Hans-Herbert Brintzinger

1H-, 13C-NMR and ethylene polymerization studies of zirconocene/MAO catalysts: effect of the ligand structure on the formation of active intermediates and polymerization kinetics

Abstract Using 1 H- and 13 C-NMR spectroscopies, cationic intermediates formed by activation of L 2 ZrCl 2 with methylaluminoxane (MAO) in toluene were monitored at Al/Zr ratios from 50 to 1000 (L 2 are various cyclopentadienyl (Cp), indenyl (Ind) and fluorenyl (Flu) ligands). The following catalysts were studied: (Cp-R) 2 ZrCl 2 (R=Me, 1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 , Me 5 , n -Bu, t -Bu), rac-ethanediyl(Ind) 2 ZrCl 2 , rac-Me 2 Si(Ind) 2 ZrCl 2 , rac-Me 2 Si(1-Ind-2-Me) 2 ZrCl 2 , rac-ethanediyl(1-Ind-4,5,6,7-H 4 ) 2 ZrCl 2 , (Ind-2-Me) 2 ZrCl 2 , Me 2 C(Cp)(Flu)ZrCl 2 , Me 2 C(Cp-3-Me)(Flu)ZrCl 2 and Me 2 Si(Flu) 2 ZrCl 2 . Correlations between spectroscopic and ethene polymerization data for catalysts (Cp-R) 2 ZrCl 2 /MAO (R=H, Me, 1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 , Me 5 , n -Bu, t -Bu) and rac-Me 2 Si(Ind) 2 ZrCl 2 were established. The catalysts (Cp-R) 2 ZrCl 2 /AlMe 3 /CPh 3 + B(C 6 F 5 ) 4 − (R=Me, 1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 , n -Bu, t -Bu) were also studied for comparison of spectroscopic and polymerization data with MAO-based systems. Complexes of type (Cp-R) 2 ZrMe + ←Me − -Al≡MAO ( IV ) with different [Me-MAO] − counteranions have been identified in the (Cp-R) 2 ZrCl 2 /MAO (R= n -Bu, t -Bu) systems at low Al/Zr ratios (50–200). At Al/Zr ratios of 500–1000, the complex [L 2 Zr(μ-Me) 2 AlMe 2 ] + [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) 2 ZrCl 2 /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) 2 ZrCl 2 /MAO (R=1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 ) and rac-Me 2 Si(Ind) 2 ZrCl 2 /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.

Development of ansa-Metallocene Catalysts for Isotactic Olefin Polymerization

The development of ansa-metallocene catalysts is considered along several lines of interest – ansa-metallocene complexes with different ligand frameworks, insights gained with regard to relevant reaction intermediates and contributions of ansa-metallocene catalysts to industrial polymer production – with a view toward the present state of the art in these fields of catalysis research.