Polymerization-Induced Self-Assembly for Thermosensitive Hydrogels: How Sequence Structure Modulates Material Properties

Stimuli-responsive hydrogels with well-defined nanostructures hold great potential in emerging fields such as soft robotics and biomedicine. While the role of chemical composition has been widely explored, the impact of the sequence architecture of the functional polymer on the macroscopic properties of the corresponding hydrogels remains poorly investigated. This work addresses this gap by designing hydrogels with different sequence structures but similar compositions via RAFT-based polymerization-induced self-assembly (PISA). These hydrogels feature a common hydrophilic midblock, flanked by temperature-responsive nanodomains composed of either poly(diacetone acrylamide- co - N -isopropylacrylamide) (P(DAAM- co -NIPAM)) random copolymer (hydrogel-R 1 ) or poly(diacetone acrylamide)- b -poly( N -isopropylacrylamide) (PDAAM- b -PNIPAM) block copolymer (hydrogel-B). The sequence architecture fundamentally dictates the thermoresponsive behavior of the hydrogels, particularly in terms of their mechanical properties and energy-dissipation mechanisms. Hydrogel-R 1 exhibits a wide-range transition of mechanical properties in response to temperature variations in either water or air, and even undergoes a gel–sol transition upon cooling in the presence of excess water. Hydrogel-B shows a low-magnitude, temperature-responsive transition in mechanical properties in either water or air, and maintains a robust gel network even in the presence of excess water at low temperatures. Small-angle X-ray scattering (SAXS) analysis shows that the P(DAAM- co -NIPAM) random-copolymer nanodomains of hydrogel-R 1 undergo integrated, temperature-responsive swelling/collapse due to the random distribution of NIPAM units in the P(DAAM- co -NIPAM) segments. In contrast, the nanodomains of hydrogel-B are constituted by an inert PDAAM core and a functional PNIPAM corona, where only the PNIPAM corona undergoes temperature-responsive swelling/collapse, while the inert PDAAM core remains unchanged across all temperatures. This structural discrepancy results in distinct mechanical properties. Hydrogel-R 1 exhibits significant thermoresponsive concurrent improvements in tensile strength, elongation at break, and toughness, attributed to an efficient energy dissipation mechanism enabled by its deformable nanodomains. In contrast, hydrogel-B suffers from stress concentration at the rigid core–shell interfaces of the PDAAM- b -PNIPAM nanodomains, resulting in higher strength at elevated temperatures but limited extensibility. Temperature-dependent dynamic viscoelasticity and cyclic tensile tests further elucidate the sequence-structure-dependent energy-dissipation mechanisms of these hydrogels. This work establishes a clear sequence-structure–property relationship, providing critical guidance for the rational design of transparent, high-strength, and smart-responsive hydrogels.