PHASE-TRANSFORMATIONS IN COPOLYESTERS BAS ED ON POLY(ETHYLENE-TEREPHTHALATE) AND HYDROXYBENZOIC ACID

Phase transformations in copolyesters between poly(ethylene terephthal ate) and para-hydroxybenzoic acid, having various characteristic visco sities and different ratios of the flexible and mesogenic fragments, w ere studied by method of X-ray diffraction. The X-ray diffraction patt ern of a copolymer with minimum viscosity exhibits an are-like feature with increased scattering intensity against the amorphous scattering background having the shape of the Debye ring. As the the temperature increases, the texture first vanishes and then spontaneously appears a gain at 250 degrees C, with the ''new'' texture axis making an angle o f about 30 degrees with respect to the initial direction. The domains of existence of a two-phase structure (local crystallites in a nematic matrix) and homogeneous (nematic) structures in the copolyester melt were determined. The effect of the phase state of melt on the mechanic al properties of extruded copolyesters was studied.