DSC and Optical Texture Studies of Copolymers Based on Poly(butyleneterephthalate)/PHBA and PET/PHBA

Abstract

Copolyesters based on poly(butyleneterephthalate) (PBT) and p-hydroxybenzoic acid (PHBA) wereobtained by transesterification in the melt and the resulting products were characterized as to theirliquid crystalline properties. Thermal transitions and the mesophases formed during heating and coolingwere examined by differential scanning calorimetry and hot stage polarizing microscopy. All the polymermelts were strongly birefringent and showed nematic threaded optical textures, accompanied by randomly-distributed regions of isotropic PBT and small crystallites of PHBA oligomers. During themicroscopic studies of the PET/60PHBA copolymer, regions were observed where a second nematicphase appeared if the temperature was held above 260°C for a long enough time. This can be explainedby the high content of PHBA and relatively low molecular weight of the copolymer.