A team of French chemists has developed a new process to create plastics that are almost entirely recyclable.
This process relies on the use of a nitrogen-based molecule that initiates polymerization and leaves a reactivatable end group on the polymer chains. With simple heating, this end group can trigger depolymerization of the chains to return to the original monomers. This new step toward clean and controlled chemical recycling of polymers has been published in
Angewandte Chemie International Edition.
Using a tetrazene (TMTZ) as a polymerization initiator for PMMA or PS leaves a functional end group that enables subsequent depolymerization of the chain and reversion to monomers through simple heating
© Jean Raynaud
The recycling of plastics, particularly PMMA (better known as "acrylic glass") and polystyrene, remains one of the blind spots in the ecological transition. Current recycling processes, whether mechanical or thermal, often result in lower-quality materials (downcycling) or require expensive catalysts and energy-intensive procedures that are not economically viable. As a result: less than 5% of the PMMA produced annually is effectively recycled.
In their dreams, chemists envision polymers that could, as if by magic, gently deconstruct (depolymerize) at the end of their life cycle. What if this dream became reality? This is what Lyon-based chemists are attempting to demonstrate by exploring the remarkable properties of tetrazene, a unique nitrogen-based molecule containing four consecutive nitrogen atoms.
These chemists from the Hydrazines and Polyazotated Energetic Compounds Laboratory (CNRS/CNES/ARIANEGROUP/Université Claude Bernard) and the Catalysis, Polymerization, Processes and Materials Laboratory (CNRS/CPE Lyon/Université Claude Bernard) discovered that a specific tetrazene, tetramethyltetrazene or TMTZ, could initiate polymer formation through radical polymerization while remaining intact at the chain ends.
Unlike conventional polymerization initiators that disappear during the reaction, TMTZ leaves a stable and functional "chemical signature" at the chain end. Even better, when the polymer is heated beyond a certain temperature, this end group transforms and acts like a fuse: it triggers depolymerization, allowing the polymer chain to disassemble cleanly, like a chemical zipper.
This capability has been successfully tested on several plastics, including PMMA and polystyrene. The monomer recovery yields reach up to 62% for polystyrene—a breakthrough for this polymer—and 88% for PMMA. The process requires no additives or metal catalysts, which is a significant advantage for cleaner, more economical recycling that could potentially be adapted for industrial use. The regenerated molecules could even be reused to produce new plastics, supporting a circular economy.
This breakthrough opens exciting prospects, ranging from plastic objects designed for on-demand chemical recycling to smart materials capable of self-destructing under well-defined conditions. Scientists naturally plan to adapt this chemistry to other families of plastics. This new step toward eco-designed polymer materials has been published in the journal
Angewandte Chemie International Edition.
Author: AVR