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

The changes in the crystalline structure and molecular mobility in the semi-crystalline vinylidene fluoride (VDF) and trifluoroethylene (TrFE) copolymer P(VDF75/TrFE25) caused by the ferroelectric -> paraelectric phase transition were analyzed using variable temperature solid-state F-19 magic angle spinning (MAS) and H-1 -> F-19 cross polarization/MAS nuclear magnetic resonance spectroscopy in the temperature range of 42-129 degrees C. The conformational exchange between trans and gauche at the VDF and VDF-TrFE head-to-head linkage gradually increases at temperatures above 77 degrees C, and the conformational exchange at the head-to-tail linkage has a key role in the ferroelectric -> paraelectric phase transition. The anomalous decrease in the amorphous peak intensities and the presence of a T-1 rho(F) value similar to that of the crystalline domain at 122 degrees 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 degrees C, which significantly increases the crystallinity to below T-c, as indicated by the shape of the spectra, and identical T-1 rho(F) and T-1(F) values for the two domains at 85 degrees C. Polymer Journal (2012) 44, 786-794; doi:10.1038/pj.2012.114; published online 13 June 2012