Anion Exchange Membranes Prepared by Amination of Cross-linked Membranes Having Chloromethyl Groups with 4-Vinylpyridine and Trimethylamine

摘要

Ion exchange membranes have been required to have perrnselectivity between ions with the same charge: seawater concentration to produce sodium chloride, acid concentration from acidic solutions, etc. In particular, concentration of nitrate ions in groundwater has been greatly increasing due to excess use of artificial fertilizers. Electrodialytic removal of nitrate ions is the most promising method to solve this problem because nitrate ion permselective anion exchange membranes can be developed At the same time, it is desirable to separate ions with the same charge each other by electrodialysis 1). It is well known that 4-vinylpyridine polymerizes by quaternization with alkyl halides 2). Many studies have been done in the presence of polystyrene sulfonic acid, polyacrylic acid, etc. This is called matrix polymerization. Though polymerization of 4-vinylpyridine with alkylation was mainly studied in solutions, the reaction of 4-vinylpyridine with haloalkyl groups bonded to cross-linked polymer matrix is interesting in preparation of anion exchange membranes having permselectivity for specific anions because a ladder-like polymer, of which one polymer is cross-linked, is formed in the membrane. The obtained membranes should have highly tight structure. In this work, after cross-linked copolymer membranes having chloromethyl groups were reacted with 4-vinylpyridine and then with trimethylamine to completely aminate chloromethyl groups in the membrane, transport properties of the obtained membranes were evaluated: basic electrochemical properties and transport numbers of various anions relative to chloride ions.