The known rac-[ethylenebis(4,7-dimethyl-n5-1-indenyl)]ZrCl2 (2r) and its meso isomer (2m) have been compared with the prototypal chiral isospecific rac-[ethylenebis(η5-1-indenyl)]-ZrCl2 (1r) and its aspecific meso isomer 1m in terms of molecular structures, solution dynamics, and ligand substitution effect on polymerization performance. In liquid propene at 50°C, 2r/MAO produces iPP with appreciably higher isotacticity but lower molecular weight and regiospecificity than 1r/MAO. The lower molecular weight obtained with 2r in liquid monomer is due to predominant chain transfer to the monomer after a secondary propene insertion, producing >90% cis-2-butenyl- end groups. At lower propene concentration, 2r/MAO allows both β-hydrogen transfer after a primary insertion and β-methyl transfer. The low-activity 2m/MAO catalyst produces low molecular weight aPP. The diastereoselective synthesis of 2r,m via the corresponding rac- and meso-bis(4,7-dimethyl-1-(trimethylsilyl)-3-indenyl)ethane is reported. The crystal and molecular structures of meso-bis(4,7-dimethyl-1-(trimethylsilyl)-3-indenyl)ethane, 2r,m, have been determined.
|Titolo:||Diastereoselective synthesis, molecular structure, and solution dynamics of meso- and rac-[ethylenebis(4,7-dimethyl-η5-1-indenyl)]zirconium dichloride isomers and chain transfer reactions in propene polymerization with the rac isomer|
|Settore Scientifico Disciplinare:||Settore CHIM/03 - Chimica Generale e Inorganica|
|Data di pubblicazione:||1996|
|Appare nelle tipologie:||01 - Articolo su periodico|