| Characterisation of polypyrrole (PP) films by X-ray photoelectron spectroscopy (XPS), and in combination with a thickness-shear-mode (TSM) acoustic sensor illustrates differences between the oxidised and neutral forms of the polymer. Comparisons to poly(N-methylpyrrole) (PMP) and poly(N-phenylpyrrole) (PPP) are also made. Converting the conducting form of PP to its neutral form increases the solvation level of the polymer and, upon removal of the counteranions, allows the polymer to form an intramolecular hydrogen-bonded network. The strong role of hydrogen bonding on the behavior of polypyrrole is evident from reductions performed in solvents with varying hydrogen bonding capabilities; stronger hydrogen bonding solvents are found to more thoroughly disrupt the intramolecular polymer structure.; Polypyrrole-coated TSM mass-based sensors exhibit sensitivities of 14%, 15%, 6%, 12% and 3%, towards acetonitrile, water, ammonia, methanol and toluene, respectively (normalised to the frequency decrease measured from polymerisation). This methodology allows the frequency responses towards the gas probe molecules to be measured over a range of polymer oxidation states. This in turn helps to determine the relative importance of the modes of interaction with the polymer. Long-term gas exposures are found to result in partial retention of the probe molecules following flushing with pure helium and, in some cases, the removal of a portion of the original water and acetonitrile solvation sheath.; Several procedures designed to modify polypyrrole are examined. Copolymerisation of pyrrole with a number of nitro-functionalised reagents (for example 2- and 4-nitrotoluene) increases the oxidation state of the resulting PP without incorporating any new species. The general synthesis of dipyrrylphenylmethanes (DPMs) is described, and their polymerisation produces polymers with a controlled amount of desired functionality throughout the film. Derivatisation of PP through the amine is also possible but the reaction only occurs with approximately the top 300 A of the film. The four reagents employed, p-nitrobenzoyl chloride, 5-nitro-2-furoyl chloride, 2,4-dinitrofluorobenzene and pentafluorobenzoyl chloride, demonstrate varying stabilities to oxidising and reducing potentials. |
