Periodic Reporting for period 4 - DEPO (Reversing Controlled Radical Polymerisation: Towards Complete Depolymerisation)
Reporting period: 2025-03-01 to 2025-08-31
The DEPO project set out to show that plastics made by controlled radical polymerization can be taken apart just as precisely as they are built. Its overall goal was to create a quantitative process for depolymerization, a chemical reaction that converts plastics back into their original building blocks or monomers. By reversing the precision of modern polymer synthesis, DEPO aimed to demonstrate the concept of chemical circularity, where materials can be made, used, and fully remade without waste.
By the end of the project, DEPO achieved this vision for a family of common plastics known as vinyl polymers, including materials similar to plexiglass (polymethyl methacrylate). The team discovered that these polymers can be converted back into monomers at relatively low temperatures and in a controlled, selective manner. This was made possible by activating polymer chains to generate reactive species known as radicals, either from special end-groups designed during synthesis (ATRP and RAFT polymers) or by creating reactive chlorine radicals that break chains in the middle.
Because the depolymerization process could be controlled so precisely, it also became a powerful analytical and design tool, allowing researchers to study the structure of complex materials and even alter their properties through targeted chemical unmaking. These results mark an important step toward more efficient and sustainable recycling technologies for modern plastics.
By the end of the project, DEPO achieved this vision for a family of common plastics known as vinyl polymers, including materials similar to plexiglass (polymethyl methacrylate). The team discovered that these polymers can be converted back into monomers at relatively low temperatures and in a controlled, selective manner. This was made possible by activating polymer chains to generate reactive species known as radicals, either from special end-groups designed during synthesis (ATRP and RAFT polymers) or by creating reactive chlorine radicals that break chains in the middle.
Because the depolymerization process could be controlled so precisely, it also became a powerful analytical and design tool, allowing researchers to study the structure of complex materials and even alter their properties through targeted chemical unmaking. These results mark an important step toward more efficient and sustainable recycling technologies for modern plastics.
The DEPO project began by exploring whether polymers made through controlled radical polymerization could be fully “unmade” back into their original building blocks. The team first focused on a method known as RAFT polymerization and demonstrated, for the first time, that this process can be reversed efficiently. Using a range of methacrylate-based plastics, they achieved up to 92 percent recovery of the original monomer. The regenerated monomers could then be reused to make new polymers with different properties, which could in turn be depolymerized again. This closed-loop process shows that chemical recycling can, in principle, be repeated many times without loss of material quality.
After establishing this proof of concept, the project investigated how the depolymerization reaction begins and how it can be controlled. Through detailed mechanistic studies, the researchers discovered how polymer chains become activated and how this initiation step determines the overall efficiency of the process. Building on these insights, DEPO developed a light-controlled depolymerization system, allowing the reaction to be switched on or off simply by changing the light exposure.
Further work revealed that adding extra RAFT agent or adjusting the reaction concentration made it possible to deactivate the growing radicals during depolymerization. This innovation produced the first example of a controlled depolymerization in which all polymer chains unzip in a coordinated way. This control makes it possible to analyze complex block copolymers with unprecedented precision and even to fine-tune polymer molecular weight by partial depolymerization.
In parallel, the project developed complementary methods for polymers made by atom transfer radical polymerization (ATRP). DEPO showed that iron catalysts could be used to depolymerize ATRP-derived polymethacrylates and that these systems could operate under oxygen-tolerant conditions, a major practical advance for chemical recycling. The team also demonstrated that depolymerization could be driven either by light or by external chemical reagents, providing flexible control over when and how the process occurs.
Finally, DEPO addressed the challenge of depolymerizing more common plastics made by free radical polymerization, which lack the special end groups used in RAFT or ATRP systems. The team first converted these materials into macromonomers, enabling efficient depolymerization under bulk conditions without the need for solvent. Building on this, they discovered that chlorine radicals generated by light from the solvent itself can attack the middle of polymer chains to create reactive fragments that depolymerize spontaneously. Using this strategy, DEPO demonstrated near-complete depolymerization, over 99 percent, for polymethacrylates including commercial-grade plexiglass at temperatures between 90 and 150 degrees Celsius.
After establishing this proof of concept, the project investigated how the depolymerization reaction begins and how it can be controlled. Through detailed mechanistic studies, the researchers discovered how polymer chains become activated and how this initiation step determines the overall efficiency of the process. Building on these insights, DEPO developed a light-controlled depolymerization system, allowing the reaction to be switched on or off simply by changing the light exposure.
Further work revealed that adding extra RAFT agent or adjusting the reaction concentration made it possible to deactivate the growing radicals during depolymerization. This innovation produced the first example of a controlled depolymerization in which all polymer chains unzip in a coordinated way. This control makes it possible to analyze complex block copolymers with unprecedented precision and even to fine-tune polymer molecular weight by partial depolymerization.
In parallel, the project developed complementary methods for polymers made by atom transfer radical polymerization (ATRP). DEPO showed that iron catalysts could be used to depolymerize ATRP-derived polymethacrylates and that these systems could operate under oxygen-tolerant conditions, a major practical advance for chemical recycling. The team also demonstrated that depolymerization could be driven either by light or by external chemical reagents, providing flexible control over when and how the process occurs.
Finally, DEPO addressed the challenge of depolymerizing more common plastics made by free radical polymerization, which lack the special end groups used in RAFT or ATRP systems. The team first converted these materials into macromonomers, enabling efficient depolymerization under bulk conditions without the need for solvent. Building on this, they discovered that chlorine radicals generated by light from the solvent itself can attack the middle of polymer chains to create reactive fragments that depolymerize spontaneously. Using this strategy, DEPO demonstrated near-complete depolymerization, over 99 percent, for polymethacrylates including commercial-grade plexiglass at temperatures between 90 and 150 degrees Celsius.
The DEPO project has redefined what is possible in polymer chemistry by demonstrating that plastics can be chemically unmade in a precise and efficient manner. It delivered the first high-conversion depolymerization method for polymers made by RAFT polymerization, achieving up to 92 percent recovery of the original monomer from a range of polymethacrylates. The recovered monomers could be used to make new materials with different properties, completing a true chemical recycling loop.
DEPO also achieved the first example of controlled depolymerization, where every polymer chain breaks down in a coordinated and predictable way. This level of control opens new possibilities for understanding complex materials, tailoring polymer properties, and developing recycling processes that avoid unwanted side reactions or material loss.
In addition, the project produced the first oxygen-tolerant depolymerization of vinyl polymers, a breakthrough that simplifies experimental handling and moves depolymerization chemistry closer to practical implementation.
Perhaps the most significant advance was the discovery of mid-chain initiated depolymerization, a completely new concept that makes it possible to recycle commercial plastics at much lower temperatures than have previously been possible. Using this approach, DEPO achieved almost complete depolymerization of materials such as commercial plexiglass at temperatures between 90 and 150 degrees Celsius, which are far lower than those required for traditional pyrolysis.
Together, these advances establish the scientific foundations for future closed-loop recycling technologies and mark a decisive step toward sustainable and circular polymer materials.
DEPO also achieved the first example of controlled depolymerization, where every polymer chain breaks down in a coordinated and predictable way. This level of control opens new possibilities for understanding complex materials, tailoring polymer properties, and developing recycling processes that avoid unwanted side reactions or material loss.
In addition, the project produced the first oxygen-tolerant depolymerization of vinyl polymers, a breakthrough that simplifies experimental handling and moves depolymerization chemistry closer to practical implementation.
Perhaps the most significant advance was the discovery of mid-chain initiated depolymerization, a completely new concept that makes it possible to recycle commercial plastics at much lower temperatures than have previously been possible. Using this approach, DEPO achieved almost complete depolymerization of materials such as commercial plexiglass at temperatures between 90 and 150 degrees Celsius, which are far lower than those required for traditional pyrolysis.
Together, these advances establish the scientific foundations for future closed-loop recycling technologies and mark a decisive step toward sustainable and circular polymer materials.