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Polyaniline and its derivatives doped with Lewis acids - synthesis and spectroscopic properites.

Abstract : The presented research is devoted to the studies of the doping of polyaniline and its ring substituted derivatives (polyanisidine, poly(2-ethylaniline)) with AlCl3 and FeCl3 as well as with their derivatives containing mixed chloride - acetylacetonate ligands (AlCl2(acac) and (FeCl(acac)2). AlCl3 and FeCl3 doped polymers are conductive and show the electronic type conductivity of the order 10-3 S/cm. Complementary spectroscopic studies involving UV-Vis-NIR, IR, EPR, 27Al NMR (in the case of AlCl3 doping) and 57Fe Mössbauer effect (in the case of FeCl3 doping), combined with elemental analysis, enabled us to elucidate the doping reaction mechanism, which in both cases is the same. The doping involves, in the first step, the self-dissociation of the dopant molecule. The cationic product of this self-dissociation is the complexed on imine nitrogen sites of the polymer chain, whereas the anionic part is incorporated into the polymer matrix to neutralise the positive charge imposed on the polymer chain. The coordination sphere of the cationic complex is completed by solvation with a nitromethane molecule. Charge rearrangement accompanying the doping process produces mobile radical cations on the polymer chain, which assure electronic conductivity of the doped polymer. This mechanism clearly explains the presence of charge carriers and the radical cation structure of the doped polymer chain detected by EPR and UV-Vis-NIR spectroscopies. FeCl3 doped polyaniline shows poor mechanical properties, which can however, be improved by post-treatment with hexafluoroacetylacetone (HFAA). This treatment results in the transformation of FeCl3 (Lewis acid) doped polyaniline into HFeCl4 (Brönsted acid) doped polymer, simultaneously plasticized with HFAA. Doping with mixed ligands (AlCl2(acac) and (FeCl(acac)2.), although being inactive with respect to polyaniline doping, readily dope polyanisidine and poly(2-ethylaniline). The chains of doped polymers adopt the radical cation structure as evidenced by UV-Vis-NIR spectroscopy, however the doping mechanism is more complex than in the case of reaction with AlCl3 or FeCl3. The doping with AlCl2(acac) results in the AlCl3 doped polymer with Al(acac)3 incorporated to the polymer matrix as a side reaction product. Doping with FeCl(acac)2 produces more than expected non-equivalent iron sites of the chemical constitution not easily identifiable by Mössbauer spectroscopy.
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Submitted on : Wednesday, July 5, 2006 - 11:38:28 PM
Last modification on : Wednesday, November 4, 2020 - 2:37:18 PM
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Krzysztof Bienkowski. Polyaniline and its derivatives doped with Lewis acids - synthesis and spectroscopic properites.. Other. Université Joseph-Fourier - Grenoble I; Warsaw University of Technology, 2006. English. ⟨tel-00084184⟩

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