| 摘要 |
A self-extinguishing expandable plastics composition comprises (A) a thermoplastic styrene copolymer which contains 95 to 99.5% by weight of styrene and 0.5 to 5.0% by weight of acrylonitrile or at least 80% by weight of styrene, 0.5 to 5.0% by weight of acrylonitrile and not more than 15% by weight of one or more other monomeric polymerizable a ,b -unsaturated compounds, (B) an organic bromine compound having a bromine content of more than 50% by weight, the amount of the bromine compound being such that the bromine content of the mixture (with reference to the styrene copolymer) is from 0.5 to 6.0% by weight and (c) 2 to 20% by weight (with reference to the styrene copolymer) of an expanding agent which is liquid or gaseous at room temperature, which does not dissolve the copolymer and which has a boiling point of less than 100 DEG C. Compositions which contain a copolymer of 99-97% by weight of styrene and 1-3% by weight of acrylonitrile have particularly advantageous properties in respect of little shrinkage. Polymerizable monomeric a ,b -unsaturated compounds which may be used in addition to styrene and acrylonitrile include esters of acrylic and methacrylic acids with alcohols having one to eight carbon atoms, nuclear halogenated styrenes, nuclear alkylated styrenes and divinylbenzene. Organic bromine compounds used are brominated polymers of butadiene or isoprene having a degree of polymerization of 2 to 20, such as octabromohexadecane, tetrabromocyclooctane, hexabromocyclododecane, tetrabromocyclododecane; esters and acetals of 2,3-dibromopropanol such as tris-(2,3-dibromopropyl) phosphate are also suitable. 1,2,5,6,9,10-Hexabromocyclododecane 1,2,5,6 - tetrabromocyclooctane and 1-chloro-2,3,4,5,6-pentabromocyclohexane are also used. Substances, such as ferrocene, which improve the flame-proofing effect, may also be added. The compositions are advantageously prepared by polymerizing the mixture of monomers in aqueous suspension in the presence of the expanding agent and the organic halogen compound. The product of this reaction can be expanded by heating with steam or hot air.
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