<scp>4D</scp> Materials of Tough and Rapid Thermoresponsive Hydrogel by <scp>PET</scp> ‐ <scp>RAFT</scp> Polymerization

ABSTRACT In the case of 4D hydrogels, thermal‐responsive behavior is typically investigated through variations in formulation parameters such as monomer ratios, ingredient composition, and solid content concentration. We developed and analyzed a thermally responsive 4D hydrogel using poly( N ‐isopropylacrylamide) (NIPAm) as a representative lower critical solution temperature (LCST) polymer, and poly( N,N‐ dimethylacrylamide) (DMAAm) as a non‐thermoresponsive polymer. The effects of varying monomer ratios and solid concentrations were investigated under two fixed NIPAm content conditions (50% and 75%), as determined based on prior experimental outcomes. Hydrogels were synthesized via photoinduced electron/energy transfer‐reversible addition–fragmentation chain transfer (PET‐RAFT) polymerization and were comprehensively characterized using Fourier‐transform infrared (FT‐IR) spectroscopy, rheological measurements, swelling ratio analysis, and 4D motion behavior assessment. Bilayer‐structured hydrogel samples were fabricated and evaluated under thermal stimuli at 70 C to investigate their deformation behavior. Based on these results, we developed a 4D hydrogel‐based gripper as a demonstration of the potential practical applications of thermoresponsive 4D materials in soft robotics and smart actuator systems.