Broadly Tunable Thermochromic Smart Windows Based on Maleimide Derivative-N-vinylpyrrolidone Copolymers With Inherent Stability, UV Shielding, and Active Photothermal/Electrothermal Modules

Engineering advanced thermochromic smart windows capable of simultaneously addressing multifaceted performance, durability, and multifunctionality requirements is crucial for their practical applications. Herein, a mini library of lower critical solution temperature (LCST) copolymers with well-defined structure and programmed hydrophile-lipophile balance (HLB) is synthesized by the reversible addition-fragmentation chain transfer (RAFT) copolymerization of highly hydrophilic N-vinylpyrrolidone (NVP) and four maleimide derivative (MI) monomers with descending hydrophilicity. MI-NVP copolymers afford a copolymer composition-dependent phase transition temperature tunable over an ultra-wide range of 20–67 °C and efficient UV shielding capability. By ingeniously doping MI-NVP copolymers into non-thermoresponsive polyacrylamide hydrogel, smart windows with outstanding thermochromic properties, solar modulation performance, inherent stability (1000 cycles), and fast response rate (14 ± 2 s) are obtained. Further integration with photothermal Cs x WO 3 or electrothermal indium tin oxide (ITO) glass delivers enhanced spectral selectivity or active-mode regulation. Overall, by meticulously tailoring the multilevel structure of thermochromic hydrogels, this strategy establishes a novel MI-NVP copolymer platform for thermochromic smart windows that significantly advances energy conservation and occupant comfort.