Relaxor Ferroelectric Behavior in Poly(vinylidene fluoride-co-bromotrifluoroethyene)

Copolymers of vinylidene fluoride (VDF) and bromotrifluoroethylene (BTFE) were prepared over a composition range up to the disappearance of crystallinity ($\sim$ 9 mol {\%} BTFE). The resulting copolymers were characterized by $^{19}$F NMR to elucidate composition and quantify the linkage defects of the polymer chain. Chain conformations were analyzed by FTIR analysis and crystal structures were studied by DSC and WAXD. The dielectric properties were evaluated by dielectric spectroscopy as a function of frequency and temperature and at high fields to investigate the influence of BTFE on dielectric behavior. The results indicate that the P(VDF-BTFE) copolymers exhibit relaxor ferroelectric behavior similar to those reported in PVDF terpolymers resulting from a mixed $\alpha $/$\gamma $ crystalline phase. Effects of processing such as stretching and crosslinking have also been studied with respect to the relaxor ferroelectric properties of the copolymers. Stretching was found to improve the breakdown strength of the films along with enhancing both the stored and discharged energy density. Preliminary crosslinking results indicate that stretched and cross-linked polymer show a reduced remnant polarization.