Oxygen‐Triggered Switchable Polymerization for the One‐Pot Synthesis of CO 2 ‐Based Block Copolymers from Monomer Mixtures

Switchable polymerization provides the opportunity to regulate polymer sequence and structure in a one‐pot process from mixtures of monomers. Herein we report the use of O 2 as an external stimulus to switch the polymerization mechanism from the radical polymerization of vinyl monomers mediated by (Salen)Co III −R [Salen= N , N ′‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamine; R=alkyl] to the ring‐opening copolymerization (ROCOP) of CO 2 /epoxides. Critical to this process is unprecedented monooxygen insertion into the Co−C bond, as rationalized by DFT calculations, leading to the formation of (Salen)Co III −O−R as an active species to initiate ROCOP. Diblock poly(vinyl acetate)‐ b ‐polycarbonate could be obtained by ROCOP of CO 2 /epoxides with preactivation of (Salen)Co end‐capped poly(vinyl acetate). Furthermore, a poly(vinyl acetate)‐ b ‐poly(methyl acrylate)‐ b ‐polycarbonate triblock copolymer was successfully synthesized by a (Salen)cobalt‐mediated sequential polymerization with an O 2 ‐triggered switch in a one‐pot process.