Molecular mobility in liquid-crystalline phase of oriented wholly aromaticcopolyester as revealed by proton magnetic resonance

Broad line proton magnetic resonance (PMR) has been used for the study of m olecular motion in wholly aromatic thermotropic liquid-crystalline (LC) cop olyester at high temperatures up to 340 degrees C. Specimens were thin high ly oriented fibers produced from a copolymer of hydroxybenzoic acid and hyd roxynaphthoic acid (HBA/HNA). In the vicinity of the thermotropic transitio n temperature a fine structure of PMR spectra was revealed for as-spun fibe rs. Annealing leads to smoothing of this structure. Theoretical spectra wer e calculated and compared with the experimental ones. This made it possible to obtain information on large-scale segmental motion of macromolecules in the LC phase. Heat treatment leads to retardation of the chain cooperative mobility. Dynamic inhomogeneity of the fibers at high temperatures is disc ussed, (C) 1999 Elsevier Science Ltd. All rights reserved.