Coumarin imparts repeated photochemical remendability to polyurethane

Coumarin, a traditional perfume substance, serves as a photosensitive crosslinker to construct a polyurethane network. Upon mechanical damage or ultraviolet illumination at a wavelength of 254 nm, the coumarin dimers on the fractured surface that link the polyurethane backbones with one another are cleft, and can be reconnected via irradiation at 350 nm. By using this feature, cracks on the polymer are mended by ultraviolet exposure or even sunlight without the aid of any catalyst. Owing to the reversibility of the photocyclization of coumarin moieties, multiple cycles of crack mending are allowed, as demonstrated by both qualitative and quantitative characterization. This repeated photo-remendability enables the polyurethane to heal the same site in the material more than once, which is of value for practical applications.