[(o-Trifluoromethyl)phonyl]acetylene polymerized in a living fashion in the presence Of CpMoCl4-cocatalyst-EtOH catalysts (Cp: cyclopentadienyl; cocatalyst: EtMgBr, Et3Al, n-BuLi). The CpMoCl4-EtMgBr-EtOH (1:2:2) catalyst was particularly effective, with which the M-w/M-n of the formed polymer and the initiation efficiency, [P*]/[Cat], were 1.06 and 7.6%, respectively. Further, [P*]/[Cat] increased up to 10-13% at low temperatures (e.g. 0 degreesC) of catalyst aging and monomer addition. [(o-Trimethylsilyl)phenyl]acetylene also provided polymer having narrow molecular weight distributions with CpMoCl4-EtMgBr-EtOH (1:2:2). CpMoCl4 was more stable to air and moisture than MoOCl4 owing to the steric and electronic effects of the Cp ligand, while the activity of the CpMoCl4-based catalysts were lower than that of the MoOCl4-based counterparts.