Vapour phase polymerisation of pyrrole induced by iron(III) alkylbenzenesulfonate salt oxidising agents

A series of iron(III) alkylbenzenesulfonate (ABS) salts were prepared by the reaction of ferric hydroxide, Fe(OH)3·xH2O, with a variety of aromatic sulfonic acids. The products were characterised by microanalysis and FTIR spectroscopy. The microanalysis data generated indicated that three of the salts were not mononuclear iron(III) compounds and were of the formula [(OH2)5Fe–O–Fe(OH2)5][C2H5C6H4SO3]4, [(OH2)5Fe–O–Fe(OH2)5][CH3C6H4SO3]4·2H2O and [(OH2)5Fe–O–Fe(OH2)5][CH3C6H4SO3]4. Some degree of condensation or cross-linking of Fe(III) centres into hydrolytic oligomers had occurred. The X-ray crystal structure of the Fe(III) toluenesulfonate salt established the formula of an oxo-centred, binuclear complex [(H2O)5Fe(μ-O)Fe(OH2)5]4+. Vapour phase polymerisation (VPP) of pyrrole monomer was carried out using iron(III) benzenesulfonate, p-ethylbenzenesulfonate, dodecylbenzenesulfonate and p-toluenesulfonate. As the chain length of the Fe(III) alkylbenzenesulfonates increased it was found that the film forming ability of the polypyrrole was enhanced, probably as a result of a decrease in polymer chain interaction resulting from increased free volume between polymer chains. Variations in the conductivity of the polypyrrole films was observed when Fe(III) p-toluenesulfonate salts obtained from different sources (two commercial samples and one synthesised in our laboratories) were used as the oxidant. Films deposited using these oxidants generally exhibited higher conductivity than those formed using the Fe(III) p-ethylbenzenesulfonate and Fe(III) p-dodecylbenzenesulfonate salts.