Melting and recrystallization of a thermotropic liquid crystalline copolyester

Oriented samples of a liquid crystalline polymer (Vectra A950) analyzed in direct contact with an aluminium pan shrunk and curled during heating in the DSC which led to a very noisy baseline and an artificial multimodal melting. Oriented samples immersed in silicone oil or surrounded by Kapton films were free to shrink, remained in good thermal contact with the aluminium pan and displayed noise-free heating thermograms with a single melting peak. The constrained samples showed noise free, unimodal melting in the 260-290 degrees C range. Annealing of Vectra samples between 250 and 300 degrees C led to a gradual increase in both the melting enthalpy and the melting peak temperature with increasing annealing time. Crystallization of the pure nematic polymer was facilitated by orientation. (C) 1998 Elsevier Science B.V.