Ethene/norbornene copolymerization using the catalyst system Prⁱ[(3-Prⁱ-Cp)Flu]ZrCl₂: Determination of the copolymerization parameters and mechanistic considerations

The (13) NMR spectra of ethane/norbornene copolymers in which there are no norbornene microblocks are much simpler than those of copolymers in which norbornene microblocks are present, making it possible to completely assign all the C-13 resonances to the corresponding pentads in the copolymer chain. However, there is disagreement in the literature over several assignments of the ethane C-13 NMR signals. In this paper these discrepencies are summarized and discussed. This contribution also reports ethane/norbornene copolymerizations carried out at various temperatures using the homogeneous catalyst system Pr[(3-Pr-Cp)Flu]ZrCl2. The C-13 NMR spectra of the copolymers were analyzed in the light of the discussion above and the triad discussions were used to determine the copolmerization parameters by Markov first- and second-order statistical models. On the basis of these results, the mechanism generating such an alternating microstructure in these copolymers is discussed and compared with the mechanism previously proposed in the literature. The C-13 NMR spectrum with signal assignments of an ethane/norbornene copolymer without norbornene microblocks