Synthesis and thermal properties of polystyrene-graft-PEG copolymers as new kinds of solid-solid phase change materials for thermal energy storage

A series of polystyrene-graft-PEG ₆₀₀₀ copolymers were synthesized as new kinds of polymeric solid-solid phase change materials (SSPCMs). The synthesized SSPCMs storage latent heat as the soft segments PEG ₆₀₀₀ of the copolymers transform from crystalline phase to amorphous phase and therefore they can keep its solid state during the phase transition processing. The graft copolymerization reaction between polystyrene and PEG was verified by Fourier transform infrared (FT-IR) and ¹H NMR spectroscopy techniques. The morphology of the synthesized SSPCMs was characterized by polarization optical microscopy (POM). Thermal energy storage properties, thermal reliability and thermal stability of the synthesized SSPCMs were investigated by differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis methods. The DSC results showed that the synthesized SSPCMs had typical solid-solid phase transition temperatures in the range of 55-58 °C and high latent heat enthalpy in the range of 116-174 J g ^-1. The TG analysis findings showed that the synthesized SSPCMs had high thermal durability above their working temperatures. Also, thermal conductivity measurements indicated that the synthesized PCMs had higher thermal conductivity compared to that of polystyrene. The synthesized polystyrene-graft-PEG ₆₀₀₀ copolymers as new kinds of SSPCMs could be used for thermal energy storage.