This invention relates to bio-based polyfunctional carboxylic acids reacted with vinyl ether compounds to form liquid vinyl-blocked bio-based polyfunctional carboxylic acids. These liquid vinyl-blocked bio-based polyfunctional carboxylic acids can be mixed with a polyfunctional vegetable oil-based epoxy resin to form a homogeneous curable coating composition. Upon curing at elevated temperature, thermoset coatings are formed which have excellent hardness, solvent resistance, adhesion, and flexibility. The invention also relates to the use of a curable coating composition comprising at least one polyfunctional vegetable oil-based epoxy resin and at least one vinyl-blocked bio-based polyfunctional carboxylic acid, which may be coated onto a substrate and cured thermally. Methods of making the vinyl-blocked bio-based polyfunctional carboxylic acids and curable coating compositions and substrates containing the same are also disclosed.