Polyhydroxyalkanoates (PHAs) have attracted significant research attention and investment as biobased, biodegradable, and biosynthesizable alternatives to petroleum-based plastics. But PHAs can also be made by traditional chemical synthesis, which gives researchers more control over their properties.
Researchers at Colorado State University and the National Laboratory of the Rockies (NLR) developed a synthetic PHA that is more scalable, easier to chemically recycle, and has more-tunable properties compared with other synthetic PHAs (Science 2026, DOI: 10.1126/science.aed3914).
“When we tried to solve one issue, we kind of synergistically solved other issues,” says Eugene Y.-X. Chen, the Colorado State professor who co-led the work with NLR’s Gregg Beckham.
NLR postdoctoral scholar James May says the project started as a follow-up to a paper that the Chen group published in 2023 showing that adding two methyl groups to the β-butyrolactone monomer made the resulting polymer more thermally stable and enabled chemical recycling back to the monomer. But that monomer was too expensive to make on a large scale. May’s job was to figure out a more industrially viable alternative.
Searching through old patents, May came across a ketene dimer with the same dimethyl substitution pattern as the monomer he was trying to improve, which could be easily converted to a lactone and then polymerized to make a PHA. Better yet, the dimer is already produced industrially as a precursor to the polyester used in Nalgene water bottles. “When I saw that, I was like, ‘Okay, this is great. There are already people in industry making essentially the exact same thing on scale.’”
May’s redesigned PHA bears a side chain with a carbon-carbon double bond. That feature blocks a decarboxylation side reaction that had limited the researchers’ ability to depolymerize other synthetic PHAs they had worked on previously. The group was able to get up to 93% yield of pure monomer back after heating the polymer with a catalytic amount of sodium hydroxide.
The double bonds also make the polymer stronger, stiffer, and more thermally stable than other PHAs. The initial thermal properties were similar to the polyesters used in textiles, and indeed the researchers were able to spin, draw, and anneal the polymer to make fibers. The researchers also found they could partly or fully hydrogenate the side chains to create ductile thermoplastics and strong adhesives.
“We can form various materials for designer properties for specific applications,” Chen says. The caveat is that hydrogenation somewhat lowers the recyclability and leads to mixtures of saturated and unsaturated monomers that would have to be separated or copolymerized.
The researchers created a detailed model for how to produce the polymer starting from isobutyric acid, which can come from biobased feedstocks. They determined that 70% of the production cost would come from the isobutyric acid starting material and 5% from the organic superbase they used as a polymerization catalyst. The retail price would likely be around $4.43 per kilogram.
Sophie Guillaume, who researches circular polymer chemistry at the Rennes Institute of Chemical Sciences and was not involved in the study, calls the work “elegant and smart” in an email to C&EN. Making a commercially viable recyclable polymer from biobased feedstocks is a major challenge, and the researchers have come up with a very compelling and well-researched solution that highlights the value of “simple ideas with [a] straightforward industrial approach.”
There are many directions for future work on the system, Beckham says, including further exploring the range of properties they can get, exploring what other monomers they can access using ketene chemistry, and working out how to practically recycle the polymers. They’re also working on understanding if their modified synthetic PHAs are still biodegradable and what the environmental fate of the monomers might be. “We’re really excited about the platform,” he says.
