Fluorinated bis(phenoxy-imine)titanium complexes with methylaluminoxane for the synthesis of ultra high molecular weight polyethylene

Three fluorinated bis(phenoxy-imine)titanium complexes bearing ortho-halide substituents on the phenoxy rings [Cl (1), Br (2), I (3)] were synthesized, characterized and evaluated as precatalysts for the polymerization of ethylene in conjunction with methylaluminoxane (MAO) under atmospheric pressure. These C2-symmetric catalysts exhibit high activity toward ethylene polymerization and produce ultra high molecular weight polyethylene (UHMWPE) (MW > 3,000,000). The living polymerization was presented as evidenced by the narrow molecular weight distribution. The living nature of these catalysts is attributed to the interaction of a fluorine atom adjacent to the imine nitrogen and a β-hydrogen of a polymer chain resulting in the suppression of β-hydrogen transfer. The highest activity at 11.65 kg PE/mmol cat h was observed for the polymerization using complex 2. In comparison with complex 1, the more bulky bromo substituents can induce an effective ion-pair separation between the cationic active species and an anionic cocatalyst yielding a higher polymerization rate. However, in case of complex 3 with iodo substituents, the enhancement of the steric congestion at the metal center results in the decreased polymerization activity.