Trigonox® 117 can be used as an initiator for the polymerization and copolymerization of styrene in the temperature range between 100°C and 130°C. In a mass process Trigonox® 117 can be advantageously used to increase polymerization rates. In suspension polymerization processes Trigonox® 117 is an efficient peroxide for reduction of residual styrene concentration during the final polymerization stage.