Abstract
Copolyesters of poly(ethyleneterephthalate) (PET), poly(ethylene-2,6-naphthalenedicarboxylate) (PEN) and poly(p-hydroxybenzoate) (PHB) form liquid crystalline (LC) phases if the fraction of PHB is larger than about 30%. In some of these copolyesters the liquid crystalline state as well as the isotropic state can be frozen in by quenching the material from different temperatures. This makes it possible to compare both states with each other. By means of dynamic mechanical analysis it is demonstrated that the glass transition temperature Tg of the LC-state is about 30°C lower than that of the isotropic state. Neutron scattering measurements show that the radius of gyration of the molecules in the LC-state is larger than for molecules in the isotropic state. The molecular mobility below and above Tg in both the LC and the isotropic state is investigated by means of deuteron NMR.
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