Process of preparing styrenic polymer foams

Claim 1

In a suspension polymerization process for preparing foamable styrenic polymer particles from a styrenic monomer and styrenic polymer particles having particle sizes in a definite particle size range which comprises suspending the styrenic polymer particles in water containing a surface active agent and a suspending agent selected from the group consisting of a water-soluble high molecular weight material and a slightly soluble inorganic material and adding to the aqueous suspension the styrenic monomer and a suspension polymerization catalyst to cause the polymerization, the improvement which comprises reducing the amount of powdery polymer particles which pass through a 32 mesh sieve to thereby obtain said styrenic polymer particles having a uniform particle size by adding: (1) a polymerization catalyst suspension prepared from a polymerization catalyst solution comprising (a) 100 to 60% by weight of the suspension polymerization catalyst selected from the group consisting of organic peroxides, azo compounds and mixtures thereof and (b) 1 to 10% by weight of styrene monomer with up to 50% by weight of a different monomer copolymerizable therewith selected from the group consisting of methylacrylate, ethylacrylate, butylacrylate, methylmethacrylate, ethylmethacrylate, dimethylmaleate, diethylmaleate, acrylonitrile, α-methylstyrene, divinylbenzene and a mixture thereof having been admixed with an aqueous solution containing an emulsifying agent or a suspending agent to form a finely suspended polymerization catalyst suspension; and (2) a monomer solution comprising (a') 0 to 40% by weight of the suspension polymerization catalyst and (b') 99 to 90% by weight of styrene monomer with up to 50% by weight of a different monomer copolymerizable therewith, dropwise and simultaneous but separately from each other to the aqueous suspension of the polymer particles selected from the group consisting of styrene homopolymer and a copolymer of styrene monomer and up to 50% by weight of a different monomer copolymerizable therewith selected from the group consisting of an acrylic ester, a methacrylic ester, a maleic ester and a fumaric ester wherein the alcohol moiety is an alkyl group having 1 to 12 carbon atoms, to cause the polymerization, and conducting the polymerization in the presence of a foaming agent which does not dissolve or at most slightly swells the styrenic polymer particles produced; the amount of said styrene monomer and styrene homopolymer or copolymer being 95 to 40% by weight and 5 to 60% by weight, respectively, based on the total amount thereof; and the particle size of said styrene homopolymer or copolymer being about 0.2 to 1.8 mm.