PURPOSE: To obtain expandable polymer bends capable of shortening the cooling time of a molded product without imparting effect inadvantageous to the heat conductivity of an obtd. molded product by subjecting a vinyl aromatic monomer to aq. suspension polymn. in the presence of a specified additive under a specified condition and adding a blowing agent to the polymn. mixture.

CONSTITUTION: A vinyl aromatic monomer is suspended in water in the presence of an effective amt. of a polymn. initiator (e.g.; benzoyl peroxide) and an effective amt. of a suspension stabilizer (e.g.; hydroxyapatite) at 80-150°C under pressure of 1-20 bar for 6-20 hr (A) and an effective amt. of a blowing agent (e.g.; pentane) is added to the suspension (B) to produce expandable polymer beads. In this method, the vinyl aromatic monomer is polymerized in the presence of 0.01-0.6% by wt. of the monomer of polyethylene wax and 0.005-0.1 wt.% of a nonionic surfactant having an HLB value of 7-16.