A one-pot method for producing a range of degradable, partially recyclable thermosetting plastics by polymerising the same monomer in two different ways has been developed by US researchers.1 The plastic could be the basis of a 3D printing ink and, in future, could provide sustainable alternatives for many widely-used polymers today.
Whereas thermoplastics melt at high temperatures, thermosetting plastics such as epoxy resins and melamine have highly crosslinked polymer chains, making them heat resistant and much more robust. Around 15–20% of polymers produced are thermoset. Unfortunately, they are also far harder to recycle as they cannot be melted and reshaped. Researchers are therefore attempting to produce chemically degradable polymers that can be broken at the crosslinks. ‘People have designed dual functional monomers that have two different functionalities and you can polymerise those through two different mechanisms,’ says polymer chemist Brett Fors at Cornell University, US. ‘The problem with those is that it’s pretty inefficient and usually pretty expensive.’
Since the 1950s, it’s been known that the cyclic vinyl ether 2,3-dihydrofuran (DHF) can undergo cationic polymerisation to yield the strong, rigid poly(c-DHF). In 2022, Fors’ group showed that this could be oxidatively degraded.2 Polymer chemists John Feist and Yan Xia at Stanford University in California had separately and unexpectedly shown in 2020 that the same monomer could also undergo ring-opening metathesis polymerisation (Romp).3 In the new work, researchers led by Fors’ graduate student Reagan Dreiling used this dual functionality to create a new class of tunable polymers.
They combined the DHF with a ruthenium catalyst and a photoacid generator. Romp begins immediately, producing long-chain, soft, stretchable poly(r-DHF) while leaving the vinyl ether’s double bonds intact. Irradiation with blue light then triggers the formation of a superacid, which leads to cationic polymerisation. This causes crosslinking of the poly(r-DHF) double bonds and polymerisation of the unreacted DHF. The simultaneous two types of polymerisation – one producing an elastic polymer and the other producing a brittle polymer, allows the researchers to tune the properties of the finished product. ‘We can change the properties by changing either the catalyst loading or when we start irradiating,’ says Fors. ‘That’s going to dictate how much of the Romp polymer we’re going to have, how much of the cationic polymer we’re going to have and how much crosslinking we’re going to have.’
The researchers’ materials ranged from thermoset elastomers to strong, tough rigid polymers. All of the Romp-polymers could be depolymerised to the monomer by heating, whereas the sections linked by cationic polymerisation could be degraded by acid hydrolysis. The researchers are now seeking applications. One possibility, says Fors, is to 3D print an object by selectively exposing the poly(r-DHF) to light. This could produce an embedded object of a desired shape composed of the crosslinked polymer. The poly(r-DHF) block could then be heated to recover the uncrosslinked monomer, exposing the object inside.
‘These two polymerisations give you very different material properties,’ says Xia. ‘That’s really the key invention of this paper as it’s quite interesting and creative. We didn’t think about this – I wish we had.’ He is also interested by the potential of 3D printing the polymer, pointing out that it could manufacture degradable materials with spatially varying properties. ‘Who knows what this will be useful for?’ he says
References
1 RJ Dreiling, K Huynh and BP Fors, Nature, 2025, DOI: 10.1038/s41586-024-08386-w
2 SW Spring et al, J. Am. Chem. Soc., 2022, 144, 15727 (DOI: 10.1021/jacs.2c06103)
3 JD Feist and Y Xia, J. Am. Chem. Soc., 2020, 142, 1186 (DOI: 10.1021/jacs.9b11834)
No comments yet