Reducing Dielectric Loss by PVDF-CTFE Graft Copolymers

Polymer film capacitors with high energy density and low loss are very attractive in potential applications. Maintaining the high dielectric breakdown strength in high dielectric constant films with a low loss will also be a challenge. Poly(vinylidene fluoride) (PVDF) and its copolymers are well-known ferroelectric polymers that exhibit excellent electromechanical properties as candidates for high-performance, high-energy-density capacitor. However, the dielectric loss of commercially extruded PVDF films is high (0.02). In our work, lower dielectric loss polystyrene (PS) were introduced to improve PVDF dielectric properties. PVDF-CTFE-g-PS graft copolymers were synthesized via the ``graft from'' process. The quality of films from graft polymer was improved, resulting high energy density and low loss. A series of graft polymers with different electric properties were prepared, since the breakdown strength and dielectric loss of PVDF were influenced by the crystallinities and crystal sizes.