Abstract
Hydrogels are attractive for applications in intelligent soft materials and flexible electronics. Herein, we report a new hydrogel with a hierarchical hydrogen bond system consisting of (1) weak hydrogen bonds between N,N-dimethylacrylamides (DMAA) and acrylic acids (AAc) and (2) strong multiple hydrogen bonds between 2-ureido-4[1H]-pyrimidinone units. By optimizing the ratios of DMAA and AAc and the balance of weak and strong hydrogen bonds, the hydrogels have unique properties. The transparent hydrogels have tunable Young’s modulus (70–1,250 kPa) and are highly stretchable (up to 4,340% strain), tough (fracture energies of 10.8 kJ/m2, matching natural rubber) and insensitive to notches when it is highly stretched (λ = 19.6).
Highlights
Hydrogels are attractive for applications in intelligent soft materials and flexible electronics
The hydrogel was synthesized by copolymerization of acrylamide, acrylic acid and a 2-ureido-4[1H]-pyrimidinone motif (UPy). 2-Ureido-4[1H]-pyrimidinone motif forms quadruple hydrogen bonds and has a high dimerization constant (Kdim ≈ 6 * 108 M−1 in toluene)[30], which makes it very attractive building blocks for tough hydrogels
Hydrogels were synthesized by one-pot free radical copolymerization of N,N-dimethylacrylamide, acrylic acid and 2-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl) ureido) ethyl acrylate (UPyEA) under UV radiation (λ = 365 nm) (Scheme 1a)
Summary
Hydrogels are attractive for applications in intelligent soft materials and flexible electronics. We report a new multiple energy-dissipating hydrogel with hierarchical hydrogen bonds. The physical dissociation and re-association of hydrogen bonds at different force level dissipates energy and synergically contributes to the hydrogel with remarkable mechanical properties.
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