Polyaromatic Perfluorophenylsulfonic Acids with High Radical Resistance and Proton Conductivity

We report on the straightforward metal-free synthesis of poly(p-terphenyl perfluorophenylsulfonic acid)s by efficient superacid-catalyzed Friedel-Crafts polycondensations of commercially available perfluoroacetophenone and p-terphenyl, followed by sulfonation of the pendant pentafluorophenyl groups via a selective and quantitative thiolation-oxidation procedure. The stiff and well-defined polymer structure with precisely sequenced and highly acidic units induces efficient ionic clustering, restricted water uptake and swelling, excellent resistance against radical attack, and very high proton conductivity. At 120 °C, the conductivity reaches 40 and 232 mS cm^-1 at 50 and 90% relative humidity, respectively, which very closely matches the benchmark Nafion NR212 membrane. The properties are further tuned by copolymerizations. Overall, the results demonstrate that these materials possess a very attractive combination of characteristics for use as high-performance proton-exchange membranes for fuel cells and water electrolyzers.