Ethylene polymerization and ethylene/hexene copolymerization by vanadium(III) complexes bearing bidentate phenoxy-phosphine oxide ligands



A series of novel vanadium(III) complexes bearing bidentate phenoxy-phosphine oxide [O,P=O] ligands, (2-R1-4-R2-6-Ph2P=O-C6H2O)VCl2(THF)2 (2a: R1 = R2 = H; 2b: R1 = F, R2 = H; 2c: R1 = tBu, R2 = H; 2d: R1 = Ph, R2 = H; 2e: R1 = R2 = Me; 2f: R1 = R2 = tBu; 2g: R1 = R2 = CMe2Ph) have been synthesized by adding 1 equiv of the ligand to VCl3(THF)3 dropwise in the presence of excess triethylamine. Under the same conditions, the adding of VCl3(THF)3 to 2.0 equiv of the ligand afforded vanadium(III) complexes bearing two [O,P=O] ligands (3c, 3f). All the complexes were characterized by FTIR and mass spectra as well as elemental analysis. Structures of complexes 2c and 3c were further confirmed by X-ray crystallographic analysis. On activation with Et2AlCl and ethyl trichloroacetate, these complexes displayed high catalytic activities for ethylene polymerization (up to 26.4 kg PE/mmolV·h·bar) even at high reaction temperature (70 °C) indicative of high thermal stability, and produced high molecular weight polymers with unimodal molecular weight distributions. Additionally, the complexes with optimized structure exhibited high catalytic activities for ethylene/1-hexene copolymerization. Catalytic activity, comonomer incorporation, and polymer molecular weight can be controlled in a wide range via the variation of catalyst structure and the reaction parameters such as Al/V molar ratio, comonomer feed concentration, and reaction temperature. The monomer reactivity ratios rE and rH were determined according to 13C NMR spectra, which indicated these complexes preferred ethylene to 1-hexene in the copolymerization. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 5298–5306