Allyl-terminated alicyclic benzoxazine monomer: An active modifier for curing regulation and hydrothermal properties enhancement of bismaleimide

To address the issues of bismaleimide (BMI) resins, such as high curing temperature, inherent brittleness, and insufficient hydrothermal stability, a bio-based liquid benzoxazine monomer (E-pacm) featuring a terminal allyl group and alicyclic backbone was synthesized, and employed as a reactive modifier for a commercial BDM/DBA-based BMI resins. Compared with the BDM/DBA system, the introduction of E-pacm effectively regulated the curing behavior, decreasing the main exothermic peak temperature from 256.0 °C to 239.5 °C. With an optimal loading of E-pacm, the BDM/15EPBz system exhibited a flexural strength of the reached 171.74 MPa, a 27.22% increase relative to the unmodified BDM/DBA system. Meanwhile, the dielectric constant at 1 MHz for the BDM/15EPBz system decreased to 3.29, relative to 3.70 for the BDM/DBA system. Owing to hydrophobic alicyclic skeleton and extra crossing network, the modified resins displayed diminished water absorption and consequently superior hydrothermal stability. Although the introduction of E-pacm entailed a sacrifice in the glass transition temperature (T_g), the modified resin still maintained a T_g above 268 °C. After immersion in hot water at 100 °C for 48 h, the wet T_g retention rate increased from 91.71% to 96.42%. The research shows that E-pacm can realize the synergistic regulation of the curing behavior, mechanical properties, dielectric properties, and hydrothermal stability of BMI resins.