Highly stretchable and tough hydrogels using cyclic polymers as crosslinkers

The development of highly stretchable and tough hydrogels is essential for advanced applications in materials science, biomedicine, and soft robotics. Herein, we report a novel approach to fabricating organic polyacrylamide (PAAm) hydrogels using vinyl-functionalized cyclic polythioethers as crosslinking agents. These cyclic polymers were synthesized via anionic ring-opening polymerization (AROP) of thiirane initiated by thiazolidine-2,4-dione, followed by partial thiol-ene click modification with 3-mercaptopropionic acid to enhance hydrophilicity. In situ polymerization of acrylamide in the presence of the cyclic crosslinkers (P2n) and potassium persulfate (KPS) yielded hydrogels with outstanding mechanical performance. Compared to hydrogels crosslinked with linear analogues, those incorporating cyclic polymers exhibited significantly improved properties, including stretchability up to 1200%, an elastic modulus of 0.85 MPa, and toughness of 8.06 MJ m−3. These enhancements are attributed to the unique topological features of cyclic polymers, namely, absence of chain ends, compact conformations, enlarged entropic elasticity, and the ability to form interpenetrating networks, resulting in improved elasticity and energy dissipation. This study demonstrates the effectiveness of topological crosslinker design in hydrogel engineering and highlights the promising potential of cyclic polymers for high-performance soft materials.