Thermo/pH-Responsive\nMultiamide-Functionalized Y-Junction-Bearing\nPolyacrylamides with Substituent-Dependent Thermal Reversibility

Chain architecture and chemical composition\nof polymers\ncan play\nvital roles in regulating thermoresponsive properties. Despite tremendous\nprogress, it remains difficult to achieve LCST/upper critical solution\ntemperature (LCST/UCST) behavior with tunable thermal hysteresis and\noutstripping. This study affords a promising strategy of an integrated\nmultiamide and specific substituents to address the challenge. The\nincorporation of two substituents involving isopropyl, 2-diethylaminoethyl,\nor carbamoylmethyl into each Y junction of multiamide-functionalized\nY-junction-bearing\npolymers (MAYJPs) allows enhancing polymer–polymer interactions.\nThe disruption of intrinsic balances among hydrogen bonding, electrostatic\ninteractions, and hydrophilic-to-hydrophobic ratio renders a multitunable\nphase transition. The location switching of heterosubstituents can\nresult in either an inverse phase transition or a significantly different\nphase transition temperature. The thermodynamic or dynamic control\nover the hydration status of subunits leads to the occurrence of four\nkinds of thermal reversibility involving slight or significant hysteresis,\nconsecutive outstripping and hysteresis, and pronounced outstripping\nupon heating–cooling cycles. The solvent isotope effect results\nin a distinct type or temperature of phase transition, and the pH\neffect is reflected in the pH-induced increase, decrease, or V-shaped\nevolution of phase transition temperature. In addition, the phase\ntransition can accompany morphology transformation among spheres,\nvesicles, nanotubes, and lamellae. These fundamental findings are\nbeneficial for gaining insights into the multiamide-related phase\ntransition and thermal reversibility. Owing to the diversity of substituents,\nMAYJPs may serve as promising thermoresponsive polymers for multipurpose\napplications.