Sunflower oil-based thermosets via the Passerini three‑component reaction

Tricarboxylic acids are molecules of interest for the synthesis of cross-linked polymers. Herein, a recently established route to a tricarboxylic acid from high oleic sunflower oil was utilized to synthesize renewable cross-linked polymers via the Passerini three-component reaction. Ten different polymers were synthesized by variation of the diisocyanide and monoaldehyde components and subsequently characterized via infrared spectroscopy, swelling tests, thermogravimetric analysis, differential scanning calorimetry, and tensile tests. The characterization of the insoluble polymeric networks was complemented by the synthesis of model compounds to enable analysis in solution via nuclear magnetic resonance spectroscopy. Due to the fast curing of all polymers at room temperature, adhesive tests were performed to demonstrate their potential application as glues. At last, one Passerini polymer was chemically reused by transesterification with methanol and catalytic amounts of sulfuric acid to establish a proof-of-concept of the circularity of these materials. Azelaic acid dimethyl ester, an industrially relevant compound used for the synthesis of polyamides, and a difunctional α hydroxyamide were recovered in a yield of 75%. Repolymerization of the α hydroxyamide to a polyurethane was performed to demonstrate a potential second life cycle of these compounds.