Manufacture of particulate expandable styrene polymers requiring shot minimum residence times in the mold

A process for the manufacture of particulate expandable styrene polymers requiring short minimum mold residence times by polymerizing styrene or mixtures of styrene and other copolymerizable monomers in the presence of low-boiling hydrocarbon expanding agents and from 0.001 to 0.1% by weight, based on the monomers, of a brominated oligomer or polymer of a 1,3-diene having a maximum degree of polymerization of 2000 and containing more than 40% by weight of bromine at elevated temperatures, wherein the particles forming during polymerization of styrene or said mixtures in the presence of the bromine compounds are heated, in the course of their manufacture, to temperatures of from 110.degree. to 140.degree.C.