Scientists develop high-performance plastic from CO2 that can be repeatedly recycled

Researchers at Colorado State University and Northwestern University have developed a polymer platform that uses carbon dioxide as a building block for high-performance polyesters that can later be chemically broken down and rebuilt. The study, published in Nature under the title "Alternating CO2 and bicycloalkane copolymerization to circular polyesters", uses bicyclic butane (BCB) and bicyclic pentane (BCP) in a direct alternating copolymerization process. The method produced high-molar-mass polymers containing up to 50 mol% carbon dioxide while allowing their molecular building blocks to be recovered for further polymer production.

The work addresses a long-standing challenge in polymer chemistry: carbon dioxide is widely available but relatively chemically inert, making it difficult to incorporate efficiently into useful plastic materials. Instead of relying on highly reactive comonomers, the researchers used bicycloalkanes and a simple organic catalyst to create polyester chains with controlled structures and adjustable thermal and mechanical characteristics.

The resulting materials were also designed for chemical recycling. Depending on the bicycloalkane used, the researchers were able to selectively depolymerise the polymers and recover reusable molecular components, then carry out repolymerisation to demonstrate repeated material cycles.


Also Read: 16-year-old Class 11 student built hybrid stove using kerosene and steam, IIT Guwahati found it could help save 20% fuel

BCB and BCP provide the building blocks for CO2-based polyester

The research team focused on two bicyclic monomers, bicyclic butane and bicyclic pentane, abbreviated as BCB and BCP. These compounds were combined directly with carbon dioxide in an alternating copolymerization reaction, meaning the two components were incorporated into the growing polymer chain in a controlled sequence.

A simple organic catalyst initiated the reaction. According to the study, the process produced high-molar-mass polyesters while allowing carbon dioxide to account for as much as 50 mol% of the resulting material.

The approach differs from earlier strategies for making polymers from carbon dioxide, which have generally depended on combining CO2 with more reactive comonomers and catalyst systems. The researchers instead designed the reaction around bicycloalkanes, enabling carbon dioxide to become part of the polyester backbone.

The resulting polymer chains have defined architectures. Their structures can also be modified by changing the bicycloalkane monomer, giving researchers a way to tune the thermal and mechanical properties of the final material.

Ring-containing backbones give the materials tunable properties

The bicyclic structures do more than help the polymerisation process. The rings become part of the polymer backbone, where their presence influences the behaviour of the finished material.

The study found that the resulting polyesters could offer different thermal and mechanical characteristics depending on the monomer used. This gives the platform flexibility in designing materials for different performance requirements rather than producing a single polyester with fixed properties.

The BCB-CO2 materials showed particularly strong resistance to both heat-related degradation and hydrolysis. The researchers reported exceptional thermal and hydrolytic stability across the full pH range tested.

These characteristics are important because a recyclable polymer needs to remain sufficiently durable during use while still being capable of controlled breakdown under appropriate recycling conditions.

BCB polyester can release its monomer at more than 90% yield

The researchers investigated what would happen to the new materials once they reached the end of their useful life. Rather than treating the polymers as disposable materials, they tested selective depolymerisation, a chemical process that breaks the polymer back into recoverable molecular components.

Under bulk and base-catalysed conditions, the BCB-CO2 polyester could be selectively depolymerised to regenerate pure BCB monomers. The study reported more than 90% isolated yield for the recovered BCB.

The process also released carbon dioxide, allowing the researchers to recover both major components involved in the original polymer system.

The high recovery level is significant for the closed-loop design described in the study because the goal is not merely to break the plastic apart, but to retrieve useful starting materials that can be put back into the manufacturing cycle.

BCP polyester follows a different recycling route

The second polymer system, based on bicyclic pentane, behaved differently during chemical recovery. Instead of returning directly to the original BCP monomer, selective depolymerisation of the BCP-CO2 polyester produced bicyclolactones.

The researchers found that this difference came from the distinct chemistry of the two bicycloalkane monomers. Although both systems were created using the same broader carbon dioxide-based polymerisation strategy, their end-of-life pathways were not identical.

The bicyclolactones generated from the BCP material were not treated simply as waste products. Researchers used them as new molecular building blocks in a subsequent polymerisation step, rebuilding the polyester before subjecting it to another depolymerisation cycle.

Repeated cycles demonstrate a chemical route to circular plastics

To test whether the system could support repeated use, the team carried out sequential depolymerisation and repolymerisation experiments.

For the BCB-based material, the cycle involved producing the polyester, selectively breaking it down, recovering BCB and carbon dioxide, and then using those components again. The study also proposes a mechanism to explain how the BCB polymer undergoes depolymerisation.

The BCP system required a different sequence. Its depolymerisation generated bicyclolactone monomers, which were then repolymerised into polyester. The newly formed material could subsequently be subjected to another depolymerisation step.

These repeated experiments demonstrate what the researchers describe as chemical circularity. Instead of producing a polymer that is made once and then discarded or mechanically reprocessed into a lower-value material, the platform is designed around repeated conversion between a polymer and recoverable molecular building blocks.

Also Read: 16-year-old built an AI tool after becoming a victim of a deepfake, here’s what happened next

Carbon dioxide incorporation is combined with high-performance material design

The study brings together three elements that are often difficult to achieve simultaneously: substantial incorporation of carbon dioxide into a polymer, useful material performance and chemical recyclability.

The copolymerisation process can produce high-molar-mass polyesters with as much as 50 mol% carbon dioxide in the polymer. The BCB-CO2 materials combine that carbon dioxide content with strong thermal and hydrolytic stability, while selective depolymerisation can recover BCB at more than 90% isolated yield.

The BCP-CO2 materials provide a separate recycling pathway through bicyclolactone formation and subsequent repolymerisation.

Taken together, the two systems establish a closed-loop approach in which carbon dioxide is incorporated into polyester materials and the resulting polymers can be chemically converted back into reusable building blocks. The research therefore connects carbon dioxide utilisation with polymer design and end-of-life recovery within the same platform.