Melt-Recyclable Shape-Memory Elastomers Containing Bisurea Segments

Shape-memory (SM) elastomers can undergo triggered actuation from metastable deformed states to permanent shapes, offering diverse applications. Covalently crosslinked, semicrystalline SM networks are capable of storing large amounts of elastic energy (>3 MJ/m³) with full recovery; however, these materials cannot be melt-processed, limiting their use across various device geometries. Here, we demonstrate that replacing covalent crosslinks with bisurea H-bond interactions can enable fully melt-recyclable SM elastomers with little performance loss. Two high molecular weight poly(ε-caprolactones) with main-chain hydrogen bonding groups have been synthesized and show excellent strain fixation and shape recovery before and after shredding, melt-pressing, and annealing. Dynamic mechanical analysis reveals a stiffness plateau that persists to temperatures over 100°C above the shape-triggering temperature. Stress relaxation studies are combined with X-ray scattering and calorimetry data to explain viscoelastic behavior and evaluate the role of phase segregation. Relaxation kinetics are consistent with chain disentanglement as the primary relaxation mode, and bisurea linkages slow the reptation timescale by over three orders of magnitude.