UV-curable self-healing polyurethane coating based on thiol-ene and Diels-Alder double click reactions

Abstract

Endowing UV-curable coatings with self-healing properties by incorporating dynamic bonds into their cross-linking network is of vital significance. However, in practical applications, self-healing polymers are often plagued with problems such as a high healing temperature and long healing time. To address this challenge, we developed a new type of UV-curable polyurethane coating by the combination of Diels-Alder and thiol-ene click reactions. The Diels-Alder bonds in the polyurethane samples developed in this work furnished perfect mechanical properties and self-healing ability. Self-healing of polyurethane based on Diels-Alder bonds usually occurs at 120 °C. Thiol-ene click reaction is a robust, novel polymerization method, and it improved the structural performance of the polymer with a more homogenous structure being formed than that achieved with traditional UV-curing. Herein, a novel UV-curable self-healing coating, which is referred to as a PU-SH system, was designed by integrating thiol-ene into polyurethane resins containing Diels-Alder bonds. Results of analyses by assorted techniques (including Fourier-transform infrared spectroscopy, different scanning calorimetry, rheology, optical microscopy, and 3D optical interferometric profilometry) strongly indicated that the self-healing ability of the prepared coatings is superior to those of previously studied traditional UV-curing coatings, which are referred to as PU systems. The resultant coatings of the PU-SH system showed a remarkable reduction in the healing temperature from 120 °C for the PU system to 90 ˚C. The rapid scratch-healing properties of the UV-curable coatings, taken together with the moderate healing temperature makes the material attractive for a variety of applications, such as in flexible electronic screens, car paint film, and aircraft interior finishes.