Water-soluble copolymer (A) has K value 8-100 (determined by the method of Fikentscher on a 1 wt.% soln. of the Na salt at 25 deg. C and pH 7) and comprises (molar) (a) 15-99% at least one monoethylenically unsatd. 5-6C monocarboxylic acid (I); (b) 0.5-84.5% at least one monoethylenically unsatd. 4-6C dicarboxylic acid (II); (c) 0-20% at least one 2-6C hydroxyalkyl ester (III) of monoethylenically unsatd. 3-6C carboxylic acids; (d) 0-30% other copolymerisable, water-soluble, monoethylenically unsatd. monomers; and (e) 0.5-15% at least one comonomer (IV) with at least 2 ethylenically unsatd., non-conjugated double bonds and at least one COOX gp. (X = H, alkali or alkaline earth metal equiv. or NH4). Specifically, (A) may also include 0.05-10% at least one comonomer, other than (IV), having at least 2 non-conjugated ethylenic double bonds.
