Trigonox® 121 can be used to initiate the (co)polymerization of acrylates and methacrylates in the temperature range between 70°C and 120°C. Trigonox® 121 can be applied in suspension as well as in solvent and bulk polymerization. Trigonox® 121 can also be used for the copolymerization of styrene and acrylonitrile and for vinyl acetate based copolymers.