Solid-State 19F MAS, 19F CRAMPS, and 19F → 13C CP/MAS NMR Study of an Amorphous Perfluoropolymer

Abstract

Solid-state 19F high-speed MAS, 19F CRAMPS, and 19F → 13C CP/MAS NMR spectra have been investigated for an amorphous fluoropolymer (CYTOP) having a five-membered heteroring in the main chain. In the 19F MAS spectra, spinning at 35 kHz is necessary to ensure no spectral overlap of spinning sidebands (SSB) with the isotropic signals. The integrated areas obtained are consistent with the molecular structure, and the signal assignments were confirmed using shielding calculations by the GIAO method at a density functional level of theory, B3LYP/6-31G(d). A 19F CRAMPS spectrum measured at a spinning speed of 6 kHz gives slightly narrower half-height widths despite SSB overlap. All fluorine signals show monoexponential decays in the 19F spin-lock experiment with the same , indicating the structure is monophasic. Two fluorines connected to the same carbon give separate peaks at ambient temperature, which reflects the magnetic inequivalence at the axial and equatorial positions of the heteroring. However, they sta...