Strongly Dipolar Polythiourea and Polyurea Dielectrics with High Electrical Breakdown, Low Loss, and High Electrical Energy Density
Dielectric materials with high electric energy density and low loss are of great importance for applications in modern electronics and electrical systems. Strongly dipolar materials have the potential to reach relatively higher dielectric constants than the widely used non-polar or weakly dipolar polymers, as well as a much lower loss than that of nonlinear high K polymer dielectrics or polymer–ceramic composites. To realize the high energy density while maintaining the low dielectric loss, aromatic polythioureas and polyureas with high dipole moments, high dipole densities, tunable molecular structures and dielectric properties were investigated. High energy density (>24 J/cm3), high breakdown strength (>800 MV/m), and high charge–discharge efficiency (>90%) can be achieved in the new polymers. The molecular structure and film surface morphology were also studied; it is of great importance to optimize the fabrication process to make high-quality thin films.