Cross-Linked Polymeric Network with Aniline Trimer as Solid-Solid Phase Change Materials for Efficient Solar-to-Thermal Energy Conversion and Storage

Herein, we report the synthesis and characterization of a novel series of sunlight-driven solid-solid phase change materials (S-SPCMs) based on cross-linked polyurethane networks. These materials were engineered by reacting epoxy-terminated poly (ethylene glycol)-containing polyurethane macromonomer (EPU) with amine-terminated aniline trimer (ATD). The design leverages the crystalline domains of poly (ethylene glycol) (PEG) as the phase-change functional component, while the aniline trimer serves a dual role: acting as a covalent cross-linker and enabling efficient solar energy harvesting through its photothermal conversion properties. The molecular structure, phase-change behavior, thermal conductivity, solar-thermal conversion efficiency, crystallinity, and thermal stability of the synthesized S-SPCMs were systematically investigated. Notably, the materials achieved latent heat values of 57.1–79.2 J/g, comparable to state-of-the-art solid-solid PCMs, while maintaining structural integrity during phase transitions. The incorporation of ATD into the polyurethane network enhanced thermal conductivity, facilitating rapid heat transfer across the material. Optimized formulations with tailored ATD concentration demonstrated exceptional thermal reliability, retaining > 95% of their latent heat storage capacity after 50 thermal cycles, alongside robust thermal stability up to 250 °C. Furthermore, the S-SPCMs exhibited outstanding solar-thermal conversion efficiency under simulated sunlight, underscoring their potential for real-world solar energy applications. These results highlight the synergistic interplay between the PEG phase-change domains and the photothermal ATD cross-linker, which collectively enable efficient energy capture, storage, and release. This work advances the development of multifunctional, recyclable phase-change materials for sustainable thermal management systems, offering a promising pathway toward reducing reliance on fossil-fuel-derived energy in heating and cooling applications.