content have been synthesized through fixing the content of sulfonic group at 60% in the experiment and changing the molar fraction of phenolphthalein (PPL). Then, the SPEN-60-CN-x were prepared by grafting nitrile groups onto the SPEN-60-COOH-x via carboxyl groups. NMR and FTIR were used to characterize the construction of polymers. The TGA results showed that the thermal stability of CSPEN-60-CN-x was significantly improved by the cross-linking network structure formed by side chain nitrile groups. As the degree of cross-linking increases, the water uptake of CSPEN-60-CN-x membranes showed a downward trend. The results also indicated that the dimension stability of CSPEN-60-CN-x membranes was effectively improved by cross-linking reaction, and the dimension stability of CSPEN-60-CN-x membranes was further improved by increasing the content of nitrile groups. The selectivity of CSPEN-60-CN-x membranes increased significantly after crosslinking. CSPEN-60-CN-30 has the highest selectivity of 5.37 x 10(5) S.s.cm(-3) among all the membranes, about 11.9 times that of Nafion 117.