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

Ethene/propene copolymerizations were performed with catalytic systems composed of a stereorigid racemic isospecific metallocene and polymethylalumoxane. A number of complexes were used as representatives of three different classes of metallocenes. r-Me2C(3-t-Bu-Cp)(2)ZrCl2, r-Me2C(3-t-Bu-Ind)(2)ZrCl2, r-EBDMIZrCl2, r-EBDMTHIZrCl2, and r-Me2Si(2-Me-4-Ph-Ind)(2)ZrCl2 were chosen 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 such 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. The complexes that were particularly demanding from the steric point of view were identified as suitable candidates for promoting copolymerizations with 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 reactivity ratios r(E) and r(P) are concerned. The enhancement of the steric hindrance brought about in most cases an increase of r(E) but not a substantial decrease of r(P). In some cases, r(E) was found to remain almost unchanged and r(P) dramatically increased. A correlation between the reactivity ratios and the metallocene structure is attempted.