Structure-property correlation of poly(ethylene glycol) based form stable phase change materials with different crosslinking structure

Chemical crosslinking is an important strategy for preparation of form stable phase change materials (FSPCMs). However, the influence of different crosslinking structure on the properties of FSPCMs is not very clear currently. In this work, PEG-based FSPCMs are synthesized by free-radical polymerization. They possess different crosslinking densities, and the location of PEG moieties include two different sites (backbone or side chain). The chemical structure, phase change property, crystal structure, mechanical performance, and thermal reliability of the FSPCMs are studied and compared with respect to their different crosslinking structure. It is found that the phase change enthalpy and degree of crystallinity increase with decreasing crosslinking density, and PEG moieties locating in side chain is preferable. With decreasing crosslinking density, the spherulites of the FSPCMs become larger, but always smaller than that of pristine PEG. The results can be explained by the restriction on movement/assembly of PEG moieties by the crosslinking network. The mechanical performance of FSPCMs with PEG moieties located in backbone is preferable than that in side chain. Tensile strength is maximized with poly(ethylene glycol) acrylate (Mn = 12000) as monomer, and elongation at break increases monotonically with decreasing crosslinking density. The findings of this work will contribute to the future design of FSPCMs with optimized overall thermal energy storage and mechanical properties.