Glassy liquid crystalline poly(p-hydroxy-benzoic acid-co-ethylene terephthalate) is after rapid cooling from temperatures above Tg in a non-equilibrium state and exhibits physical ageing. It is shown that enthalpy and volume decrease with increasing annealing time. At the same undercooling, with respect to middle temperature of the major glass transition (Tgl), the rate of the equilibration process is significantly slower in the studied polymer than in an ordinary glassy amorphous polymer. The presence of a constraining ETP-rich phase exhibiting a 25 K higher glass temperature than Tgl may be the cause for this retarded enthalpy relaxation.

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.

AbstractThe microstructure of injection molded bars (2.9 and 5.8 mm thick) of thermotropic liquid crystalline poly(p‐hydroxy‐benzoic acid‐co‐ethylene terephthalate) has been studied by SEM on samples etched with n‐propylamine, SEM fractography, DSC, IR, ESCA, WAXS and polarized microscopy. The 2.9 mm bar consists of three different layers: a highly oriented surface skin, an oriented intermediate layer and a non‐oriented core. The 5.8 mm bar has a more complex microstructure and is composed of five different layers: a highly oriented surface skin, an oriented layer just beneath, a non‐oriented layer, another oriented layer and a non‐oriented core. The thicknesses of the different layers vary, significantly, with distance from the mold gate. The thickness of the core increases, significantly, with increasing distance from the mold gate at the expense of the oriented layers. The structure within the different morphological layers is not perfectly uniform. Tensile testing demonstrated the mechanical anisotropy of the surface material (a ratio of almost 20 between the longitudinal and transverse moduli) and the isotropy of the central core material.

AbstractDSC, IR, ESCA, macroscopic etching rate measurements, analysis of etchant solution, and electron microscopy conclusively show that n‐alkylamines (ethylamine, n‐propylamine, n‐butylamine, and n‐pentylamine) and NaOH selectively degrade (etch) the ethylene terephthalate (ET)‐rich phase in glassy liquid crystalline poly(p‐hydroxybenzoic acid‐co‐ethylene terephthalate) [P(HBA–ET)] with molar compositions 0.60:0.40 and 0.80:0.20. ESCA demonstrates the excellent selectivity of the n‐alkylamine etchants in the 0.60:0.40 copolymer. The 50 Å top layer of the etched samples contains 95 mol% HBA. Treatment with H2SO4 and NH3 gives ambiguous results, and these compounds are not suitable as etchants. It is demonstrated by electron microscopy on the 0.60:0.40 copolymer, in accordance with earlier reports by Joseph et al.,5–8 that the ET‐rich phase is discontinuous (1–2 μm spheres) and surrounded by an HBA‐rich matrix. SEM is a useful tool for characterization of this morphology. However, both phases have a substracture which is revealed only by TEM. The morphology of the 0.80:0.20 copolymer is fine‐textured, which means that SEM is a less suitable method for the characterization of etched samples.