Semicrystallinity and polymorphism in PVDF:: a solid-state 19F nmr investigation

Solid-state F-19 nuclear magnetic resonance spectroscopy has been employed to investigate the semicrystallinity and polymorphism of poly(vinylidene fluoride) (PVDF). Fast MAS and high-power proton decoupling were applied to separate the spinning sidebands from the relevant spectral range and to remove the effects of dipolar coupling between the protons and the fluorine nuclei. Amorphous and crystalline regions provide distinct chemically-shifted signals. The application of relaxation filters can suppress the signal either of the amorphous or of the crystalline part. The polymorphism, which characterizes the PVDF crystallites, is reflected in spectra of the crystalline part. Some of the variety of possible conversions between the modifications have been exemplified. Variable-temperature experiments demonstrate both crystallization effects and changes in the modifications. (C) 1998 Elsevier Science Ltd. All rights reserved.