Thermally-stable low-loss polymer dielectrics enabled by attaching crosslinkable antioxidant to polypropylene.

Polymer dielectrics with low loss and high-temperature tolerance are extremely desirable as electrical energy storage materials for advanced electronics and electrical power applications. They can allow fast switching rates during power conversion and therefore achieve high power densities without thermal issues. Here we explore polypropylene (PP), the state of the art dielectric polymer, and present an innovative approach to substantially improve the thermal stability and concurrently reduce the dielectric loss of PP. In particular, crosslinkable antioxidant groups, hindered phenol (HP), are incorporated into PP via well-controlled chemical synthesis. The grafted HP can simultaneously serve as radical scavenger and crosslinker, thereby constraining thermally decomposed radicals and charge transport in the synthesized PP-HP copolymer. As a result, the upper temperature limit of PP-HP is greatly extended to 190 ⁰C and the electrical loss is even gradually reduced upon thermal annealing. The copolymer after heating under 190 ⁰C exhibits better dielectric properties than the PP without any thermal treatment. The experimental results indicate that the PP-HP copolymers are promising materials for high temperature, low loss, and high voltage dielectric applications.