The Preparation Of Supported Metallocene Catalysts And Their Application To Ethylene Polymerization

In this work, we prepared a series of novel supports that were used to immobilizemetallocene for catalyzing ethylene polymerization. The polyethylenes of special morphologyand different types of composites were obtained. The preparation of the supports andsupported catalysts, ethylene polymerization behavior and the properties of the resultingpolyethylenes were studied. The detail is listed as below:（1） TiO₂nanotube supported metallocene catalysts for ethylene polymerization.1. TiO₂nanotube with the diameter of14.6nm and the length of0.7±0.2μm wassuccessfully prepared and used as support of metallocene for ethylene polymerization. Thenanotube support and supported catalyst were characterized by BET, IR, SEM and TEM.2. The effects of polymerization conditions, such as Al/Zr molar ratio, polymerizationtemperature, and polymerization time, on ethylene polymerization behaviors wereinvestigated. With the increase of Al/Zr molar ratio, the rate of polymerization andpolyethylene molecular weight increased. The polymerization temperature had little effect onthe polymerization rate and molecular weight; with the extension of polymerization time, thepolymerization rate decreased, but the molecular weight was gradually increasing. Amongthem the Al/Zr molar ratio has the most significant influence in ethylene polymerization.3. The effects of Al/Zr molar ratio, polymerization temperature and polymerization timeon the morphologies of the polyethylene were studied, and the nanofibers, floccules andnanosheets of polyethylenes were obtained by controlling the polymerization conditions.When the Al/Zr molar ratio was relatively low, the nanotube acted as a nano-reactor togenerate polyethylene nanofibers by extrusion polymerization. With the increase of Al/Zrmolar ratio, the polymerization rate was very fast, resulting in the fracture of the nanotube. Sothe polyethylene sheets were generated due to replication effect of support fragment. Thepolymerization rate decreased gradually with the increase of polymerization time, producingmore and more polyethylene flocci. Obviously, the synergistic effect of tubular structure ofTiO₂nanotube and polymerization rate contributed to the morphologies of the resultingpolyethylene.（2） The preparation of polyethylene composites by in situ ethylene polymerization usingmodified graphite oxide supported metallocene catalysts.1. Graphite oxide （GO, d=0.821nm） was synthesized from natural graphite powderaccording to the Hummers and the organic guests （phenylalanine, butylamine, octylamine or3–aminopropyltriethoxysilane） were introduced into the spaces of graphite oxide layers. The GO and the modified GO were used as supports of metallocene for ethylene polymerization.The supports and the supported catalysts were characterized by XRD and SEM.2. The modified GO supported catalysts showed higher catalytic activity than GOsupported catalyst and homogeneous catalyst. Among them, Cp₂ZrCl₂/MAO/AGO exhibitedthe highest catalytic activity （1.01×106g of PE/mol of Zr·h）. Two different types ofcomposites were obtained from heterogeneous polymerization:（1） the traditional phaseseparated composite from ethylene polymerization catalyzed by the unmodified GO supportedMAO/Cp₂ZrCl₂catalyst system;（2） the nanosheet–shaped nanocomposites from in situintercalated ethylene polymerization catalyzed by the modified GO supported MAO/Cp₂ZrCl₂catalyst system.3. The effect of different supporting modes on catalytic behaviors （using GO and AGOas the supports）:Mode1: Surpport+Cp₂ZrCl₂â†'Cp₂ZrCl₂/SurpportMode2: Surpport+MAO+Cp₂ZrCl₂â†'Cp₂ZrCl₂/MAO/SurpportThe loading efficiency and catalytic activity of the supported catalysts from mode2werehigher than those from mode1. However, obtaining phase separated composite or nanosheet–shaped nanocomposite, it was determined by the characteristic properties of supports, but notthe supporting modes.