Synthesis of a Series Novel Titanium Complexes with Salicylaldimine Ligands and Their Catalytic Performance for Ethylene Polymerization postprint

Abstract: Four salicylaldimine ligands (called after 5, 6, 7 and 8 respectively) and their titanium complexes containing bis(phenoxy-imine) ligands, namely [O-C6H4-ortho-CH=N-2, 6-(i-Pr)2-C6H3]2TiCl2(called after 13), [O-(5-NO2)-C6H3-ortho-CH=N-2, 6-(i-Pr)2-C6H3]2TiCl2(called after 14), [O-(3, 5-di-Br)-C6H2-ortho-CH=N-2, 6-(i-Pr)2-C6H3]2TiCl2(called after 15) and [O-(3, 5-di-C(CH3)3)- C6H2-ortho-CH=N-2, 6-(i-Pr)2-C6H3]2TiCl2 (called after 16) have been synthesized with salicylaldehyde and TiCl4 as raw materials. The prepared ligands and complexes were characterized by means of 1H-NMR and elemental analyses as well as mass spectra. After activated with methyaluminoxane (MAO), the complexes 13-16 become efficient catalysts for ethylene polymerization in methylbenzene. Under the conditions of T= 60℃, P=2.0 MPa and n(MAO)/n (cat)=1500∶1, the catalytic activities for the activated complexes 14-16 reached 1022.73-1302.27 g·PE /(mmol·Ti·h·MPa), which were much higher than that for the activated complex 13. The prepared polyethylene possessed a viscosity-average molecular weight in a rang of 19266-44754 measured by viscometry and a molecular weight distribution Mw /Mn in a rang of 1.88-2.12 measured by Gel Permeation in Chromatography. Among others the activated complex 15 displays the highest activity for ethylene polymerization under the same conditions. The characterization by 13C-NMR and DSC showed that the polymer synthesized with catalyst of the activated complex 15 was actually a kind of linear and crystalline polyethylene.