Improved amphoteric ion exchanger and its manufacturing method

This invention relates to an amphoteric ion exchanger comprising a block copolymer composed of a polymer chain poly A(-) having a cation exchange group, poly B(+) polymer chain having an anion exchange group, and poly C polymer chain not having an ion exchange group, among which the constituent poly chain C is produced by adding hydrogen to a diene-group polymer. A multiphased structure material having both regions of cation and anion exchange groups is expected to provide an unusual characteristic because of its effect of fixed level of amphoteric electric charge. An amphoteric ion exchange is to be manufactured with the use of a three-dimensional block copolymer having a diene-group polymer chain as a constituent block capable of being easily bridgeable without introducing an ion exchange group in addition to the use of polymer chains to which a cation or anion exchange can be introduced. This method requires, at the same time, very careful selections of reaction conditions for sulfonizing the added diene-group polymer, which does not have sufficient chemical strength. The present inventors have found that an amphoteric ion exchange with excellent chemical strength can be manufactured by hydrogenating the polydiene group region of a block copolymer, consisting of three constituents having such a diene-group polymer chain.