Metallocene-Catalyzed Propene Polymerization: From Microstructure to Kinetics. Cs-Symmetric ansa-Zirconocenes

Highly syndiotactic propene polymn. in the presence of Cs-sym. metallocene cations is much less obvious than it may appear based on symmetry considerations alone. Effectively preventing the generation of m stereo-defects requires the assistance of a counterion able to slow site epimerization more than monomer insertion, but also seconding chain-migratory insertion in such a way that the pathway are not competitive. A good success in this delicate balance was achieved at the first attempt with MAO, in turn serendipitously discovered.