Of Poisons and Antidotes in Polypropylene Catalysis

Quenched‐flow studies of MgCl 2 ‐supported Ziegler–Natta catalysts were combined for the first time with 13 C NMR fingerprinting of the nascent polymer and conclusively proved that, depending on the catalyst formulation, propene polymerization can be slowed down significantly by the occurrence of the few regiodefects (2,1 monomer insertions), changing active sites into dormant sites. Catalysts modified with ethylbenzoate show little dormancy. The more industrially relevant phthalate based catalysts, instead, are highly dormant and require the presence of H 2 to counteract the deleterious effect of this self‐poisoning on productivity and stereoselectivity.