Regioselective partial hydrogenation of tricyclopentadiene (TCPD) was achieved with a high turnover number of 10 000 by catalysis with a N-heterocyclic carbene-palladium complex. Copolymerization of ethylene and the partially hydrogenated product, dihydrotricyclopentadiene (HTCPD), was realized using a catalytic system of [8-The copolymer was unambiguously characterized through the analysis of one-and two-dimensional NMR spectra. The monomer reactivity ratios, r ethylene and r HTCPD , determined through the Fineman-Ross plot, were 2.8 and 0.025, respectively, indicating negligible successive insertion of two HTCPD. A nearly alternating copolymer with a HTCPD content of 45 mol % was obtained with a satisfactory activity (4.7 Â 10 6 g/(mol Ti h)), of which T g was 177 °C, significantly higher than that of norbornene/ethylene copolymer at the same cycloolefin content. Tensile stress-strain curves indicated that the brittleness observed for a high-T g norbornene/ethylene copolymer was relieved to show some ductile property for the HTCPD/ethylene copolymer of the same level of high T g .