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

Abstract 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.