Ethylene polymerization activity under practical conditions displayed by zirconium complexes having two phenoxy-imine chelate ligands

Abstract

Ethylene polymerization using zirconium complexes having two phenoxy-imine chelate ligands was investigated at 50 and 75°C at 0.9 MPa ethylene pressure. The activity of the proto-catalyst, N-[(3- t-butylsalicylidene)anilinato]zirconium(IV)dichloride ( 1), decreased by increasing the polymerization temperature (50°C: 1192 kg-PE/mmol-Zr·h, 75°C: 209 kg-PE/mmol-Zr·h). The introduction of an electron donating group, such as an n-hexyl and a methoxy group, on the imine nitrogen or at the para-position of phenoxy oxygen in a benzene ring suppressed the activity decrease, however, the activity at 75°C was still lower than that at 50°C. The combination of an n-hexyl or a cyclohexyl group on the imine nitrogen and a methoxy group at the para-position of the phenoxy oxygen enhanced activity at 75°C. Thus, N-[(3- t-butyl-5-methoxysalicylidene)- n-hexylaminato]zirconium(IV)dichloride ( 5) and N-[(3- t-butyl-5-methoxysalicylidene)cyclohexylaminato]zirconium(IV)dichloride ( 6) displayed activities of greater than 1000 kg-PE/mmol-Zr h. Moreover, the introduction of an adamantyl or a cumyl group at the position adjacent to the phenoxy oxygen further increased the activity. N-[(3-Adamantyl-5-methoxysalicylidene)cyclohexylaminato]zirconium(IV)dichloride ( 7), N-[(3-cumyl-5-methoxysalicylidene)- n-hexylaminato]zirconium(IV)dichloride ( 8), and N-[(3-cumyl-5-methoxysalicylidene)cyclohexylaminato]zirconium(IV)dichloride ( 9) displayed exceptionally high activity ( 7: 3052 kg-PE/mmol-Zr·h, 8: 7078 kg-PE/mmol-Zr·h, 9: 7224 kg-PE/mmol-Zr·h).