Homo- and copolymerization of ethylene and alpha-olefins over 1- and 2-siloxy-substituted ethylenebis(indenyl)zirconium and ethylenebis(tetrahydroindenyl)zirconium dichlorides

The influence of siloxy substitution of ethylene-bridged bis(indenyl)- and bis(tetrahydro-indenyl)zirconium dichlorides on ethylene/alpha-olefin copol ymerization and ethylene homopolymerization performance was investigated. E thylene was copolymerized with 1-hexene and 1-hexadecene over rac-[ethylene bis(1-(tert-butyldimethylsiloxy)-3-indenyl)]zirconium dichloride (1), rac-[ ethylenebis(1-(tert-butyldimethylsiloxy)-4,5,6,7-tetrahydro-3-indenyl)]zirc onium dichloride (H1), rac-[ethylenebis(2-(tert-butyldimethylsiloxy)-1-inde nyl)] zirconium dichloride (2), and rac-ethylenebis(1-indenyl)zirconium dic hloride (EBI) using methylaluminoxane (MAO) as cocatalyst. 1-Siloxy substit ution was found to remarkably improve the copolymerization ability and 2-si loxy substitution to enhance the polymerization activity of ethylenebis(ind enyl)zirconium dichlorides. Optimum homo- and copolymerization performance was observed at a very low Al(MAO) concentration, which for 2 could be redu ced to a level of 0.2 mmol/dm(3) by using a small amount of triisobutylalum inum. The 1-siloxy-substituted metallocene catalysts 1 and H1 (hydrogenated 1) revealed decreasing comonomer incorporation and increasing induction ti mes with increasing Al(MAO) concentration, which indicates the presence of unfavorable interactions between these metallocenes and MAO. Chain terminat ion occurred mainly by chain transfer to the monomer and beta-hydrogen tran sfer to the metal for catalysts with indenyl and tetrahydroindenyl ligands, respectively.