Effect of chemical structure on thermomechanical and physical properties of bio‐based epoxy thermosets

Abstract A series of bio‐based epoxy monomers were efficiently synthesized from di‐/tri‐hydroxy precursors, which were prepared via the cross‐aldol condensation of vanillin with various ketone reagents. The epoxy precursors and resulting networks were thoroughly characterized and cured with different amine‐based hardeners to investigate the correlation between the chemical structures of the reagents and the resulting properties. Among the tested systems, the epoxy cured with triethylenetetramine (DDN) exhibited the highest glass transition temperature ( T g ) and α‐transition temperature ( T α ), along with the highest loss modulus ( E ″) and crosslinking density ( υ ) (145 °C, 157 °C, 126.6 MPa and 72.8 × 10 3 mol m −3 , respectively). In contrast, the epoxy cured with 1,10‐diaminodecane (DD) which has the lowest functionality in both the epoxy monomer and the curing agent showed the highest molecular weight between crosslinks ( M c ) (375.6 g mol −1 ) and the lowest crosslinking density ( υ ) (9.6 × 10 3 mol m −3 ). Furthermore, the epoxy sample cured with 1,8‐diamino‐3,6‐dioxaoctane (DDO) demonstrated the highest ultimate tensile strength (22.90 MPa) and elongation at break (6.56%). Thermal stability analysis revealed that the DDN‐cured epoxy thermoset exhibited the highest char yield (38.4%), indicating superior thermal resistance. However, the DD‐based thermoset displayed the highest statistical heat‐resistance index ( T s ), longest half‐life (1311 s) and highest degradation temperature ( T d = 447 °C), suggesting enhanced long‐term thermal stability. © 2026 Society of Chemical Industry.