INVESTIGATION OF THE MOLECULAR MOBILITY IN A TERNARY COPOLYESTER IN THE LIQUID-CRYSTALLINE AND ISOTROPIC STATES BY MEANS OF DEUTERON NMR

Selectively deuterated ternary copolyesters of poly(ethylene terephtha late) (PET), poly(ethylenenaphthalene-2,6-dicarboxylate) (PEN) and pol y(p-hydroxybenzoic acid) (PHBA) showing the molar composition 35:35:30 were synthesized. In these copolyesters the liquid crystalline state, as well as the isotropic state, can be frozen in by quenching the mat erial from different temperatures. In this way it is possible to compa re the molecular mobility in both states. By means of dynamic mechanic al analysis it was shown in previous investigations that the glass tra nsition temperature, T-g, of the liquid crystalline state is about 35 degrees C lower than that of the isotropic state. The molecular mobili ty of the ethylene groups and of the phenylene rings below and above T -g in both the liquid crystalline and the isotropic state is now inves tigated by means of deuteron n.m.r. It is shown that the trans-gauche jumps of the CH2 groups in the elongated chains in the liquid crystall ine state can occur at lower temperatures than in the coiled chains in the isotropic state. As a consequence, the fraction of flipping pheny lene rings in the liquid crystalline state is larger than in the isotr opic state, when compared at the same temperature.