Solid-state 19F MAS and 1H → 19F CP/MAS NMR study of the phase-transition behavior of vinylidene fluoride-trifluoroethylene copolymers: 2. semi-crystalline films of VDF 75% copolymer

Abstract

The changes in the crystalline structure and molecular mobility in the semi-crystalline vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer P(VDF 75 /TrFE 25) caused by the ferroelectric → paraelectric phase transition were analyzed using variable temperature solid-state 19 F magic angle spinning (MAS) and 1 H → 19F cross polarization/MAS nuclear magnetic resonance spectroscopy in the temperature range of 42-129°C. The conformational exchange between trans and gauche at the VDF and VDF-TrFE head-to-head linkage gradually increases at temperatures above 77°C, and the conformational exchange at the head-to-tail linkage has a key role in the ferroelectricparaelectric phase transition. The anomalous decrease in the amorphous peak intensities and the presence of a T 1ρ F and T 1ρ value similar to that of the crystalline domain at 122°C indicate that cooperative motion occurs in both phases just above the transition temperature (T c). The amorphous domain is assimilated by the crystalline domain upon lowering the temperature from 129 to 85°C, which significantly increases the crystallinity to below T c, as indicated by the shape of the spectra, and identical T 1 F and T 1 F values for the two domains at 85°C. © 2012 The Society of Polymer Science, Japan (SPSJ) All rights reserved.