Ethylene/Higher α-Olefin Copolymerization Behavior of Fluorinated Bis(phenoxy−imine)titanium Complexes with Methylalumoxane: Synthesis of New Polyethylene-Based Block Copolymers

Abstract

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 α-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 α-olefin copolymers with very narrow molecular weight distributions [e.g., PEs, Mw/Mn = 1.05−1.16, Mn = 44000−412000; ethylene/1-hexene copolymers, Mw/Mn = 1.07−1.19, Mn = 49000−102000, 1-hexene content 3.2−22.6 mol %], indicative of living polymerization. The incorporation ability for higher α-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 α-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 α-olefins. These block copolymers exhibited lower peak melting temperatures (Tm) relative to the corresponding homo-PE. The molecular weight and 1-hexene content of the copolymer segment had a considerable effect on the Tm values of the resultant block copolymers. A polyethylene-b-poly(ethylene-co-1-hexene) (Mw = 79900, Mw/Mn = 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.