Surface orientation of a liquid-crystalline polymer studied by polarized reflection spectroscopy

The polarized reflection spectrum was used to evaluate the surface orientation of extruded sheets of liquid-crystalline copolyester consisting of 73 mol % 4-hydroxybenzoic acid units and 27 mol % 2-hydroxy-6-naphthoic acid units. The anisotropy of absorption index was evaluated from the specular reflectance using the Fresnel equation and the Kramers-Kronig relation. An intense absorption and observed in the ultraviolet region was assigned to the π^* ←π transitions of the constituent monomeric units. The observed spectra of the liquidcrystalline polymer were successfully interpreted by use of the spectroscopic data on the monomers. The transition moment directions of the monomeric units were calculated by molecular orbital calculations within the framework of the CNDO/S-Cl approximation. The Surface orientation functions obtained from polarized reflection spectra were compared with the crystal orientation functions in the bulk, which were obtained from the azimuthal intensity distribution of wide-angle x-ray diffraction. The orientation behaviour at the surface of the liquid-crystalline polymer was shown to be equivalent to the orientation behaviour in the bulk at higher draw-down ratio.