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 Ph3CB(C6F5)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 Et3Al, He3Al, or Me3Al 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. [Copyright &y& Elsevier]