Designing Strong, Tough, Fire‐Retardant and Self‐Healing Elastomers with Phosphorus/Nitrogen‐ and Biphenyl‐Containing Segments

ABSTRACT High‐performance polyurethane (PU) elastomers have demonstrated many important industrial applications in areas such as soft robotics, flexible sensors and electronic devices. However, it has been challenging to design strong and tough elastomers that are capable of fire‐extinguishing and self‐healing due to different governing mechanisms associated with these properties. Here we present a molecular engineering strategy to achieve strong, tough, fire‐retardant, and healable PU elastomers by rationally designing a phosphorus/nitrogen (P/N)‐ and π–π interacting biphenyl‐containing diol as hard segments with side groups. The formation of relatively strong interchain π–π stacking enables the elastomer to achieve superior mechanical and self‐healing properties, while the combination of π–π stacking and P/N elements promotes exceptional fire retardancy. The resultant elastomer displays a record‐high large break strain of ∼2500%, a large toughness (ca. 379 MJ/m 3 ) and a tensile strength of 46 MPa, and a healing efficiency as high as 95% (tensile strength) and 99% (break strain). Also, the elastomer can self‐extinguish with a high limiting oxygen index of 38.6%. We then demonstrate its application for high‐sensitivity multi‐mode tattoo sensors. This work opens new avenues for developing strong, flexible, tough elastomers with multiple integrated functionalities.