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To elucidate the particle growth mechanism in propylene polymerization with high‐yield MgCl2‐supported Ziegler‐Natta catalysts, observations have been carried out by electron microscopy on a series of samples having different degrees of polymer growth (from 0.1 to 1000 g/g of catalyst). Topics such as surface and bulk morphology, catalyst fragmentation, as well as distribution of the catalyst residues in the polymer have been investigated. The experimental data suggest that if the site distribution in the catalyst is uniform and the polymerization conditions are mild, the polymer growth starts uniformly throughout the catalyst particle, which then undergoes an even and progressive fragmentation into very fine units homeogeneously dispersed in the polymer matrix. The above results thus provide further experimental support to the particle growth mechanism outlined in the multigrain or polymeric flow models. © 1994 John Wiley & Sons, Inc.

ABSTRACT:A new process that combines the excellent morphology control of Ti-based catalysts with the unique features of polyolefins from metallocenes has been devised. First, propylene is polymerized with the Ti-based catalysts, having spherical form; then, activated metallocene catalysts are introduced into the porous PP spheres, through an in situ impregnation and drying process, once the Ti has been deactivated. Then, the olefins polymerization, catalyzed by the metallocene, is carried out in gas phase. This step, as well as the morphology of the as-polymerized polymer particles, has been investigated in detail. New heterophasic copolymers (PP/EPR) having free-flowing spherical form have been achieved, and the morphology of the copolymer spheres pointed out that the rubber is well dispersed inside the polymer granule.

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Scanning electron microscopy and microanalysis by energy dispersive system show that the structure of the foamed char obtained on burning polypropylene fire retarded with an intumescent additive system, can be strongly modified in the presence of typical inorganic fillers. Modifications involving both the physical and chemical characteristics of the char might be related to chemical reactions between fillers and acid phosphorus moieties of the fire retardant. Fillers that modify the structure of the char tend to decrease the efficiency of the fire retardant system. ZUSAMMENFASSUNG:Rasterelektronenmikroskopie und Mikroanalyse mit einem energiedispersiven System zeigen, daR die Struktur des Kohleschaumes, der bei der Verbrennung eines mit einem intumeszierenden Additiv ausgerusteten, mineralgefullten Polypropylens entsteht, von der Art des anorganischen Fullmaterials abhangt. Dies konnte durch chemische Reaktionen zwischen dem Fullmaterial und sauren Phosphorbestandteilen des flammhemmenden Additivs verursacht werden. Eine Veranderung der Kohlestruktur ist mit einer Abnahme der Wirkung des flammhemmenden Zusatzes verbunden.