Preparation and characterizations of thermotropic copolyesters of p‐hydroxybenzoic acid, sebacic acid, and hydroquinone

A series of copolyesters of p‐hydroxybenzoic acid (HBA), sebacic acid and hydroquinone were prepared by melt polycondensation of p‐acetoxybenzoic acid, sebacic acid and p‐phenylene diacetate. The copolyesters were characterized by IR, NMR, DSC, polarized microscopy, and X‐ray diffraction. It was found that the copolyesters exhibited liquid crystallinity when the HBA content was 25–67 mol %. The copolyesters with an HBA content of 25–43 mol % showed a nematic phase and a biphasic range, and the isotropization temperature increased as the HBA content increased. The copolyesters with an HBA content of 54–67 mol % showed a nematic phase up to above 400°C. The liquid crystalline order increased as the HBA content increased due to the increased of the average length of the rigid moieties.