AbstractThe results of a study on a new generation of MgCl2supported Ziegler‐Natta catalysts that contain dialkyl propane diethers as internal donors and produce highly stereospecific polypropene even without any external donor are presented. The results concerning three different catalysts containing 2,2‐diisobutyl‐1,3‐dimethoxy propane (DIBDMP), 2,2‐dicyclopentyl‐1,3‐dimethoxy propane (DCPDMP) and 2‐ethyl,2‐butyl‐1,3‐dimethoxy propane (EBDMP) as internal donors are compared. The same donors have also been studied by using them as external donors with a catalyst contaning diisobutyl phthalate as internal donor. The present results, along with previously obtained findings on traditional supported Ziegler‐Natta catalysts, permit a general comprehension of the role of inter