Highly improved mechanical and thermal properties of bismaleimide via a novel thermoplastic isoindolinone polyether sulfone

Abstract To improve the mechanical and thermal properties of thermosetting bismaleimide resins, a novel thermoplastic isoindolinone‐based polyether sulfone (PES‐In) resin was synthesized as a toughening agent for the N , N ′‐(4,4′‐methylenediphenyl)bismaleimide/2,2′‐diallylbisphenol A (BDM/DABPA) system. The incorporation of this toughening agent not only enhanced the material's overall toughness but also significantly improved its thermal performance. The effects of PES‐In's viscosity and dosage on toughening efficiency were systematically studied, leading to the identification of optimal conditions. Specifically, 7.5 phr PES‐In with a viscosity of 0.4 dL/g resulted in a remarkable increase in the impact strength of the PES‐In/BDM/DABPA system to 37.20 kJ/m 2 , representing a 497% improvement over the base BDM (6.23 kJ/m 2 ). Thermal properties, as assessed by dynamic thermomechanical analysis and thermogravimetric analysis, also showed significant enhancements, with T d5% and T g reaching 425 and 267°C, respectively, and the storage modulus rising from 2.0 to 2.5 GPa. Scanning electron microscope analysis revealed a typical “sea‐island” toughening structure with multiple crack deflections on the impact fracture surface. The introduction of PES‐In thus broadens the application potential of bismaleimide in higher‐temperature‐resistant structural materials. Highlights Novel isoindolinone‐based polyether sulfone (PES‐In) was synthesized. Toughness of bismaleimide networks by PES‐In was significantly improved. Thermal performance of the PES‐In/ BDMN /DABPA system was improved. Relative toughening mechanism was clearly elucidated.