Pratt, Colin (2003) Effects of metal ions on the synthesis and properties of conducting polymers. (PhD thesis), Kingston University, .

Abstract

Polythiophene derivatives are amongst the most technologically promising conducting polymers both for their high stability in both their doped and undoped states, and for their processability. For these reasons polythiophene derivatives are excellent candidates for use as electrochromic conducting polymers. It is well known that the inclusion of metal moieties in conducting polymer structures can alter the polymer’s properties. In order to explore this phenomenon, polythiophene derivatives with pendant transition metal sulfonate groups were synthesised from the ammonium salt. These polymers were then studied by cyclic voltammetry (CV) and their key electro chromic properties were examined. The colour change produced upon doping was measured, as were the kinetics of this colour change and the stability of the doped state. The different metal ions caused small changes in the colour of the undoped and doped polymer. The interband absorption peaks of the more ionic metal salts were red-shifted relative to the more covalent ones. In addition, salts of metals good at complexing were insoluble in water, unlike the salts of metals that are not. The complex also correlated with the stability of the doped state, the better complexing metal salts being more stable. The switching times were a few seconds for most of the polymers, although the chromium, copper and tin salts were significantly slower. Poly(3-alkylthiophene)s (P3AT) are of great commercial and scientific interest because of electrical conductivity, stability in air and processability. The most cost effective method of their synthesis is oxidative polymerisation using iron (III) chloride. It has been found that this can be enhanced by small amounts of nickel and cobalt chloride used during polymer synthesis. In order to understand this phenomenon, the mechanism of the oxidative polymerisation of 3-hexylthiophene (3HT) and the effects of reaction modifiers on the resulting polymer properties were investigated. Gel permeation chromatography (GPC), UV-visible spectroscopy and proton NMR spectroscopy were employed to investigate the effects of specific organic inhibitors and of cobalt chloride catalyst. The mechanism of polymerisation was identified using inhibitors that each affected one specific reaction pathway. Polymerisation was observed to proceed by two' different mechanisms, one of which was greatly inhibited by cobalt chloride whilst the other was enhanced. Cobalt chloride was found to increase the molecular weight of the polymer and to make it more regioregular. As a result, the conductivity of the iodine-doped polymer was strongly enhanced.

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