PURPOSE: A crosslinked polystyrene in which alkylene glycol links to benzyl carbons is oxidatively cleaved at ether linkages to produce at a high reaction rate the titled carboxylic acid derivative used as a weak-acid ion-exchange resin.

CONSTITUTION: A crosslinked polystyrene in which an alkylene glycol of formulaI(R is lower alkylene; n is positive integer; X is H, residue of ether or ester, or group in crosslinked polystyrene of formula II) or formula III (Y is crown ether) or its derivative or a crown ether links to benzyl carbons is oxidized with oxygen to cleave the ether linkages and convert the benzyl carbons into carboxyl groups to give the objective carboxylate crosslinked polystyrene.