Ethylene Polymerization Catalyzed by Monocyclopentadienyl Titanium Complex Containing 8-Quinolinolato Ligand and ADF Study on the Formation Mechanism of Active Species

摘要

A monocyclopentadienyl titanium complex containing 8-quinolinolato (QCpTiCl2) was synthesized. Its activities in ethylene polymerization at various Al/Ti molar ratios, different temperatures and activation time were investigated. The activity with a Al/Ti molar ratio of 500 exhibited a maximum of 2.8× 105 g/(mol.h) at 30 ℃. The activation time of QCpTiCl2 with MAO before polymerization also plays a role on the activity. The structural properties of the produced polyethylene (molecular weight, molecular weight distribution and melting point) were discussed. Kinetic behaviors of ethylene polymerization with the QCpTiCl2/MAO system at different Al/Ti molar ratios were studied. For the QCpTiMeCl/MAO system and the CpTiMe2Cl/MAO system, binding energies of the examined intermediates were calculated by quantum-mechanical method based on ADF program, respectively. It is confirmed that the chlorinebridged adduct formed by the reaction of QCpTiMeCl with MAO is thermodynamically steady. In the case of the QCpTiMeCl/MAO system, olefin-separated ion pair (OSIP) mechanism is much favorable than ion-pair dissociation (IPD) mechanism. The experimental result on the CpTiMe2Cl/MAO system showed lower activity for ethylene polymerization than that on the QCpTiMeCl/MAO system, which revealed that the CpTiMe2Cl/MAO system is unfavorable to form active species with ethylene.