High performance sulfonated poly(phthalazinone ether phosphine oxide)s for proton exchange membranes

A series of sulfonated poly(phthalazinone ether phosphine oxide)s with disulfonated moieties (dsPPEPO) were synthesized. Sulfonated poly(phthalazinone ether phosphine oxide)s with mono-sulfonated moieties (msPPEPO) were also prepared for comparative study. These two series of polymers represented two kinds of distribution modes of sulfonic acid side groups. The distribution mode of the sulfonic acid side groups within membranes could remarkably change their microstructure. As a result, dsPPEPO exhibited better dimensional and oxidative stability as compared to msPPEPO on condition of equal sulfonation degree. Moreover, the as-synthesized dsPPEPO showed enhanced proton conductivity further by increasing sulfonation degree while remaining excellent dimensional and oxidative stability. Therefore, the resulting membranes displayed excellent overall properties. For example, the dsPPEPO membrane with a sulfonation degree of 110% presented a lower swelling and much higher proton conductivity than those of Nafion 117. Its oxidative stability was also comparable to the highly durable aromatic PEMs.