THE ROLE OF DORMANT SITES IN PROPENE POLYMERIZATION USING METHYLALUMOXANE ACTIVATED METALLOCENE CATALYSTS

Propene polymerization of methylalumoxane (MAO) activated rac-Me(2)Si(Benz[e]Indenyl)(2)ZrCl2 (BI) and rac-Me(2)Si(2-Me-Benz[e]Indenyl)(2)ZrCl2 (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 H-1- and C-13-NMR spectroscopy. Dormant sites, resulting from 2,1-propene insertion, were reactivated either by beta-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 beta-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.