Crystal to condis-crystal transition in poly(VDF-co-TrFE) copolymers studied by NMR and SAXS-WAXS

The relationship between chain mobility and semi-crystalline organization of two P(VDF- co -TrFE) copolymers with 65/35 and 46/54 VDF/TrFE ratios was studied by combining various experimental techniques (DSC, SAXS-WAXS, and solid-state NMR). This allowed to associate low-density crystalline phases, such as the relaxor ferroelectric (RFE) and the paraelectric (PE) ones, with high molecular mobility, close to the mobility of the amorphous phase. Conversely, the high-density ferroelectric (FE) and defective ferroelectric (DFE) phases, were found to have low and comparable mobility, which decreases after polarization. Moreover, the PE hexagonal phase was investigated, its representation was found to be consistent with the description of condis phase made by Wunderlich in the late 80s. Indeed, the PE hexagonal phase, obtained through a 1st or 2nd order transition (from the FE and RFE phases, respectively), was confirmed to exhibit a long-range positional and orientational order, but with dynamic conformational disorder and high molecular mobility.