Axial correlation lengths for aromatic copolyesters

Abstract

X-ray methods were used to investigate the structure of Vectra(R) and Xydar(R) polyesters. Xydar(R) is based on the aromatic polyester prepared from p-hydroxy-benzoic acid (HBA), terephthalic acid, and biphenol. Vectra(R) consists of HBA and 2-hydroxy-6-naphthoic acid. X-ray fiber diagrams of these materials consist of a series of nonperiodic layer lines, which are consistent with a structure consisting of parallel chains of a random comonomer sequence. The meridional peak positions are predicted accurately for fully extended, infinite chains, and the observed and calculated intensities are also in reasonably good agreement. However, there is a less adequate match between the observed and calculated peak profiles, which are predicted to be much sharper than those observed. The latter agreement is improved with a model consisting of finite chain segments with a slightly nonlinear (sinuous) conformation. The best agreement for the observed peak profiles is obtained with an ordered segment length of 90 +/-6 Angstrom and a sinuosity of g = 3.67 +/-0.08% for Vectra(R) fibers and with an ordered segment length of 104 +/-6 Angstrom and a sinuosity of g = 3.33 +/-0.08% for Xydar(R) fibers. (C) 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1839-1847, 2001.