Segmented copolymer systems composed of an amorphous g1assy engineering polymer as one segment and a potentially anisotropic polyester as the second segment were synthesized and investigated. The engineering thermoplastic segment was based on various all aromatic poly(arylene ether sulfooes) derived from the nucleophilic aromatic substitution reaction between hydroquinone, biphenol, and dichlorodiphenylsulfone. This reaction was conducted in the presence of potassium carbonate and anhydrous aprotic dipolar solvents. Poly(biphenol terephthalate) and poly(oxybenzoate) were synthesized in situ as the second, potentially anisotropic, sem;crystalline segment. These segmented copolymers were synthesized either by solution t interfacial, or melt acidolysis techniques. The melt acidolysis technique was used to synthesize the segmented copolymers with high poly(arylate) contents. The morphology of the copolymers was found to be totally amorphous for those capolymers with low levels of the poly(arylates). They were semicrystalline when the poly(arylate) contents were increased beyond a critical value of about 15 weight percent. Differential scanning calorimetry, optical microscopy, and wide angle X-ray scattering were used to probe the copolymer morphology. The chemical structures of the segmented copolymers were studied through the use of Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy (both ¹H and ¹³C). As the weight percentage of the poly(arylate) was increased, a very significant improvement in the solvent resistance was noted. Evidence of anisotropy and liquid crystallinity in the copolymers was provided by optical microscopy, differential scanning calorimetry, and wide angle X-ray scattering.