Thermal-driven self-healing waterborne polyurethane with robust mechanical properties based on reversible phenol-carbamate network and Fe3+-catechol coordination bond

Abstract

Realizing environment-friendly and thermal-driven self-healing polymers with robust mechanical properties is an important challenge for the development of next-generation smart materials. Herein, by combining dynamic phenol-carbamate bonds and Fe3+-catechol coordination bonds in polymer chains, novel hyperbranched waterborne polyurethanes (FTWPU) with desirable thermal-driven self-healing properties were prepared through two steps, i.e., introducing tannic acid to prepare tannic acid based waterborne polyurethane (TWPU) bearing phenol-carbamate bonds firstly, and subsequently further incorporating Fe3+ ions to prepare FTWPU in possession of Fe3+-catechol moieties. The results exhibited that TWPU possessed good emulsion stability with differing tannic acid content, and improved thermal and mechanical properties, owing to the presence of cross-linking between polyurethane chains, and FTWPU still possessed outstanding storage stability, as well as much higher mechanical properties (tensile strength of 18.4 ± 0.4 MPa, elongation at break of 533.5 ± 5.2 %). Meanwhile, FTWPU presented desirable self-healing ability (i.e., healing efficiencies of tensile strength and elongation at break were 87.5 % and 91.9 %, respectively) after healing under 120 °C for 1.5 h and 85 °C for 30 min, demonstrating a satisfactory balance between good self-healing ability and high mechanical properties. Importantly, reversible phenol-carbamate bonds and metal coordination bonds are predominant factors during the healing process of FTWPU films, as well as high mobility of soft segments and hydrogen bonding effect play a significant role to achieve ultimate healing ability. We can envision that the promising design idea, based on synergistic effect between phenol-carbamate bonds and Fe3+-catechol coordination bonds, could provide inspiration for preparing self-healing polymers with superior mechanical properties.