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The chemistry of the catalyst-cocatalyst interaction was investigated in systems containing different internaVexterna1 donor pairs. Qualitatively similar results were obtained with the ethyl benzoate/methyl p-toluate (EB/MFT) and dibutyl phthalate/triethoxy(henyl)silane (DBPIEPS) systems, which thus were assumed to follow the same model. Quantitative differences were accounted for by assuming a different basic strength of the two donor pairs towards MgC12 and AIEt,.-Catalyst C: containing DBP as internal donor.(EB = ethyl benzoate, DBP = dibutyl phthalate). 0 1991, Huthig & Wepf Verlag, Basel CCC 0025-1 16)

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The new third generation Ziegler-Natta catalysts give extremely high yield and produce highly stereoregular polypropylene of controlled morphology and size. The role of Lewis bases and MgCl, is underlined and their mechanisms of action is discussed in the light of the most significant experimental data. Furthermore, technological and economical advantages are emphasized. ZUSAMMENFASSUNG:Die neuen Ziegler-Natta-Katalysatoren der sog. dritten Generation erlauben mit hohen Ausbeuten die Herstellung von hochstereoregularem Polypropylen mit kontrollierbaren morphologischen Eigenschaften und KorngrdBen. Die Roue von Lewis-Basen und von MgCl, wird unterstrichen, und ihre Wirkungsmechanismen im Hinblick auf signifikante experimentelle Daten werden diskutiert . Weiterhin werden die technologischen und wirtschaftlichen Vorteile betont.

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