Improving the Dimensional Stability of Polyphenylene Oxide without Reducing Its Dielectric Properties for High-Frequency Communication Applications

The 5th generation mobile communication technology (5G) requires materials with high reliability, high dimensional stabilities, and low dielectric constant (Dk) and low loss factor (Df). However, achieving both high dimensional stabilities and low dielectric is difficult. In this work, we propose a strategy to improve dimensional stabilities of printed circuit board (PCB) substrates without reducing their dielectric properties by introducing crosslinking agents with trifluoromethyl groups and allyl groups to polymers. Polyphenylene oxide (PPO) was selected as the representative research object, and a series of cured PPO-Allyl-F with varying contents of trifluoromethyl and allyl side chains were designed and synthesized. The molecular structures of the thermosetting PPO were characterized using 1H nuclear magnetic resonance (1H NMR) and Fourier transform infrared (FTIR) spectroscopy. The isothermal curing kinetics of the thermosetting PPO were monitored with in situ FTIR. The thermal stability, mechanical properties, glass transition temperature (Tg), coefficient of thermal expansion (CTE), and dielectric properties of the cured PPO-Allyl-F materials were investigated in detail. The results show that the obtained thermosetting PPO with improved dimensional stabilities and low dielectrics has great potential for the application in high-frequency electronic circuits. This work provides a new approach for developing high-performance polymers that can address the contradiction between dielectric properties and dimensional stability.