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Chap._300009 - metal sites with extremely high catalyst...

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Several generations of catalyst have been developed in the past 4 decades. The major advances wereto increase the efficiency of catalyst and the control of polymer structure, i.e. molecular weight, molecular weight distribution and composition distributions in copolymer cases. Supported catalyst: An expensive heterogeneous transition metal catalyst (Ti, Zr. etc.) physically dispersed and supported on another very unexpensive material, such as Silica (SiO 2 ), Alumina (Al 2 O 3 ), clay, referred to as a support. Support or MgO SiO 2 Ti Cl Cl CH 3 CH 2 The supported catalyst provides large surface area of polymerization-active transition
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Unformatted text preview: metal sites, with extremely high catalyst efficiency (g P/g cat x hour). Most commercial supported catalysts have the effcientcy > 10 6 g/g cat. h. The heterogeneous catalysts usually contain several type of active sites, dependent on the surface of the crystal structure. The multiple sites produce polymers with broad molecular weight distribution. Metallocene homogeneous (single-site) catalysts (methaluminoxane cacatalyst is essential to prepare high polymers) + MAO Dicyclopentadienyl Zirconocene Dow "In-site" Catalyst Kaminsky Catalyst ZrCl 2 (CH 3 ) 2 Si N TiCl 2 C(CH 3 ) 3 TiCl 2...
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