Effect of the thermal history on the phase transition and the liquid crystalline structure of thermotropic polyesters

Abstract

A series of triad type thermotropic polyesters based on phenylsulfonyl hydroquinone and α,ω-bis(4-caboxyphenoxy)alkane was prepared, and the effect of the thermal history on the phase transition and the liquid crystalline structure of the polyesters was studied. the phase transition was sihnificantly affected by the thermal history. When annealed at various temperatures, multiple endotherms were observed for all polyesters in DSC thermograms. A phase stability concept was employed to explain the complicated phase transitions. The time evolution of the liquid crystalline structure was investigated by optical microscopy and transmitted light intensity measurement under crossed polars during annealing. The steady decrease in the density of disclinations with accompanying increase of transmitted light intensity was observed. Depending on the surface conditions of the main growth patterns and different textures were found on isothermal annealing; the continuous wormlike texture and the discontinuous droplet texture. The structural relaxation of the deformed texture during annealing was also studied. When shear was applied, the characteristic banded texture was formed in all polyesters.