Norbornene copolymers functionalized with methyl ester group or carboxy group are facilely synthesized by the copolymerization of norbornene and 7-octenyldiisobutylaluminum (ODIBA) with ansa-dimethylsilylene(fluorenyl)(t-butylamido)dimethyltitanium (1) activated by Ph3CB(C6F5)(4), and the sequential CO2/methanolysis reactions or CO2/hydrolysis reactions, respectively. The methanolysis and the hydrolysis are simply switched by engaging acidic methanol or acidic aqueous acetone as the quenching/washing solution, respectively. Meanwhile, the increase of ODIBA in the copolymerization abruptly decreases the yield and number-average molecular weight (M-n) of the product. However, the addition of triisobutylaluminum (8 mM) and the use of excess Ph3CB(C6F5)(4) (twofold of 0.4 mM of 1) significantly increase the yield, accompanying the increase in the M-n and the narrowing of the molecular weight distribution (M-w/M-n), especially in the case of the use of excess Ph3CB(C6F5)(4). The yield (g polymer/g monomers), M-n, and M-w/M-n reach up to 0.82, 341,000, and 1.46, respectively, at a copolymerization condition. The carboxy groups in the norbornene copolymers are controlled in the range of 0-1.8 mol % in high polymer yields with high M-n and narrow M-w/M-n accompanied by the decrease in the contact angle with water from 104 degrees to 89 degrees. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 5085-5090