Trialkylaluminums: Efficient cocatalysts for bis(phenoxy-imine)zirconium complexes in ethylene polymerization

Abstract

Trialkylaluminums as cocatalysts for bis(phenoxy-imine)Zr complexes, bis[ N-(3- tert-butylsalicylidene)-anilinato]zirconium dichloride ( 1) and bis[ N-(3- tert-butylsalicylidene)-cyclohexylaminato]zirconium dichloride ( 2), are investigated for ethylene polymerization without MAO or Ph 3CB(C 6F 5) 4. The effects of alkylaluminums, Al/Zr molar ratio, polymerization temperature and time as well as the comonomer 1-hexene on polymerization performance are examined. In appropriate range of Al/Zr molar ratio, the catalyst system bis(phenoxy-imine)Zr complex/trialkylaluminum shows high activity for ethylene polymerization, which approximates to bis(phenoxy-imine)Zr complex/MAO system. Their catalytic activities depend on not only the nature, but also the amount, of the trialkylaluminum. Both the molecular weights and the polydispersities ( M w/ M n) of PEs produced by 1 with Et 3Al, He 3Al, or Me 3Al are higher than those with MAO. The nature, rather than the amount, of alkylaluminum determines the M w and the polydispersity of polymer in polymerization with the same complex. Unexpectedly, M w of the polyethylenes produced with complex 1/triethylaluminum increases with polymerization time. The catalyst system bis(phenoxy-imine)Zr complex/trialkylaluminum has low capacity of copolymerization.