Copolymerizations of 1-decene (DC) with 1,9-decadiene (DCD), 1-dodecene (DD) with 1,11-dodecadiene (DDD), and 1-tetradecene (TD) with 1,13-tetradecadiene (TDD), using Cp*TiMe2(O-2,6-(Pr2C6H3)-Pr-i) (1)-[Ph3C][B(C6F5)(4)] (borate) catalyst in the presence of (AlBu3)-Bu-i/Al(n-C8H17)(3) proceeded in a quasi-living manner in n-hexane at -30 to -50 degrees C, affording ultrahigh molecular weight (UHMW) copolymers containing terminal olefinic double bonds in the side chain with rather low PDI (M-w/M-n) values. In the DC/DCD copolymerization, the resultant copolymer prepared at -40 degrees C possessed UHMW (M-n = 1.40 x 10(6) after 45 min) with low PDI (M-w/M-n = 1.39); both the activity and the PDI value decreased at low polymerization temperature (M-n = 5.38 x 10(5), M-w/M-n = 1.18, after 120 min at -50 degrees C). UHMW poly(TD-co-TDD) was also obtained in the copolymerization at -30 degrees C (M-n = 9.12 x 10(5), M-w/M-n = 1.51, after 120 min), using this catalyst.