Ethylene copolymerizations with norbornene (NBE) using half-titanocenes containing imidazolin-2-iminato ligands, CpTiCl2[1,3-R2(CHN)2CN] [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. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 25752580