Reactivity of Z and E isomers, growing chain isomerization, and chain transfer reactions in ethene/2-butene copolymerization by metallocene-based catalysts

Copolymerization of Z and E isomers of 2-butene with ethene, in the presence of catalytic systems based on C_2v-, C_s-, and C₂-symmetric group 4 ansa-metallocenes is investigated. Higher reactivities of Z and E isomers of 2-butene, in the presence of C₂- and C_s-symmetric metallocenes, respectively, are predicted by molecular modeling and are proved by polymerization tests relative to pure isomers as well as to mixtures of them. The copolymerization experiments have also shown that both growing chain isomerizations and chain transfer reactions are dependent on the configuration (Z or E) of 2-butene while are independent of the metallocene symmetry. To account for this behavior, isomerization mechanisms involving intermediates with metal-allyl bonds are suggested. Possible mechanisms of chain transfer reactions are also discussed.