Process for producing expandable thermoplastic resin beads

A process for producing expandable thermoplastic graft copolymerized resin beads which consists essentially of suspending in an aqueous medium from 20 to 70% by weight of a random copolymer of propylene and ethylene containing 1 to 10% by weight of ethylene and 99 to 90% by weight propylene and 30 to 80% by weight of a vinyl aromatic monomer;

• adding a polymerization catalyst and polymerizing the vinyl aromatic monomer to form graft copolymerized thermoplastic resin beads and subsequently impregnating the graft copolymerized thermoplastic resin beads with an easily volatilizable hydrocarbon or halogenated hydrocarbon blowing agent.

In a process for producing expandable thermoplastic graft copolymerized resin beads which consists essentially of suspending in an aqueous medium containing 0.01 to 5% by weight, based on water present in the aqueous medium, of a dispersing agent selected from the group consisting of polyvinyl alcohol, methyl cellulose, calcium phosphate, magnesium pyrophosphate and calcium carbonate, from 20 to 70% by weight of a random copolymer of propylene and ethylene containing 1 to 10% by weight of ethylene and 99 to 90% by weight propylene and 30 to 80% by weight of a vinyl aromatic monomer;

• adding a polymerization catalyst and polymerizing the vinyl aromatic monomer to form graft copolymerized thermoplastic resin beads and subsequently impregnating the graft copolymerized thermoplastic resin beads with an easily volatilizable hydrocarbon or halogenated hydrocarbon blowing agent, the improvement comprising heating the aqueous medium to a temperature at which the vinyl aromatic monomer can be polymerized before adding the vinyl aromatic monomer and the polymerization catalyst thereto, and adding said vinyl aromatic monomer and said polymerization catalyst to the heated aqueous medium.