Multifunctional, robust, and self‐healable polyurethane coatings cross‐linked by Diels–Alder reaction of calix[4] arenes containing furan groups

Abstract Self‐healing coatings can restore their performance after inevitable damage and are promising in the industry owing to their longer service life and lower repair cost. The use of Diels–Alder reaction bonds is well‐known to generate thermally self‐healing coatings. In this study, a series of cross‐linked self‐healing polyurethane (PU) coatings were synthesized through Diels–Alder reactions of p ‐ tert ‐butyl calix[4]arene bearing furan groups (C4A‐FA) as a new chain extender and a bismaleimide (BMI) polyether amine as a Diels–Alder cross‐linking agent. Adding C4A‐FA to PUs improves their mechanical properties, thermal stability, and self‐healing ability. Additionally, these modifications can result in the formation of composite networks with PU that exhibit thermoreversibility and self‐healing properties. These changes have led to PUs containing modified calix[4]arene (C4A‐FA) having better properties compared with unmodified calix[4]arene PUs. The properties of prepared coatings were evaluated by Fourier transform infrared spectroscopy, scanning electron microscope, differential scanning calorimetry (DSC), thermogravimetric analyses (TGA), and tensile tests compared with a typical PU sample. The tensile and TGA results show an improvement in the thermal and mechanical properties of the polymers by increasing the C4A‐FA content. By replacing 15% of butandiol (BDO) with C4A‐FA in PU pure, the tensile strength increased from 1.69 to 5.14 MPa. Furthermore, adding diels–alder (DA) bonds enhanced the tensile strength to 10.49 MPa for PU‐C4A15‐DA. According to DSC results, a broad endothermic peak from nearly 80–140°C confirmed the retro‐DA reactions in the synthesized thermoreversible samples. The healing efficiency of the PU‐C4A15‐DA sample was obtained at 92.5% (measured by tensile test), which is the highest value among cross‐linked self‐healing PUs reported in the literature.