The morphology of the aromatic copolyester of poly(ethylene terephthalate) and 80 mol % of p‐acetoxybenzoic acid

The structure of the aromatic copolyester of poly(ethylene terephthalate) and 80 mol % of p‐acetoxybenzoic acid was investigated by optical and electron microscopy, wide angle X‐ray, and thermal analysis. The results of optical (LM) and electron microscopy (TEM and STEM) suggest the existence of ordered domains which appear as large lamellar thickness (∼200 Å) as has been described earlier for single crystals of the pure hompolymer of p‐hydroxybenzoic acid (PHBA). However, the characteristic reversible endotherm at 330–360°C for PHBA could not be obtained. In isolated cases, the lamellar blocks retained their general dimensions up to 535°C whereas the surrounding matrix had degraded severely. An irreversible endotherm was observed at 303°C which suggested the presence of a higher degree of order than expected for a random copolymer. The irreversible nature of the endotherm is consistent with a transition from a semicrystalline structure to a liquid crystalline state. X‐ray analysis with as received samples and thermally treated specimen provided additional support for more ordered regions. Copyright © 1982 John Wiley & Sons, Inc.