A facile crosslinking method of polybenzimidazole with sulfonyl azide groups for proton conducting membranes

A facile crosslinking method of polybenzimidazole (PBI) with sulfonyl azide groups (sPBI-SA) for proton conducting membranes is proposed. Thermally crosslinkable sPBI-SA is synthesized from sulfonated PBI (sPBI) and sodium azide. The structures of sPBI, sPBI-SA, and crosslinked sPBI are confirmed by FTIR and 1H NMR. Upon heating, sPBI-SA loses nitrogen and form nitrene, which reacts with CH-bond of the backbone of another chain of PBI via the reactions of hydrogen abstraction, recombination, or CH-bond insertion. The crosslinking structure of PBI membranes is thus formed. Compared with the uncrosslinked membranes, the crosslinked sPBI membranes exhibit improved tensile strength, migration stability of phosphoric acid (PA), dimensional stability, and chemical oxidative stability. Whereas, the doping ability of PA and the proton conductivity of the crosslinked membranes decrease a little.