Method for producing modified polystyrene resin particles, method for producing expandable modified polystyrene resin particles, and uses thereof

Provided is a method for producing modified polystyrene resin pellets with which it is possible to obtain a foam molded body having little fluctuation in crack resistance. This method for producing modified polystyrene resin particles comprises a polymerization step for obtaining modified polystyrene resin particles by copolymerizing a conjugated diene monomer and a styrene monomer impregnated in polystyrene resin particles, a polymerization initiator dissolved in a solvent having an SP value in a specific range and having 8 or less carbon atoms is added. 提供：可以得到抗裂性的波动少的发泡成型体的改性聚苯乙烯系树脂颗粒的制造方法。改性聚苯乙烯系树脂颗粒的制造方法包括如下聚合工序：使浸渗于聚苯乙烯系树脂颗粒内的苯乙烯系单体与共轭二烯系单体共聚，得到改性聚苯乙烯系树脂颗粒，前述聚合工序中，添加已溶解于SP值为特定的范围且碳数为8以下的溶剂中的聚合引发剂。