Development of zwitterionic polyurethanes with multi-shape memory effects and self-healing properties

Recently, multi-shape-memory polymers have attracted significant attention due to their technological impact. This study reports novel zwitterionic multi-shape-memory polyurethanes (ZSMPUs) from N-methyldiethanolamine (MDEA), hexamethylene diisocyanate (HDI) and 1,3-propanesultone (PS). The ZSMPUs feature excellent multi-shape-memory properties that are capable of remembering four different shapes, and shape recovery decreases with increasing sulfobetaine content. Ionic interactions greatly influence the structure, morphology and properties. Increasing the sulfobetaine content promotes the phase mixing and zwitterions serve as organic fillers in the zwitterionic polyurethane. Immersing the zwitterionic polyurethane in moisture-rich conditions and drying at low temperature preserves the shape-memory capabilities and demonstrates good self-healing properties. Furthermore, both the shape memory effect and self-healing effects are repeatable. The self-healing mechanism is ascribed to the spontaneous attraction of zwitterions, followed by slower re-entanglement.