Vegetable oils are often thermally polymerized to provide a vehicle for printing inks and paints. The formations of isomerization, and the intra‐ and intermolecular bonds involved in the thermal process are crucial in designing a product with the appropriate characteristics. It was found, with a differential scanning calorimeter, that the thermal polymerization of various vegetable oils could be activated at lower temperatures under a dry‐air purge and/or in the presence of metallic catalysts. The Diels‐Alder reaction and the formation of intermolecular bonds in alkali‐refined soybean oil under a dry‐air purge could be activated at 99 and 161°C in the presence of metallic catalysts, compared with 231 and over 300°C in the absence of metallic catalysts, respectively. The energies needed to activate the Diels‐Alder reaction and to form intermolecular bonds were calculated, and is in good agreement with available data. The hardness test of baked vegetable‐oil systems was also implemented to qualitatively determine the degree of cross‐linking.
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Wang et al. (1999) studied this question.