Active Ester-Functionalized Polyphenylene Oxide for Low-Dielectric and High-Thermal-Stability Epoxy Composites in Advanced Packaging

Epoxy-based composites combining low dielectric loss, high thermal stability, and mechanical robustness are highly desirable for high-frequency and high-speed electronic packaging. In this study, hydroxyl-terminated poly(phenylene oxide) (PPO) was functionalized via esterification to introduce active ester groups, yielding active ester-terminated PPO (AEPPO). The modified AEPPO exhibited improved compatibility with the epoxy matrix and was incorporated into a dicyclopentadiene-type active ester-cured epoxy/SiO 2 system. The resulting composites demonstrated significantly enhanced thermomechanical and dielectric properties. With 20 wt % AEPPO, the Young’s modulus increased from 10,087 to 11,315 MPa, and the glass transition temperature ( T g ) reached 165.1 °C, with a low coefficient of thermal expansion of 20 ppm/°C and a water absorption of just 0.13%. Optimized dielectric performance was achieved at 15 wt % AEPPO, exhibiting a dielectric constant of 2.91 and an ultralow loss of 0.0049 at 20 GHz. These results highlight the potential of AEPPO as a multifunctional modifier for epoxy composites in next-generation high-performance electronic packaging applications.