Self-healing waterborne polyurethanes containing disulfide bonds in the main chain
Materials with intrinsic self-healing ability have attracted tremendous interest in literature, especially coatings in anti-corrosion applications. In this work, environmentally friendly waterborne polyurethanes containing disulfide bonds in the main chain were synthesized. Poly (ε-caprolactone) glycol with a molecular weight of 1000 was used as soft segment, and isophorone diisocyanate, 2-bis(hydroxymethyl) propionic acid, and 2-hydroxyethyl disulfide were used as hard segment. The influence of 2-hydroxyethyl disulfide/2-bis(hydroxymethyl) propionic acid molar ratios on stability of dispersions and the self-healing property of the waterborne polyurethane films was investigated. The self-healing system was triggered by the chain exchange reaction of disulfide bonds and assisted by the shape memory effect to bring the crack on the waterborne polyurethane surfaces in spatial proximity. The tensile strength of the scratched waterborne polyurethane film was recovered to 90.5 % in 10 min at a modest healing temperature of 65 °C. Meanwhile, the prepared waterborne polyurethanes exhibited excellent dispersion stability and improved thermal stability.