Synthesis and characterization of aniline-containing anion-conducting polymer electrolyte membranes by radiation-induced graft polymerization

Poly(trimethylaminostyrene hydroxide)-grafted poly(ethylene-co-tetrafluoroethylene) (ETFE) membranes (An-AEM/OH) were prepared by the radiation-induced graft polymerization of N,N-dimethylaminostyrene and successive quaternization and anion-exchange reactions. An-AEM/OH with an ion-exchange capacity (IEC) of 1.59 mmol/g exhibited a conductivity of 74 mS/cm (60°C) and a water uptake of 66%. These values were lower than those of poly(vinylbenzyltrimethylammonium hydroxide)-grafted ETFE (BA-AEM/OH) with a similar IEC. The conductivities of An-AEM/OH with IECs = 0.67 mmol/g and 1.59 mmol/g decreased to 40% and 46% of the initial values after a week, while the membranes maintained their shape even after immersion in 1 M KOH at 80°C for 3 weeks. An-AEM/OH exhibited higher chemical stability than BA-AEM/OH. The main degradation route is confirmed to be the nucleophilic attack of hydroxide ions on the methyl groups of the aniline nitrogen from the results of thermal and chemical stability.