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. (c) 2012 Elsevier Ltd. All rights reserved.
The present invention relates to coumarins of formula (I), polyols and polyurethanes produced from said coumarin, as well as the method for producing said polyurethanes, the use thereof in the preparation of coating films and method thereof for repairing a damaged surface of said polyurethane. Formula (I)