In this article, the synthesis and characterization of the new unsaturated epoxyoligoester suitable for further modification have been presented. The new unsaturated epoxyoligoester was prepared by the chemical modification of the structure of the unsaturated oligoester obtained in polycondensation process of cyclohex-4-ene1,2-dicarboxylic anhydride, maleic anhydride, and ethylene glycol. The chemical modification of the structure of initial oligoester by 38-40% peracetic acid in mild conditions allowed to introduce the oxirane groups into the oligoester backbone. The structure of the samples before and after epoxidation was characterized by FTIR, H-1 NMR, DSC, and elemental analyses. The FTIR and H-1 NMR analyses confirmed that the oxidation reaction took place through the double bonds in cyclohexenyl rings, whereas the double bonds in the unsaturated chain remained unaltered. Moreover, the epoxiciation reaction was performed at 20 and 40 degrees C for 1-6 h to define the optimum temperature and time conditions of this process. The optimum temperature and time conditions were 40 degrees C and 2.5 h, respectively. In this conditions, the maximum conversion of the double bonds (98.3%) and minimal epoxide degradation were observed. (c) 2008 Wiley Periodicals, Inc.