Partially fluorinated poly(arylene ether)s bearing long alkyl sulfonate side chains for stable and highly conductive proton exchange membranes

Condensation polymerization of two diallyl-containing bisphenol monomers with decafluorobiphenyl catalyzed by CsF at low temperatures yielded quantitatively the diallyl-containing fluorinated poly(arylene ether)s, which after the thiol-ene click reaction with sodium 3-mercapto-1-propanesulfonate yielded sulfonated fluorinated poly(arylene ether)s (SFPAEs) with long alkyl sulfonate side-chains. The sulfonate groups were spaced by 7 atoms away from the aromatic backbone, in stark contrast to the previous reports where only 6 spacing atoms could be achieved using a similar chemistry but rather harsh reaction conditions. Two series of SFPAEs based on bisphenol A and bisphenol S units, respectively, were both found to exhibit distinct phase separation and enhanced proton conductivity. Specifically, the SFPAE-A-70 with an ion exchange capacity (IEC) of 1.62 mmol g−1 exhibited an in-plane proton conductivity of 90 mS cm−1 at room temperature, which was slightly higher than that of Nafion 212. Furthermore, all of the SFPAEs showed significantly improved oxidative stability in Fenton's reagent when comparing to non-fluorinated analogs. This study offered a new strategy for the synthesis of highly branched ionomers with long and flexible aliphatic side-chains for high performance PEMs.