Abstract
A new pulse sequence for obtaining 19F detected DOSY (diffusion ordered spectroscopy) spectra of fluorinated moleculesis presented and used to study fluoropolymers based on vinylidene fluoride and chlorotrifluoroethylene. The performanceof 19F DOSY NMRexperiments (and in general any type ofNMR experiment) on fluoropolymers creates someunique complicationsthat very often prevent detection of important signals. Factors that create these complications include: (1) the presence of manyscalar couplings among 1H, 19F and 13C; (2) the large magnitudes of many 19F homonuclear couplings (especially 2JFF); (3) the large19F chemical shift range; and (4) the low solubility of these materials (which requires that experiments be performed at high temperatures).A systematic study of the various methods for collecting DOSY NMR data, and the adaptation of these methods to obtain19F detected DOSY data, has been performed using a mixture of low molecular weight, fluorinated model compounds. Thebest pulse sequences and optimal experimental conditions have been determined for obtaining 19F DOSY spectra. The optimumpulse sequences for acquiring 19F DOSY NMR data have been determined for various circumstances taking into account the spectraldispersion, number and magnitude of couplings present, and experimental temperature. Pulse sequences and experimentalparameters for optimizing these experiments for the study of fluoropolymers have been studied.