Synthesis of a stereoblock polyketone through ancillary ligand exchange

We report a new strategy for synthesis of stereoblock polymers involving ancillary ligand exchange during a living transition-metal-catalyzed polymerization. We have also demonstrated cooperativity between chain-end and site control mechanisms through ligand exchange. On the basis of these results, stereoblock copolymer synthesis was approached by first growing an isotactic segment with I-2, then switching on syndiotactic growth by displacing the bisoxazoline ligand from the Pd(II) catalyst with bipyridine.