Synergistic Enhancement of High-Temperature Properties for Capacitor Film by Cyclic Olefin Copolymer and Polypropylene

As the working dielectrics of film capacitors, polypropylene (PP) has been widely used in renewable energy power generation, high-voltage power transmission, electric vehicles and other related applications. However, degraded dielectric performance under thermal stress critically compromises capacitor reliability. Herein, cyclic olefin copolymer (COC), which has high glass transition temperature <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\left(T_{g}\right)$</tex> is blended with PP, introducing saturated rigid bicyclic structures to impede the mobility of molecular chains at high temperatures. Consequently, it synergistically enhances the high-temperature dielectric properties of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{P P}$</tex>. The results show that the introduction of COC decreases the crystallinity of the blend, leading to the diminishing of DC breakdown strength at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$25{ }^{\circ} \mathrm{C}$</tex>. However, when the blending mass fraction of COC is <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathbf{1 0 \%}$</tex>, the DC breakdown strength reaches <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$239.88 \text{kV} / \text{mm}$</tex> at <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$150{ }^{\circ} \mathrm{C}$</tex>, exceeding pure PP by 3.11 %, indicating that COC's efficacy in enhancing high-temperature dielectric behavior. Collectively, this paper proposes a novel design paradigm for capacitorgrade high-temperature dielectrics.