Synthesis and Characterization of Perfluoroalkyl Sulfonic Acid Functionalized Polyphosphazene for Proton-Conducting Membranes

Polyphosphazenes containing perfluoroalkyl sulfonic acids (PSA-P) were synthesized by the copper-catalyzed coupling reaction of poly[(4-bromophenoxy)(phenoxy)phosphazene] with potassium 1,1,2,2-tetrafluoro-2-(1,1,2,2-tetrafluoro-2-iodoethoxy) ethanesulfonate. Two synthetic protocols have been developed to obtain the polymers and 1, 10-phenanthroline was found benefit for improving the efficiency of the coupling reaction. The PSA-P membranes prepared by solution casting showed excellent thermal stability, oxidative stability and low swelling ratios. In addition, compared with the sulfonated poly[bis(phenoxy)phosphazene] membrane with similar IEC, the PSA-P membrane displayed significant superiority in proton conductivity, water resistance, oxidative and thermal stability, indicating that it is a good candidate for proton exchange membranes.