Ethylene homo- and copolymerization catalyzed by vanadium, zirconium, and titanium complexes having potentially tridentate Schiff base ligands

Abstract

New potentially tridentate Schiff base ligands, 2-[({4-[(3-N,N-dimethylamino)propyl] phenyl}imino)methyl]-4,6-di-tert-butylphenol (L1H) and 2-[{2-(N-phenyl-N-methylaminomethyl)-phenylimino}-methyl]-4,6-di-tert-butylophenol (L2H) were prepared and after deprotonation they were reacted with VOCl3 or MCl4 (where M = Zr or Ti) to produce corresponding complexes (L1-V, L2-V, L1-Zr, L2-Ti) with good yields. All new compounds were characterized by the 1H and 13C NMR as well as FTIR spectroscopic methods. Upon activation with Et2AlCl or EtAlCl2, both the vanadium complexes exhibited exceptionally high catalytic activities in the ethylene polymerization (up to 69,000 kg/(molV⋅h) for L1-V and 101,500 kg/(molV⋅h) for L2-V) and remarkable thermal stability, and they produced UHMWPE. The complexes of group 4 metals were tested in the ethylene polymerization in conjunction with MMAO and Al(iBu)3/Ph3CB(C6F5)4, and L1-Zr was highly active (11,300 kg/(molZr⋅h)) and L2-Ti was moderately active (750 kg/(molTi⋅h)) when activated with MMAO. Furthermore, L1-2-V/EtAlCl2 systems were found to be very efficient in 1-octene incorporation and they produced copolymers with narrow chemical composition distributions and very narrow molecular weight distributions (Mw/Mn ≈ 2). In contrast to them, the catalysts based on titanium and zirconium complexes in conjunction with Al(iBu)3/Ph3CB(C6F5)4 gave copolymers with very broad comonomer and molecular weight distributions as well as with high molecular weights (Mw = 440,000–690,000 g/mol). It was also found that the chain transfer mechanism involved in the copolymerization process in the presence of vanadium and group 4 metal complexes was different.