Aromatic disulfide-induced self-reinforcing polyurethane elastomer with self-healability

Abstract

Developing new strategies to improve the mechanical robustness of self-healing polymer materials to meet engineering requirements remains a great challenge and research focus. Herein, a self-reinforcing strategy of self-healing polyurethane (PU) elastomer is presented to achieve simultaneous giant tensile strength (33.3 ± 1.7 MPa) and toughness (141.9 ± 3.7 MJ m−3). Two chain extenders, diethyl 2,2-bis(hydroxymethyl)malonate (BDMH) and bis(4-hydroxyphenyl) disulfide, are elaborately regulated in the molecular structure to balance the mechanical and self-healing properties. On the one hand, BDMH containing abundant ester groups provide a large number of hydrogen bond (H-bond) acceptors. On the other hand, the incorporation of aromatic disulfide forms reversible hierarchical H-bonds confined to loosely-stacked hard domains and improves the physical crosslinking density, thus realizing the self-reinforcing of PU elastomer based on the strain-induced crystallization (SIC) of polytetramethylene ether glycol (PTMEG) as the soft segment. Hierarchical H-bonds with dynamic nature acting as sacrificial bonds can dissociate and regenerate and dissipate a large amount of energy, thus contributing to mechanical robustness and self-healing properties. In addition to constructing a self-healing PU elastomer with mechanical robustness, a remarkable progress over previous work is that we perform fundamental study at the molecular level and reveal the three-stage evolution of H-bonds and aggregation structure during stretching, thus revealing the SIC behavior and mechanism, which provides a theoretical basis for the strengthening and toughening of self-healing PU elastomer.