Microwave-assisted Diels-Alder polycondensation of proton conducting poly(phenylene)s

An exploratory microwave-assisted synthesis of a promising proton-conducting, Diels-Alder poly(phenylene) is reported and comprehensively compared against a traditional, thermal polymerization approach. A 24-fold reduction in reaction time is achieved by microwave synthesis. Characterization of polymers prepared by microwave-assisted synthesis vs. the thermal approach reveals little difference in their physicochemical and solid state electrochemical properties. However, membranes cast from polymers prepared by microwave synthesis possess a 7.0% increase in tensile strength but 38.6% lower elongation at break, which may be due to an increase in the number of para - para linkages found along the polymer backbone. High ex situ proton conductivities, up to 186 mS cm −1 at 95% RH and 80 °C, are obtained for cast membranes. When assessed in situ as fuel cell membranes, the microwave-assisted polymer provided a similar maximum power density (1217 mW cm −2 ) to that prepared thermally (1206 mW cm −2 ). The consistency between the materials synthesized highlight the efficacy of microwave chemistry for rapid, scalable, and reproducible synthesis of advanced functional materials, such as proton-conducting Diels-Alder poly(phenylene)s. A 24-fold reduction in reaction time is achieved in the preparation of sulfonated poly(polyphenylene)s using microwave synthesis.