Tailoring the Hard-Soft Interface with Dynamic Diels-Alder Linkages in Polyurethanes: Toward Superior Mechanical Properties and Healability at Mild Temperature

The current thermoremendable polyurethanes (PUs) based on reversible Diels-Alder (DA) chemistry featuring both good mechanical properties and efficient macrodamage healability are up to now built with the DA bonds located in the hard domains with restricted mobility, which hinders the DA reversibility. Thus, the healing process in these materials requires predissociation of DA bonds via the retro reaction at high temperatures (110-180 degrees C) followed by DA re-formation, which may compromise the material performance integrity. Here, we show a design of thermoset PUs containing dynamic DA entities engineered at the interface between the hard and soft domains that combine high modulus and toughness with mild-temperature-triggered molecular mobility, which is a prerequisite for efficient healing capability. This concept of molecular design enables PUs to have great mechanical properties (Young's modulus similar to 80-225 MPa, ultimate tensile strength similar to 16-30 MPa, and toughness similar to 26-96 MJ m(-3)) and simultaneously remarkable healing ability at mild temperatures (60-70 degrees C) of macroscratches, punctures, and complete cuts. The mechanical and healing properties can be tuned by varying the DA bond content. These materials are the first reported DA-based PU materials showing excellent healing efficiency at mild temperatures without compensation of their great mechanical properties.