The influence of polymerization temperature (Tp) on the isoselectivity of the C2‐symmetric zirconocene catalysts rac‐Me2Si(2‐Me‐4‐PhInd)2ZrCl2/MAO ( 1 /MAO), rac‐Me(CyHex)Si[2‐Me‐4‐(4′‐tBuPh)Ind]2ZrCl2/MAO ( 2 /MAO), and rac‐Me2Si(2‐Me‐4‐Ph‐5‐OMe‐6‐tBuInd)2ZrCl2/MAO ( 3 /MAO) in propene polymerization, has been studied in the range 30–85 °C in liquid propene. All three catalysts show similar polymerization activity versus Tp profiles, with a maximum at about 60 °C ( 1 /MAO), 80?85 °C ( 2 /MAO), and 70?80 °C ( 3 /MAO). 3 /MAO shows the highest activity at any Tp. The isoselectivity of the three catalysts remains high and approximately constant in the whole Tp range investigated, as indicated by the roughly constant isotactic triad content (mm > 99%) of the produced isotactic poly(propylene)s (iPP). Surprisingly, the melting and crystallization temperatures of iPP increase by increasing TP. This behavior is due to an unexpected increase in catalyst regioselectivity with Tp, as indicated by the decrease in the content of 2,1‐erythro regiodefects (2,1e) at increasing Tp. A mechanism involving a metal cation–2,1‐coordinated propene slow state is proposed to account for this so far unnoticed behavior. The correlations between Tp, Tm, and [2,1e] are defined for these three catalysts.
