A Self-Healing and Highly Stretchable Polyelectrolyte Hydrogel via Cooperative Hydrogen Bonding as a Superabsorbent Polymer

Poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) hydrogels are attractive materials for various application areas due to their pH-independent large swelling capacities. However, their covalently cross-linked network structure leads to a brittle behavior even at low strains. We present here for the first time highly stretchable superabsorbent PAMPS hydrogels formed via H-bonds entirely that are stable in water. UV polymerization of AMPS in aqueous solutions at 23 ± 2 °C without a chemical cross-linker produces hydrogels with large swelling capacities exceeding 1000 times their original mass. Although the hydrogels are stable in water, they easily dissolve in chaotropic solvents, suggesting that they form via H-bonding interactions between PAMPS chains. We show that the high molecular weight of the primary chains of PAMPS hydrogels formed via UV polymerization contributes to the H-bonding cooperativity and hence is responsible for their stability in water. Incorporation of N,N-dimethylacrylamide (DMAA) segments into the physical PAMPS network further increases the molecular weight of the primary chains, leading to enhanced mechanical strength of the hydrogels. PAMPS/DMAA hydrogels in their as-prepared states exhibit a high modulus (up to 0.41 MPa), tensile fracture stress (up to 0.57 MPa), and high stretchability (∼1000%) together with an extraordinary swelling capacity (up to ∼1700 g·g–1) and complete self-healing efficiency.