Abstract
Based on the modified Higashi’s direct polycondensation method,a series of poly(ester imide)s (PEIs) derived from N,N′-hexane-1,6-diylbis(trimellitimide),4,4′-dihydroxybenzophenone and 6-hydroxy_2-naphthoic acid (HNA) were synthesized by a "step-feeding" polycondensation process.The liquid crystalline behavior,structure and thermal properties of these PEIs were characterized by nuclear magnetic resonance (NMR),polarized-light microscopy (PLM),wide-angle X-ray diffraction (WAXD),differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).The results showed that all the copolymers possessed a typical nematic thermotropic liquid crystalline character,if the feeding HNA ratio is greater than 33 mol% to the total monomer content.However,this type of liquid crystalline polymers shows only the liquid crystalline phase transitions during heating.In the cooling process,the phase transitions of liquid crystalline phase were not observed.These polymers possessed high glass transition temperature (T_g) and relatively lower melt temperature (T_m),which would find their potential usages as a new category of liquid crystalline polymer materials having a lower processing temperature but a higher application temperature.
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