Thermotropic Copolyesters Based on Polyethylene Terephthalate and 4-Hydroxybenzoic Acid for High Modulus Fibers

The copolyesters derived from dimethyl ester of terephthalic acid, ethylene glycol, and 4-hydroxybenzoic acid (HBA) have been synthesized via catalytically promoted polycondensation omitting the acetylation step. FTIR spectroscopy results have evidenced an insertion of HBA along a polymer backbone. Of note, thermal gravimetric analysis has shown that the HBA moieties substantially improved the thermal stability of polyesters. As found by differential scanning calorimetry and polarizing microscopy, the copolyesters are capable of forming an anisotropic phase in a temperature range of 150-170 °C. Additionally, the free surface energy of the samples was determined to evaluate the compatibility of thermotropic copolyesters with other high-molecular compounds.