Self-healing polymer coatings of polyurea-urethane/epoxy blends with reversible and dynamic bonds

It is necessary to explore polymer blend coatings with self-healing capability. The challenge is to pursue the balance between high properties and self-healing behavior that consists of crack closure and healing. In the present work, we offered a solution by designing polyurea-urethane/epoxy blend coatings, where reversible and dynamic bonds were incorporated into polyurea-urethane matrix, epoxy domains, and their interface. Furan groups terminated thermoplastic polyurea-urethanes (FTPU) with dynamic disulfide bonds were blended with epoxy oligomers having dangling furan groups. The coating properties were highly improved by the phase-separated epoxy domains that were induced by the Diels-Alder (DA) reaction between maleimide groups in bis(4-maleimidophenyl)methane (BMI) and furan groups in epoxy oligomers. Results showed that the tensile strength was almost doubled, and the tensile modulus was increased from 71 to 209 MPa. The pencil hardness was increased from 3B-2B to F–H as well. The blends presented excellent shape-memory effects, i.e., fixation ratio of 91 % can be achieved by cold draw and recovery ratio of 99 % was attained by heating. The crack closure, thus, was facilitated. The dynamic DA reaction between epoxy oligomer and FTPU as well as the reversible disulfide bonds in FTPU ensured the subsequent crack healing. The healing efficiencies, determined from tensile tests, can reach 80 %. Good self-healing behaviors were also confirmed from anti-contamination and anti-corrosion experiments. The shape-memory assisted crack closure and variations in morphologies during healing were studied. Such blend materials with dynamic and reversible bonds in the two components and interface can be useful for self-healing polymer coatings.