Robust Proton-Exchange Membranes Based on Perfluorosulfonic Acid-Functionalized Poly(phenyl-alkane) and Polyxanthene: Effects of Skeletal Structures on Membrane Properties

Perfluorosulfonic acid-functionalized aromatic polymers are attractive alternatives to commercial Nafion membranes; however, the heteroatoms (O, S, etc.) in traditional poly(arylene ether)s can initiate undesired chemical degradation by radical specie attacks. Herein, two robust proton-exchange membranes (PEMs), PA-BP-PFSA and PX-BP-PFSA, based on perfluorosulfonic acid-functionalized poly(phenyl-alkane) and polyxanthene, respectively, were prepared by copper-catalyzed postfunctionalization of poly(phenyl-alkane) and polyxanthene precursors containing bromine substituents. Molecular simulation results showed that polyxanthene had a higher rigidity than that of poly(phenyl-alkane). Hence, PX-BP-PFSA had higher Brunauer-Emmett-Teller surface area (124 versus 58 m(2) g(-1)) and fractional free volume (0.303 versus 0.228), compared to that of PA-BP-PFSA. The ionic clusters in PA-BP-PFSA were obviously larger than those in PX-BP-PFSA and showed a higher water uptake and swelling ratio. PX-BP-PFSA exhibited higher conductivity than that of PA-BP-PFSA due to its better microporous nanochannels for ion transport. Both PEMs exhibited an excellent oxidative stability, with no noticeable changes in the thermogravimetric analysis and H-1 and F-19 NMR spectra after immersion in Fenton's reagent for 2 h at 80 degrees C. This work presents a feasible approach to develop highly robust perfluorosulfonic acid-functionalized PEMs and provides meaningful insights into the structure-property relationship.