Monomer sequence segregation in the liquid crystalline phase of thermotropic copolyester amide. In-situ X-ray scattering

Abstract

In-situ wide-angle X-ray scattering of a sheared thermotropic random copolyester amide revealed monomeric sequence segregation in the liquid crystalline phase. The copolyester amide is based on 60 mol% 2,6-hydroxynaphthoic acid, 20 mol% terephthalic acid and 20 mol% amino phenol (designated N-T-AP). The solid phase exhibits unusual crystallinity and the fiber X-ray diffraction exhibits aperiodic meridional reflections consistent with sequence segregation along the chain. In the liquid crystalline phase at 305 °C polarized optical microscopy showed a “worm” texture, and X-ray scattering showed an amorphous halo denoting no preferred macromolecular orientation. Upon application of shear the X-ray pattern became anisotropic with an increase of intensity on the equatorial axis consistent with the macromolecules being aligned along the flow axis. Strikingly, the X-ray pattern also exhibited a meridional reflection in the melt indicative of spatial monomer register along chains axes. Increasing the shear rate increased the equatorial intensity and reduced the azimuthal spread of the meridional reflection corresponding to an increase of longitudinal monomer register. The monomer register was preserved over a range of temperatures and upon quenching the polymer under shear. Therefore, the unusual crystallinity in solid state would be explained by the existence of monomer sequence segregation already present in the melt.