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(epsilon-caprolactone) diol (PCL-diol), either with molecular weight n = 530 or 2000 g mol(-1). 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 (n = 530 g mol(-1)) and the highest amount of CD present higher reversibility processes. Therefore, these polymers are promising for application as coating systems.