Phase transformations in a thermotropic liquid crystalline copolyester and its blends with polyether sulfone

Mesophase transitions in a thermotropic liquid crystalline polymer comprising p‐hydroxybenzoic acid (PHB) and polyethylene terephthalate (PET) in a copolymer ratio of 60/40 were studied by means of optical microscopy, light scattring, and wide‐angle X‐ray diffraction (WAXD). According to time‐resolved light scattering and optical microscopic studies, at about 250°C, a mesophase transition was evident in which Schlieren texture developed with elapsed time. This transition has been identified as a solid crystal‐nematic mesophase transition associated with the melting of PHB‐rich crystals. It is concluded that the copolymer sequence may not be random. An isotropic, amorphous blend of PHB‐PET/polyether sulfone (PES) was prepared by solvent casting from hexafluoro‐2‐propanol solution. However, this homogeneous blend appears to be kinetically entrapped during solvent removal. Thermally induced phase separation takes place upon heating slightly above the glass transition temperature of PES. Morphology development within phase‐separated domains has been qualitatively examined by light scattering and optical microscopy.