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1. (EP0483523) Compositions of crystalline propylene polymers having a low seal temperature
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Claims

1. A composition of (A) a copolymer of propylene with a C 4-C 8 α-olefin and (B) a copolymer of propylene with ethylene and optionally a C 4-C 8 α-olefin, wherein the content of the fraction which is soluble in xylene at 25°C is of less than 20% by weight, said copolymer (A) being a crystalline copolymer which contains from 98 to 80% by weight of propylene and is present in an amount of from more than 40 to 65% by weight; said copolymer (B) being a crystalline copolymer which optionally contains from 2 to 10% by weight of a C 4-C 8 α-olefin, and contains 2 to 10% by weight ethylene when the C 4-C 8 α-olefin is absent and 0.5 to 5% ethylene when the C 4-C 8 α-olefin is present, and said copolymer (B) being present in an amount of from 35 to less than 60% by weight.
  2. The composition of claim 1 in the form of nonextruded spheroidal particles having a diameter of 0.5 to 4.5 mm.
  3. The composition of claim 1, wherein the C 4-C 8 α-olefin is selected from the group consisting of 1-butene; 1-hexene, 4-methyl-1-pentene; 1-octene.
  4. The composition of claim 1, wherein the content of the fraction which is soluble in n-hexane at 50°C is of less than 5.5% by weight.
  5. A process for the preparation of the composition of claim 1, comprising polymerizing the relevant monomers in the presence of stereospecific catalysts supported on magnesium dihalides in active form and capable of producing polypropylene having an isotacticity index higher than 90%, operating in at least two stages, thus preparing fractions (A) and (B) in separate and successive stages, with each subsequent stage being conducted in the presence of the polymer formed and the catalyst used in the immediately preceding stage.
  6. The process of claim 5, wherein all stages of the polymerization are carried out in gas phase.
  7. A sealable film comprising the composition of claim 1.
  8. A sealable film according to claim 7, in the form of multilayered film wherein at least one layer is of polypropylene and one layer is of the composition of claim 1.