GB1287410A - Suspension polymerisation process - Google Patents

Abstract

1287410 Polymers of vinyl aromatic compounds; foamable polystyrene MONSANTO CHEMICALS Ltd 3 Dec 1969 [24 Dec 1968] 61251/68 Headings C3C and C3P Vinylaromatic polymers are prepared by polymerizing the monomer in an aqueous suspension system comprising a first suspending agent which is a vinyl alcohol homopolymer or a copolymer containing at least 95 mol. per cent of polymerized vinyl alcohol, a second suspending agent which is a copolymer containing 75-91 mol. per cent of vinyl alcohol, and a further suspending agent which is a copolymer of an acrylic acid (including alpha-substituted acrylic acids) and an acrylate (including alpha-substituted) ester, the first two suspending agents being present in the system before the proportion by weight of polymer is 30%, based on the total weight of polymer and monomer, and the further suspending agent being added after that proportion reaches 20% but not before the first and second suspending agents are present in the system. Blowing agents such as pentane may be present during the polymerization. The aqueous system may also contain a water-soluble inorganic salt or a surface active agent. In the examples styrene is polymerized in an aqueous solution containing a 98% hydrolysed polyvinyl acetate and an 88% hydrolysed polyvinyl acetate as first and second suspending agents respectively, benzoyl peroxide tertiary butylperbenzoate and pentane, and after 6 hours of polymerization an aqueous solution of a copolymer of acrylic acid and 2-ethylhexyl acetate is added as the further suspending agent. The product is foamable beads of polystyrene which can be prefoamed with steam.