Various elastomeric polypropylenes (PPs) are synthe- sized through homogeneous propylene polymerization with met- allocene catalyst (2-PhInd)2ZrCl2 in the presence of different cocatalyst mixtures: triethylaluminum (TEA)/methylaluminoxane (MAO) or triisobutylaluminum (TIBA)/MAO in the range of AlAlR3/ AlMAO ¼ 0.0–0.9. The cocatalyst formulation impacts the resultant polymer microstructure and the thermal and dynamic mechanical properties of the produced PPs. 13 C NMR analysis of the polymers reveals essentially atactic PP, with mmmm ¼ 7.9%, when AlAlR3/ AlMAO ¼ 0.0. The mmmm pentad content is maximized when AlAlR3/AlMAO ¼ 0.8; for TIBA, mmmm ¼ 23.5%; and for TEA, mmmm ¼ 17.6%. Differential scanning calorimetry analysis and dynamic mechanical thermal analysis corroborate these findings. Specifically, Tm, DHm,and Tg are essentially maximized under these conditions, and the minimum damping is observed for AlAlR3/AlMAO ¼ 0.6–0.8. 1 H NMR analysis of themixtures of catalyst and cocatalysts (without monomer) shows very minor differences for [Zr]:AlAlR3 in the range of 1:1–1:5.V C 2012Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51,724–731

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