Photo-stimulated self-healing polyurethane containing dihydroxyl coumarin derivatives

A novel polyurethane was synthesized, which consisted of isophorone diisocyanate, polyethylene glycol and photo-reversible moiety 5,7-bis(2-hydroxyethoxy)-4-methylcoumarin. By taking advantage of reversible photodimerization and photocleavage habit of coumarin, the polyurethane can be repeatedly crosslinked and de-crosslinked under successive UV irradiations at 350 and 254 nm. More importantly, damages in crosslinked version of the polyurethane can be re-bonded through chain reconnection on fracture surfaces resulting from the photochemical reactions, as characterized by mechanical strength restoration tests. Compared to the previous proof-of-concept trial with monohydroxyl coumarin derivatives as the photosensitive groups, the application of dihydroxyl coumarin derivatives in the present work prevented the undesirable gelation during synthesis and enabled properties-oriented structure adjustment of polymerization products. Besides, structure–performance relationship study of the polyurethane revealed that rubbery domains resulting from microphase separation were necessary for the photo-remending with high efficiency.