Metallocenes for ethene/propene copolymerizations with high product of reactivity ratios

Ethene/propene copolymerizations were performed with catalytic systems comp osed of a stereorigid racemic isospecific metallocene and polymethylalumoxa ne. A number of complexes were used as representatives of three different c lasses of metallocenes. r-Me2C(3-t-Bu-Cp)(2)ZrCl2, r-Me2C(3-t-Bu-Ind)(2)ZrC l2, r-EBDMIZrCl2, r-EBDMTHIZrCl2, and r-Me2Si(2-Me-4-Ph-Ind)(2)ZrCl2 were c hosen as sterically hindered complexes. The parent metallocenes, r-Me2C(Ind )(2)ZrCl2, r-EBIZrCl2, and r-Me2Si(Ind)(2)ZrCl2 were also employed as well as other compounds bearing different substituents on the indenyl ligands su ch as r-Me2C(3-Me3Si-Ind)(2)ZrCl2, r/m-Me2C(3-Me-Ind)(2)ZrCl2, and r-Me2Si( 2-Me-Ind)(2)ZrCl2. The reactivity ratios of copolymerization (r(E) and r(P) ) were determined and examined in the light of the metallocene structure. T he complexes that were particularly demanding from the steric point of view were identified as suitable candidates for promoting copolymerizations wit h a high product of reactivity ratios, giving r(E)r(P) in a range from 1.7 to 3.0. The other two classes of metallocenes gave rise to r(E)r(P) clearly lower than 1. A more complex situation was observed as far as the reactivi ty ratios r(E) and r(P) are concerned. The enhancement of the steric hindra nce brought about in most cases an increase of r(E) but not a substantial d ecrease of r(P). In some cases, r(E) was found to remain almost unchanged a nd r(P) dramatically increased. A correlation between the reactivity ratios and the metallocene structure is attempted.