Ethylene and Ethylene/α-Olefin (Co)Polymerization Behavior of Bis(phenoxy−imine)Ti Catalysts: Significant Substituent Effects on Activity and Comonomer Incorporation

The ethylene and ethylene/α-olefin (co)polymerization behavior of bis(phenoxy−imine)Ti complexes 1−7 possessing a series of substituents ortho to the phenoxy O's (ortho substituents 1, iPr; 2, cyclohexyl; 3, cyclooctyl; 4, cyclododecyl; 5, tBu; 6, CMe2Ph; 7, Ph) with dried methylaluminoxane activation was investigated. At 50 °C, all complexes displayed some of the characteristics of living ethylene polymerization and produced polyethylenes (PEs) with very narrow molecular weight distributions (Mw/Mn 1.08−1.19, Mw 14 900−62 100), albeit under limited conditions. Generally, the Ti complexes with sterically bulkier ortho substituents exhibited higher activities [e.g., 6: activity 93.2 kg of PE/(mol of cat. min)]; the ortho substituents with quaternary α-C atoms attached to the phenoxy rings, providing higher activities than those with tertiary α-C atoms on the basis of the steric bulk of the entire ortho substituent. To our surprise, complex 7 incorporating an ortho phenyl group displayed the highest activity and formed the highest-molecular-weight PE [activity 230 kg of PE/(mol of cat. min), Mw 456 000], demonstrating the beneficial effects of the ortho phenyl group. Conversely, as to ethylene/propylene copolymerization, an increase in the steric bulk of the ortho substituent resulted in reduced activity for complexes 5 and 6 having quaternary α-C atoms, although the increase led to enhanced activity for complexes 1−4 having tertiary α-C atoms. In addition, complexes 1−4 displayed far higher propylene incorporation (25.5−26.4 mol %) than complexes 5 and 6 (6.3 and 4.2 mol %). Again, complex 7 with the ortho phenyl group displayed exceptional behavior and had the highest copolymerization activity coupled with the highest propylene incorporation (38.8 mol %). It should be noted that a wide range of propylene incorporation (4.2−38.8 mol %) was achieved with complexes 1−7 under identical conditions. Moreover, for ethylene/1-hexene and ethylene/1-decene copolymerizations, complexes 4 (cyclododecyl) and 7 (phenyl) achieved high comonomer incorporation while maintaining high catalytic efficiency.