Proton NMR relaxation study of thermotropic copolyesters.

Sato Kazuo, Suzuki Shun-ichi, Inaba Nobuyuki, Murai Hideya

doi:10.1295/polymj.19.815

p-Hydroxybenzoic acid/poly(ethylene terephtharate) (PHB/PET) and p-hydroxybenzoic acid/6-hydroxy-2-naphthoic acid (PHB/PHN) thermotropic copolyesters were investigated in the temperature range from −120 to 180°C by observing the proton magnetic relaxation times T₁, T_1ρ, and the line width. In the temperature dependence of T_1ρ of PHB/PET two minima of the relaxation times were observed. The one at higher temperature corresponds to the glass transition, and the other at lower temperature (40°C) is considered to result from the phenylene group motion. For PHB/PHN, the transition similar to the low temperature one of PHB/PET was observed. The transition temperature of PHB/PHN is higher by 30–40°C as compared with PHB/PET due to the rigid structure. From analysis of line width, it was found that there are two motional regions for both copolyesters, and the activation energies could be obtained. The T₁ minimum associated with the glass transition was observed in the T₁ experiment. The mesophase formation seems to narrow the distribution of the correlation times of motion.

Proton NMR relaxation study of thermotropic copolyesters.

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