Synthesis of Stereoblock Elastomeric Poly(propylene)s Using a (2‐PhInd) 2 ZrCl 2 Metallocene Catalyst in the Presence of Co‐Catalyst Mixtures: Study of Activity and Molecular Weight

The effect of adding various aluminum alkyls (R = Et, i ‐Bu) on the polymerization of propylene is studied using a (2‐PhInd) 2 ZrCl 2 pre‐catalyst. A mild deactivating effect is found upon addition of TIBA, whereas TEA shows a sharp deactivating effect. Increasing amounts of AlR 3 results in a significant activity increase for TIBA, but an activity plateau for TEA. AlR 3 imposes remarkably different effects on the molecular weight and stereochemical microstructure of polymers. As the TIBA concentration increases, $\overline {M} _{{\rm v}} $ increases at first, growing from 49 000 to 72 000, but subsequently drops to 40 000. For TEA, $\overline {M} _{{\rm v}} $ decreases sharply, plummeting from 49 000 to 17 000. Both TIBA and TEA increase the mmmm pentad content from 7.9 to 23.5% and 17.6%, respectively.