Liquid crystalline block copolymers containing different compositions of terephthaloyl bis(4-oxybenzoyl) (triad) mesogen and flexible ethylene terephthalate (ET) units, were synthesized in tetrachloroethane/pyridine (TCE/Py) at 150 degrees C and in 1-chloronaphthalene (1-CN) at elevated temperatures. Inherent viscosities of the PET block copolymers were always lower than 0.25 dL/g. By replacing the ET blocks with butylene terephthalate (BT) blocks, a copolymer of higher inherent viscosity (> 0.8 dL/g) was synthesized in 1-CN at 220 degrees C. Formation of low molecular weight PET copolymers was attributed to : (1) insolubility of the block copolymer in TCE/Py and (2) formation of side products which alter the stoichiometry of the reactants when the reaction was carried out in 1-CN. The block copolymers were characterized by H-1 and C-13-NMR spectroscopy. Copolymer compositions were calculated from H-1 and C-13-NMR data. Thermal behavior of these copolymers was analyzed by DSC and polarizing optical microscopy. All copolymers exhibited a nematic liquid crys talline texture.