Polyurethane Elastomers with Mechanochromic and Self-Healing Functions for Strain Sensor.

Polyurethane is formed by the reaction of a polyol and an isocyanate by covalent bonds, which have been rapidly developing due to their good processability and mechanical properties. However, polyurethane is subject to micro-damage due to external stresses during service, which can lead to rapid performance failure. Currently, the nondestructive assessment methods generally require complex and expensive equipment. Therefore, it is of great importance to develop a simple and easy-to-follow detection method. Mechanochromic polyurethane offers great possibilities to achieve this purpose, which can produce easily detectable optical signals that can be used for direct visualization of damage or even in dynamic stress processes. In addition, improving the durability of polyurethane materials by introducing self-healing features has become an effective way to extend the service life of polyurethanes. Therefore, this work reports a smart polyurethane material that combines self-healing capability with mechanochromic properties. The prepared polyurethane realizes efficient self-healing at low temperature by introducing a dynamic Schiff base covalent bond. Under external stimulation, the change of its molecular chain orientation triggers π-π stacking reconstruction, leading to the reversible color switching. This multifunctional design provides new ideas for flexible sensors.