Scientists turned carbon dioxide into high-performance polyester; the material can be chemically recycled into reusable building blocks |
Carbon dioxide is abundant but chemically inert, which makes it difficult to turn into useful polymers. A study describes a closed-loop platform that uses carbon dioxide with bicycloalkanes to make high-performance, recyclable polyesters. They used bicyclic butane, or BCB, and bicyclic pentane, or BCP, monomers in a direct alternating copolymerization. A simple organic catalyst initiated the process, producing high-molar-mass polyesters with up to 50 mol% carbon dioxide incorporation. The resulting materials have defined backbones and tailorable thermal and mechanical properties. The study published by Colorado State University, as well as collaborators from Northwestern University, in Nature titled ‘Alternating CO2 and bicycloalkane copolymerization to circular polyesters‘ demonstrates selective depolymerisation and repolymerization, allowing the materials to undergo circular lifecycles.
How researchers used carbon dioxide to make new polyesters
Researchers developed the polyester platform to address a difficulty in using carbon dioxide for polymer production. Previous approaches have generally relied on copolymerization with reactive comonomers and catalysts, but making polyesters from carbon dioxide has remained challenging. The study uses bicycloalkanes instead, specifically bicyclic butane and pentane. These monomers undergo direct alternating copolymerization with carbon dioxide.The reaction is initiated by a simple organic catalyst and proceeds in a perfectly alternating manner. This produces high-molar-mass polyesters with a maximum of 50 mol% carbon dioxide incorporation. Their backbones are architecturally defined, while the in-chain ring structure allows the thermal and mechanical properties to be adjusted through monomer design. This design addresses the difficulty of incorporating carbon dioxide into polyester backbones.
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How the new polyesters can be broken down for recycling
The resulting polyesters combine defined molecular structures with different material properties. According to the study, the in-chain ring structure enables tailorable thermal and mechanical properties, allowing the polyester structures to be varied through the bicycloalkane monomers used. The BCB-CO2 polyesters showed exceptional thermal and hydrolytic stability across the full pH range. The researchers also examined their end-of-life behaviour through selective depolymerisation.Under bulk and base-catalysed conditions, the BCB-CO2 polyesters could be depolymerised to regenerate pure BCB monomers in more than 90% isolated yield. The BCP-CO2 polyesters could also be selectively depolymerised, producing bicyclolactones rather than the original BCP monomers. The products reflect the distinct chemistry of the two monomers during recycling in practice.
The polyesters can be repeatedly recycled into reusable building blocks
A key part of the study was showing that the materials could move through repeated production and recovery steps. The researchers carried out sequential depolymerisation–repolymerization cycles to establish circular lifecycles for BCB/BCP-CO2 high-performance polyesters. For the BCB system, selective depolymerisation regenerated the BCB monomer and carbon dioxide. The study also describes the proposed depolymerisation mechanism for this process. For the BCP system, selective depolymerisation generated bicyclolactone monomers.Those bicyclolactones were then re-polymerised to reform polyester, followed by another depolymerisation step. These experiments demonstrate chemical circularity through repeated conversion between polymer and recoverable molecular building blocks, rather than treating the polyester as a material with only one use.
What makes carbon dioxide-based polyesters suitable for chemical recycling
The researchers describe the work as a closed-loop carbon dioxide-based polyester platform that combines material performance with chemical recycling. The copolymerization reaches high molar masses while incorporating as much as 50 mol% carbon dioxide into the polyester. The study reports especially high thermal and hydrolytic stability for BCB-CO2 polyesters, alongside selective recovery of BCB monomers at more than 90% isolated yield.BCP-CO2 polyesters follow a different recycling pathway and produce bicyclolactones during depolymerisation. Together, the polymerisation and recovery steps establish circular lifecycles for these high-performance polyesters. The platform connects carbon dioxide incorporation with polymer properties and recovery.
