Diskret kompakte Einbettungen in Sobolewschen Räumen

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Invariante Differentiale bei der Operation einer endlichen zyklischen Gruppe

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Stereospecific Polymerization of Propylene: An Outlook 25 Years after Its Discovery

In 1955 Natta and his co-workers from the Istituto di Chimica Industriale del Politecnico di Milano reported the properties of highly crystalline polypropylene and other poly-α-olefins^[1] which posses, at least in long sections of the main chain, asymmetric carbon atoms of the same absolute configuration (isotactic poly-α-olefins). The discovery of the new crystalline polymers was judged at that time “revolutionary in its significance”^[2] and heralded a new era in polymer science and technology. Indeed, crystalline polypropylene, because of its relatively high melting point and its outstanding mechanical properties, has found very extensive application in the field of plastics films and fibers.—25 years after this publication, it is worthwhile examining the further developments following this discovery which has had such a great scientific and industrial impact, and the problems which are still open concerning the structure of the catalytic centers and the mechanisms by which practically completely stereoregular polypropylenes are formed.