Although many polymers exhibit excellent dielectric performance including high energy density with high efficiency at room temperature, their electric and dielectric performance deteriorates at high temperatures (~150°C). Here, we show that nanofillers at very low volume content in a high-temperature (high–glass transition temperature) semicrystalline dipolar polymer, poly(arylene ether urea), can generate local structural changes, leading to a marked increase in both dielectric constant and breakdown field, and substantially reduce conduction losses at high electric fields and over a broad temperature range. Consequently, the polymer with a low nanofiller loading (0.2 volume %) generates a high discharged energy density of ca. 5 J/cm3 with high efficiency at 150°C. The experimental data reveal microstructure changes in the nanocomposites, which, at 0.2 volume % nanofiller loading, reduce constraints on dipole motions locally in the glassy state of the polymer, reduce the mean free path for the mobile charges, and enhance the deep trap level.

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The electrical percolation threshold of carbon black (CB) in thermoplastic polyurethane (TPU) decreases by 46% with the incorporation of 20 wt% polyamide copolymer (COPA) through selective localization of CB particles at the interface of sea-island structured TPU/COPA blends. Composites with a composition of TPU/20 wt% COPA/9 wt% CB were prepared by four different mixing sequences and their morphologies were investigated by FESEM and TEM. The majority of CB particles were observed at the interface of sea-island structured blends irrespective of the compounding sequence used, although the percentage of CB particles at the interface is considerably less in the composite prepared by adding COPA to premixed TPU/CB. The driving force for the interfacial localization of most CB particles is the hydrogen bonding of CB with both TPU and COPA, which is confirmed by FTIR and DMA investigations. CB particles act like Janus particle-type compatibilizers with bonded TPU molecules toward the TPU phase and bonded COPA chains toward the COPA phase. Highly efficient conductive paths are formed through the CB-covered domains and a short inter-domain distance.

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