Preparation of copolymers of monoethylenically unsaturated monocarboxylic acids and dicarboxylic acids

A process for the preparation of copolymers containing monoethylenically unsaturated monocarboxylic acids and dicarboxylic acids as copolymerized monomer units, which comprises copolymerizing:

• a) 10-60% by weight, based on the total weight of the monomers, of a monoethylenically unsaturated dicarboxylic acid having 4-6 carbon atoms or an anhydride thereof or an alkali metal salt thereof;
• b) 40-90% by weight of a monoethylenically unsaturated monocarboxylic acid having 3-10 carbon atoms or an alkali metal salt thereof;
• and
• c) 0-20% by weight of another monoethylenically unsaturated monomer not having carboxyl groups which is copolymerizable with a) and b);
• in an aqueous medium in the presence of 0.5-5% by weight, based on the total weight of the monomers, of a water-soluble initiator consisting of hydrogen peroxide with a total monomer content of from 20-70% by weight at 60.degree.-150.degree. C. and wherein monomers a) and b) are 20-80% neutralized during said polymerization reaction, thereby forming a copolymer having less than 1.5% by weight of unreacted dicarboxylic acids therein.