Impact of Crystallinity on Discharge Energy Density in Chemically Modified Polyethylene Dielectric Materials

The growing demand for next-generation electronic technologies necessitates the advancement of dielectric materials with high dielectric constant (εs) and low dielectric loss (tan δ), which are essential for storing energy, smoothing voltage fluctuations, and transducing electrical signals to mechanical movements. Simultaneous maximization of εs while maintaining low tan δ is still a major challenge, especially for polyolefins. Recently, we reported a substantial increase in the dielectric constant of chemically modified linear low-density polyethylene (LLDPE) from εₛ ≈ 2.8 to 12, but at the expense of increasing tan δ. The increase in tan δ was attributed to the presence of ionic impurities, but there was a concurrent reduction in the degree of crystallinity, posing the question of what role does crystallinity play in polymer dielectrics. Here, we apply the same postpolymerization modification strategy to high‑density polyethylene (HDPE), which retains crystallinity upon chemical functionalization, enabling a systematic evaluation of dielectric response and discharge energy density performance. The resulting amine‑ and zwitterion‑modified HDPE exhibits modest increases in εₛ (≈ 1.5 to 2.7 and 3.5, respectively) while maintaining ultralow dielectric loss (tan δ < 10⁻²), consistent with dissipation constrained by preserved semicrystalline order. Notably, amine-functionalized HDPE achieves Ud = 1.32 J/cm³ at 250 MV/m with a high efficiency of 95.1%, which is 3.7 times greater than pristine HDPE. These results establish crystallinity retention as a key design parameter for maintaining low dielectric loss in chemically functionalized polyolefins while highlighting postpolymerization modification as a potential route to upcycle polyethylene into capacitor-grade dielectric films.