Orientational ordering in fibers made of wholly aromatic main chain LC polyesters

Abstract Molecular chain orientation characterized by an order parameter in fibers about 102 μm n in diameter of poly(phenyl-p-phenylene terephthalate) and related copolyesters was investigated by means of infrared attenuated total reflectance (IR ATR) spectroscopy. Samples had a tensile strength of about 1 GPa, which could be increased to 2–3 GPa by a heat treatment under appropriate conditions. It has been found that the chain orientation is parallel to the fiber axis in the surface layer. At a distance of about 10–15 μm from the surface, the orientation decreases, with the most oriented surface layer being easily detachable from the weakly oriented fiber core. The great difference between the molecular orientation in the surface layer and in the fiber bulk was supported by wide-angle x-ray scattering (WAXS) data.