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As the rubber and plastic burden on the planet grows steadily, scientists look to the promise of closed-loop recycling to reduce waste. Researchers in the Department of Chemistry at Princeton University have discovered a potentially revolutionary new molecule with broad implications for keeping this promise.
A team of scientists led by Paul Chirik, chemistry professor Edwards S. Sanford, rin Nature Chemistry that this molecule connects in a very unusual way: as a repeating sequence of squares, which allows the process to go back under certain conditions. In other words, the molecule can be “zipped” to make a new polymer for use in plastic, then unzipped – depolymerized – to its original state, ready to be reused.
Princeton researchers led by Paul Chirik (socially distant, background) and Megan Mohadjer Beromi (foreground) have discovered a potentially revolutionary new molecule with broad implications for making plastics that are truly recyclable.
The molecule – officially named oligocyclobutane, but casually referred to in Chirik’s lab as “the polymer of squares” – could one day allow plastic products to be used multiple times, unlike most plastics today which. can only be recycled once, if at all.
“I honestly think this work is one of the most important things that ever came out of my lab,” said Chirik, the main author of the article.
Associate Alex Carpenter, former chemist at ExxonMobil Chemical. simply called it “transformer”.
Research is still at an early stage and the performance attributes of the material still need to be explored in depth. But Chirik’s lab provided a conceptual precedent for a chemical transformation that is generally not considered practical for some materials.
In the past, returning a material like this to its original state has been made with expensive specialty polymers and only after a multitude of steps – and never with a raw material as common as this. The molecule is a form of polybutadiene, known for over a hundred years and used to make rubber and plastic products such as tires and shoe soles.. Butadiene, its parent material, is an abundant organic compound and a major by-product development of fossil fuels.
The molecule can be “zipped” to create a polymer of squares for use in plastics, then decompressed – depolymerized – to its original state, ready to be reused.
“Take a very common chemical that people have been studying and polymerizing for many decades and make it into a fundamentally new material – let alone this material has some interesting innate properties – not only is it unexpected, it’s really a big one. step forward, ”Carpenter said.
The Chirik lab explores sustainable chemistry by studying the use of iron to build new molecules. In this particular research, the iron “persuades” the monomers to fit together to form the polymer of squares. Normally, the monomers connect to form a polymer – which is simply a repeating unit of monomers – through an S-shaped structure often described as resembling spaghetti. But with this new molecule, the monomers come together in a chain of squares.
To decompress them, the molecule is exposed to a vacuum in the presence of the iron catalyst, which reverses the process and recovers the original material, making it a rare example of closed-loop chemical recycling.
The project dates back to 2017, when C. Rose Kennedy, then a postdoctoral researcher at the Chirik laboratory, noticed a viscous liquid accumulating at the bottom of a balloon during a reaction. Investigate further, she found evidence that polymerization had taken place.
“It was immediately pretty clear how it would be possible to click the monomers together in a different or continuous fashion,” Kennedy said. “We immediately recognized that this could be something potentially extremely valuable.”
Chirik added: “You can make very strong materials from this monomer. What people tend to assume is that when you have a chemically recyclable polymer, it must be inherently weak or not durable. We have created something that is very durable, but also chemically recyclable. We can extract pure monomer from it. And that surprised me.
Megan Mohadjer Beromi, a postdoctoral researcher in the lab and lead author of the article, said the material has other intriguing properties that will form the basis for future research on chemically recyclable materials.
She added, “It’s the coolest thing I’ve ever worked on in my life.”
“Iron Catalyzed Synthesis and Chemical Recycling of Telechelic Oligocyclobutanes, 1,3-Enchained,” is co-authored by Paul Chirik and Megan Mohadjer Beromi of the Chirik Lab; C. Rose Kennedy, formerly of the Chirik Lab; Jarod M. Younker, ExxonMobil Chemical; Alex E. Carpenter, formerly of ExxonMobil Chemical; Sarah J. Mattler, ExxonMobil Chemical; and Joseph A. Throckmorton, ExxonMobil Chemical. The article appears in the January 25 issue of Nature Chemistry (DOI: 10.1038 / s41557-020-00614-w). Initial funding for this work was provided by Firmenich and the National Institutes of Health Ruth L. Kirschstein National Research Service Award (F32 GM134610 & F32 GM126640). Funding was also provided by ExxonMobil through Princeton E-filliates Partnership.
This article has been abridged from a more complete account of discovery of oligocyclobutane, available on the Home page of the Department of Chemistry.
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