The Transition of the Structure of P-Hydroxy Benzoic Acid and 2-Hydroxy-6-naphthoic Acid Copolyester Caused by Heat Treatment

The transition of the structure of p-hydroxy benzoic acid (HBA) and 2-hydroxy-6-naphthoic acid (HNA) copolyester caused by heat treatment was studied by the X-ray diffraction method. On the asspun fibers, three meridional maxima (scattering angles of 2θ=13.1, 29.0, 43.4°) were observed, with an aperiodic period. The result shows extended random copolymer chains. On the heat treated fibers, a new shoulder in the X-ray diffraction pattern appears in addition to the three maxima. This indicates that a partial change of the crystal stmcture takes place. However, the sequence disthbution of the copolyester was not changed by heat treatment, the analysis of 13C NMR spectra of the fiber showed that the sequence distribution of the copolyester was random before and after heat treatment. In this study, the meridional X-ray diffraction profile of the polymer chain was calculated as a function of blockiness. The copolyester having a random sequence as a whole may still have some blocky parts. The X-ray profile calculated as Markovian sequence agreed with the observed one. We conclude that the crystallization occurred in the high blocky parts of HBA components due to heat treatment.