Preparation and Properties of Form-stable Phase Change Materials Based on Side-chain Liquid Crystal Polymer without Flexible Spacer

A series of monomers 4'-alkoxy-4-biphenol methacrylates MbiCm, with different alkoxy tail lengths (m = 1, 2, 4, 6, 8, 10, 12, 14, 16, 18), and their corresponding polymers PMbiCm were synthesized via free radical solution polymerization. The phase transition temperature and thermal stability of the polymers were studied by DSC and TG. Experimental results revealed that all the polymers were liquid crystal and exhibited high clear points. The clear point of the polymers was first decreased and then increased with increasing the alkoxy chain length. All the polymers showed excellent thermal stability, and their decomposition temperatures were all above 310 degrees C. The novel P6biCm/paraffin composite, form-stable phase change materials (FSPCM), was prepared by introducing PMbiCm into paraffin. The minimum gelation concentration (MGC) and gel-to-sol transition temperature (TGS) were tested by tube-testing method. It was found that the gelation stability of PMbiCm was closely linked with alkoxy chain length. PMbiCm (m = 1, 2, 4, 6) were insoluble in paraffin at high temperature, and not able to form gel in paraffin. PMbiCm (m = 8, 10) were partly paraffin-soluble, while PMbiCm (m = 12, 14, 16, 18) formed stable gel in paraffin. The MGC and TGS decreased with the increase of the alkoxy tail length owing to enhanced interaction between the polymer and paraffin. The thermal properties and rheological properties were studied. The results showed that the PMbiCm/paraffin were of high phase transition enthalpy, excellent thermal stability and high gel strength. The structure and morphology of the FSPCMs were also investigated by FTIR, POM and SEM. The results revealed that paraffin was restricted because the gelators PMbiCm could self-assemble into three-dimensional netted structures, leading to the formation of shape-stable PCMs without leakage even above their melting point of the phase change materials.