Copolymers of poly(ethylene terephthalate) (PET) containing 6-oxy-2-carboxyanthracene (OA) and 6-oxy-2-carboxynaphthalene (ON) structural units are prepared by reactive blending of acetoxyarenecarboxylic acid comonomers with PET. The new copolymers are characterized by H-1 and C-13 NMR, DSC, dilute solution viscometry, optical microscopy, and wide-angle X-ray diffraction and compared to poly(ethylene terephthalate-co-4-oxybenzoate), PET-co-OB. Whereas 40 mol % of the OB unit is required to induce liquid crystallinity in PET-co-OB, only 20 mol % of OA or 30 mol % of ON units are required. This is also in contrast to copolymers containing similar amounts of symmetrical arenedicarboxylate structural units which do not form liquid crystalline phases.