Sulfo-Phenylated Polyphenylenes Containing Sterically Hindered Pyridines

We systematically investigated the effect of incorporating a sterically hindered pyridyl group into a sulfo-phenylated polyphenylene to control the polymer’s physicochemical properties through acid–base interactions. Homopolymers with similar molecular weights and comparable structures that vary by only one atom (N– vs C−) per repeat unit along the polymer chain were prepared. Compared to a non-pyridyl reference membrane, incorporation of a pyridyl group improves the oxidative stability against free radicals, increases the elongation at break to 55% (from 37%), and enhances the thermal stability to 326 °C (from 246 °C). In an accelerated fuel cell degradation test, polymeric membranes containing the sterically encumbered pyridyl unit exhibited exceptional stability (0.16 mV h–1 degradation rate over 1000 h) and retained ∼80% of their peak power density over this time.