Self-healing polymers significantly extend the service life and enhance the operational reliability of devices. However, conventional self-healing polymers are often ineffective against macroscopic deformations and holes. Shape memory-assisted self-healing (SMASH) provides a feasible solution to this challenge. Efficient shape recovery relies on stable cross-links. While chemical cross-links provide a powerful driving force for shape recovery, they inherently hinder self-healing due to their irreversibility. Conversely, weak physical cross-links generally result in lower tensile strength and unsatisfactory shape recovery. Herein, metal coordination bonds are utilized as dynamic cross-links to construct tough thermal-step-responsive SMASH polyurethanes. Strong Zn2+-pyridine coordination bonds endow the elastomers with the ability to repair macroscopic punctures. Without external load intervention, centimeter-sized punctures (d = 1.4 cm) in such elastomers can autonomously close within 1 min at 40 °C, followed by complete healing at 70 °C to repair macroscopic damage. These coordination bonds serve as dynamic cross-links to significantly enhance mechanical properties (49.71 MPa for strength and 138.17 MJ/m3 for toughness). The coordination cross-links play three key roles in the repair process: (1) during the damage process, they act as network anchors to ensure maximum storage of entropic energy within the polymer network; (2) during hole closure, they facilitate efficient release of this stored energy to provide the recovery driving force; and (3) during the healing stage, their reversible dissociation releases polymer chains, which accelerates dynamic bond exchange at the damaged interfaces. This study provides valuable insights into developing tough self-healing soft materials for macroscopic damage repair.
Zhu et al. (Thu,) studied this question.