Effects of solvents on thermotropic liquid crystalline copolyesters

Morphological studies were carried our on thermotropic liquid crystalline copolyesters based on poly(ethyleneterephthalate) (PET) and para hydroxybenzoate (PHB), where PHB content varied from 0 mole percent up to 80 mole percent. The technique of chemical etching coupled with SEM and WAXS was utilized to obtain structural information. Morphological changes that occur when these materials are exposed to solvents such as dioxane or acetone and dye carriers were also studied using SEM.

Electron microscopy results on the thermally pressed, quenched and chemically etched films indicate that selective chemical etching, i.e. etching of PET rich regions, occurs. This indicates a heterogeneous structure. An oversimplified molecular model has been proposed based on these results where at low PHB levels a PET rich phase is the continuous phase and at higher PHB levels (≥60 mole%PHB) a PHB rich phase is the continuous phase. SEM results on pressed, quenched, annealed and etched films show a "bricklike" structure similar to that seen when pure PET is chemically etched. WAXS studies show that crystallization is induced by solvent (etchant) at small etching times which indicates that the etching of PET rich regions is a two step process; (i) solvent induced crystallization, (ii) chemical etching. Dyeing studies carried out the PET/PHB systems using two different dye carriers indicate that dyeing occurs preferentially in the PET regions. Morphological studies on the dyed materials show a "puffed up" structure present only in the 50 mole% PHB material.