| 摘要 |
A metallocene catalyst system for the polymerization of alpha -olefins to yield stereospecific polymers including syndiotactic, and isotactic polymers. The catalyst system includes a metal and a ligand of the formula <IMAGE> wherein: R1, R2, and R3 are independently selected from the group consisting of hydrogen, C1 to C10 alkyl, 5 to 7 membered cycloalkyl, which in turn may have from 1 to 3 C1 to C10 alkyls as a substituent, C6 to C15 aryl or arylalkyl in which two adjacent radicals may together stand for cyclic groups having 4 to 15 carbon atoms which in turn may be substituted, or Si(R8)3 where R8 is selected from the group consisting of C1 to C10 alkyl, C6 to C15 aryl or C3 to C10 cycloalkyl; R4 and R6 are substituents both having van der Waals radii larger than the van der Waals radii of groups R1 and R3; R5 is a substituent having a van der Waals radius less than about the van der Waals radius of a methyl group; E1, E2 are independently selected from the group consisting of Si(R9)2, Si(R9)2-Si(R9)2, Ge(R9)2, Sn(R9)2, C(R9)2, C(R9)2-C(R9)2, where R9 is C1 to C10 alkyl, C6 to C15 aryl or C3 to C10 cycloalkyl; and the ligand may have CS or C1-symmetry. Preferred metals are selected from the group consisting of group III, group IV, group V or lanthanide group elements. The catalysts are used to prepare stereoregular polymers including polypropylene from alpha -olefin monomers.
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