Copolycondensations of TPA, PhHQ, and several aromatic diacid and diol modifiers were examined for which kind of the modifiers incorporated is more effective to reduce the transition temperatures of the resulting copolyesters and how they affect the temperatures. The acid modifiers are more effective than the diol ones, significantly when they have substituents. As another type of modifier, HBA forming the ester bond of an AB structure different from the AABB structure of TPA/PhHQ polyester was also effective, and the lowering effect on the temperatures was varied by the mode of copolycondensations, being most remarkable when HBA was randomly introduced. The results obtained were discussed in terms of the disturbance and thereby weakening of the interchain dipole-dipole interaction between the carbonyl groups in the ester linkages due to the introduction of the diacid modifiers and of HBA having an ester bond of a different directionality.