Iso-specific Ziegler-Natta polymerization of {alpha}-olefins with a single-component organoyttrium catalyst
- California Institute of Technology, Pasadena, CA (United States)
Three types of well-defined, homogeneous Ziegler-Natta {alpha}-olefin polymerization systems have been described recently: (1) two-component catalysts consisting of group 4 metallocene dihalides and a large excess of methylalumoxane cocatalyst; (2) simpler two-component systems based on group 4 metallocene dialkyls with a stoichiometric (or near stoichiometric) amount of an activator such as [C{sub 6}H{sub 5}(CH{sub 3}){sub 2}NH{sup +}][B(C{sub 6}F{sub 5}){sub 4}{sup -}], {sup 3}[(C{sub 6}H{sub 5}){sub 3}C{sup +}][B(C{sub 6}F{sub 5}){sub 4}{sup -}],{sup 4} or B(C{sub 6}F{sub 5}){sub 3},{sup .5} and (3) single-component catalysts such as Lewis base adducts of cationic group 4 metallocene alkyls{sup 6} or the isoelectronic neutral group 3 or lanthanide metallocene hydrides or alkyls. The group 4 metallocene/methylalumoxane and [Cp{sub 2}MCH{sub 3}{sup +}][B(R)(C{sub 6}F{sub 5}){sub 3}{sup -}] catalysts (M = Zr, Hf; R = C{sub 6}F{sub 5}, CH{sub 3}) exhibit higher activity in {alpha}-olefin polymerizations, and with the chiral, C{sub 2}-symmetric ansa-metallocene dihalide or dimethyl precursors (M = Ti, Zr, Hf) developed by Brintzinger, Ewen, Collins, and others, highly isotactic polypropylene is obtained. Unfortunately, the meso (C{sub s} symmetric) isomer is normally formed along with the preferred chiral isomer in the synthesis of the metallocene dihalide. Herein the authors report the synthesis of the first iso-specific, single component Ziegler-Natta polymerization catalyst, [rac-Me{sub 2}Si(2-SiMe{sub 3}-4-CMe{sub 3}C{sub 5}H{sub 2}){sub 2}YR]. Its simplicity makes it particularly well suited to in situ mechanistic studies. Moreover, the [Me{sub 2}Si(2-SiMe{sub 3}-4-CMe{sub 3}C{sub 5}H{sub 2}){sub 2}] ligand has been designed to coordinate to yttrium to produce only the desired racemic isomer in the synthesis of the chloride precursor. 16 refs., 2 figs.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 539907
- Journal Information:
- Journal of the American Chemical Society, Vol. 114, Issue 19; Other Information: PBD: 9 Sep 1992
- Country of Publication:
- United States
- Language:
- English
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