ABSTRACT Bismaleimide (BMI) resins, as thermosets, usually lack toughness and are enhanced by incorporating thermoplastics. However, the traditional high‐performance PES‐C (phenolphthalein‐type polyaryl ether sulfone) toughened BMI system (BDM/DABPA) faces phase separation, which diminishes PES‐C's toughening impact. This study designed and synthesized three types of polyaryl ether sulfone resins with polymer free volume gradient increasing, including propenyl‐containing polyaryl ether sulfone (RPES‐10), propenyl‐containing phenolphthalein‐type polyaryl ether sulfone (RPES‐C‐10) and propenyl‐containing thymolphthalein‐type polyaryl ether sulfone (RPES‐T‐10), all of which contained quantitative reactive propenyl groups. These groups participated in crosslinking reaction of the BMI resin, effectively enhancing impact toughness of the system. Effects of polyaryl ether sulfones with different free volumes on toughening of the BMI system were also investigated. RPES‐10 and RPES‐C‐10 successfully “anchored” the molecular chains within the cross‐linked network, effectively enhancing the toughness of the system. Furthermore, compared to RPES‐10, RPES‐C‐10 possessed a larger free volume and exerted a more superior toughening effect on the thermosetting network. After incorporating 7.5 phr (parts per hundred parts of BDM/DABPA resin) of RPES‐C‐10 into the BMI system, the unnotched impact strength was significantly increased by 157.5%. However, despite owning the largest free volume, RPES‐T‐10 did not further enhance the toughening effect. This study provides insights and references for designing molecular structures of future reactive thermoplastic tougheners.
Wang et al. (2026) studied this question.