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.
