An oligomer with terminal unsaturated double bonds (unsaturated oligomer, UO) has been synthesized from epoxy resin Epidian 5 and ethylacrylic acid. The impact of the catalyst nature, temperature, and reaction duration on the progress of the reaction between the resin and the acid has been studied. A synthetic technique is proposed for producing the UO. The UO has been characterized by chemical and FTIR-spectroscopic analyses. The UO has been examined in the cross-linking processes with oligoesteracrylates TGM 3 and MGP 9 as well as unsaturated polyester PE 246. In order to prepare structurally colored films, unsaturated azo dyes have been additionally used. A mixture of cumene hy-droperoxide and cobalt naphthenate dissolved in styrene has been utilized as an initiating system for the cross-linking of the formulations. By using FTIR-spectroscopy, the chemistry of the development of the cross-linked structures of the oligoester mixtures in the presence of the UO has been revealed.