Process for the preparation of expandable polystyrene by continuous injection of a liquid organic peroxide

Process for the preparation of expandable polystyrene comprising the following steps:

• I°)a) preparing an aqueous suspension comprising styrene monomer and at most 40% by weight of at least one organic peroxide initiator of formula (I), based on total weight of the peroxide used during polymerization,
• I°)b) heating the suspension at a polymerisation temperature ranging from 100° C. to 120° C.,
• I°)c) adding by continuous addition over a period of about 2 hours to about 4 hours, before, during and/or after step I°)b) a remaining amount of the at least one organic peroxide initiator of formula (I) while present as a dilute solution or dispersion and an additional peroxide initiator of formula (II) in pure form after at least 5% of said styrene monomer has been polymerized where:
• (I) is 1-alkoxy-1-t-alkylperoxycyclohexane, in which the alkoxy group contains 1 to 4 carbon atoms, the t-alkyl group contains 4 to 12 carbon atoms, and the cyclohexane ring may optionally be substituted with 1 to 3 alkyl groups each, independently having 1 to 3 carbon atoms, and
• (II) is OO-t-alkyl-O-alkyl monoperoxycarbonate wherein t-alkyl contains from 4 to 12 carbon atoms and alkyl contains 3 to 12 carbon atoms, and their mixtures, and
• ii°) adding a blowing agent selected from the group consisting of alkanes having from 4 to 6 carbon atoms and mixtures thereof;
• wherein the expandable polystyrene has a maximum molecular weight of 206,000 g/mol and a minimum molecular weight of 170,000 g/mol.