Fundamental studies of a new series of anion exchange membranes: Membranes prepared from bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) and pyridine

Anion exchange membranes with pyridinium groups were prepared by aminating the base membranes of 100% bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) with pyridine. Properties of the prepared membranes were characterized by ion exchange capacity (IEC), water content, area resistance, membrane potential and the selectivity for counter-ions (chloride ions). The results showed that the membranes possess relatively low IEC, high water content and low membrane potential, which was due to the erosion of pyridine during the amination reaction. To decrease the erodibility of the membranes, an attempt to cross-link the base membranes with ammonia before the reaction with pyridine was conducted. It was found that cross-linking with ammonia helped to maintain the stability of the membrane in the reaction bath of pyridine, enhanced the IEC and membrane potentials, and decreased the water content. To further improve the properties, the membranes were immersed in the aqueous trimethylamine (TMA) solution after aminating with pyridine. It was shown that the amination reaction with TMA further increased the membrane's IEC, water content and membrane potential, and decreased the membrane area resistance. Thus, by properly controlling the cross-linking and the amination processes, membranes with ideal properties for application in many industrial separation processes, such as concentrating or removing of specific anions from a solution, can be prepared.