Copolyesters having tertiary amine groups or zwitterion moieties in the main chain were prepared from terephthaloyl chloride (TPC) and mixtures of bisphenol A and aliphatic diols such as N-ethyldiethanolamine (EDA), N,N-bis(2-hydroxyethyl)-2-aminoethanesulfonic acid (BES) and N,N-bis(2-hydroxyethyl)glycine (BHG) by a liquid/solid biphase polycondensation in trimethyl phosphate (TMP) as well as a water phase/organic phase interfacial polycondensation. The composition of copolymers obtained by the biphase polycondensation is close to that of the feeds. The nucleophilicity of hydroxyl groups of these aliphatic diols is increased in TMP and the solvent TMP participates in the reaction. In the water phase/organic phase interfacial polycondensation, the copolyester (P1) from EDA has a higher aliphatic diol residue content than P2 and P3 from BES and BHG, because the self-nucleophilic catalysis of the tertiary amine groups of the resulting polymer occurs in the organic phase. The copolyesters (P2 and P3) having pendant hydrophilic groups contain very few aliphatic diol residues because the self-nucleophilic catalysis of the tertiary amine groups takes place in the water phase and the extensive hydrolysis of the intermediate occurs, which results from TPC with the tertiary amine groups during the reaction.