Chemically Stable, Highly Anion Conductive Polymers Composed of Quinquephenylene and Pendant Ammonium Groups

To evaluate the effect of five consecutive phenylene units on the properties of anion conductive polymer membranes, a series of quaternized copolymers (QP-QAF) composed of quinquephenylene and fluorene groups functionalized with pendant hexyltrimethylammonium groups were designed and synthesized. Precursor copolymers, QP-AF, with controllable copolymer compositions were synthesized by Yamamoto coupling reaction as high molecular weights. Quaternization of QP-AF using dimethyl sulfate followed by solution casting provided bendable and tough QP-QAF membranes with the ion exchange capacity (IEC) ranging from 0.80 to 2.78 mequiv g ^-1 . The QP-QAF membranes contained phase-separated morphology due to the hydrophilic/hydrophobic differences in the components as confirmed by TEM images. High hydroxide ion conductivity (up to 134 mS cm ^-1 in water at 80 °C) was obtained with the membrane (IEC = 2.25 mequiv g ^-1 ). The membranes were stable in strongly alkaline conditions (4 M KOH at 80 °C) for 1000 h. An H ₂ /O ₂ alkaline fuel cell using the QP-QAF membrane exhibited 248 mW cm ^-2 of the maximum power density at 60 °C under fully humidified conditions.