Melt-Processable Shape-Memory Elastomers Containing Bisurea Segments

Cross-linked semicrystalline shape-memory networks are capable of storing large amounts of elastic energy with negligible plastic deformation; however, thermosets are not easily melt-processed or recycled. Here, we demonstrate a shape-memory polymer that is melt-recyclable with high processability and little performance loss. Catalyst-free isocyanate chemistry is used to prepare two linear poly(caprolactone)s with bisurea hydrogen-bonding groups periodically positioned along the main chain. Compared to an entangled poly(caprolactone) homopolymer of similar molecular weight, the segmented poly(bisurea)s exhibit minimal stress relaxation when elastically strained at identical conditions. Furthermore, the materials' single relaxation times combined with small-angle X-ray scattering results indicate that stress relaxation is limited more by disentanglement kinetics rather than by phase segregation of hard domains. The polymers show excellent shape fixity and recovery before and after shredding, melt-pressing, and annealing into a reprocessed film. Together with thermomechanical cycling, creep experiments provide insight into the relationship between stress relaxation and shape-memory training.

Automated summary

The study demonstrates a novel shape-memory polymer material that is melt-recyclable, prepared using catalyst-free isocyanate chemistry, with high processability and minimal performance loss. Compared to traditional poly(caprolactone) homopolymers, the new material shows better elastic performance and stress relaxation characteristics. Furthermore, the shape-memory properties of the material remain excellent even after multiple recycling processes.