<p>High-temperature capacitive energy storage demands that dielectric materials maintain low electrical conduction loss and high discharged energy density under thermal extremes. The temperature capability of dielectric polymers is limited to below 200 °C, lagging behind requirements for high-power and harsh-condition electronics. Here we report a molecular topology design for dielectric polymers with mechanical bonds that overcomes this obstacle, where cyclic polyethers are threaded onto the axles of various polyimides. From density functional theory and molecular dynamics calculations, we found that the local vibrations of the encircled polymer chains were damped by the cyclic molecules through mechanical bonding, substantially inhibiting the phonon-assisted interchain charge transport that dominates conduction loss when approaching the thermal extremes. At 250 °C, we experimentally observed a d.c. electrical resistivity four orders of magnitude greater than that of commercial polyimides, with the discharged energy density reaching 4.1 J cm⁻³ with 90% charge–discharge efficiency, exceeding conventional dielectric polymers and polymer composites. These findings open up opportunities for substantially promoting the temperature capability of dielectric polymers given the rich diversity of existing molecular topologies modified with mechanical bonds.</p>