Bio-based amines from urethane oligomer for tunable epoxy thermosets

The scarcity of bio-based amines, particularly ones with more than two primary amines, limits the development of sustainable thermosets. Herein, novel bio-based hardeners structures were synthesized from widely available building blocks, including a pentanediisocyanate isocyanurate trimer ( t PDI or STA-NCO) and urethane prepolymers prepared from polypropanediol (PPD, 500–2,000 g·mol -1 ). A controlled hydrolysis process allowed the obtention of four amines: STA-NH 2 ( = 3) and PPD-based amines V500-NH 2 , V1000-NH 2 , and V2000-NH 2 ( = 4), with biobased carbon content above 83 %. Their structures were confirmed by NMR and FTIR, and Amine Hydrogen Equivalent Weights (AHEW) were determined by 19 F NMR titration after derivatization. Curing behavior with vanillin-based epoxy (DGEVA) was investigated by FTIR and gel time measurements. Reactivity depended on amine functionality, viscosity, and AHEW, with gelation times as low as 12 min at 50 °C. STA-NH 2 produced rigid networks with high stress at break (55 MPa), while PPD-based amines introduced soft segments and phase segregation, yielding ductile materials with Young’s modulus down to 4.0 MPa and elongation up to 114%. A dual hardener strategy combining STA-NH 2 and V2000-NH 2 enabled continuous tuning of thermomechanical and tensile properties. Soft segments dominated below 20 wt.% STA-NH 2 , whereas hard segments dictated properties above this threshold. This study demonstrates a versatile approach for designing bio-based amines, providing tunable epoxy thermosets with adjustable rigidity, ductility, and thermal performance. The approach paves the road to create biobased materials with tailored properties for various applications. • Biobased amines with high functionality were synthetized • Amines were employed as hardener for vanillin derived epoxy • Poly(propane diol) soft segment allowed tunable properties • Amine synthesis methodology paves the way to specific functional materials