Oxygen-Triggered Switchable Polymerization for the One-Pot Synthesis of CO2 -Based Block Copolymers from Monomer Mixtures

Abstract

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 O₂ 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 CO₂ /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 CO₂ /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 O₂ -triggered switch in a one-pot process.

Keywords: block copolymers; organometallic-mediated radical polymerization; poly(propylene carbonate); ring-opening copolymerization; switchable catalysis.