Effects of MgCl2 Crystallographic Structure on Active Centre Formation in Immobilized Single‐Centre and Ziegler–Natta Catalysts for Ethylene Polymerization

The ability of a Mgcl 2 support to activate a transition metal catalyst has been found to depend both on the crystallographic structure of the support and on the nature of the catalyst. A high degree of crystallographic disorder can be very effective for the immobilization and activation of titanium and vanadium complexes, but is not necessarily effective for zirconocene activation. A highly disordered support prepared by the reaction of MgBu 2 with HCl gave high activity with TiCl 4 but low activity with (n-PrCp) 2 ZrCl 2 . High polymerization activities with the zirconocene were only obtained with supports of type MgCl 2 /AlR n (OEt) 3-n prepared from the reaction of AlR 3 with MgCl 2 ·1.1EtOH. These supports are characterized by additional peaks in the X-ray diffraction pattern, indicating the presence of a crystalline structure which is absent in the other supports and contains highly Lewis acidic sites able to generate the active metallocenium species.

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