Expandable polypropylene interpolymer particles

Claim 1

A process for producing expandable polypropylene particles comprising (a) suspending in an aqueous medium, a copolymer of propylene and sufficient olefin comonomers to give said copolymer a melting peak of less than 140° C., with the aid of a suitable suspending agent system; (b) adding to said suspension vinyl aromatic monomer and a catalyst system such that the amount of monomer is 40 to 80% by weight based on copolymer plus monomer; (c) polymerizing said monomer in the interior of said copolymer to form a polypropylene-polyvinylaromatic monomer interpolymer; (d) separating said interpolymer from said suspension by acidifying, filtering, washing with water and drying in air; (e) extruding said interpolymer in admixture with a lubricant and cell control agent and a peroxide, if used, to viscbreak said interpolymer to a melt flow (condition L) of at least 10, under conditions to minimize orientation stress in the final extrudate; (f) impregnating said extrudate with a blowing agent to give expandable polypropylene-polyvinyl aromatic monomer interpolymers which can be expanded at 100° C. to fine cell structure foams of density less than 2.0 pounds per cubic foot.