| Abstract
| - A study on a new generation of MgCl2-supportedZiegler−Natta catalysts, which containdialkylpropane diethers as internal donors and have the property ofproducing highly active andstereospecific catalysts without any external donor, has beenperformed. The behavior of three differentdiethers (2,2-diisobutyl-1,3-dimethoxypropane,2,2-dicyclopentyl-1,3-dimethoxypropane, and 2-ethyl-2-butyl-1,3-dimethoxypropane) as internal donors is compared with thebehavior of the same diethers whenthey are used as external donors with a catalyst containing diisobutylphthalate as internal donor. Theresults obtained show that the same isospecific centers are producedwhen the same diether donor ispresent as an internal donor or replaces diisobutyl phthalate duringpolymerization when it is added asan external donor. The sum of the present results and of thepreviously obtained findings on traditionalsupported Ziegler−Natta catalysts has enabled us to reach someconclusions on the role and reciprocalbehavior of internal and external donors.
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