Carbonated soybean oil (CSO) containing five-membered cyclic carbonate groups has been obtained in the reaction of epoxidized soybean oil with carbon dioxide in the presence of KI activated by 18-crown-6 under 6 MPa CO2 pressure at 130 degrees C. The CSO was used for modification of bisphenol-A based epoxy resin. The composition epoxidecyclic carbonate was cured using polyamine hardeners by one-step and two-step procedures. All cured compositions were characterized for their thermal and mechanical proper-ties and compared with the parent epoxy network. The optimal properties were obtained for compositions containing CSO and cured by one-step method when phase separation takes place. The mechanical properties were discussed in terms of morphology observed by SEM. (c) 2006 Wiley Periodicals, Inc.