Transforming abundant but inert CO2 into useful polymers has been pursued since the 1960s (ref. 1) and has typically been achieved by copolymerization with a reactive comonomer, aided by a catalyst, which can address both thermodynamic constraints and high kinetic barriers associated with CO2 fixation and incorporation2–5. However, making polyesters remains a challenge as alternating copolymerization of CO2 with alkenes is thermodynamically infeasible6. Here we introduce a closed-loop CO2-based polyester platform for producing high-performance yet recyclable polyesters by direct alternating copolymerization of CO2 with bicycloalkanes, bicyclic butane (BCB) and pentane (BCP) monomers. This copolymerization is initiated by a simple organic catalyst and proceeds in a perfectly alternating fashion to high-molar-mass polyesters with maximum (50 mol%) CO2 incorporation and architecturally defined backbones, in which the in-chain ring structure enables tailorable thermal and mechanical properties. These polyesters exhibit desired orthogonal performance and end-of-life outcomes. Although the BCB-CO2 polyesters exhibit exceptional thermal and hydrolytic stability across the full pH range, they can be selectively depolymerized in bulk and base-catalysed conditions to regenerate pure BCB monomers in >90% isolated yield. The BCP-CO2 polyesters can also be selectively depolymerized but to bicyclolactones. Sequential depolymerization–repolymerization cycles establish circular lifecycles for BCB/BCP-CO2 high-performance polyesters.
