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 presenc e of catalytic systems based on C-2 upsilon-, C-s-, and C-2-symmetric group 4 ansa-metallocenes is investigated. Higher reactivities of Z and E isomer s of a-butene, in the presence of C-2- and C-s-symmetric metallocenes, resp ectively, are predicted by molecular modeling and are proved by polymerizat ion tests relative to pure isomers as well as to mixtures of them. The copo lymerization experiments have also shown that both growing chain isomerizat ions and chain transfer reactions are dependent on the configuration (Z or E) of 2-butene while are independent of the metallocene symmetry. To accoun t for this behavior, isomerization mechanisms involving intermediates with metal-allyl bonds are suggested. Possible mechanisms of chain transfer reac tions are also discussed.