Chain Topology Engineering in Amphiphilic Block Copolymers: Crosslinking‐Induced Nanodomain Refinement for Ultrahigh Energy Density under Extreme Conditions

The growing demand for high-performance capacitors in extreme environments drives the development of polymer dielectrics with high energy capability and thermal stability. Here, an amphiphilic block copolymer constructed via self-assembly-induced nanoscale microphase separation is presented, in which fluorinated polyimide (FPI) and flexible polyetheramine (PEA) segments form thermally entropy-driven domains. Density-of-state model reveals significant electronic heterogeneity of the resultant copolymer, in which FPI exhibits an energy gap of 3.49 eV while PEA demonstrates a wide gap of 7.31 eV, resulting in an interfacial offset of 5.28 eV that inherently restrains the migration of charge carriers. A trifunctional crosslinker with dual electron-withdrawing groups (─CF₃/─O─) is introduced to refine the PEA phase domain that decreases to 13.7 nm from an initial long period of 19.2 nm. The crosslinking system achieves record-high energy densities of 11.07 J cm^-3 (150 °C/700 MV m^-1) and 6.45 J cm^-3 (200 °C/600 MV m^-1) with an efficiency of >90%, which is attributed to the diminished hopping distance of charge carriers under high-temperature electric field. The received copolymer film retains 1.56 J cm^-3 and an efficiency of 94% with fluctuation of <5% after 10⁵ charge-discharge cycles at 200 °C and 300 MV m^-1. By synergizing amphiphilic energy-level engineering with entropy-driven phase refinement, this strategy establishes a robust material platform for a high-temperature capacitor, balancing ultrahigh energy storage and dielectric reliability.