Selective etching of thermotropic liquid crystalline polyesters

DSC, 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 H 2 SO 4 and NH 3 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.