Prevost, Adeline (2002) Synthesis and properties of some novel conducting polymers. (PhD thesis), Kingston University, .
Abstract
Because of the nature of conduction in conjugated polymers, an improvement in the planarity of the backbone results in a smaller energy gap and increased electron mobility, and hence in a higher conductivity. From this consideration was born the idea of combining two types of material to create a new one: a side-chain liquid crystal conducting polymer possessing externally controllable backbone planarity. Firstly, a small number of potentially conducting polymer backbones was chosen. For a polymer to be conducting a stable conjugated system is required, therefore an obvious choice was a type of backbone that includes aromatic or heteroatomatic rings. Three different backbone units were used in this project: aniline, pyrrole, and carbazole. The aniline derivatives were chosen to be ortho-substituted so as to favour a regular 'head to tail' polymerisation in positions 1 (N) and 4. Both pyrrole and carbazole are symmetrical when substituted on the nitrogen, making the 'head' position equivalent to the 'tail' one. This property maximises the chances of a regular polymerisation pattern. The next stage of the project was to produce suitable monomers. Previous work was considered to choose the liquid crystal moieties that would be attached. This was achieved by optimising the synthetic route using model compounds before synthesising liquid crystal monomers. The model monomers, and some commercially available compounds, were employed in the following step of the project to optimise the polymerisation route for the various types of polymers. Both oxidative chemical polymerisation and electropolymerisation in different media were used. The novel polymeric products were characterised and their electronic conductivities were measured. Films of the polymer that showed the greatest potential for alignment (liquid crystalline polypyrrole) were studied in more detail, and treated with a focussed laser beam to locally align the polymer backbone. This significantly increased the local conductivity. Most of the monomers and polymers were modelled using a software package (CAChe 3.2) to predict and compare some of their properties. The results of modelling the pyrrole derivative were combined with preliminary X -ray diffraction data for the aligned and unaligned polymer, allowing the proposal of a new explanation for the alignment phenomenon at a molecular level.
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