Synthesis and characterization of thermotropic liquid crystalline copolyesters containing poly(etylene tereftalate), 4-hydroxyphenylacetic acid and acetocxybenzoic acid

In this study, a range of wholly aromatic copolyesters based on p-acetoxybenzoic acid (p-ABA), m-acetoxybenzoic acid (m-ABA) and p-hydroxyphenylacetic acid (p-HPAA) monomers with poly(ethylene terephtalate) (PET) polyester have been synthesized by melt polycondensation reaction at 280oC, 5 hours. Characterization of copolyesters were performed by WAXD, TGA, DSC, hot-stage polarized light microscopy, SEM and 13C solid-state NMR. According to the WAXD and TGA results obtained; with increasing composition of linear monomers in polymer chains, an increase in the amount of crystal structure and thermal stability were observed. DSC and hot-stage polarized light microscopy results showed that; copolyesters containing 55-70 mole % of p-ABA units have nematic liquid crystalline behavior and appropriate melting temperature for melt processing. The molecular orientations in fibers obtained from copolyesters were characterized by SEM. According to the 13C solid-state NMR results, the presence of the all monomer units in the copolyesters was established.