A Shape Memory Polyurethane with Extended Service Life by Self-Healing and Recyclable Properties

Stimuli-responsive intelligent polyurethanes (PUs) have garnered interest recently because of their transdisciplinary nature and wide variety of applications. Despite significant advancements in stimuli-responsive intelligent polymers, it is still a challenge to integrate multiple features including high toughness, reversible shape memory (SM), self-repair, and recyclability into a single PU. In this work, a series of cross-linked PUs were synthesized using poly(ε-caprolactone) diol (PCL), hexamethylene diisocyanate (HDI), 1,4-butanediol (BDO), or (2-hydroxyethyl) disulfide (HEDS) as a chain extender, and pentaerythritol (PE) as a cross-linker. The effect of HDI content and chain extender species on the stimuli-responsive features of PU was discovered. When the molar ratio of HDI/PCL was 5/1 and HEDS was chosen as the chain extender, the PU exhibited excellent SM and self-repair features. The shape recovery rate exceeded 90% at 58 °C in 16 s. Its tensile strength and elongation at a break are 19.8 MPa and 694.9% after self-repair at 70 °C, respectively, and it can bear a weight of 1 kg. The self-repair efficiency reaches 96.7%. At the same time, self-repair can be boosted by SM behavior, and the corresponding mechanism is put forward. The mechanical properties of PU which undergoes 3 rounds of recycling can still match those of the original material. This work provides versatility and sustainability for PU and opens more possibilities for PU in engineering applications.