Synthesis and characterization. To obtain the main component of the photocurable resin, the first step was the addition of methacrylic groups on the fatty acids in the starting microalgal oil through epoxidation and methacrylation reactions. The double bonds of the fatty acid from the commercial microalgal oil were epoxidated using H₂O₂ and formic acid (Figure ). The reaction was exothermic, and it was placed for the first two hours on ice and then at 35°C to avoid overheating and, consequently, side product and safety hazards. Due to the potential thermal instability, the reaction was conducted five times to assess the reproducibility of the procedure without observing relevant variations between different batches. At the end of the reaction, the product obtained was a bright orange oil, which was neutralized with a solution of NaHCO₃. The epoxidized microalgal oil (EMO) was stored at 4 °C until used. Samples of EMO and the oil used as starting material were used for 1H NMR spectroscopy (Figure ). Comparing the raw microalgae spectrum to those of the epoxidation products, peaks at 5-5.5 ppm indicate the decrease of double bonds, and new peaks around 3 ppm appear, corresponding to the formation of epoxide groups during the epoxidation process . The Degree of Modification (DoM) obtained with the different batches of EMO is 2.3 ± 0.1. A detailed NMR characterization of the EMO can be found in the supporting materials. The EMO obtained was then methacrylated using methacrylic acid, triphenylphosphine (TPP) as a catalyst, and hydroquinone (HQ) as a radical scavenger (23) (Figure ). Different procedures were tested for methacrylation because of the selfpolymerization of the reaction mixture at various conditions. From the observations made and the evidence from literature , the temperature has a vital role in this side reaction. It was also observed that slowing down the addition of methacrylic acid at a lower temperature helped to prevent this effect. The methacrylic acid was therefore added dropwise at room temperature to avoid polymerization. The reaction was also performed with different concentrations of the reagents, and an interesting behavior was observed when different amounts of TPP were used. By varying the concentration of TPP from 1% to 2%, a relevant increase in methacrylic groups bound to triglyceride molecules was observed, allowing materials with different degrees of modification to be obtained reproducibly. Although the mechanism of methacrylation in the presence of TPP is not yet clearly understood, we also observed that increasing TPP reduces the incidence of self-polymerization of methacrylic groups during the reaction.