Abstract: A process is described for effectively reducing the residual monomer content of an aqueous polymer dispersion by aftertreatment at atmospheric pressure or above with an initiator system comprising a) a hydroperoxide, hydrogen peroxide or a peracid, and b) an &agr;-hydroxy carboxylic acid, such as tartaric acid, or with a salt thereof.

Abstract: A process for reducing the amount of residual monomer in aqueous polymer dispersions operates by aftertreatment with an initiator system essentially comprising a) from 0.001 to 5% by weight, based on the total monomer amount used to prepare the polymer dispersion, a1) of an oxidizing agent R1OOH,  where R1 is hydrogen or a C1-C8-alkyl or a C6-C12-aryl group, and/or a2) of a compound which in aqueous medium releases hydrogen peroxide, and b) from 0.

Abstract: The present invention relates to a process for preparing polymer powders from aqueous polymer dispersions in which the dispersed polymer P comprises in copolymerized form: i) at least one vinylaromatic monomer (a), ii) 1,3-butadiene as monomer (b), and iii) one or more monomers (c) different than the monomers (a) and (b), which comprises drying the aqueous polymer dispersion in the presence of polyvinyl alcohol as drying agent. The present invention also relates to the polymer powders obtainable by this process and to the use of these polymer powders as binders in paints, varnishes and coating compositions generally, in adhesives, and for modifying mineral construction materials. The present invention also relates to mineral construction materials in the form of dry formulations comprising the polymer powders of the invention.