Novel copolyesters have been prepared by melt mixing poly(ethylene terephthalate) (PET) with an ethoxylated bisphenol S, with the aim to prepare new polyesters with increased T-g, to be used in a wider range of temperatures with respect to neat PET. No side reactions occur during the synthesis of the samples, as proved by NMR analysis. The insertion of the bisphenol S (sulfonyl-diphenol) groups does not significantly alter the thermal stability of PET. The thermal analysis showed that T-m and crystallization rate of the copolymers decreased with incasing co-unit content. The T-g of the copolyesters can be increased by bisphenol S insertion, up to 40 degrees C higher with respect to neat PET, that allows the use of amorphous PET in a wider range of applications. (C) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 128: 416-423, 2013