Polypropylene "Chain Shuttling" at Enantiomorphous and Enantiopure Catalytic Species:Direct and Quantitative Evidence from polymer Microstructure

The synthesis of olefin block copolymers and stereoblock polymers in the presence of Ziegler−Natta (and related) catalysts is a long-standing important industrial target, in view of the peculiar physical properties anticipated for the resulting materials (e.g., thermoplastic elastomers). The results reported in this Communication, demonstrate the wide scope of chain shuttling in catalytic olefin polymerization but also a fairly narrow operation window. In particular, for a given catalyst/CSA combination, the precondition that the alkyl-bridged, hetero-bimetallic intermediates assumed to be involved are labile seems to be exquisitely dependent (inter alia) on the chemical identity of the monomer (and therefore of the growing polymeryl), of the catalyst activator, andlast but not leastof the reaction solvent.