Polyhydroxyurethane Networks from Soybean Oil and CO₂: Thermal Behavior, Hybrid Features, and Structural Insights

In response to increasing global demand for biobased polymers, this study presents the synthesis and comprehensive thermal characterization of nonisocyanate polyurethanes (NIPUs) derived from soybean oil, focusing on the identification of volatile compounds released during thermal analysis and proposing a degradation mechanism. The materials were obtained via epoxidation, CO₂ cycloaddition, and aminolysis using different aminesIPDA, TRIS, and APTESforming poly-(hydroxyurethanes) (PHUs) with variable cross-link densities and hybrid features. Structural analyses via ¹H NMR and FTIR confirmed successful conversion at each step, with epoxy group titration indicating ≈91% conversion to cyclic carbonate and efficient catalyst removal, as confirmed by XRF (Br < 0.3% after purification). PHUs achieved high cross-linking, with gel contents up to 91.9%. The presence of APTES significantly modified network architecture, reducing gel content to 33% in some formulations but introducing inorganic siloxane domains. TGA revealed multistage degradation between 250 and 475 °C, with TRIS-based networks demonstrating enhanced thermal resistance. Deconvoluted DTG curves and TG-IR data identified primary volatiles including CO₂, amines, ketenes, and silanols, elucidating degradation pathways involving urethane cleavage, retro-aminolysis, and glycerol decomposition. This work advances the understanding of structure-property-degradation relationships in NIPUs and highlights their viability as green engineering alternatives to conventional polyurethanes, aligning with SDGs 9, 12, and 13.