A series of 2-(1-(arylimino)propyl)quinolin-8-olate half-titanocene dichlorides, Cp'TiCl2L (Cp' = ?5-C5H5 or ?5-C5Me5, L = 2-(1-(2,6-R1-4-R2-phenylimino)propyl)quinolin-8-olate), was synthesized via the stoichiometric reaction of Cp'TiCl3 with the corresponding potassium 2-(1-(2,6-R1-4-R2-phenylimino)propyl)quinolin-8-olate salt. All titanium compounds were characterized by elemental analysis, 1H NMR and 13C NMR spectroscopy; the molecular structures of two representative compounds were determined by single crystal X-ray diffraction. On activation with methylaluminoxane (MAO), all half-titanocene compounds showed high activity in ethylene polymerization, and furthermore, performed with good to high activities in the co-polymerization of ethylene with either 1-hexene or 1-octene affording polyethylenes with high co-monomer incorporation. Less bulky ortho-substituents (R1) on the phenylimino groups were found to enhance the catalytic activities of their titanium compounds. In general, the titanium pro-catalysts containing ?5-C5Me5 (C7–C12) exhibited higher activities than did their analogues bearing ?5-C5H5 (C1–C6). Some of the resultant polyolefins were ultrahigh molecular weight polyethylene.