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

Abstract

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.

Determination of Molecular Orientational Order in Cold-Stretched Poly(p-phenylene vinylene) Thin Films by DECODER 13C NMR

“…at ambient temperature [39,40]. In our DECODER experiments of unstretched and stretched PPV films, we do not observe a significant NMR signal contribution from these rapidly flipping phenylene rings.…”

“…[39]. From our DECODER experiments and simulations, we estimated the value for s zz to be 18 ppm; as opposed to 30 ppm; as reported previously [39]. The 13 C tensor values listed in Table 1 for the protonated carbons in the aromatic ring are similar to those for aromatic sites in other polymers (for example, poly(ethylene terephthalate)) [28].…”

“…The values obtained for the vinyl carbons differ from values determined for polyacetylene. This discrepancy is attributed to an overlapping contribution to the 13 C signal with the isotropic chemical shift at 128 ppm from a population of phenyl rings that are undergoing fast 1808 flips around the 1,4-axis; this results in an average 13 C chemical shift tensor with an isotropic shift value of 128 ppm as well, see Table 1 [39]. By analyzing 2 H and 13 C CPMAS line shapes, Simpson et al determined that between 15% and 40% of the phenylene rings in their PPV sample were flipping at a rate greater than 3:0 Â 10 3 s…”

“…[39]. From our DECODER experiments and simulations, we estimated the value for s zz to be 18 ppm; as opposed to 30 ppm; as reported previously [39].…”

“…These distinct positions with respect to the vinyl group result in different isotropic chemical shifts for these two pairs of carbon sites, leading to observed frequency differences between the two pairs of protonated aromatic carbons (C 2 and C 5 ; C 3 and C 6 ). Previous solid-state 13 C NMR studies have determined the isotropic 13 C chemical shifts of the different carbon sites in PPV to be 136; 131; 125; and 128 ppm for C 1;4 ; C 2;5 ; C 3;6 ; and C 7;8 ; respectively [37][38][39].…”