Polymers jump through rings to find durable materials

Recyclable plastics containing ring-shaped polymers can be a key element in the development of sustainable synthetic materials. Despite promising advances, the researchers said, it remains difficult to understand how to turn ring polymers into practical materials. In a new study, researchers have identified a mechanism called "threading" that occurs when a polymer is stretched – a behavior never observed before. This new understanding could lead to new processing methods for durable polymeric materials.

Most consumer plastics are linear polymer blends. The concept of plastic made solely from cyclic polymers – molecules forming a closed cycle – represents an interesting opportunity for sustainability, as has been shown in the Beckman Institute for the Science of Materials independent material systems group. and advanced technologies. Once a single bond holds the ring polymers together, the entire molecule breaks down, causing disintegration on demand. However, the transformation of such polymers into concrete materials remains a challenge, the researchers said.

A study conducted in 2013 by the University of Illinois showed that ring polymers could be broken by heat, but that this had a price: the resulting plastics would likely become unstable and start to break down prematurely.

In this new study, Charles Schroeder and Yuecheng (Peter) Zhou, researchers at the II University, examine the dynamics of the flow of linear polymer solutions and ring-based polymers. DNA to reveal clues about how synthetic polymers interact during treatment. Their results are published in the journal Nature Communications.

"We do not have a fundamental understanding of how ring polymers stretch and move in the flow while navigating around neighboring polymer chains." This work has allowed us to probe these questions at the same time. molecular level, "said Schroeder, professor in chemical and biomolecular engineering, a researcher at the Beckman Institute and co-author of the study.

In Schroeder's lab, researchers stretched and squeezed polymers, casting them and allowing direct observation of the behavior of individual molecules by monomolecular fluorescence microscopy.

"There is a fluctuation in the shape of the ring polymers and it depends on the concentration of linear polymers in the solution," said Zhou, a graduate student researcher at the Beckman Institute and lead author of the study. "We do not see this behavior in pure solutions of cyclic or linear polymers, which tells us that something unique happens in mixed solutions."

By combining direct observations with a molecule and physical measurements, the team concluded that changes in the shape of cyclic polymers occur because linear molecules slip into cyclic molecules when stressed. causes a fluctuation of the cyclic form under the fluid flow.

"We observed this behavior even when there is a very low concentration of linear polymers in the mixture," Zhou said. "This suggests that it only takes a very small level of contamination to cause this phenomenon."

This threading of linear polymers through cyclic polymers during stress is something that had been theorized before, using large-scale studies of physical properties, but it has now been observed at the scale molecular, the researchers said.

"Bulk studies generally mask the importance of what happens on a small scale," Schroeder said.

The researchers said that the way these observations would lead to continued development of sustainable plastics remains unclear. However, any knowledge of the fundamental molecular properties of mixed polymer solutions goes in the right direction.

"For pure annular polymer plastics to become a reality, we need to understand mixed and pure solutions at a fundamental level," said Schroeder. "Once we understand how they work, we can then synthesize them, and ultimately how to use them in sustainable plastics."