| 摘要 |
Propylene polymer compositions having good transparency and improved impact resistance at low temperature comprising: (a) 70-98% by weight of a crystalline copolymer of propylene with (i) ethylene or (ii) a CH2=CHR alpha olefin, where R is a linear or branched alkyl radical with 2-8 carbon atoms, or (iii) a mixture of (i) and (ii), containing 85 to 99.5% by weight of propylene; (b) 2-30% by weight of an elastomeric copolymer of ethylene with (i) propylene or (ii) a CH2=CHR alpha olefin, where R is as defined above, or (iii) a mixture of (i) and (ii), containing from 20 to 70% by weight of ethylene, said copolymer (b) being partially soluble in xylene at room temperature and being furthermore characterized by the fact that the ratio between the ethylene weight content in the copolymer and the weight of the portion of copolymer soluble in xylene is equal to or less than 1.5, while the intrinsic viscosity (I.V.2.) of the portion soluble in xylene satisfies the following relation: 0.2 ~ (I.V.2/I.V.1) x (C2) < 0.6 where I.V.1 is the intrinsic viscosity of the crystalline propylene copolymer (a), I.V.1 and I.V.2 are expressed in dl/g, and (C2) is the ethylene weight content of the elastomeric copolymer (b). The compositions are prepared by sequential polymerization of the monomers in the presence of Ziegler-Natta stereospecific catalysts which include a titanium compound supported on a magnesium dihalide in active form.
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