Synergistic Nanoconfinement and UV Crosslinking Enabling Self-Strengthening, Ultra-Robust Shape-Memory Elastomers

Fatigue-induced degradation of mechanical properties remains a major challenge in achieving long-term, reliable service of elastomers. We present a synergistic strategy that couples hydrazone-linked covalent organic framework (H-COF) nanoconfinement with UV-triggered cross-linking to realize self-strengthening poly(urea-urethane) (PUU) elastomers. H-COF nanochannels provide abundant H-bonding sites that immobilize chains and restrict mobility; upon UV irradiation, terminal C = C groups undergo confined radical polymerization within these channels, installing covalent cross-links precisely in highly dynamic regions. This cooperative mechanism strengthens the network while preserving the dissipation of H-bonds, yielding a 3.01× increase in tensile strength (85.1 MPa), a 2.10× enhancement in toughness (327.27 MJ•m^{- 3}), and a 2.20× improvement in fracture energy (303.65 kJ•m^{- 2}). Microstructural analysis reveals reduced domain spacing and homogenized morphology, while digital image correlation demonstrates suppressed strain localization. Moreover, UV irradiation shortens the shape-memory recovery time (R_r up to 99.06%) and intensifies fluorescence, providing a direct optical signal of the recovery process. This work establishes a generalizable design principle for stimuli-programmed self-strengthening under nanoconfinement, advancing elastomers toward adaptive durability.