Thermally reversible polymer networks for scratch resistance and scratch healing in automotive clear coats

This study investigated the application of a thermally reversible polymer network fabricated using Diels-Alder (DA)/retro-DA (rDA) reactions for use as a scratch-healing automotive clear coat. For this purpose, a new scratch-healing poly(urethane acrylate) network containing a DA adduct unit (DA-CL) was prepared, and its material properties and scratch-healing performance were compared to the properties of a commercial clear coat system (C-CL). The thermally reversible crosslinking and de-crosslinking reactions among the DA-CL, via DA and rDA reactions, were systematically evaluated using in-situ oscillatory rheology coupled with FT-IR spectroscopy. The material properties of the DA-CL and C-CL materials, including the thermal stability, thermal transitions, hardness, and scratch resistance, were measured using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), nanoindentation, and nanoscratch test methods. The scratch-healing performance of the DA-CL was quantitatively characterized and compared to the performance of the C-CL using a nanoscratch tester equipped with an optical microscope (OM) and an atomic force microscope (AFM). The DA-CL polymer network exhibited superior scratch healing and scratch resistance compared to the C-CL polymer network. These data indicated that the DA self-healing polymer network is potentially useful as a scratch-healing clear coat for the automotive industry.