Fundamental studies of a new series of anion exchange membranes: Membranes prepared through chloroacetylation of poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) followed by quaternary amination

Abstract

A novel route for preparing anion exchange membranes from a linear engineering plastics polymer, poly(2,6-dimethyl-1,4-phenylene oxide) (PPO), is presented in this paper. This method employed Friedel–Crafts chloroacetylation to avoid the use of the carcinogenic chemicals: chloromethylmethylether (CME) or bis-chloromethylether (BCME). They both are broadly used in the conventional chloromethylation process. Furthermore, the method presented in the paper extended the polymers for anion exchange membrane preparation from those containing benzyl groups, such as PPO, to general aromatic polymers. The reaction conditions in chloroacetylation processes such as the quantity of the added catalyst and the reaction temperature, and the amination processes such as amine concentration, amination temperature and amination time were fully investigated. The products of Friedel–Crafts reaction were identified by both FTIR and 1H NMR. The final anion exchange membranes were characterized by ion exchange capacity, water content and membrane area resistance. It was founded that the medium degree of substitution, e.g. 50%, provided a flexible, mechanically useable membrane. The optimum reaction conditions were found to be: amination time = 48–50 h, amination concentration = 0.91 mol/l and amination temperature = 35–45 °C. The intrinsic properties of the membranes under these conditions were ion exchange capacity [IEC] = 1.15 mequiv./g dried membrane, water content = 0.4–0.6 g/g wet membrane and area resistance = 0.2 Ω cm 2.