Characterization of the changes in the initial morphology for MgCl2‐supported Ziegler‐Natta polymerization catalysts

Recently considerable detail has become available on the initial morphology and the morphological changes that occur for silica based Cr catalysts for ethylene polymerization. These catalysts are produced as a dry powder and may be employed either in gas phase or in slurry processes. MgCl2‐supported Ziegler‐Natta polymerization catalysts are often prepared and employed as slurries. They usually are never dried and thus few studies have employed the spectra of physical techniques common to the characterization of pore structure. In the current study, we have carefully removed the solvent for both ball‐milled and precipitated MgCl2‐supported catalysts. These catalysts are characterized by physical sorption, mercury porosimetry, and electron microscopy both as prepared and during the initial stages of polymerization (to ∼ 100 g of polymer/g of catalyst). We find that the initial catalyst may be represented by a complex agglomerate of small crystallites as contrasted with the branched pore network found in Cr/silica catalysts. As a result, it is concluded that the initial fragmentation of the MgCl2 based systems is more uniform as contrasted with the progressive fragmentation of the silica‐based system. This fragmentation mechanism facilitates the retention of greater polymer/catalyst surface during the initial stages of the polymerization.