Switching-Temperature-Tunable Thermochromic Polymer Blend Based on Poly( <i>n-</i> alkyl Acrylate) for Smart Roof and Smart Window Applications

Thermoresponsive smart systems for building envelopes, such as smart roofs and windows, require thermochromic materials with tunable switching temperatures to adapt to regional climate and seasonal changes. Herein, we propose thermochromic polymer blends comprising poly(n-alkyl acrylates) (PnAAs) as phase-change polymers. The switching temperature of the thermochromic polymer blend was determined by the alkyl side-chain length of PnAAs. The polymer blend exhibited high-contrast haze regulation when the refractive index of the matrix phase of the miscible polymer blend matched that of PnAAs. Smart roofs constructed using a composite of the thermochromic polymer blend, carbon black absorber, and Ag reflector showed temperature-adaptive reflectance, and outdoor demonstrations confirmed that the solar absorption of the smart roofs adapts to seasonal temperature variations. Smart windows exhibiting privacy protection under cool conditions were developed using the polymer blends, and switching temperature adjustment in the range of 20–37 °C by the copolymerization of n-alkyl acrylates with different side-chain lengths further improved their applicability.