The invention relates to a process for free-radically initiated heterophase polymerization, in which the polymerization of ethylenically monomers proceeds in a phase dispersed in the continuous phase, characterized in that one or more additives which are soluble in the continuous phase and insoluble in the disperse phase and stop the polymerization of the ethylenically unsaturated monomers in the continuous phase is/are added before or during the polymerization.