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

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 (Mw/Mn) 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 Mw and the polydispersity of polymer in polymerization with the same complex. Unexpectedly, Mw 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.

Graphical abstractTrialkylaluminums such as triethylaluminum (Et3Al), trihexylaluminum (He3Al), or trimethylaluminum (Me3Al) could be efficient cocatalysts to activate bis(phenoxy-imine)Zr complexes, for highly active ethylene polymerization. Figure optionsDownload full-size imageDownload as PowerPoint slide