Graft Architectured Poly(phenylene oxide)-Based Flexible Films with Superior Dielectric Properties for High-Frequency Communication Above 100 GHz

The surge of fifth-generation communication has intensified the demand for advanced dielectric layers in flexible copper-clad laminates (FCCL). These layers must ensure a low dielectric constant ( D k ) and dielectric loss ( D f ) at high frequencies while meeting essential criteria, including thermal and chemical stability, flexibility, and low water uptake to achieve signal transmission efficiency and FCCL reliability. Herein, we have developed flexible dielectric layers based on poly(phenylene oxide)- g -poly(butadiene) (PPO- g -PB) that exhibit low D k and D f values at high-frequency regimes. Two PPO- g -PB samples with different PB graft densities were synthesized to explore the effect of PB side chains on the thermophysical properties of the resulting PPO- g -PB film. The as-synthesized PPO- g -PB demonstrated excellent film-forming ability, allowing for straightforward fabrication through a simple casting process followed by thermal curing. To determine the potential of these dielectric polymers in high-frequency communication applications, dielectric properties of thermally cured PPO- g -PB (TC-PPO- g -PB) were investigated at high-frequency regimes (from 10 to 110 GHz). Furthermore, we also monitored the water uptake behavior and changes in dielectric properties during an 85 °C and 85% relative humidity reliability test to demonstrate the practical application of these dielectric polymers as advanced dielectric materials.