High-Performance Bismaleimide Resin with an Ultralow Coefficient of Thermal Expansion and High Thermostability

The mismatch of thermal expansion between polymer materials and metals/inorganics causes interface failure and shortens the life cycle of the composites and devices. Traditionally, modulating the coefficient of thermal expansion (CTE) of polymer materials without sacrificing other performance features is challenging. Herein, we report a new strategy for regulating the thermal expansion behaviors of the bismaleimide (BMI) resin, which is one of the most important commercial thermosets. A novel diamine with a disubstituted benzocyclobutene unit was first synthesized and used as the modifier. Through copolymerization and subsequent thermal annealing, we obtained cross-linked BMI resin networks containing thermally contractile submolecular units, dibenzocyclooctadiene (DBCOD). Upon heating, the conformational transition of DBCOD led to an obvious macroscopic volume shrinkage, and consequently, the CTE was reduced dramatically. Record-low CTE values (22 to −19 ppm/K) were achieved for the DBCOD-containing BMI resins. Additionally, the resins also possessed excellent thermal stability (e.g., Tg > 368 °C) and enhanced toughness. By taking advantage of the novel diamine modifier, the ultralow CTE, high heat resistance, and excellent mechanical properties of the BMI resin were well integrated. The enhanced comprehensive performance makes the novel BMI resin a good candidate for many cutting-edge applications.