Marianne Westdahl

Cold-crystallization in liquid crystalline poly(p-hydroxybenzoic acid-co-ethylene terephthalate)

Abstract Quenched samples of thermotropic liquid crystalline poly(p-hydroxybenzoic acid (HBA)-co-ethylene terephthalate (ETP) with a HBA/ETP molar ratio of 0.6:0.4 have been annealed at temperatures between 401.3 K and 451.5 K. Thermal analysis (differential scanning calorimetry, d.s.c.) and wide-angle X-ray scattering indicate that two types of crystallization occur at these temperatures: comparatively large (> 10 nm) HBA-rich crystals of a high melting point are formed most probably due to a transesterification reaction-induced crystallization; thin, about 3 nm thick, HBA-rich crystals are formed by ‘normal’ cold-crystallization. Avrami analysis of the latter process recorded by d.s.c. yields Avrami exponent values in the range 0.2–0.4 which is consistent with the occurrence of a highly restricted one-dimensional crystal growth. This can be explained on the basis of the limited length of the crystallizable units and on the rigid-rod character of the molecules in the nematic mesophase.