Preparation and properties of anion exchange membranes having pyridinium or pyridinium derivatives as anion exchange groups

Anion exchange membranes with pyridinum groups and various pyridinium derivative groups were prepared from a copolymer membrane composed of chloromethylstyrene and divinylbenzene, and pyridine and pyridine derivatives. The anion exchange membranes obtained showed excellent electrochemical properties in electrodialysis. The transport numbers of sulfate ions, bromide ions, nitrate ions, and fluoride ions relative to chloride ions were evaluated in connection with the species of a substituent and the position of the substituent in the pyridinium groups. In general, when a hydrophilic substituent (methanol groups) existed at the 2-position of the pyridinium groups, nitrate ions and bromide ions, which are less hydrated, permeated through the membranes with difficulty, and sulfate ions permeated selectively through the membranes. On the other hand, when hydrophobic groups, for example, ethyl groups, existed at the 2-position of the pyridinium groups, bromide ions and nitrate ionspermeated selectively through the membranes and fluoride ions had difficulty permeating through the membranes. The carbon number of the alkyl chain of 4-alkyl pyridinium groups also affected permeation of nitrate ions and bromide ions due to the change in hydrophilicity of the membranes. Though the hydration of the anions and the species of the substituent at the 2-position of the pyridinium groups were related to selective permeation of the anion through the membranes, permeation of sulfate ions was not as sensitive to the hydrophilicity of the membranes. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 49–58, 1998