X-ray diffraction of thermotropic liquid-crystalline copoly(vanillate-4-hydroxybenzoate-ethylene terephthalate)

Precision X-ray diffractometry was used to study directly the structure of as-made films and fibers, which were uniaxially extruded from thermotropic liquid-crystal line nematic melts of copolymers consisting of vanillate (V), 4-hydroxybenzoate (B) and ethylene terephthalate (E) units with various molar ratios. The addition of a small amount of unit V (at most 5 mol-%) to the well-known poly(4-hydroxybenzoate-ethylene terephthalate) (B/E) polymer will produce an increase in orientation, but an addition of 15-34 mol-% of unit V might result in the decrease of the orientation. The X-ray diffractions of the oriented samples of V/B/E and B/E copolymers show a series of aperiodic intensity maxima on the meridian, which are consistent with that expected for a random sequence of the units. The equatorial scans exhibit single broad peaks centered at 0.437-0.446 nm due to intermolecular scattering. The meridional and equatorial maxima shift in position with the V/B/E ratio of the copolymers. The positions of the meridional maxima are slightly affected by spinning temperature. The linewidth of the most intense maximum at the spacing of 0.207 nm on the meridian was used to determine the correlation length of extended V/B/E copolymer chains. No discrete maxima are observed in both meridional and equatorial small-angle X-ray scattering curves.