FINELY DIVIDED STARCH-CONTAINING POLYMER DISPERSIONS, METHOD FOR THE PRODUCTION THEREOF AND USE THEREOF AS SIZING AGENT IN PAPER MANUFACTURING

Finely divided, starch-containing polymer dispersions which are obtainable by free radical emulsion polymerization of ethylenically unsaturated monomers in the presence of at least one redox initiator and starch, (a) from 30 to 60% by weight of at least one optionally substituted styrene, (b) from 1 to 60% by weight of at least one C1-C12-alkyl acrylate and/or C1-C12-alkyl methacrylate, (c) from 0 to 10% by weight of at least one other ethylenically unsaturated copolymerizable monomer, being used as ethylenically unsaturated monomers and (d) from 15 to 40% by weight of at least one degraded starch which has a molar mass Mw of from 1000 to 65 000 g/mol being used as the starch, the sum (a)+(b)+(c)+(d) being 100% and being based on the total solids content, and the polymerization being carried out in the presence of at least 0.01% by weight, based on the monomers used, of at least one terpene-containing chain-transfer agent, processes for the preparation of the finely divided, starch-containing polymer dispersions by emulsion polymerization of the monomers (a), (b) and (c) with redox initiators in the presence of (d) degraded starch and at least 0.01% by weight, based on the monomers used, of at least one terpene-containing chain-transfer agent, and use of the finely divided, starch-containing polymer dispersions as sizes for paper, board and cardboard.