Mending polymers with light

Mending polymers with light. We know all too well from daily life that materials made from polymers can be damaged: Tires get punctured, garbage bags rip, plastic eyeglass lenses get scratched. But over the past decade, several ways have been developed to heal polymers. Some methods are autonomous, drawing only on resources within the material. More commonly, though, the repair process is externally activated, typically by heat: When heated above their glass transition or melting temperature, the polymer chains can rearrange, diffuse, and re-entangle. Stuart Rowan (Case Western Reserve University), Christoph Weder (University of Fribourg), and colleagues have now demonstrated a healing mechanism activated by light. The team’s method exploits so-called supramolecular polymers, in which noncovalent bonds connect large repeating units. In the new work, the repeating units were elastic, hydrophobic hydrocarbon segments terminated by hydrophilic ligands. Those building blocks, termed macromonomers, were joined together into chainlike structures by metal...