Basf Aktiengesellschaft

Juergen Beck

Heinrich Hartmann

Manfred Niessner

Christos Vamvakaris

Stefan Wickel

Bernhard H Nowakowsky

Walter Schneider

Thomas Meyer

Andreas H Kemna

Finely divided, water-soluble polymers are prepared by polymerization of water-soluble, monoethylenically unsaturated monomers in not less than 20% strength by weight aqueous solution in the presence of a polymerization initiator in a kneader by a process in which from 0.1 to 10% by weight, based on the total monomers, of a surfactant are used in the polymerization, the polymerization initially being carried out to a conversion of the monomers of not less than 60% in the absence of the surfactant or in the presence of not more than 50% of the amount of surfactant, and the remaining amount of surfactant then being added to the reaction mixture and the polymerization completed. The addition of surfactant causes the polymer gel to disintegrate with formation of fine particles.

Preparation of finely divided, water-soluble polymers

The water absorption capacity of crosslinked, water-swellable polymers is improved by a process in which a water-containing, finely divided polymer gel having a solids content of from 20 to 65% by weight is treated with steam at not less than 50.degree. C., the solids content of the water-containing polymer gel increasing by not more than 30% by weight, and the polymer gel is then dried in a conventional manner.

Improving the water absorption capacity of crosslinked, water-swellable

Crosslinked, finely divided, water-absorbing polymers are prepared in a batchwise process by copolymerization of 100 parts by weight of a monomer mixture of acrylic acid or methacrylic acid, each of which is neutralized with from 0 to 100 mol% of an alkali metal or ammonium base,or acrylamide, methacrylamide or N-vinylpyrrolidone with, as a crosslinking agent, from 0.01 to 5 parts by weight of a monomer containing two or more ethylenically unsaturated double bonds in 20-80% by weight aqueous solution in the presence of an initiator in a multistage procedure in a batchwise mixing apparatus wih constant thorough mixing in all stages, in the first stage the aqueous monomer solution being copolymerized at from 45.degree. to 95.degree. C. and under from 0.1 to 0.8 bar with removal of some of the water by distillation, in the second stage the copolymerization being completed at from 100.degree. to 170.degree. C. under a pressure of up to 8 bar, and in the third stage the water content of the resulting finely divided copolymer being decreased to 0.5-10% by weight under reduced pressure.

Batchwise preparation of crosslinked, finely divided polymers

Finely divided, gel-like crosslinked polymers are prepared by a continuous method in which a monomer mixture which contains, per 100 parts by weight of acrylic acid or methacrylic acid, from 50 to 100 mol % of which in each case are neutralized, acrylamide, methacrylamide or N-vinylpyrrolidone, from 0 to 30 parts by weight of other water-soluble monoethylenically unsaturated monomers and from 0 to 20 parts by weight of water-insoluble monoethylenically unsaturated monomers is copolymerized with from 0.01 to 5 parts by weight of a crosslinking agent, in 20-65% strength by weight aqueous solution in the presence of an initiator at from 45.degree. to 95.degree. C. in a single-screw cylindrical mixer whose stirrer shaft possesses disk segments which have, at the outer end, mixing bars which are arranged in a manner such that the substances fed in at the entrance of the mixer are conveyed in the axial direction to the exit of the mixer, the aqueous monomer solution in the mixer is polymerized under from 100 to 800 mbar, and some of the water is removed during the polymerization, so that a crumb-like gel having a solids content of from 30 to 70% by weight is discharged.

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Viernheim, Germany

Juergen Beck