Self-healable spray paint coatings based on polyurethanes with thermal stability: Effects of disulfides and diisocyanates

As the interest in self-healing and scratch-resistant coatings has increased, studies on incorporating dynamic covalent bonds in protective elastomeric coating materials have increased. The incorporation of reversible disulfide bonds into polyurethane (PU) elastomers imparts self-healing property and recyclability, which not only reduce maintenance costs but also extend the service lives of the coated products. In this study, we developed two-component self-healing PU spray paint materials with superior healing properties and thermal stability. This achievement involved the synthesis of oligomeric precursor diols of PU incorporating disulfides of different molecular weights and controlling the hardener ratio in the final spray-coating material. Variations in the scratch-healing ability and stability of the coating films were investigated based on the type of the disulfide employed in the aromatic and aliphatic moieties and the combination of diisocyanates. Among the tested specimens, a coating film fabricated from a precursor denoted as H13 (molar feed ratio of isophorone diisocyanate:bis(4-hydroxyphenyl)disulfide:carbonate-type soft diol = 10:5:8) cured with a hardener (molar ratio of methylene diphenyl diisocyanate:isophorone diisocyanate = 1:1) showed excellent healing performance, showing >95 % scratch recovery within 2 h at 30 °C. It also exhibited transparency, solvent resistance, and thermal stability.