Ethylene/higher α-olefin copolymerization behavior of fluorinated bis(phenoxy-imine)titanium complexes with methylalumoxane:: Synthesis of new polyethylene-based block copolymers

The catalytic behavior of fluorinated bis(phenoxy-imine)titanium complexes bearing a series of substituents ortho to the phenoxy oxygen was studied for ethylene and ethylene/higher alpha-olefin (i.e., 1-hexene, 1-octene, and 1-decene) (co)polymerizations. Independent of the magnitude of steric bulk of the ortho-substituent, all the complexes that were investigated produced polyethylenes (PEs) and ethylene/higher alpha-olefin copolymers with very narrow molecular weight distributions [e.g., PEs, M-w/M-n = 1.05-1.16, M-n = 44000-412000; ethylene/1-hexene copolymers, M-w/M-n = 1.07-1.19, M-n = 49000-102000, 1-hexene content 3.2-22.6 mol %], indicative of living polymerization. The incorporation ability for higher alpha-olefins is highly dependent on the nature of the ortho-substituent, and Ti complexes with a sterically less encumbered ortho-substituent incorporated a higher amount of higher alpha-olefins. A number of unique block copolymers consisting of highly linear PE and ethylene/1-hexene copolymer segments were prepared using one of the living catalysts with enhanced incorporating capability for higher alpha-olefins. These block copolymers exhibited lower peak melting temperatures (T-m) relative to the corresponding homo-PE. The molecular weight and 1-hexene content of the copolymer segment had a considerable effect on the T-m values of the resultant block copolymers. A polyethylene-b-poly(ethylene-co-1-hexene) (M-w = 79900, M-w/M-n = 1.26, 1-hexene content 4.3 mol %) possessed unique tensile properties with a good combination of extensibility and toughness compared to the corresponding blend and random (co)polymers.