A broad range of crosslinked polyesters were prepared by curing epoxidized soybean oil with various dicarboxylic acid anhydrides in the presence of cure catalysts such as tertiary amines, imidazoles, or aluminum acetylacetonate. The mechanical and thermal properties of the casting resins were dependent upon the type of anhydride. While the anhydrides of hexahydrophthalic acid, succinic acid, and norbornene dicarboxylic acid yielded highly flexible rubbery materials with glass transition temperatures below room temperature, the more rigid anhydrides of maleic and phthalic acid gave amorphous stiff polyesters with higher glass transition temperatures varying between 43 and 73-degrees-C. When the cure reaction was carried out in polypropylene melts, multiphase polymers were formed containing polyester phases dispersed in the continuous polyolefin matrix.