Efficient ethylene/norbornene copolymerization by half‐titanocenes containing imidazolin‐2‐iminato ligands and MAO catalyst systems

Ethylene copolymerizations with norbornene (NBE) using half‐titanocenes containing imidazolin‐2‐iminato ligands, Cp′TiCl2[1,3‐R2(CHN)2CN] [Cp′ = Cp (1), tBuC5H4 (2); R = tBu (a), 2,6‐iPr2C6H3 (b)], have been explored in the presence of methylaluminoxane (MAO) cocatalyst. Complex 1a exhibited remarkable catalytic activity with better NBE incorporation, affording high‐molecular‐weight copolymers with uniform molecular weight distributions, whereas the tert‐BuC5H4 analog (2a) showed low activity, and the resultant polymer prepared by the Cp‐2,6‐diisopropylphenyl analog (1b) possessed broad molecular weight distribution. The microstructure analysis of the poly(ethylene‐co‐NBE)s prepared by 1a suggests the formation of random copolymers including two and three NBE repeating units.