Metallocene catalyzed ethene- and propene co-norbornene polymerization: Mechanisms from a detailed microstructural analysis

Cyclic olefin copolymers are one of the new families of olefinic copolymers made available by metallocenes. Owing to their unique combination of properties, they are engineered polymers which are produced and commercialized. This review provides an overview of recent progress regarding ethene (E)– and propene (P)–norbornene (N) copolymerization with early transition metal catalysts. Metallocenes and some of post metallocene catalyst precursors most frequently utilized for the synthesis of norbornene copolymers are presented.The synthesis and the experimental studies which provided our current knowledge of factors governing copolymerization activity, copolymer tacticity, and molar mass are reviewed. In particular, we focus on the elucidation of E–N and P–N copolymer microstructure through 13C NMR analysis. Advances in signal assignments of the complex spectra of these copolymers are reviewed together with various methodologies utilized to achieve them. The microstructural description of the E–N chain, attained from such assignments, is summarized along with information achieved on the copolymerization mechanisms. The detailed information on the microstructure of these copolymers at tetrad or at pentad level has been applied to determine the kinetic copolymerization parameters and shed light on the polymerization mechanisms. Finally, a few relevant topics which contribute to our understanding of the mechanisms of initiation, propagation, termination, and chain-transfer steps are presented. These include a few examples of modern density functional calculations, chain end groups analysis, and synthesis of hydro-oligomers.