Coumarin imparts repeated photochemical remendability to polyurethane

Synthesis, kinetics of photo-dimerization/photo-cleavage and physical properties of coumarin-containing branched polyurethanes based on polycaprolactones

“…For polymers PCL900+ PCL530+HDI+HEOM 10% and PCL1000+PCL530+ HDI+HEOMC 10% a single peak was obtained with the peak end located at 74.6°C thus both melting endotherms (PCL and coumarin end-groups melting) are merged in a single peak (see Figure 5). A similar peak was found in polymers prepared from PEG400-diol+HDI-trimer+HEOMC [20], with the maximum at 58.6°C. In that work the endothermic peak was assigned to hard segment glass transition, although a glass transition should show a change in heat capacity and the authors found a broad endotherm as the ones shown in Figures 2 and 3.…”

“…In Figure 6, the absorption spectra of the film can be seen. Absorption of coumarin shows a &-&* transition between 260 and 300 nm attributed to electrons of the conjugated benzene nucleus and another &-&* transition between 310 and 340 nm assigned to the pyrone nucleus [20,28]. Emission spectrum of the 313 nm lamp was almost coincident, whereas emission spectrum of the 354 nm lamp was coincident in the range 310-350 nm and emission spectrum of the 365 nm lamp barely overlapped at the very end of the absorption band of coumarin.…”

“…In the following table, the weight amounts of each reactant, calculated for a total amount of 100 g of branched polymer are listed. Branched polymers were prepared in 1,2-dichloroethane by mixing all reactants and using stannous Similar branched polymers have been described in literature with poly(ethylene glycol) as the soft segment, a HDI trimer as the polyisocyanate and HEOMC as the coumarin monomer [20], but in that case the polymer structure was not controlled. Although not explained in that work, in a following paper by these authors [19] it was explained that some gelation occurred during synthesis as a consequence of the actual composition of the HDI trimer, in fact a mixture of compounds with some of them of higher functionality (4, 5, etc).…”

“…methylcoumarin (HEOMC) 7-hydroxyethoxy-4-methylcoumarin (HEOMC) was prepared as described in literature in two steps [20,23], as shown in Figure 2. The characterization of the molecule was made using nuclear magnetic resonance (NMR) analysis.…”

“…Some applications of these materials are biomedical, coating and adhesive applications [26,27]. When incorporated in a polyurethane chain, the coumarin monomer was introduced as a chain end [20,28] or as a chain extender [19]. In both cases coumarin monomer was linked to the isocyanate monomer by a polar urethane group, and when introduced as a chain extender, coumarin units were within the hard segments.…”