Process for preparing styrenic polymer particles

Claim 1

A process for reducing the amount of powdery polymer particles which pass through a 32 mesh sieve to thereby obtain styrenic polymer particles having a uniform particle size of 0.6 to 3 mm by preparing styrenic polymer particles by the suspension polymerization of a system comprising styrenic monomer droplets and styrenic polymer particles using the styrenic monomer and styrenic polymer particles as raw materials, which comprises suspending styrene homopolymer particles or copolymer particles of styrene monomer and up to 50% by weight of a different copolymerizable ester monomer comprising an alkyl alcohol having from 1 to 12 carbon atoms and being selected from the group consisting of acrylic esters, methacrylic esters, maleic esters and fumaric esters, having particle sizes of 0.4 to 1.8 mm in water containing 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 suspension styrene monomer with up to 50% by weight of a different copolymerizable monomer selected from the group consisting of methylacrylate, ethylacrylate, butylacrylate, methylmethacrylate, ethylmethacrylate, dimethylmaleate, diethylmaleate, acrylonitrile, α-methylstyrene, divinylbenzene and mixtures thereof, a suspension polymerization catalyst, and a polymerization retarder which is soluble in the styrene monomer and which has a molecular weight of at least 200, said retarder being selected from the group consisting of 3,5-di-tertiary butyl-4-hydroxytoluene, 1,1-bis(4-hydroxy-phenyl) cyclohexane, 4,4'-butylidene-bis(3-methyl-6-tertiary butyl phenol), 1,3,5-trimethyl-2,4,6-tris-3,5-di-tertiary-butyl-4-hydroxybenzylbenzene, 2,2'-methylenebis (6-tertiary-butyl-4-methylphenol, dilaurylthiodipropionate, 4,4'-thiobis (3-methyl-6-tertiary-butylphenol), N,N'-di-β-naphthyl-p-phenylenediamine, and N-phenyl-N-isopropyl-p-phenylenediamine in an amount of 1/100 to 1/25 mol per mol of said suspension polymerization catalyst to conduct the polymerization of said styrenic monomer while absorbed in said polymer particles, whereby the size of said polymer particles is increased, said polymerization retarder retarding the polymerization of said styrenic monomer droplets until said styrenic monomer is absorbed by said polymer particles, the amount of said polymer and said monomer used as raw material being 5 to 60 weight % and 95 to 40 weight %, respectively, of the polymer particles produced, to thereby obtain sytrenic polymer particles having a uniform particle size of 0.6 to 3 mm.