POLYMORPHISM IN A LIQUID-CRYSTALLINE POLYESTER BASED ON 4,4'-BIPHENOL, TEREPHTHALIC ACID, AND P-HYDROXYBENZOIC ACID (1-1-2)

The polyester from 1 mol of 4,4'-biphenol, 1 mol of terephthalic acid, and 2 mol of p-hydroxybenzoic acid, synthesized by the acidolysis condensation reaction of the acetylated mixture, was studied by using wide-angle X-ray diffraction and differential scanning calorimetry (DSC). X-ray diffraction demonstrated a reversible crystal-crystal transition at about 100 degree C. The transition was also observed with DSC as a small endotherm. The most prominent calorimetric feature is an endotherm at about 427 degree C corresponding to the crystal-nematic transition. There is also a small endotherm at about 472 degree C which may correspond to the nematic-isotropic transition. On cooling from 450 degree C at 10 deg/min, there is observed about 40 deg of supercooling before crystallization occurs.