Relaxation and Transition of Copolymers of Vinylidene Fluoride and Trifluoroethylene with High Trifluoroethylene Content

Abstract

Dielectric behavior and related properties were investigated for copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) with TrFE content from 35 to 87 mol%. Three dielectric loss peaks, designated as β′, β, and Tt were observed in increasing order of temperature. The β′ relaxation was predominant in samples with high crystallinity for all copolymers and was connected with molecular motion around defects due to anomalous linkages of head-to-head and tail-to-tail of TrFE rich sequences. The β relaxation found in samples with low crystallinity was related to micro-Brownian motion of VDF rich sequences in main chains for 35 to 67 mol% TrFE copolymers. In copolymers with 71 and 87 mol% TrFE, the β relaxation was considered to consist of two components, βa and βc, due to the local molecular motions in amorphous and crystalline regions, respectively. The Tt loss peak was related to a transition between the phase of antiferroelectric nature and paraelectric phase for 48 to 87 mol% TrFE copolymers. The transition for 63 and 71 mol% TrFE copolymers exhibited characters of the first or second order of the transition, depending on the physical properties observed. Pressure dependence of the Tt transition temperature was smaller for 63 and 71 mol% TrFE copolymers than that for 48 and 35 mol% TrFE copolymers.