Binary Mixtures (Alk_nAlCl_3–n + Alk₂Mg) as Catalyst Components for Ethylene Polymerization and the Role of Titanium Oxidation State in Their Catalytic Activity

It was shown by EPR spectroscopy that Ti(IV) was gradually reduced to Ti(III) when a titanium(IV) dichloride complex with a saligenin ligand was used as a model pre-catalyst in the presence of (Et_nAlCl_3–n + Bu₂Mg) as an activator. Pre-activation of this complex (by stirring in an inert atmosphere with a half-load of the Al/Mg activator before being introduced into the reactor) significantly (about twofold) enhanced its catalytic activity, up to 4100 kg_PE mol_Ti^–1 h^–1 atm^–1. All the synthesized polyethylene samples were linear ultrahigh-molecular-weight polymers (UHMWPEs) with M_v = 1.0–3.5×10⁶ g/mol. This pre-activation technique was further employed to test a series of Al/Mg activators that differed in the nature of their organometallic compounds and in their Al/Mg molar ratio. The test data suggest that the catalytic system under study had active sites with titanium being present mainly in the oxidation state of +3. Most samples of UHMWPE produced with the pre-activated complex proved suitable for solvent-free processing into high-strength oriented films.