Transparent, self-extinguishing thermoplastic compositions comprise a mixture of 35 to 55 parts by weight of a methylmethacrylate homopolymer or copolymer with styrene, a -methyl styrene, an acrylic or methacrylic ester or acrylonitrile and 65 to 45 parts by weight of a vinyl chloride homopolymer or copolymer with vinyl acetate, vinylidene chloride, an acrylic, methacrylic, maleic or fumaric ester or acrylonitrile. The compositions may also comprise polyvinyl chloride stabilizers, e.g. dibutyl tin maleate; ultra-violet light absorbers, e.g. hydroxyphenylbenzotriazole; antioxidants, e.g. 4,41-thio-bis-(6-t-butylmetacresol); blueing compounds, e.g. anthraquinone derivatives; lubricants, e.g. stearic acid; other polymers, e.g. copolymers of acrylonitrile with styrene or a -methyl styrene; pigments; fillers; and plasticizers, e.g. trichlorethyl phosphate. The compositions are said to be self-extinguishing, highly transparent, and weather and chemical resistant, and may be used for making plane or corrugated sheets for roofing, skylights and wall panels, and pipes. Examples describe compositions comprising polyvinyl chloride, dibutyl tin maleate, stearic acid, hydroxyphenylbenzotriazole, 4,41 - thio - bis - (6 - t - butyl metacresol) and an anthraquinone blueing agent together with (1) a vinyl chloride/vinyl acetate copolymer and polymethyl methacrylate; (2, 5, 7 and 8) polymethyl methacrylate; (3) polymethyl methacrylate and a styrene/acrylonitrile copolymer; (4) a methyl methacrylate/methyl acrylate copolymer; and (6) a methyl methacrylate/methyl acrylate copolymer and trichlorethyl phosphate.
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