Synthesis and characterization of novel urethane resins based on eugenol: A preliminary assessment of their utility for one-component, oxidatively-curable coatings

Authors: Forson, Kelton; Chisholm, Bret; Biswas, Atanu; CHENG, H - US Department Of Agriculture (USDA)

Submitted to: Journal of Polymer Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2025
Publication Date: 12/11/2025
Citation: Forson, K.G., Chisholm, B.J., Biswas, A., Cheng, H.N. 2025. Synthesis and characterization of novel urethane resins based on eugenol: A preliminary assessment of their utility for one-component, oxidatively-curable coatings. Journal of Polymer Science. https://doi.org/10.1016/j.polymer.2025.129471.
DOI: https://doi.org/10.1016/j.polymer.2025.129471

Interpretive Summary: Synthetic alkyd resins, which are commonly used in paints and coatings, have been commercially available for almost a century and still have a global market size of over $24 billion. In an effort to use more agriculturally based materials in coatings, ARS researchers in Peoria, Illinois, synthesized and evaluated new high-performance resins derived from eugenol, a naturally occurring compound found in the oil of herbal plants such as cloves. Three novel resins were formulated and compared to a commercial oil-derived alkyd resin. The eugenol-based coatings exhibited significantly faster drying and curing times. Two of the resins achieved chemical resistance similar to the alkyd resin coatings and over three times its hardness. These findings demonstrate the viability of these eugenol-based resins with enhanced curing behavior and long-term performance. The results of this study further expand market opportunities for agricultural commodities and will be useful for people interested in biobased materials for coating applications.

Technical Abstract: Three novel, oxidatively curable urethane resins were synthesized using eugenol (EUG), biobased epichlorohydrin, and various di- or tri-isocyanates, resulting in coatings with 69–77 wt% biobased content. These one-component coatings were compared to a commercial long-oil alkyd derived from soybean oil. All experimental coatings exhibited significantly faster drying and curing times than the alkyd benchmark. Mechanical and chemical resistance properties varied depending on the isocyanate used and the molecular characteristics of the resins. During the initial 20-day ambient curing period, the alkyd coating demonstrated steadily increasing chemical resistance and uniform wear during solvent rub testing. In contrast, the EUG-based coatings exhibited lower early-stage chemical resistance, with failure mechanisms involving microcracking and gel particle formation. This was attributed to their low molecular weight and compact, globular structures, which limited polymer entanglement and favored intramolecular oxidative crosslinking, leading to heterogeneous network formation. After extended curing (148 days), two of the EUG-based coatings achieved chemical resistance comparable to the alkyd and demonstrated over threefold increases in hardness, though with reduced reverse impact resistance. The third resin, having the lowest molecular weight and highest glass transition temperature, produced a coating with the highest hardness but the poorest resistance to solvent and impact stress, likely due to extensive microcracking. These results confirm the potential of eugenol-based urethanes for sustainable coatings, with performance highly dependent on molecular design—highlighting the critical role of molecular architecture in tailoring long-term durability and mechanical properties.