The influence of bridge type on the activity of supported Metallocene catalysts in ethylene polymerization
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Ethylene polymerization was carried out by immobilization of rac-ethylenebis(1-indenyl)zirconium dichloride (Et(Ind)2ZrCl2) and rac-dimethylsilylbis(1-indenyl)zirconium dichloride (Me2Si(Ind)2ZrCl2) preactivated with methylaluminoxane (MAO) on calcinated silica at different temperatures. Polymerizations of ethylene were conducted at different temperatures to find the optimized polymerization temperature for maximum activity of the catalyst. The Me2Si bridge catalyst showed higher activity at the lower polymerization temperature compared to the Et bridge catalyst. The highest catalytic activities were obtained at temperatures about 50 °C and 70 °C for Me2Si(Ind)2ZrCl2/MAO and Et(Ind)2ZrCl2/MAO catalysts systems, respectively. Inductively coupled plasma-atomic emission spectroscopy results and polymerization activity results confirmed that the best temperature for calcinating silica was about 450 °C for both catalysts systems. The melting points of the produced polyethylene were about 130 °C, which could be attributed to the linear structure of HDPE.
KeywordsSlurry polymerization Olefin polymerization ansa-Metallocene Silica support
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