| 摘要 |
Catalyst component comprising Mg, Ti, Hf, a halogen and, optionally, —OR groups where R is a C1-C20 hydrocarbon group, characterized in that (a) the Mg atoms are present in an amount higher than 7% based on the total weight of the said catalyst component, (b) the amount of Mg, Ti, and Hf atoms is such that the Mg/Ti molar ratio ranges from 3 to 25 and the Hf/Ti molar ratio is lower than 1.5 and (c) when —OR groups are present their amount is such that the —OR/Ti molar ratio is lower than 2.
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