Transport properties of anion exchange membranes prepared by the reaction of crosslinked membranes having chloromethyl groups with 4-vinylpyridine and trimethylamine

The electrodialytic transport properties of new anion exchange membranes we re evaluated that included the transport numbers of various anions, sulfate , bromide, fluoride, and nitrate ions, relative to chloride ions and curren t efficiency. The anion exchange membranes were prepared by the reaction of copolymer membranes crosslinked to different extents having chloromethyl g roups with 4-vinylpyridine to form a ladder-like polymer in the membranes a nd then with trimethylamine to convert the remaining chloromethyl groups to benzyl trimethylammonium groups. The transport numbers of the sulfate and fluoride ions relative to the chloride ions were markedly less for the memb ranes that had been reacted with 4-vinylpyridine and then with trimethylami ne compared with those of the membranes that had been reacted only with tri methylamine. On the other hand, the selective permeation of nitrate and bro mide ions through the membranes was enhanced by the reaction with 4-vinylpy ridine although the membranes became tighter by the reaction. The decrease in permeation of the sulfate ions was attributed to a synergistic effect in volving the decrease in sulfate ions ion-exchanged with the membranes and t he decrease in mobility of the sulfate ions in the membranes with a low deg ree of crosslinking. Though the ion-exchanged sulfate ion content was the l owest in the highly crosslinked membranes, the mobility ratio between the s ulfate ions and chloride ions did not decrease in the membranes. However, t he increase in the permeation of nitrate ions was based on the increase in the ion-exchanged amount of nitrate ions with the membrane, and not the cha nge in the mobility ratio between the nitrate and chloride ions. The format ion of the ladder-like polymer in the membrane matrix brought on a decrease in the hydrophilicity of the membranes due to pyridine groups and an incre ase in their tightness. The current efficiency of all membranes was greater than 99% during the electrodialysis of 0.50 N salt solutions. (C) 1999 Joh n Wiley & Sons, Inc.