Ring-opening polymerization of epoxidized soybean oil (ESO) catalyzed by a super acid, fluoroantimonic acid hexahydrate (HSbF6 center dot 6H(2)O) in ethyl acetate was conducted in an effort to develop useful biodegradable polymers. The resulting polymerized ESO (SA-RPESO) was characterized using infrared (IR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), H-1 NMR, C-13 NMR, solid state 13 degrees C NMR, and gel permeation chromatography (GPC). The results indicated that ESO was effectively polymerized by fluoroantimonic acid and formed polymers with relatively high crosslink density. Glass transition temperatures of these polymers ranged from 13 degrees C to 21 degrees C. TGA results showed the SA-RPESO polymers were thermally stable at temperatures up to 200 degrees C. Decomposition of the polymers was found to occur at temperatures greater than 350 degrees C. GPC results indicated the extracted soluble substances from SA-RPESO polymers were oligomers of ESO. These soybean oil-based polymers will be functionalized to hydrogels and their applications explored in the personal and health care areas. Published by Elsevier B.V.