Synthesis and property comparison of mono-, di-, and trisulfonated poly(arylene ether phosphine oxide)s with fluorenyl moieties as proton exchange membranes

The microstructure of proton exchange membranes (PEMs) is seldom to be adjusted by the distribution modes of the sulfonic-acid groups to enhance their overall properties. Herein, monosulfonated poly(arylene ether phosphine oxide)s (msPAEPO), disulfonated poly(arylene ether phosphine oxide)s (dsPAEPO), and trisulfonated poly(arylene ether phosphine oxide)s (tsPAEPO) with fluorenyl moieties are synthesized. The distribution modes of the –SO3H groups and the structural unit of diphenol monomer markedly affect the properties of the resulting PEMs. From msPAEPO to dsPAEPO, and then to tsPAEPO, the size of the hydrophilic ionic channels enhances but their connectivity reduces, thus forming distinct microstructures. The resulting PEMs achieve superior comprehensive properties by further adjusting sulfonation degree. As a result, the approach of the distribution adjustment of the sulfonic acid groups is equally effective to tune the microstructure and properties of the sPAEPO membranes with different structural units of diphenols and can be extended to fabricate various high-performance PEMs.