The copolymerizations of ethylene with cyclic dienes [dicyclopentadiene (DCPD) and 2,5-norbornadiene (NBD(] using bis(beta-enaminoketonato)titanium complexes [PhN = C(R-2)CHC(R-1)O](2)TiCl2 (1a: R-1 = CF3, R-2 = CH3; 1b: R-1 = t-Bu, R-2 = CF3; 1c: R-1 = Ph, R-2 = CF3) have been investigated. In the presence of modified methylaluminoxane, these complexes exhibited high catalytic activities in the copolymerization of ethylene with DCPD or NBD, affording high molecular weight copolymers with unimodal molecular weight distributions. H-1 and C-13-NMR spectra reveal ethylene/DCPD copolymerizations by catalysts la c proceeds through the enchainment of norbornene ring. Catalysts la and 1c showed a tendency to afford alternating copolymers. More noticeably, catalysts 1b and 1c bearing bulky substituents on the ligands promote ethylene/NBD copolymerization without crosslinking, affording the copolymer containing intracyclic double bonds. The NBD incorporation as high as 27.2 mol % has been achieved by catalyst 1c. Moreover, the microstructures of the copolymers were further confirmed by the measurement of reactivity ratios and dyad monomer sequences as well as mean sequence lengths. The intracyclic double bonds of ethylene/DCPD or ethylene/NBD copolymers can be fully converted into polar groups such as epoxy, amine, silane, and hydroxyl groups under mild conditions. Convenient synthesis of hydroxylated polyethylene can be provided for the first time through the ring opening reaction of epoxide. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1764-1772, 2010