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Propene polymerization of methylalumoxane (MAO) activated rac-Me2Si(Benz[e]Indenyl)2ZrCl2 (BI) and rac-Me2Si(2-Me-Benz[e]Indenyl)2ZrCl2 (MBI) was studied to investigate the influence of the ligand substitution pattern and the role of dormant sites. Poly(propene) end group composition as well as regio- and stereoirregularities were examined by means of 1H- and 13C-NMR spectroscopy. Dormant sites, resulting from 2, 1-propene insertion, were reactivated either by β-hydrogen transfer to propene, yielding 2-butenyl end groups, or by 1, 2-insertion of propene, yielding regioirregularities. Propene polymerization in the presence of hydrogen gave n-butyl end groups and less regioirregularities as expected for hydrogenolysis of such dormant sites. Methyl substitution in 2-position of the benz[e]indenyl ligand suppressed β-hydrogen transfer to propene, and increased molecular weight with increasing propene concentration. Also, activation energy increased from 30 kJ/mol (BI/MAO) to 59 kJ/mol (MBI/MAO). For both catalysts activity depended on propene concentration. The order of reaction relative to propene was 1.7. |
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