Probing phase structure and location of reverse units in poly(vinylidene fluoride) by solid-state NMR

Investigation of phase structure of poly(vinylidene fluoride) and characterization of its NMR fingerprints from three main polymorphs are presented by exploiting C-13-{F-19,H-1} and F-19-{H} MAS NMR experiments. Selective excitation of F-19 NMR signal from different phases has been used for a straightforward identification and separation of spectroscopic signatures not only from the amorphous part but also from alpha, beta, and gamma polymorphs. A new insight into the phase structure of morphologically different samples has been gained by T-1p,(F-19) relaxation measurements in the conditions of very high spinning speeds and strong radio-frequency field. Motional heterogeneity of the reverse units has been revealed, and their spatial location in the amorphous, intermediate, and crystalline phases was quantified for the first time. The spectroscopic fingerprints along with phase structure features of PVF2 and the ways exploited in this work for their retrieval might be useful to obtain structural information on PVF2 of different origin as well as on other types of fluoropolymers.