Nowadays, paper-foil and metalized paper capacitors have been replaced by polymer film capaciors. Advanced dielectric capacitors require new high permittivity and high energy density materials. Ferroelectric polymers, such as PVDF and its copolymers with high dielectric constant (10-20) and high electric breakdown strength (ca. 700 MV/m for a test area of 2 cm~2), are attractive and have been widely investigated. However, because of ferroelectric hysteresis (Scheme 1A), the high energy loss restricts their application as dielectric capacitor films. Even at low electric fields, the dielectric loss of PVDF and its copolymers (tanδ～0.02) is about 100 times higher than that of biaxially stretched polypropylene (BOPP, tanδ～0.0002). Recently, novel ferroelectric behaviors have been proposed for this purpose, namely, relaxor ferroelectric (Scheme 1B) and antiferroelectric (Scheme 1C) behaviors. Nonetheless, currently challenge lies in achieving high melting temperatures for these PVDF-based copolymers.
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