Method for preparing an aqueous polymer dispersion from a vinyl aromatic compound and a conjugated aliphatic diene

The present invention relates to a process for producing an aqueous polymer dispersion by free-radically initiated aqueous emulsion polymerization, by polymerizing, in an aqueous medium,(a) 40 to 75 parts by weight of at least one vinylaromatic compound and(b) 24.9 to 59.9 parts by weight of at least one conjugated aliphatic diene(c) 0.1 to 10 parts by weight of at least one monomer comprising acid groups and(d) 0 to 20 parts by weight of at least one other monoethylenically unsaturated monomer,the amounts of the monomers (a) to (d) adding up to 100 parts by weight,in a monomer feed process in the presence of at least one inorganic peroxide and at least one organic peroxide, with the proviso thatthe continuous metering of the inorganic peroxide starts at the same time as the continuous metering of the vinylaromatic compound,the metering of the organic peroxide is started at a time at which at least 5% and not more than 20% of the vinylaromatic compound has already been metered in in a continuous mass flow under polymerization conditions andoptionally a portion of the inorganic peroxide is initially charged,and also to the aqueous polymer dispersions produced by the process and to the use of these as a binder, adhesive, sizing agent for fibers, for the production of coatings or for the production of a paper coating slip.