A new material mimics the malleability of glass but retains the toughness and stability of thermoset plastics (Science, DOI:10.1126/
science.1212648). Developed by chemists in France, the material could be useful in the automotive and aerospace industries, as well as a number of other areas.
“Anywhere you have a complex shape, you can use this material,” says lead researcher Ludwik Leibler of the School of Industrial Physics & Chemistry, in Paris, part of France’s Centre National de la Recherche Scientifique (CNRS). “It’s much lighter than metal or glass, it’s chemically resistant, and it’s recyclable.”
Thermoset plastics, such as Bakelite, are stable to solvents and extreme temperatures. But they must be polymerized in a mold to give them a shape. And once they’ve been polymerized, thermosets can’t be reshaped or reprocessed, either with heat or with solvent. Leibler’s polymer has the stability of thermosets but behaves like glass: Simply heat the material and shape it as desired.
The key to the glassy behavior lies within the polymer’s molecular structure; it has an equal number of ester and alcohol groups. When the material is heated it transesterifies; that is, its ester cross-links transfer from one region of the polymer to another with the help of an embedded zinc catalyst. “You exchange links, but you never diminish the chemical bonding” that gives the polymer its strength, Leibler explains. “The number of chemical links always stays constant.”
The researchers have been able to recycle the material so that it has the same properties as the original. Also, scratches and small breaks in the plastic can be repaired by heating it. Leibler’s team has patented the material and hopes to see it commercialized soon. The chemical components, he says, are inexpensive and readily available.
“The reported results demonstrate how, in a very simple way, one can make new easily processable materials with excellent properties,” comments polymer expert and Carnegie Mellon University chemistry professor Krzysztof Matyjaszewski. “The chemistry is very simple, robust, and provides unique organic materials that behave better than classical inorganic glasses.”
“Although malleability certainly isn’t an attribute typically associated with thermosets, that is precisely what the Leibler group has achieved by cleverly employing transesterification to rearrange the connectivity of these covalently cross-linked polymer networks,” adds Timothy F. Scott, a chemical engineering professor at the University of Michigan who studies polymers. “Given the tremendous potential for reversible covalent chemistries to generate dynamic, reconfigurable polymers, we’re certain to see more extraordinarily creative and exciting work in the field over the next several years.”