Grafting modification is an effective method to enhance the electrical characteristics of polymeric materials by establishing deep traps that prevent carriers from being injected and transmitted. However, grafted polymers for electrical insulation suffer from large leakage current at elevated temperatures, limiting their application in harsh environments. We report that an itaconic anhydride grafted polypropylene synthesized by the solution grafting method preserves excellent insulating properties up to 120 °C. It is demonstrated that the grafted itaconic anhydride restrains free electrons employing strong electrostatic attraction and obstructs charge injection and transport. Furthermore, we reveal that strong intramolecular forces, deep energy traps, and fragmentized spherulites are essential factors contributing to grafted polymers' superior high-temperature electrical properties. This work provides insights into the sophisticated charge transport mechanisms in grafted polymers and their effects on the insulation characteristics, which is critical for the suitable design of polymeric materials with exceptional electrical properties.

Introducing deep traps by grafting functional groups on molecular chains of polymeric dielectric materials has been proved as an effective way to improve their electrical properties, especially suppressing the space charge injection and accumulation. However, the underlying physical mechanism of the origins and effects of deep traps on the electrical properties of polymeric dielectrics has not been fully understood. In order to explore the origins and effects of deep traps in grafted polymers, both simulations of electronic band structures as well as 3D electric potential distributions at molecular level and experiments on the macroscopic trap level distributions are carried out. The simulation and experiment results reveal that the deep traps in grafted polymers originate from the different electronic band structures of the grafted polymer compared with the pristine polymer. The deep traps would capture charge carriers and inhibit the charge transport, which leads to decreased conduction current and suppressed space charge injection and accumulation. This work provides a deep understanding of the origins of deep traps in grafted polymers and their effects on the electrical properties, which may guide the rational design of high-performance polymeric dielectric and insulation materials.

Polypropylene (PP)-based nanocomposite is a promising insulation material for recyclable high-voltage direct current (HVDC) cables, where the coupling agent plays an important role. In this study, four silane coupling agents with different alkyl chain groups (methyl, propyl, octyl, and octadecyl) were used to surface-modify magnesium oxide (MgO) nanoparticles. The surface-modification effect on the electrical properties of PP/MgO nanocomposites was investigated. The results show that surface-modified nanoparticles introduce quantities of deep traps, whose quantity increases as the alkyl chain length increases. The similar tendency also occurs on DC volume resistivity. All these nanocomposites show remarkable space charge suppression ability and improved DC breakdown strength. Among them, the nanocomposites with octyl-modified MgO show the best electrical properties, which could be attributed to the introduction of a large quantity of deep traps. The work may give a reference for the selection of coupling agents in PP-based nanocomposite insulation material for HVDC cable.

The urgent demand for next-generation high-temperature film capacitors with excellent energy storage properties originates from the electrical-power applications under harsh environments. However, the state-of-the-art commercial capacitor dielectric biaxially oriented polypropylene...

Polymer dielectrics need to operate at high temperatures to meet the demand of electrostatic energy storage in modern electronic and electrical systems. The polymer nanocomposite approach, an extensively proved strategy for performance improvement, encounters a bottleneck of reduced energy density and poor discharge efficiency beyond 150 °C. In this work, a polymer/metal oxide cluster composite prepared based on the “site isolation” strategy is reported. Capitalizing on the quantum size effect, the bandgap and surface defect states of the ultrasmall inorganic clusters (2.2 nm diameter) are modulated to markedly differ from regular‐sized nanoparticles. Experimental results in conjunction with computational simulation demonstrate that the presence of ultrasmall inorganic clusters can introduce more abundant, deeper traps in the composite dielectric with respect to conventional polymer/nanoparticle blends. Unprecedented high‐temperature capacitive performance, including colossal energy density (6.8 J cm−3), ultrahigh discharge efficiency (95%) and superior stability at different electric field frequencies, are achieved in these polymer/cluster composites up to 200 °C. Along with the advantages in material preparation (inexpensive precursors and one‐pot synthesis), such polymer/inorganic cluster composite approach is promising for high‐temperature dielectric energy storage in practical power apparatus and electronic devices.