Modification of polythioesters obtained by interfacial polycondensation bis (4-mercapto-phenyl) ether and adipoyl, sebacoyl, or isophthaloyl chlorides with the use of 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) has been described. Polycondensates with 10, 50, or 90% molar of bisphenol A in relation to dithiol were obtained under the same conditions as those established earlier as optimal for synthesis of polythioesters from dithiol and adipoyl, sebacoyl, or isophthaloyl chlorides. The structure of all the polycocondensates was determined by infrared spectra and X-ray analysis. Thermal and some mechanical and electrical properties for polycocondensates containing 50% molar bisphenol A in relation to dithiol were defined. © 1993 John Wiley & Sons, Inc.