| abstract |
A process for producing aqueous solutions of acrylic acid polymers by polymerization of acrylic acid in feed operation with a free-radical starter in the presence of hypophosphite in water as solvent, which comprises (i) initially charging water and optionally acrylic acid in acidic, unneutralized form, optionally one or more ethylenicaliy unsaturated comonomers, optionally aqueous hypophosphite solution and optionally initiator, (ii) adding acrylic acid in acidic, unneutralized form, optionally one or more ethylenicaliy unsaturated comonomers, aqueous free-radical starter solution and aqueous hypophosphite solution, (iii) adding a base to the aqueous solution after termination of the acrylic acid feed, wherein the comonomer content does not exceed 30 wt% based on the total monomer content, wherein the acrylic acid, the aqueous free-radical starter solution and the aqueous hypophosphite solution are added such that the molar ratio x of acrylic acid to phosphorus-bound hydrogen [AA]/[P-H] over a time period in which at least 75% of the acrylic acid is converted has a value x which is constant to within ± 0.5 and is in the range from 0.8 to 2. |