Patent ID: 8846773

Claim:
A method for manufacturing a cation exchange resin, the method comprising: (1) copolymerizing a monovinyl aromatic monomer and a cross-linkable aromatic monomer, then crosslinking, to obtain a cross-linked copolymer; (2) specifying a content of a leachable compound or oligomer represented by formula (I) to be 400 μg or less relative to 1 g of the cross-linked copolymer, wherein: Z represents a hydrogen atom or an alkyl group; l represents a natural number; and the specifying comprises at least two steps selected from the group consisting of (i) adjusting the polymerizing temperature within the range of room temperature or higher to 250° C. or lower, (ii) employing at least one oxygen-degassed monomer., (iii) employing at least one monomer from which a polymerization inhibitor is removed, (iv) employing a cross-linkable aromatic monomer having reduced impurities, (v) adjusting a proportion of the cross-linkable aromatic monomer within the range of 0.5 to 30 percent by weight relative to a total weight of monomers, and (vi) washing the cross-linked copolymer with a solvent at a washing temperature ranging from 50° C. or higher to 150° C. or lower; and then (3) sulfonating the cross-linked copolymer to form a sulfonylated cross-linked copolymer.