Effect of the Ratio of Acetylacetate Groups on the Properties of a Novel Plant-Based Dual-Cure Coating System

A novel plant-based dual-cure coating system based on a Michael addition reaction between bismaleimide (BDM) and modified acetoacetylated castor oil was developed. The BDM has a high reactivity toward acetylacetate groups, and the catalyst 1,4-diazabicyclo[2.2.2]­octane (TEDA) was optimized by the rheological viscosity. The gel was characterized by Fourier transform infrared (FTIR) spectroscopy. Then, three films were prepared with the TEDA catalyst and analyzed with solid-state ¹³C NMR and FTIR spectroscopy. The thermal and mechanical properties of the three films were characterized by differential mechanical analysis, thermogravimetric analysis, and differential scanning calorimetry. We found that the cross-linking density, glass transition temperature (T_g), and Young’s modulus of the coating films increased with an increase in the ratio of acetylacetate groups from the modified acetoacetylated castor oil. This is the first study of the reaction of BDM with plant-based acetylacetate groups. Importantly, a quantitative ratio of acetylacetate groups can be obtained by a thiol–ene coupling reaction and a transesterification reaction, resulting in the formation of films having excellent performance.