Design and synthesis of UV-cured calixarene polyurethane coatings: balancing robust mechanical properties with high self-healing efficiency

In this study, we present the design and synthesis of a calixarene polyurethane coating, which exhibits a novel structure comprising a rigid core and flexible arms. This unique configuration enables the coating to possess both high pencil hardness while retaining efficient self-healing capabilities. The synthesis process began with the preparation of a polyurethane (PU) prepolymer (PCDL-PU), using polycarbonate diol (Mn = 500 g/mol, PCDL500) and isoflurone diisocyanate (IPDI). This prepolymer was subsequently reacted with coumarin (CM) and varying quantities of tetra-c-methylcalix[4]resorcinarene (C-4-R), yielding a series of UV-cured self-healing calixarene polyurethane compounds (PCDL-PU-CM)-(C-4-R). The molecular structure of these compounds was characterized using nuclear magnetic resonance (1 H NMR) and Fourier transform infrared spectroscopy (FTIR). A range of UV-cured self-healing polyurethane coatings were formulated using (PCDL-PU-CM)-(C-4-R), and their properties were systematically investigated. The study focused on analyzing the impact of different grafting ratios on the coatings’ properties. The findings reveal that these coatings maintain excellent self-healing abilities up to 99% efficiency, and demonstrate a significant improvement in mechanical properties. Notably, the pendulum hardness of these coatings consistently exceeded 172, while maintaining a pencil hardness of 3H.