Ellen Phiddian
Cosmos science journalist
Synthetic polymers – from plastics to Teflon – are crucial materials for modern life. But they’re also notoriously wasteful, and difficult to recycle.
According to Dr Athina Anastasaki, an assistant professor at ETH Zurich in Switzerland, one of the solutions might be looking at the way we make them – and doing it backwards.
Anastasaki gave a keynote speech on her lab’s depolymerisation work to the American Chemical Society’s Fall 2024 meeting this week.
Polymers are long molecules made from chains of repeating smaller molecules, called monomers. Plenty of polymers exist in nature, from cellulose to DNA, but human-made polymers have become increasingly useful – particularly as plastics, which are all polymers.
Polymers are strong molecules, making it difficult for other organisms to break them down. This is an important property when you’re making a laptop casing or food container (or any number of other items), but problematic when trying to dispose of the material at the end of its use.
One common way to make carbon-based polymers is through “controlled radical polymerisation”: taking monomers, and using a reactive type of molecule called a “radical” to connect them together.
“There are 30,000 publications in making polymeric materials through controlled radical polymerisation,” said Anastasaki at the conference.
“However, there is almost nothing available in reversing the process. The reason why there is nothing available is because those are ‘vinyl’ polymers: they consist of a very powerful carbon-carbon bond, and that’s really challenging to break.
“However, as with most challenging things in life, they can be very rewarding if you are able to address them.”
Anastasaki’s work has been directed at using radicals to turn polymers back into monomers.
“From a sustainability perspective, it’s really important to be able to regenerate back the monomer, and then you would be able to use that monomer in order to either resynthesise the initial material – or why not come up with a completely new material with completely new properties?” she said.
“It’s up to you. You can design what you want.”
Other advantages of the work include the fact that the process can regenerate “end groups” – molecules that sit at the end of the polymer chain – which are typically very expensive components for industry. Anastasaki adds that the work can help to understand the basic chemistry of polymers.
“We’re looking into depolymerisation as a way to understand the fundamentals behind the processes,” she said.
Anastasaki’s lab has been working on several different avenues to depolymerise materials.
This includes depolymerisation with a substance called a RAFT agent and heat (in the range of 200°C, which is low by industrial standards), and using light to trigger depolymerisation reactions.
Many of these processes have shown to regenerate pure monomers, with the researchers collecting more than 90% of their original monomer materials from the depolymerisation reactions.
Anastasaki said that in still-to-be-published work, her former PhD student Dr Hyun Suk has been able to turn commercial polymers back into monomers.
Next, the team is planning to investigate other sources of energy, like electrical and mechanical energy, to trigger their reactions. They’re also planning to apply their work to other polymer classes.
