Synthesis of Ultrahigh Molecular Weight Ethylene-Based (Co)polymers with Titanium Complexes Bearing Nonsymmetric Amine-bis(phenolate) Ligands

A series of novel Ti(IV) complexes bearing new type of nonsymmetric amine-bis(phenolate) tetradentate ligands, Me2NCH2CH2N[2-O-3-R1-5-tBuC6H2] [CH2(2-O-3-R2-5-tBuC6H2)]TiCl2 [R1 = R2 = tBu (1); R1 = R2 = CPhMe2 (2); R1 = R2 = CPh2Me (3); R1 = CPh3, R2 = tBu (4); R1 = CPh3, R2 = CPhMe2 (5); R1 = CPh3, R2 = CPh2Me (6); and R1 = R2 = CPh3 (7)], have been synthesized and characterized by 1H and 13C NMR. The X-ray crystallography analysis on complexes 5 and 6 demonstrates that both complexes exhibit a distorted octahedral geometry around their central metals. When activated with methylaluminoxane (MAO), dry-MAO, MAO/2,6-Ditert-butyl-4-methylphenol (BHT), or AliBu3/CPh3B(C6F5)4, these new complexes display moderate to high catalytic activities for ethylene polymerization and produce ultrahigh molecular weight polyethylenes (up to 3.74 × 106 g mol–1). Polymers with low to moderate isotacticity are formed from the polymerization reactions of propylene or 1-hexane, and the isotacticity of the produced polymers increases with the increase in bulkiness of the ligands of the titanium complexes. For copolymerization reactions of ethylene/1-hexene or ethylene/1-octene, the MAO/BHT or dry-MAO activated catalytic systems show relatively high catalytic activities [106–107 g of polymer (mol Ti)−1 h–1] and produce polyolefin thermoplastic elastomer (POE) or linear low-density polyethylene with high to ultrahigh molecular weights (105–106 g of mol–1) and moderate to high comonomer incorporations. The mechanical properties for some typical UHMWPE and POE samples were also determined and the results are in line with expectations. In most cases, these new titanium complexes display notable high thermal stability and long lifetime for the examined olefin polymerization reactions.