Fast self-healing engineered by UV-curable polyurethane contained Diels-Alder structure

A series of UV-curable polyurethanes were made by copolymerization of isocyanate monomers with various diols (PLA1000/PEG2000/HPDMS). The structure of the resulting polyurethanes with DA-generated bonds was characterized by Fourier transform infrared spectroscopy (FTIR) and H-1 NMR. In addition, the UV-curing behavior was studied by FTIR. Diels-Alder (DA) and retro-Diels-Alder (r-DA) reactions within cured films was monitored by differential scanning calorimeter (DSC) and dynamic mechanical analysis (DMA), which indicated that the cured film exhibited excellent thermal reversibility over at least three cycles. The resulting PU resins show different healing effect and PLAPU exhibited the most rapid thermal healing with the defect (a scratch with a width of 100 mu m) completely healed within 100 s at 120 degrees C. Furthermore, PLAPU has high tensile strength (3MPa) and robust hardness (H) at the same time which is an advantageous feature for applications in which extreme softening or reverse gelation of a self-healing coating would be unacceptable.