Tough and Recyclable Diketopiperazine-Based Poly(urethane-urea) Elastomers from Renewable 4-Nitro-l-Phenylalanine

To develop the next generation of polyurethane elastomers with exceptional recycling capabilities and comprehensive mechanical properties and advance the application of diketopiperazine (DKP) in functional polymeric materials, we designed a chain extender carrying one DKP unit and two aromatic rings, which was easily synthesized from 4-nitro-l-phenylalanine, and fabricated tough and recyclable poly(urethane-urea) elastomers (denoted as DKP-PUU). The hierarchical hydrogen bonds and π–π stacking were incorporated as dynamic physical cross-links that dissipate strain energy through efficient reversible bond dissociation and reassociation, thus imparting DKP-PUU elastomers with a maximum tensile strength reaching up to 44.3 MPa, a high stretchability of 1158%, and superior toughness of 189.2 MJ m–3. Meanwhile, the DKP-PUU elastomers exhibit good fatigue and crack resistance and can be recycled under mild conditions by cutting/recycling to restore their original mechanical strength. Moreover, the reprocessable elastomers can be conveniently incorporated with organic dyes to achieve desired colors and luminescence.