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 deri vatives. The anion exchange membranes obtained showed excellent electr ochemical properties in electrodialysis. The transport numbers of sulf ate ions, bromide ions, nitrate ions, and fluoride ions relative to ch loride ions were evaluated in connection with the species of a substit uent and the position of the substituent in the pyridinium groups. In general, when a hydrophilic substituent (methanol groups) existed at t he 2-position of the pyridinium groups, nitrate ions and bromide ions, which are less hydrated, permeated through the membranes with difficu lty, and sulfate ions permeated selectively through the membranes. On the other hand, when hydrophobic groups, for example, ethyl groups, ex isted at the 2-position of the pyridinium groups, bromide ions and nit rate ions permeated selectively through the membranes and fluoride ion s had difficulty permeating through the membranes. The carbon number o f the alkyl chain of 4-alkyl pyridinium groups also affected permeatio n 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 rel ated to selective permeation of the anion through the membranes, perme ation of sulfate ions was not as sensitive to the hydrophilicity of th e membranes. (C) 1998 John Wiley & Sons, Inc.