LOCAL DYNAMICS IN A THERMOTROPIC TERPOLYESTER AS REVEALED BY DYNAMIC-MECHANICAL ANALYSIS, H-2 NMR AND DIELECTRIC-SPECTROSCOPY

Dynamic mechanical, H-2 NMR and dielectric spectroscopy techniques wer e used to identify the nature of the local motions involved in the sec ondary relaxations of a thermotropic aromatic terpolyester prepared fr om para-hydroxybenzoic acid, hydroquinone and isophthalic acid. Three secondary relaxations, denoted beta, gamma, and delta, were detected. A beta relaxation, pointed out by dynamic mechanical measurements, is quite close to the large amplitude pi-flip processes observed by H-2 N MR. Correlated motions of the para-substituted rings and adjacent carb onyl groups may also participate in the beta process. Then, at lower t emperatures, a gamma process is detected by both dielectric and dynami c mechanical experiments. It is assigned to small amplitude oscillatio ns of the isophthalic acid units of the HBA33 polymer. At high tempera tures, a heavy overlap of broad rate distributions for the beta and ga mma processes observed in the measurements precludes a more detailed a nalysis. A dielectric relaxation, denoted delta relaxation, is observe d at very low temperatures. It likely comes from motions of a very sma ll number of water molecules trapped in the structure of the terpolyes ter.