Compounds represented by the formula ##STR1## and addition polymers thereof where m is an integer from 2 to about 10, x--is chlorine, hydroxy, carboxy or--AC--R).dbd.CH.sub.2--R is hydrogen or methyl, --R' is an ethylene or propylene group and--AC--R).dbd.CH.sub.2is one of ##STR2## These compounds and their addition polymers form complexes with alkali metal or alkaline earth metal salts and permit the concentration of aqueous solutions of said salts. For example, a compound of the formula ##STR3## is polymerized with an azobis(isobutyronitrile) catalyst to form addition polymers of the repeating unit ##STR4## When cross-linked, rendering it water-insoluble, such an addition polymer concentrates an aqueous solution of sodium chloride when contacted with same at about 0.degree. C.