Cross-Linked Sulfonated Poly(arylene ether sulfone) Membranes Formed by in Situ Casting and Click Reaction for Applications in Fuel Cells

Sulfonated poly(arylene ether sulfone) membranes with cross-linked structures (C-SPAES) were simply prepared by simultaneously casting and heating the polymer solutions composed of sulfonated poly(arylene ether sulfone) with azidomethyl side groups (SPAES-N-3), cross-linkers such as 1,4-diethynylbenzene and 4,4'-diazido-2,2'-stilbenedisulfonic acid disodium salt tetrahydrate, and a click reaction catalyst such as CuBr and N,N,N',N,N-pentamethyldiethylenetriamine in N,N-dimethylacetamide, where SPAES-N-3 were prepared by the substitution of sulfonated PAES (SPAES) through chloromethylation followed by azidation reaction. C-SPAES membranes obtained using the optimum amount of the cross-linkers showed much improved chemical and physical stabilities and mechanical strength compared with linear SPAES membrane. Since the cross-linked structures were formed by the cross-linker having sulfonic acid groups, C-SPAES membranes showed higher ion exchange capacity and proton conductivity than the linear SPAES membrane. Although the C-SPAES membrane can absorb more water than the linear SPAES membrane, less volume expansion was observed due to their physically stable cross-linked structures.