Basf Aktiengesellschaft

Bernhard H Nowakowsky

Heinrich Hartmann

Christos Vamvakaris

Juergen Beck

Graham E McKee

Klaus Muehlbach

Rainer Theysohn

Rainer Bueschl

A thermoplastic molding composition composed of, based on the total of A, B, C and D,

Blends of styrene-acrylonitrile polymer, styrene-methyl

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.

Continuous preparation of finely divided gel-like crosslinked polymers

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Ludwigshafen, Germany

Bernhard H Nowakowsky