Researchers develop completely new kind polymer

Researchers develop completely new kind of polymer

7:47 AM, 2nd February 2016
Researchers develop completely new kind of polymer
Researchers have developed a new hybrid polymer with removable supramolecular compartments, shown in this molecular model.

EVANSTON, US: Imagine a polymer with removable parts that can deliver something to the environment and then be chemically regenerated to function again. Or a polymer that can lift weights, contracting and expanding the way muscles do.

These functions require polymers with both rigid and soft nano-sized compartments with extremely different properties that are organized in specific ways. A completely new hybrid polymer of this type has been developed by Northwestern University researchers that might one day be used in artificial muscles or other life-like materials; for delivery of drugs, biomolecules or other chemicals; in materials with self-repair capability; and for replaceable energy sources.

“We have created a surprising new polymer with nano-sized compartments that can be removed and chemically regenerated multiple times,” said Samuel Stupp, materials scientist and the senior author of the study.

“Some of the nanoscale compartments contain rigid conventional polymers, but others contain the so-called supramolecular polymers, which can respond rapidly to stimuli, be delivered to the environment and then be easily regenerated again in the same locations. The supramolecular soft compartments could be animated to generate polymers with the functions we see in living things,” he said.

The hybrid polymer cleverly combines the two types of known polymers: those formed with strong covalent bonds and those formed with weak non-covalent bonds, well known as “supramolecular polymers.” The integrated polymer offers two distinct “compartments” with which chemists and materials scientists can work to provide useful features.

The study is published in the journal Science.

“Our discovery could transform the world of polymers and start a third chapter in their history: that of the ‘hybrid polymer,’” Stupp said.

Polymers get their power and features from their structure at the nanoscale. The covalent rigid skeleton of Stupp’s first hybrid polymer has a cross-section shaped like a ninja star - a hard core with arms spiraling out. In between the arms is the softer “life force” material. This is the area that can be animated, refreshed and recharged, features that could be useful in a range of valuable applications.

“The fascinating chemistry of the hybrid polymers is that growing the two types of polymers simultaneously generates a structure that is completely different from the two grown alone,” Stupp said. “I can envision this new material being a super-smart patch for drug delivery, where you load the patch with different medications, and then reload it in the exact same compartments when the medicine is gone.”

Stupp and his research team also discovered that the covalent polymerization that forms the rigid compartment is “catalyzed” by the supramolecular polymerization, thus yielding much higher molecular weight polymers.

The strongly bonded covalent compartment provides the skeleton, and the weakly bonded supramolecular compartment can wear away or be used up, depending on its function, and then be regenerated by adding small molecules. After the simultaneous polymerizations of covalent and non-covalent bonds, the two compartments end up bonded to each other, yielding a very long perfectly shaped cylindrical filament.

To better understand the hybrid’s underlying chemistry, Stupp and his team worked with George Schatz, a world-renowned theoretician and a Charles and Emma, Morrison prof of Chemistry at Northwestern. Schatz’s computer simulations showed the two types of compartments are nicely integrated with hydrogen bonds, which are bonds that can be broken. Schatz is a co-author of the study.

“This is a remarkable achievement in making polymers in a totally new way -- simultaneously controlling both their chemistry and how their molecules come together,” said Andy Lovinger, a materials science program director at the National Science Foundation.

“We’re just at the very start of this process, but further down the road it could potentially lead to materials with unique properties -- such as disassembling and reassembling themselves -- which could have a broad range of applications,” Lovinger said.

The work was supported by the National Science Foundation, the Department of Energy’s Biomolecular Materials Program and the Department of Energy’s EFRC Center for Bio-Inspired Energy Science.

© Northwestern University News

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