H-, C-NMR and ethylene polymerization studies of zirconocene/MAO catalysts: effect of the ligand structure on the formation of active intermediates and polymerization kinetics |
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Authors: | Konstantin P Bryliakov Nina V Semikolenova Vladimir A Zakharov Martin Ystenes Evgenii P Talsi |
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Institution: | a Boreskov Institute of Catalysis, Prospect Akad. Lavrentieva, 5, Novosibirsk 630090, Russia b Natural Sciences Department, Novosibirsk State University, Novosibirsk 630090, Russia c Fachbereich Chemie, University of Konstanz, D-78457 Konstanz, Germany d Department of Chemical Engineering, Norwegian University of Science and Technology (NTNU), N-7491 Trondheim, Norway e Statoil Research Centre, N-7005 Trondheim, Norway |
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Abstract: | Using 1H- and 13C-NMR spectroscopies, cationic intermediates formed by activation of L2ZrCl2 with methylaluminoxane (MAO) in toluene were monitored at Al/Zr ratios from 50 to 1000 (L2 are various cyclopentadienyl (Cp), indenyl (Ind) and fluorenyl (Flu) ligands). The following catalysts were studied: (Cp-R)2ZrCl2 (R=Me, 1,2-Me2, 1,2,3-Me3, 1,2,4-Me3, Me4, Me5, n-Bu, t-Bu), rac-ethanediyl(Ind)2ZrCl2, rac-Me2Si(Ind)2ZrCl2, rac-Me2Si(1-Ind-2-Me)2ZrCl2, rac-ethanediyl(1-Ind-4,5,6,7-H4)2ZrCl2, (Ind-2-Me)2ZrCl2, Me2C(Cp)(Flu)ZrCl2, Me2C(Cp-3-Me)(Flu)ZrCl2 and Me2Si(Flu)2ZrCl2. Correlations between spectroscopic and ethene polymerization data for catalysts (Cp-R)2ZrCl2/MAO (R=H, Me, 1,2-Me2, 1,2,3-Me3, 1,2,4-Me3, Me4, Me5, n-Bu, t-Bu) and rac-Me2Si(Ind)2ZrCl2 were established. The catalysts (Cp-R)2ZrCl2/AlMe3/CPh3+B(C6F5)4− (R=Me, 1,2-Me2, 1,2,3-Me3, 1,2,4-Me3, Me4, n-Bu, t-Bu) were also studied for comparison of spectroscopic and polymerization data with MAO-based systems. Complexes of type (Cp-R)2ZrMe+←Me−-Al≡MAO (IV) with different Me-MAO]− counteranions have been identified in the (Cp-R)2ZrCl2/MAO (R=n-Bu, t-Bu) systems at low Al/Zr ratios (50-200). At Al/Zr ratios of 500-1000, the complex L2Zr(μ-Me)2AlMe2]+Me-MAO]− (III) dominates in all MAO-based reaction systems studied. Ethene polymerization activity strongly depends on the Al/Zr ratio (Al/Zr=200-1000) for the systems (Cp-R)2ZrCl2/MAO (R=H, Me, n-Bu, t-Bu), while it is virtually constant in the same range of Al/Zr ratios for the catalytic systems (Cp-R)2ZrCl2/MAO (R=1,2-Me2, 1,2,3-Me3, 1,2,4-Me3, Me4) and rac-Me2Si(Ind)2ZrCl2/MAO. The data obtained are interpreted on assumption that complex III is the main precursor of the active centers of polymerization in MAO-based systems. |
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Keywords: | Metallocene catalysts 1H- and 13C-NMR Polyethylene Structure-property relations Transition metal chemistry |
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