Star-Shaped Compact Interface Architecture Induced by Vinyl-Terminated High-Heat-Resistant Hyperbranched Poly(carbazole-type bisphthalazinone sulfone)s for the Simultaneous Enhancement of Toughness, Thermal Performance, and Processability in Bismaleimide Resin

Conventional toughening of bismaleimide (BMI) resin with linear thermoplastic faces a critical compromise: enhanced toughness often compromises thermal properties and elevates melt viscosity, severely limitations for their application in extreme environments. To overcome this long-standing challenge, a novel strategy was pioneered by designing and synthesizing a unique class of hyperbranched poly(carbazole-type bisphthalazinone sulfone)s (h-PCBPSs) with tailored reactive groups (propenyl or allyl), with the trifunctional monomer 4,4′-(9H-carbazole-2,7-diyl)bis(phthalazin-1(2H)-one) (CZ-BDHPZ) employed as the building block via a two-step procedure for the modification of BMI resin. h-PCBPSs exhibited high thermal resistance, with glass transition temperatures ( T g ) ranging from 308 to 355°C. The rheological behavior of the h-PCBPSs/BMI blends was characterized. The temperature range corresponding to the processing window, defined by a viscosity below 0.2 Pa·s, was broadened up to 140.1-185.5°C. The formation mechanisms of sea-island, single-phase, and star-shaped morphologies were elucidated, and the effects of these three distinct morphological structures on the thermal and mechanical properties of the BMI were systematically analyzed. The T g , unnotched impact strength, and flexural strength reached 293°C, 33.5 kJ/m², and 190 MPa, respectively. Compared with the cured product of the neat BMI, these values increased by 5.4%, 196.5%, and 36.7%, respectively. The thermo-oxidative aging resistance mechanism of BMI modified by h-PCBPS-A was elucidated. After 7 days of aging at 250°C, the impact strength retention rate and flexural strength retention rate of h-PCBPS-A-10phr/BMI reached 36.3% and 88.9%, respectively. This work provides a new design strategy for BMI toughening agents and promotes the application of BMI resin in extreme environments.