Polypropylene "chain shuttling" at enantiomorphous and enantiopure catalytic species: Direct and quantitative evidence from polymer microstructure

Occurrence of chain shuttling for polypropylene chains in the presence of a chiral isotactic selective catalyst used in the racemic form was demonstrated. Details of the microstructural assignment and mechanistic conclusions by comparing the results with those achieved with the same catalyst in enantiopure form were also provided. Polymer polydispersity was the parameter that was monitored throughout the set of experiments, which for a single-center crystal was close to 2.0 when chain shuttling does not occur. NMR spectroscopy or the microstructural analysis of the polymer was inconclusive, and fabrication results showed that the samples were largely physical blends, with almost a minor fraction of stereoblock chains. Results showed a wide possibility of occurrence of chain shuttling in catalytic olefin polymerization.