Abstract: A method for demineralizing water or an aqueous solution, which comprises contacting the water or the aqueous solution to be treated to a strongly basic anion exchanger made of a crosslinked polymer having a constituting unit of the following formula (I): ##STR1## wherein A is a C.sub.1-2 linear alkylene group, B is a C.sub.4-8 linear alkylene group, each of R1, R2 and R3 which may be the same or different, is a C.sub.1-4 alkyl group or a C.sub.2-4 alkanol group, X is a counter ion coordinated on the ammonium group, and the benzene ring D may have an alkyl group or a halogen atom as a substituent.

Abstract: A method for producing an acrylonitrile crosslinked copolymer, which comprises copolymerizing, as polymerizable monomers, acrylonitrile, an alkyl ester of acrylic acid or methacrylic acid, an aliphatic or alicyclic crosslinkable unsaturated monomer having at least two allyl groups, and an aromatic crosslinkable polyunsaturated monomer, in the presence of from 10 to 45% by weight, based on the total amount of the polymerizable monomers, of an inert organic solvent having a specific gravity of at least 1.0.

Abstract: A method for producing an acrylonitrile crosslinked copolymer, which comprises copolymerizing, as polymerizable monomers, acrylonitrile, an alkyl ester of acrylic acid or methacrylic acid, an aliphatic or alicyclic crosslinkable unsaturated monomer having at least two allyl groups, and an aromatic crosslinkable polyunsaturated monomer, in the presence of from 10 to 45% by weight, based on the total amount of the polymerizable monomers, of an inert organic solvent having a specific gravity of at least 1.0.

Abstract: A process for producing an ion exchange resin having a specific surface area of at least 0.04 m.sup.2 /g, an ion exchange resin produced by the process, and a method for removing ionic and noinionic impurities from a condensate by means of the ion exchange resin produced by the process. The process comprises the steps of: (1) uniformly imbibing a monomer mixture comprising a bifunctional unsaturated aromatic monomer and a monofunctional unsaturated aromatic monomer into aromatic crosslinked copolymer particles comprising a monofunctional unsaturated aromatic monomer and a bifunctional unsaturated aromatic monomer and having a porosity of not more than 0.2 ml/g; (2) polymerizing the monomer mixture in the presence of a polymerization initiator; and (3) introducing an ion exchange group into the resulting copolymer particles. The ion exchange resin has a large specific surface area and high physical strength and is capable of removing both ionic and noinionic impurities from a condensate.