Abstract: In a suspension polymerization process of preparing styrenic polymer particles from a styrenic monomer and small particles of a styrenic polymer in a definite particle size range, styrenic polymer particles having a uniform particle size are obtained without the formation of fine polymer powders by simultaneously but separately dropwise adding to an aqueous suspension of the small particles of the styrenic polymer (1) a solution of 100-60% by weight of a suspension polymerization catalyst and 1-10% by weight of the styrenic monomer and (2) a solution of 0-40% by weight of the catalyst and 99-90% by weight of the styrenic monomer simultaneously but separately from each other.

Abstract: Styrenic polymer particles having a substantially uniform particle size are prepared by suspending styrenic polymer particles having particle sizes in a certain range in water to provide an aqueous suspension and after adding to the suspension a styrenic monomer, a suspension polymerization catalyst and a polymerization retarder in an amount of 1/200 to 1/15 mole per 1 mole of the catalyst, conducting the suspension polymerization. By conducting the polymerization in the presence of a foaming agent, one can produce foamable styrenic polymer particles having a substantially uniform particle size.