Foamable resins process

In an improved process for the production of foamable polyvinyl aromatic resin beads, the steps comprising:

• (a) polymerizing a vinyl aromatic monomer in a first aqueous suspension system forming polymeric beads of said monomer,
• (b) separating the beads from the first aqueous suspension,
• (c) suspending the separated beads under agitation in a second aqueous suspension system,
• (d) incorporating a volatile liquid blowing agent into the beads at a temperature above the softening temperature of the beads under superatmospheric pressure in a closed vessel,
• (e) cooling the second aqueous suspension under superatmospheric pressure until the suspended beads have cooled sufficiently to render the beads non-foaming at atmospheric pressures,
• (f) recovering the beads from the aqueous suspension,
• (g) drying the beads forming free flowing foamable polyvinyl aromatic polymeric beads having 1-15% of said volatile liquid blowing agent incorporated in the beads, the improvement comprising:
• drying said beads under vacuum conditions at normal temperatures of about 15.degree. to 45.degree. C., removing residual water from said beads while retaining said blowing agent in said beads and maintaining the structure of said beads as foamable non-foamed beads recovered from step (f), said vacuum being 380 to 735 mm of Hg.