Solid-state 13C NMR characterization of annealed poly (p-phenylene vinylene) PPV Films

Solid-state 13C cross-polarization magic-angle spinning (CPMAS) nuclear magnetic resonance (NMR) spectra have been obtained for annealed films of poly (p-phenylene vinylene) (PPV), prepared through the precursor route and for a deuterated PPV-d4, poly (p-2,3,5,6 tetradeuterophenylene vinylene). 13C CPMAS spectra of PPV are of high resolution, typically characteristic of a nearly fully crystalline structure. All four phenylene and vinylene resonances have been assigned, and for stretched films the 13C CPMAS linewidth and the quality of crystallinity are independent of the draw ratio. 13C CPMAS resolution and crystallite size (as determined by transmission electron microscopy, TEM) depend upon final annealing temperature. The greatest NMR resolution and largest crystallite size are obtained for films annealed at 300°C. The 13C CPMAS NMR spectra show the presence of phenylene ring 180° rotational jumps, and 13C CPMAS resolution is affected by rotational disorder about phenylene-vinylene bonds. NMR data show that PPV films possess molecular motion at elevated temperatures. Enhancement of this motion during annealing may provide a means for improving the quality of PPV crystallinity.