Method for manufacturing block copolymer

A method for manufacturing by living anion polymerization a ternary copolymer of a molecular structure formed with a macro-molecule which has a cation exchange group, a macro-molecule which has an anion exchange group and another macro-molecule which does not have any ion exchange group therein linked together into a straight chain, said method comprising:

• obtaining a crude ternary block copolymer by carrying out block copolymerization of a monomer component which is capable of forming a macro-molecular domain permitting introduction of a cation exchange group thereinto, a monomer component which is capable of forming a macro-molecular domain permitting introduction of an anion exchange group thereinto and a monomer component which is capable of forming another macro-molecular domain which contains no ion exchange group;
• a process of shaping said crude ternary block copolymer into a desired form;
• introducing a cation exchange group into said macro-molecular domain which permits introduction of a cation exchange group thereinto;
• and introducing an anion exchange group into said macro-molecular domain which permits introduction of an anion exchange group thereinto;
• wherein the percentage by weight of the monomer component which is capable of forming said macro-molecular domain having no ion exchange group is 30-90%, and the percentage by weight of the monomer which is capable of forming said macro-molecular domain permitting introduction of a cation exchange group and that of the monomer component which is capable of forming said macro-molecular domain permitting introduction of an anion group are at least 5% respectively.