Rheological and thermal properties of a commercial liquid-crystalline polyesteramide

A commercial main-chain liquid-crystalline, naphthalene-based polyesteramide, was studied by three experimental techniques: extrusion capillary rheometry, dynamic viscoelasticity, and differential scanning calorimetry (DSC). From capillary rheometry a maximum at 360°C was observed in viscosity temperature curve. This result is compared with literature data for other thermotropics, and the possibility of a transition from a nematic to an isotropic phase is considered. The results obtained from dynamic viscoelasticity and DSC agree, and reveal the existence of a glass transition at 128°C (by DSC) and 137–147°C (by viscoelastic measurements, depending on frequency) as well as melting at 282°C. Annealing below 230°C produces two types of crystals, whereas annealing above this temperature gives rise to only one type of crystal, the melting temperature of which can be, depending on annealing time, as high as 340°C. The results are compiled in a phase diagram with six regions, four of them corresponding to the solid state, one to a liquid mesophase, and one to an isotropic phase.