Doctor of Philosophy
Department of Chemistry
Majidi, Mir Reza, Development and application of chiral conducting polymers, Doctor of Philosophy thesis, Department of Chemistry, University of Wollongong, 1996. http://ro.uow.edu.au/theses/1135
This thesis describes the synthesis and characterization of optically active polyaniline its derivatives. The novel optically active emeraldine salts PAn.(+)-or (-)-HCSA and PAn.(-)-HCSA were prepared as dark green films via the enantioactive electropolymerization of aniline in the presence of (+)-or (-)-HCSA, respectively. The two films PAn.(+)- or (-)-HCSA and PAn.(-)-HCSA exhibited strong mirror imaged CD spectra. This was rationalised in terms of the polyaniline chain adopting a helical structure in which one screw-sense is preferentially maintained depending on which hand of the CSA- anion is incorporated.
The electrochemically synthesised chiral polyanilines were characterized using electrochemical techniques such as cyclic voltammetry, electrochemical quartz microbalance, and resistometry. Different electrochemical techniques could be employed for the electrosynthesis of the polymers, namely potentiostatic, potentiodynamic and galvanostatic polymerization, giving films with similar chiroptical, electrochemical and mechanical properties.
Dedoping and redoping of the optically active emeraldine salts PAn.(+)-HCSA were studied using both cyclic voltammetry and chemical (NH4OH ) methods. Interestingly, replacement of the (+)-CSA- anion by either Cl- or (-)- CSA- did not significantly alter the CD spectrum of the films, indicating that the initial macroasymmetry of the polymer chains is maintained during these treatments.
The optically active polyanilines PAn.(+)- or (-)-HCSA and PAn.(-)-HCSA were also generated chemically in solution by the enantioselective acid doping of neutral emeraldine base (EB) with either PAn.(+)- or (-)-HCSA in various solvents such as NMP , DMSO, DMF and CHCI3. Dark green films of these optically active polyaniline have also been obtained by casting onto glass from the above acid doped solutions in various solvents.
Related optically active polytoluidines were similarly chemically synthesised in solution via the acid doping of neutral polytoluidine with either (+)- or (-)- camphorsulfonic in the solvents such as DMSO, and DMF. In all cases mirror-image circular dichroism spectra were obtained when the (+)- or (-)- CSA- anions were incorporated.
These chiral conducting polyanilines were then studied as modified electrodes on glassy carbon. Compounds such as K3[Fe(CN)6], 2, 6- anthraquinone disulfonic acid disodium salt were found to undergo normal redox behaviour on these modified electrodes. Cyclic voltammetry studies also showed that citraconic acid could be reduced on these electrodes. However, attempts to achieve the asymmetric reduction of this prochiral substrate via electrolysis were unsuccessful, presumably due to the high resistance of the polyaniline at the potential required for the reduction. However, the electrochemical oxidation of methyl-p-tolyl sulfide to the corresponding sulfoxide could be carried out via electrolysis at this chiral modified electrode, giving a small degree chiral induction.
Chiral polypyrroles have been similarly synthesised by incorporating (+)- camphorsulfonate or (+)- bromo-camphorsulfonate as the chiral counterions. The electrochemical behaviour, as well as morphology and tensile strength of the PPy.(+)- CSA- obtained was examined, as well as their use as chiral modified electrodes for the electrochemical reduction and electrolysis of some simple compounds such as K3[Fe(CN)6], 2, 6- anthraquinone disulfonic acid disodium salt and citraconic acid.
Finally, the ability of chiral membranes made by depositing PAn.(+)-HCSA on either polysulfone or polyvinilidine flouride to discriminate between the enantiomeric forms CSA- has been explored. These membranes were found to transport (+)-CSA- considerably more readily than (-)-CSA-, suggesting that they have potential for the separation of the enantiomeric forms of chiral anions.