A Novel Bismaleimide-Urea Resin: Breaking the Trade-off Between Strength, Toughness and Thermal Stability via Molecular Design

The intrinsic brittleness of bismaleimide (BMI) resins has long restricted their wider application in aerospace and automotive industry. Herein, a novel BMI-urea resin network that integrates flexible urea linkages into the rigid BMI matrix is developed. The developed BMI-urea polymer combines elasticity with high strength. Molecular dynamics simulations and AI-assisted predictions revealed that Michael addition dominates over BMI self-polymerization, enabling rational design of hybrid networks. The nanoscale phase-separated morphology endowed BMI-urea with ductility and toughness while preserving strength and thermal stability. Fracture analysis revealed the enhancement of mechanical properties via rigid BMI segments providing reinforcement while flexible urea segments dissipating energy and supressing crack propagation. The developed BMI-urea exhibited (i) tensile as high as 55 MPa – 120% improvement over diamine-urea; (ii) impact strength as high as 208 kJ/m ² – 30% improvement over BMI; (iii) up to a 60-fold increase in elongation at break; (iv) preserved thermal stability above 290°C. Swelling resistance test in three different media showed a dependence of solvent uptake on soft segment content and microphase separation. The current study introduces, for the first time, an elastic BMI-urea resin that combines toughness, strength and thermal resistance – paving the way for advanced application is aerospace composites and structural adhesives.