Rising levels of carbon dioxide in the atmosphere are a major driver of climate change. As a result, researchers are exploring ways to capture this greenhouse gas and repurpose it into usable materials. But the stability of carbon dioxide makes it challenging to incorporate into polymers.
Previously, researchers have successfully polymerized carbon dioxide into polycarbonate using a variety of catalysts and other intermediates that help the notoriously non-reactive gas participate in chemical reactions.1,2 Introducing carbon dioxide into polyesters, which have a variety of industrial uses, though, is a more difficult reaction. This is because the starting materials for polyesters lack the polar bonds that would promote a chemical reaction with carbon dioxide.
Eugene Chen, a polymer scientist at Colorado State University, and his team suspected that they could overcome this limitation using certain bicyclic carbon compounds that experienced strain in their joining rings, which makes them more reactive. In a study published in Nature, the team polymerized carbon dioxide and different bicyclic carbon molecules into various recyclable polyesters with different properties.3 These findings could help researchers capture and store carbon dioxide while also developing more sustainable plastic options.
“We are developing an integrated technology that turns carbon dioxide capture into an intermediate as a building block for production of sustainable materials of many types and needs,” Chen said in a press release. “We look forward to developing this further in a collaborative approach with the larger scientific community.”
The researchers started with two bicyclic butane molecules and two different bicyclic pentane molecules, each of which contained a chemical group on the ring’s central carbon bond that contributed to the chemical reaction. To initiate a chemical reaction between their bicyclic compounds and carbon dioxide, the team used bis(triphenylphosphine)iminium ([PPN]Cl) as a catalyst. [PPN]Cl attacked the strained carbon ring of the bicyclic compounds, which allowed carbon dioxide to chemically react with it and form a carboxylate molecule. Since carbon dioxide cannot react with carboxylate, another bicyclic carbon compound binds to the newly formed carboxylate, and the chemical process begins again.
As a result of this reaction, the researchers produced polyester compounds in which the reacted bicyclic carbon compounds alternated with carboxylate molecules. The team found that butane substrates gave rise to linear polyesters while pentane substrates produced cyclic polyesters.
Next, the researchers explored the chemical properties of their new polyester compounds. The polymers produced with butane substrates transitioned from a rigid molecular structure to an amorphous one, like glass, at higher temperatures than ones made with pentanes. Similarly, the two butane-derived polyesters degraded at 325°C and 360°C, while the pentane-derived polyesters degraded at 286°C and 291°C.
Then, the researchers assessed the mechanical properties of the polyesters. The polymers made with the bicyclic butane compounds had greater strength and rigidity. The bicyclic pentane substrates gave rise to polyesters that were softer, less strong, and more ductile. These findings represent opportunities to replace existing plastics made with more carbon-intensive methods.
Finally, the team assessed how well these novel polymers could be degraded back into their original starting materials and their potential for reuse. The researchers successfully depolymerized the butane-derived and pentane-derived polyester compounds, recovering a high yield of the substrates. These results suggested that the new polymers could be recycled, representing a closed-loop process for these compounds.
“Our approach unlocks the potential for carbon dioxide as a renewable and inexpensive resource to produce recyclable polyesters that also exhibit performance-advantaged and beneficial end-of-life properties,” Chen said in the press release.
- Yang GW, et al. Evolution of copolymers of epoxides and CO2: Catalysts, monomers, architectures, and applications. Chem Rev. 2024;124(21):12305-12380.
- Xu YC, et al. Crystalline polyesters from CO2 and 2‑butyne via α‑methylene-β-butyrolactone intermediate. Macromolecules. 2016;49(16):5782-5787.
- Zhu M, et al. Alternating CO2 and bicycloalkane copolymerization to circular polyesters. Nature. 2026.
