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

Abstract

A process for the preparation of expandable polystyrene including the following steps: i°) heating an aqueous suspension including styrene monomer and at least one organic peroxide initiator of formula (I) 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, at a temperature ranging from 100° C. to 120° C.), ii°) adding a blowing agent selected from the group of alkanes having from 4 to 6 carbon atoms and mixtures thereof. Also, an expandable polystyrene obtainable according to such a process and to insulation parts and packaging including such an expandable polystyrene.

1 . Process for the preparation of expandable polystyrene comprising the following steps:
 I°)a) preparing an aqueous suspension comprising styrene monomer;   I°)b) heating the suspension at a polymerization temperature ranging from 100° C. to 120° C.;   I°)c) adding continuously, during and/or after step I°)b) at least one organic peroxide initiator of formula (I) 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, at most 40% by weight (% w/w) of the organic peroxide based on the total weight of the peroxide used during the polymerization, is present before step I°)b), while the remainder is added continuously over a period of at least 1 hour during or after step I°)b); and   ii°) adding a blowing agent selected from the group consisting of alkanes having from 4 to 6 carbon atoms and mixtures thereof.   
     
     
         2 . Process according to  claim 1 , wherein the at least one organic peroxide initiator is 1-methoxy-1-tamylperoxycyclohexane (TAPMC). 
     
     
         3 . Process according to  claim 1 , wherein said blowing agent is selected from the group consisting of butane, 2-methylbutane, pentane, cyclohexane and mixtures thereof. 
     
     
         4 . Process according to  claim 1 , wherein the temperature of step i°) ranges from 105° C. to 115° C. 
     
     
         5 . Process according to  claim 1 , wherein the aqueous suspension of step i°) further comprises at least one additional organic peroxide initiator, different from said organic peroxide initiator of formula (I). 
     
     
         6 . Process according to  claim 5 , wherein said additional peroxide initiator is of formula (II) OO-t-alkyl-O-alkyl monoperoxycarbonate, wherein t-alkyl contains from 4 to 12 carbon atoms and alkyl contains from 3 to 12 carbon atoms and their mixtures. 
     
     
         7 . Process according to  claim 1 , wherein said organic peroxide initiator of formula (I) is used in the aqueous suspension of step i°) in amounts from 4 to 25 milli equivalents of initiator per liter of styrene. 
     
     
         8 . Process according to  claim 1 , wherein the styrene monomer to be polymerized also contains up to 15 weight %, with respect to the total weight of styrene, of copolymerizable monomers other than styrene monomers. 
     
     
         9 . Process according to  claim 1 , wherein hexabromocyclododecane is added to the aqueous suspension at step i°) or at step ii°). 
     
     
         10 . Process according to  claim 5 , wherein the aqueous suspension of step i°) comprises the organic peroxide initiator of formula (I) as a first stage initiator and the at least one additional other organic peroxide initiator different from said organic peroxide initiator of formula (I) as a second stage initiator, step i°) comprises a stage I°)b′), during which said suspension is heated at the temperature ranging from 100° C. to 120° C., and a second stage I°)c′) during which said suspension is heated at a temperature corresponding to the one hour half-life temperature of the at least additional other organic peroxide different from said organic peroxide initiator of formula (I). 
     
     
         11 . Process according to  claim 1 , wherein 20 to 30% by weight of the organic peroxide is added continuously during step —I°)c)—. 
     
     
         12 . Process according to  claim 1 , wherein, at most, 5% by weight of the organic peroxide is added continuously during step —I°)c)—. 
     
     
         13 . Process according to  claim 1 , wherein the organic peroxide is added continuously over a period of at least 2 hours. 
     
     
         14 . Process according to  claim 1 , wherein the organic peroxide is added continuously over a period of 2-4 hours. 
     
     
         15 . Process according to  claim 4 , wherein the wherein the temperature of step i°) is 110° C. 
     
     
         16 . Process according to  claim 6 , wherein the t-alkyl contains from 4-5 carbon atoms and the alkyl contains 8 carbon atoms. 
     
     
         17 . Process according to  claim 7 , wherein the organic peroxide initiator of formula (I) is used in the aqueous suspension of step i°) in amounts from 12 to 20 milli equivalents of initiator per liter of styrene. 
     
     
         18 . Process according to  claim 10 , wherein the suspension is heated at a temperature ranging from 105° C. to 115° C. 
     
     
         19 . Process according to  claim 10 , wherein the suspension is heated to a temperature of 110° C.