SOLID-STATE C-13 NMR-STUDIES OF MOLECULAR-MOTION IN AN AROMATIC COPOLYESTER

Carbon-13 n.m.r. studies have been carried out on an oriented copolyes ter material comprising 73 mol% hydroxybenzoic acid (HBA) and 27 mol% hydroxynaphthoic acid (HNA). The T-1 rho values for the carbonyl carbo n, and non-protonated aromatic carbons of HBA and HNA rings have been measured over a range of temperature, and show minima at temperatures corresponding to the mechanical and dielectric relaxation transitions. The T-1 rho-temperature plots have been fitted using the Cole-Davidso n distribution, and indicate a broad distribution of correlation times . The activation energies obtained from the fits provide support for t he association of the gamma relaxation with the HBA ring, and the beta relaxation with the HNA ring. Studies of the variation in chemical sh ift anisotropy indicate an increase in oscillations of both rings abou t the chain axis, with increasing temperature, and these motions appea r not to be coupled with the motion of the carbonyl group. (C) 1998 El sevier Science Ltd. All rights reserved.