Transition metal complexation of hetrocyclic conducting polymers

Budd, Darren (1995) Transition metal complexation of hetrocyclic conducting polymers. (PhD thesis), Kingston University, .


Poly(3-alkylthiophene)s are amongst the most technologically promising organic conducting polymers owing to their high stability in both the doped and undoped states. The possibility of complex formation between these polymers and transition metal ions (Fe3+, Cu2+, Ag", Ni2+ and Au3+) was investigated in the solid state and in aprotic solvents. In this thesis the background literature relating to these polymers is reviewed, and the aims of the work described. The practical work is then reported, initially the preparation and characterisation of pure poly(3-alkylthiophene)s, and an attempt to prepare regioregular poly(3-hexylthiophene). 3-Alkylthiophenes were polymerised in the presence of transition metal cations and the pure polymers were reacted (chemically and electrochemically) with the metal cations. A full analysis of the polymers' properties reaction is recorded. The polymers' metal ion contents were determined by elemental analysis as well as by thermogravimetric analysis. Electronic absorption and Fourier- Transform infrared spectroscopy were used to detect whether or not complexation had occurred, and if so whether it acted through the sulphur or through the 7t-backbone of the polymer. The incorporation of transition metals into the polymer structure was found to generate greater interchain electron transfer, so enhancing the electrical conductivity of the polymers. The electrical conductivity of the prepared polymers were therefore measured (using the Van der Pauw four-probe technique) before and after reaction with metal ions. The incorporation of copper into poly(3-alkylthiophene)s gave the best indications that complexation had occurred. Almost all of the transition metals that were used gave an increase in the conductivity. Infrared spectroscopy ofpoly-rnethylthiopheue) showed an enhancement of the asymmetric deformation vibration whereas in poly(3-hexylthiophene) a new low-frequency band was observed which can be assigned to the Cu-S bond vibration. Thermal analysis showed that incorporating transition metals into the polymer structure gave the polymers increased thermal stability. Model complexes were prepared in order to simulate the type of complexation which occurred when transition metal cations interact with the polymer structure. The attempted complexation of bithiophene with copper(TI) perchlorate gave the best-characterised product. A preliminary study was undertaken of the feasibility of producing self-ordered aromatic/heterocyclic monomers, by intercalation into inorganic host materials. Polymerisation was attempted by mild oxidative coupling, with the aim of producing relatively defect-free, high molecular weight polymers. Materials were characterised both before and after intercalation, and also after polymerisation, by powder X-ray diffraction, thermogravimetry and Fourier-Transform infrared spectroscopy. The expansion of the inter-Iaytr spacing, together with molecular modelling calculations, indicated the orientation of the molecules within the host, and hence gave some data to predict whether polymerisation would be likely to occur easily. The intercalation of organic/heterocyclic compounds into a MPS3 host proved to be quite successful. When lattice expansion had been observed, there was evidence that the presence of aromatic molecules had caused strong deformation of the thiophosphate units.

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