Solid‐state 19F MAS NMR study on the conformation and molecular mobility of poly(chlorotrifluoroethylene)

Abstract The temperature dependence of molecular mobility and conformational changes of poly(chlorotrifluoro‐ ethylene) (PCTFE) have been investigated by solid‐state 19 F magic angle spinning (MAS) NMR spectroscopy. The pulse techniques of dipolar–filter and T 1ρ –filter allow selective observation of the amorphous and crystalline domains, respectively. The temperature dependence of T 1ρ F revealed that the segmental motion in the amorphous domain becomes vigorous above ca 80 °C, which is well above the glass transition ( T g ) temperature (52 °C) and more close to the β‐relaxation temperature (95 °C). On the other hand, vigorous molecular motions in the crystalline domain occur above 120 °C, which is much below the melting temperature (212 °C). This indicates that the polymer chains in the PCTFE crystallites are more mobile than those of typical semicrystalline fluoropolymers like poly(vinylidene fluoride) (PVDF), which can be associated with structural imperfections in the crystallites. In addition, the density functional theory (DFT) calculations of 19 F magnetic shielding suggest that the high‐frequency shifts observed for the crystalline signals above 80 °C can be ascribed to the conformational change around meso diads toward more twisted and/or helical conformations in the main chain. Copyright © 2007 John Wiley & Sons, Ltd.