Influence of Poly(ε-caprolactone) Molecular Weight and Coumarin Amount on Photo-Responsive Polyurethane Properties

Photo-reversible polyurethane (PU) coatings based on coumarin diol (CD) are obtained. Initially, pre-polymers based on different amounts of coumarin (5, 15, and 25 mol%) and 1,6-hexamethylene diisocyanate are prepared to obtain PUs with a large incorporation of CD and high molecular weight. The pre-polymer is posterior reacted with poly(ε-caprolactone) diol (PCL-diol), either with molecular weight (Formula presented.) = 530 or 2000 g mol. The thermal stabilities of the PUs are studied using thermogravimetric analysis. Polymers with a higher content of CD present higher stability. The thermal transitions and the mechanical response are analyzed using differential scanning calorimetry and strain-stress tests, respectively. Moreover, the photo-reversibility of CD-based PUs is followed by UV absorption. In general, photo-dimerization induces better mechanical properties of the final PUs. Materials obtained with short PCL-diol ((Formula presented.) = 530 g mol) and the highest amount of CD present higher reversibility processes. Therefore, these polymers are promising for application as coating systems. (Figure presented.).Acknowledgements: The authors would like to thank the Spanish Ministry of Science and Innovation (MAT2013-48059-C2-1-R and MAT2014-55778-REDT) and the Regional Government of Madrid (S2013/MIT-2862). M.P.A. and L.P. acknowledge the Juan de la Cierva (FJCI-2014-20630) and Ramon y Cajal (RYC-2014-15595) contracts from the MINECO, respectivelyPeer Reviewe