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

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