MgCl₂-Supported Non-Metallocene Single-Site Catalysts For Ethylene Polymerization

MgCl as a supporting material can greatly improve the activity and stereospecificity of heterogeneous Ziegler-Natta catalysts, leading to significant simplifications in polyolefin production processes. In particular, active species supported on spherical MgCl₂ have made spectacular progress in controlling polymer morphology as spherical particles. In this work, MgCl₂-supported non-Metallocene single-site catalysts were prepared, and the resulted solid catalysts were used in ethylene polymerization.New contributions of this work are as follows:(1) . Preparation of Spherical MgCl₂-Supported Late-Transition Metal Catalysts for Ethylene PolymerizationFacile and effective immobilization of late-transition metal catalysts. 2,3-bis-(2,6-diisopropylphenyl) butane diimine nickel (â…¡) dibromide (1) and 2,6-bis-[1-(2,4,6-trimethylphenylimino)ethyl]pyridine iron (â…¡) dichloride (2) , for ethylene polymerization has been achieved, using spherical MgCl₂ supports obtained by thermal dealcoholization of MgCl₂·2．56C₂H₅OH, and the effects of dealcoholization temperature on supported late-transition metal catalysts and the properties of resultant polymers were studied, the results indicated that:1．Supports with appropriate mechanical strength, high surface area and high porosity could be prepared by thermal dealcoholization of spherical MgCl₂·2．56C₂H₅OH supports; 2．BET, XRD, IR, SEM, GPC and DSC analyses indicate that the activities of the supported late-transition metal catalysts and the properties of resultant polymers are strongly dependent on the dealcoholization temperature. The support (SP-3) obtained by treating MgCl₂·2．56C₂H₅OH at 170℃for 4 h is very effective for immobilizing late-transition metal Fe (â…¡) and Ni (â…¡) catalysts. Compared with the corresponding unsupported homogeneous catalysts, a significant increase in activity is observed for the SP-3 supported catalysts in ethylene polymerization, and the kinetics of polymerization is stable during the reaction process. In addition, replication of the support morphology is found in final polymers;3．In this paper, 1 combined with 2 was supported on SP-3, and the resulted binary catalyst system shew high activity in ethylene polymerization, leading to the formation of spherical polymer particles with high bulk density. It is indicated that, to some extent, the proportion of high molecular weight and low molecular weight in the resultant PE can be controlled by changing the Ni/Fe molar ratio with negligible change of branches.(2) . Preparation of Spherical MgCl₂-Supported bis (phenoxy-imine) Zirconium Complex for Ethylene PolymerizationThe spherical MgCl₂ supports treated by MAO (named MAO-supports) were prepared using MgCl₂·2．56C₂H₅OH adducts as support material subjected to elimination of EtOH by thermal dealcoholization treatments. Then bis (phenoxy-imine) zirconium complex. bis-[N-(3-tert-butylsalicylidence)cyclohexyl--aminato] zirconium (â…£) dichloride (3) , was directly impregnated onto these MAO-supports, and the effects of dealcoholization temperature on supported catalysts and the properties of resultant PE were studied, the results indicated that:1．Dealcoholization temperature markedly influences the surface area and porosity of the resultant MAO-supports. When the support was pretreated at lower or higher temperature, the corresponding MAO-support shows very low surface area;2．XRD and IR analyses indicate that MAO has reacted with the residual ethanol in the supports, which is an important manner to get MAO fixed on the carrier. Morever, XPS analyse indicates that MAO can also be coordinated with MgCl₂, which is another way to get MAO fixed on the support;3．ICP and EDX analyses indicate that dealcoholization temperature not only determined the element content on the solid catalyst, but also influences the element distribution on the carrier;4．The activities of the supported phenoxy-imine catalysts and the properties of resultant polymers are strongly dependent on the dealcoholization temperature. The support (MSP-5) obtained by treating MgCl₂·2．56C₂H₅OH at 160℃for 4 h, then modified by MAO is very effective for immobilizing complex 3, the resultant solid catalyst (MSPC-5) shows very high activity in ethylene polymerization, and its kinetics of polymerization is stable during the reaction process. Finally, PEs with spherical morphology and high bulk density (over 0．35g/ml) were obtained, without reactor fouling;5．In this work, polymerization conditions such as alkylaluminums (cocatalysts), Al/Zr ratio, temperature and H₂ had a pronounced effect on the activity of MSPC-5 and properties of PE;(3) . New MgCl₂-Supported Single-Site Catalysts for Ethylene PolymerizationIn this work, a kind of new MgCl₂ support was obtained by anhydrous MgCl₂ co-milled with solid MAO, and it is a creative contribution. Then some single-site catalysts were supported on the new MgCl₂ support, and the resulted solid catalysts were tested in ethylene polymerization, the results indicated that:1．XRD and IR analyses indicate that MAO does be coordinated with MgCl₂, which is in good agreement with the results obtained by XPS;2．co-mlling time had no obvious effect on the texture of support after 12 hours;3．In this work, MgCl₂ was co-milled with solid MAO for different hours, and then complex 3 was supported on these co-milled supports. It was found that co-milling time markedly influences the activity of solid catalysts, but it had negligible effect on the kinetic profile and the properties of resultant PE. It is worth noting that the support (MS-5) obtained by co-milling 72 hr not only has low Al/Zr molar ratio, but also the resulted 3/MS-5 catalyst (MSC-5) shows the highest activity among these new supported 3 catalysts;4．Other single-site catalysts were supported using MS-5 as carrier, and the resulted solid catalysts all shew very high activity for ethylene polymerization, indicating that the new MgCl₂ support may have a good future.