Hydrogen-Bonding Toughened Hydrogels And Emerging CO₂-Responsive Shape Memory Effect

A hydrogen bonding reinforced high strength hydrogel with tear-resistant property was constructed by copolymerization of 2-vinyl-4,6-diamino-1,3,5-triazine?VDT?and N,N-dimethylacrylamide?DMA?with crosslinker polyethylene glycol diacrylates?PEG4KDA?.The hydrophobic hydrogen bonding microdomains could be formed between diaminotriazine?DAT?,and due to the reinforcement of both chemical crosslinking and hydrogen bonding physical crosslinking,the hydrogels demonstrated tunable robust mechanical properties by varying the ratio of hydrogen bonding monomer or crosslinker.Importantly,because of synergistic energy dissipating mechanism of strong DAT hydrogen bonding and possible weak hydrogen bonding between amine of DAT and C=O of DMA,the hydrogels exhibited high toughness?up to 2.32 kJ/m²?,meanwhile maintaining 0.7 MPa tensile strength,130%elongation at break and 8.3 MPa compressive strength.Moreover,rehydration could help recover the mechanical properties of the cyclic loaded-unloaded gels.Attractively,the hydrogels were responsive to CO₂ in water,and demonstrated unprecedented CO₂-triggered shape memory behavior owing to the reversible destruction and reconstruction of DAT hydrogen bonding upon passing and degassing CO₂ without introducing external acid.The CO₂ triggering mechanism may point out a new approach to fabricate shape memory hydrogels.