| 摘要 |
The invention relates to a process for the preparation of a creep-resistant polypropylene by means of the following steps: (a) copolymerizing propylene and ethylene into a random copolymer at 40 to 110° C. using: a catalyst system of the above-mentioned type; a portion of ethylene or C4-C10-alpha-olefin leading to 1.0 to 10.0% by weight of ethylene repeating units in said random copolymer; and no or a minimal amount of hydrogen leading to a MFR10 value of between 0.01 and 5.0 g/10 min for said random copolymer, if this step is performed first, or to a MFR2 value for said polypropylene of between 0.05 and 0.40 g/10 min, if this step is performed after step (b); the proportion of random copolymer of this step being from 20 to 80% by weight of said polypropylene, (b) polymerizing propylene at 40 to 110° C. using: a catalyst system of the above-mentioned type; no or a minimal portion of ethylene leading to 0.0 to 1.0% by weight of ethylene repeating units in the polymer resulting from this step; and an amount of hydrogen leading to a MFR2 value of between 30 and 300 g/10 min for said polymer, if this step is performed first, or to a MFR2 value for said polypropylene of between 0.05 and 0.40 g/10 min, if this step is performed after step (a); the proportion of polymer of this step being from 80 to 20% by weight of said polypropylene.
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