Solid-state magnetic resonance studies of polyaniline as a radical scavenger

Abstract

The first detailed study of polyaniline (PANI) and reduced PANI (R-PANI) before and after reaction with the stable organic free radical 1,1-diphenyl-2-picrylhydrazyl (DPPH) by using solidstate 13C CP MAS (cross-polarization magic-angle spinning), NQS (nonquaternary suppressed) and CPPI (cross-polarization phase inversion) nuclear magnetic resonance teehniques is reported. These techniques reveal relatively subtle structural changes that occur upon reaction with DPPH free radicals and confirm the radical scavenging ability of PANI. The integrated intensity of the PANI CP MAS spectrum after reaction with DPPH is about 8% larger than that of PANI and this cannot be explained by an oxidation process alone. The increase is attributed to a decrease in the polaron concentration in the polymer, which is consistent with electron paramagnetic resonance (EPR) data that show a decrease of the EPR signal intensity after reaction of chemically synthesized PANI with DPPH.

Synthesis of novel fluorescent molecule and its polymeric form with aniline as fluorescent and supercapacitor electrode materials

“…The peaks obtained to various carbons in the P(ANI‐2NA4ABA) structure are given in Figure B. The peak positions obtained for polyaniline at 113.1, 124.1, 138.9, 140.9, 147.5 and 155.1 ppm are due to PANI, which are in accordance with the solid‐state spectrum of PANI base reported by Zujovic et al The remaining peaks are due to carbon of the 2NA4ABA, which was confirmed from 13 C analysis using ChemDraw (PerkinElmer) software. Thus, 13 C spectrum supports the formation of P(ANI‐2NA4ABA).…”

Characterization of Polyaniline Nanotubes Formed in the Presence of Amino Acids

“…The spectrum of the doped PANI sample is relatively broad in comparison with its dedoped form, revealing heterogeneity in the sample and significant charge distribution, i.e., the local variations in charge density along the polymer backbone. [25,[44][45][46] Typical PANI peaks are seen at 163.4 ppm assigned to imine quinoid carbon (C-7 in Scheme 1). However, this is shifted 3-6 ppm downfield compared to the peak obtained from a standard PANI sample, [25,44] which could be due to distortion of the structure by possible hydrogen bonds.…”

“…[25,[44][45][46] Typical PANI peaks are seen at 163.4 ppm assigned to imine quinoid carbon (C-7 in Scheme 1). However, this is shifted 3-6 ppm downfield compared to the peak obtained from a standard PANI sample, [25,44] which could be due to distortion of the structure by possible hydrogen bonds. The peak at 146.3 ppm (C-1, attached to an imine nitrogen) is assigned to a benzenoid carbon.…”

“…Due to heterogeneity of the sample (residual charges) and overlapping of the peaks due to chemical shift dispersion in the doped and the dedoped form, some of the resonances could not be observed, e.g., C-6 seen as a peak or shoulder at 114 ppm. [44,45] Thus, heterogeneously located non-conducting and conducting domains of different morphologies, which could shift peaks significantly, contribute to the complex nature of the 13C CP MAS spectra of the PANI nanotubes' material.…”

“…The peaks at 96.5 and 180.3 ppm are not characteristic of typical PANI structures, [25,44] and their presence is not clear at the moment. The 180.3 ppm peak may be due to APS and oxidation, which shifts aromatic carbon resonance to downfield.…”