A robust self-healing polyurethane elastomer. From H-bonds and stacking interactions to well-defined microphase morphology

Self-healing materials have attracted considerable attention because of their improved safety, lifetime, energy efficiency and environmental impact. Supramolecular interactions have been extensively considered in the field of self-healing materials due to their excellent reversibility and sensitive responsiveness to environmental stimuli. However, development of a polymeric material with good mechanical performance as well as self-healing capacity is very challenging. In this study, we report a robust self-healing polyurethane (PU) elastomer polypropylene glycol-2-amino-5-(2-hydroxyethyl)-6-methylpyrimidin-4-ol (PPG-mUPy) by integrating ureidopyrimidone (UPy) motifs with a PPG segment with a well-defined architecture and microphase morphology. To balance the self-healing capacity and mechanical performance, a thermal-triggered switch of H-bonding is introduced. The quadruple H-bonded UPy dimeric moieties in the backbone induce phase separation to form a hard domain as well as enable further aggregation into microcrystals by virtue of the stacking interactions, which are stable in ambient temperature. This feature endows the PU with high mechanical strength. Meanwhile, a high healing efficiency can be realized, when the reversibility of the H-bond was unlocked from the stacking at higher temperature. An optimized sample PPG(1000)-mUPy(50%) with a good balance of mechanical performance (20.62 MPa of tensile strength) and healing efficiency (93% in tensile strength) was achieved. This strategy will provide a new idea for developing robust self-healing polymers.