Designing an elastomeric polyurethane coating with enhanced mechanical and self-healing properties: The influence of disulfide chain extender

Polyurethane has been widely used in various coating industries due to its good weathering resistance, promising appearance, excellent elasticity and good mechanical properties. However, most of the polyurethanes are elastomeric and show poor resistance to mechanical damages. Efforts have been made to design polyurethanes with proper self-healing properties. In this study the self-healable polyurethanes and polyurethane-ureas coatings were prepared using hydroxyl-terminated polybutadiene, three functional amino alcohols as cross-linker and disulfide containing compounds as a chain extender and healing agents. The mechanical and healing properties of the coatings were optimized to achieve the highest recovery properties. For this purpose, dynamic mechanical thermal analysis (DMTA) and tensile test were employed. The results revealed that using 0.8 equivalent of 2-hydroxyethyl disulfide as chain extender besides of using 0.15 equivalent of the triethanol amine as cross-linker in the polymer matrix led to the maximum recovery ability. Maintaining to about 41% of fresh polymer strength and healing of the scratch were established as a result of using the optimized contents of components. Also, tensile test results revealed that the tensile strength increased by performing the thiol-ene side reactions in PU matrix which increased the cross-linking density and decreased the healing ability due to the elimination of the metathesis reaction source.