Anionic water-in-water polymer dispersion, method for the production thereof and its use

A process for producing a water-in-water dispersion of one or more at least one finely dispersed, water-soluble and/or water-swellable anionic polymers A dispersed in a continuous aqueous phase, wherein the polymer A comprises one or more anionic monomer units and, optionally, one or more of a non-ionic, amphiphilic, and cationic monomer units and the polymer A has a Mw of >1.0×106 g/mol and, wherein the aqueous phase of the dispersion comprises polymeric dispersing agent B and said polymeric dispersing agent B consists of potassium polyacrylate having a weight average molecular weight Mw of 65,000-75,000 g/mol, the process comprising:

• in a first stage, free radically polymerizing a monomer composition comprising at least the anionic monomer units and, optionally, the non-ionic, amphiphilic, and cationic monomer units in the presence of at least 5% by weight of said potassium polyacrylate dispersing agent B based on the total weight of the dispersion and from 0.9% by weight to 1.5% by weight of an inorganic salt based on the total weight of the dispersion, to form a reaction mixture, and
• in a second stage, on completion of said radical polymerization, diluting the reaction mixture with a second amount of said potassium polyacrylate dispersing agent B to form the water-in-water dispersion,
• wherein the anionic monomers are selected from the group consisting of
• a.) an olefinically unsaturated carboxylic acid, a carboxylic anhydride, a water-soluble alkali metal salt thereof, an alkaline earth metal salt thereof, and an ammonium salt thereof.