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

Abstract

ABSTRACT:Dielectric behavior and related properties were investigated for copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) with TrFE content from 35 to 87mol%.Three dielectric loss peaks, designated as /3', {3, and T, were observed in increasing order of temperature. The {3' 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 f3 relaxation found in samples with low crystallinity was related to micro-Brownian motion of VDF rich sequences in main chains for 35 to 67mol% TrFE copolymers. In copolymers with 71 and 87mol% TrFE, the f3 relaxation was considered to consist of two components, fJ. and /Jc, due to the local molecular motions in amorphous and crystalline regions, respectively. The T, loss peak was related to a transition between the phase of antiferroelectric nature and paraelectric phase for 48 to 87mol% TrFE copolymers. The transition for 63 and 71 mo!% Tr FE copolymers exhibited characters of the first or second order of the transition, depending on the physical properties observed. Pressure dependence of the T, transition temperature was smaller for 63 and 71 mo!% TrFE copolymers than that for 48 and 35mol% TrFE copolymers.KEY WORDS Vinylidene Fluoride-Trifluoroethylene Copolymer / High Trifluoroethylene Content/ Dielectric Relaxation/ Defect/ Head-to-Head/ Tail-to-Tail / Phase Transition / The relaxation behavior of copolymers of vinylidene fluoride (VDF) and trifluoroethylene (TrFE) with high TrFE content was studied by dynamic mechanical measurements. IX and {3 relaxations due to micro-Brownian motion ofTrFE and VDF rich sequences were found at 313 and 250 K, respectively, for copolymers with 48 to 71 mol% TrFE. 1 Yagi also found two relaxations connected with micro-Brownian motion for copolymers with 40 to 63 mol% Tr FE in dynamic mechanical study. 2 Furukawa et al. 3 studied dielectric behavior of VDF-TrFE copolymers with the entire range of comonomer content and found a relaxation at 253 K at 1 kHz. The relaxation at 253 K was ascribed to the same type of molecular motion in the amorphous region as that of the transformation of trans and gauche at the ferroelectric to paraelectric transition. Koizumi et al. 4 found {3 relaxation due to micro-Brownian motion around 250 K and y relaxation connected with local molecular motion in frozen glassy state at lower temperature. Different relaxation mechanisms were presented for relaxation around 253 K by these authors. For polytrifluoroethylene (PTrFE) two types of relaxation in the crystalline region were found below room temperature and considered to be due to reorientation of main chains around row vacancy defects at chain ends and molecular motion of disordered chains around anomalous linkages such as 771

Ferroelectricity of polymers based on vinylidene fluoride

“…the previous thermal history 34 and poling conditions of the samples. 75 The appearance of dielectric anomalies points to the ferroelectric ± paraelectric transition. Therefore, if there exist two types of ferroelectric phases with different degrees of crystallographic order, the temperature dependences for the real (e H ) and imaginary (e HH ) components of the complex dielectric constant should have two maxima.…”

“…79,80 It should be noted that the presence of the QL and LT phases can account for the appearance of the `anomalous' double hysteresis patterns in VDF/TrFE copolymers with high contents of a second co-monomer. 75,81,82 The type of Curie transition in VDF copolymers is usually identified based on the presence or absence of hysteresis on the temperature dependence of one or another parameter sensitive to phase transformations. These parameters are found in the studies of thermal, electric and spectroscopic properties of objects.…”