Colorless and transparent self-healing polyurethane urea with superior tensile strength for protective coating

Abstract

Self-healing polyurethanes have gained significant attention as functional polymers, but their mechanical properties are often compromised by the introduction of dynamic covalent or noncovalent bonds during synthesis. Enhancing the mechanical properties of polyurethanes while maintaining their exceptional self-healing capabilities is a current research focus. To address this challenge, we introduced cystamine dihydrochloride as a chain extender in polyurethane systems to form partial urea bonds, strengthen hydrogen bonding, and improve polyurethane rigidity. The unique soft and hard segment structure of polyurethane facilitates the development of hydrogen bonds, enabling enhanced self-healing through the synergistic effect of disulfide and hydrogen bonds. The synthesized samples exhibit high healing efficiency, robust mechanical properties, and exceptional transparency, with over 85 % light transmittance in the visible range. Among the samples, PCUU-6 (with 40.2 wt% hard segments and 5.8 wt% disulfide bonds) demonstrates better mechanical properties, with a tensile strength of 57.5 ± 4.3 MPa, an elongation at break of 476.4 ± 26.6 %, and a self-healing efficiency of 87.7 %. Furthermore, the fracture toughness and Young’s modulus were measured at 139.9 ± 4.8 MJ/m³ and 114.6 ± 4.2 MPa, respectively, indicating excellent fatigue resistance. The self-healing PCUU samples show potential application in protective coating.