Synthesis stability and properties of processible conducting polymers

Poussin, Denis (2000) Synthesis stability and properties of processible conducting polymers. (PhD thesis), Kingston University, .


The synthesis, stability and properties of two particular processible conducting polymer types, polyaniline and polythiothene have been investigated. Those two classes of polymers have great commercial potential but their properties can be difficult to control. Polythiophene was evaluated as potentially useful in a photolithographic process. When polymers are involved in image formation, changing the solubility of the exposed polymer is usually required. Photodegradation was chosen as a way to render crosslinked polythiophene soluble. The photodegradation study was divided in two parts; in solution and in the solid state. Methylene blue was used in both cases as a generator of singlet oxygen. The polymer effectively underwent photodegradation under irradiation at 670nm. It could not be determined from our studies whether this effect was due to methylene blue or spontaneous photodecomposition of the polymer itself. This line of work was then discontinued and we focused on the polyanilines. The synthesis of various polymers of the polyaniline family was performed and different modes of polymerisation evaluated. In particular the parameters of the emulsion polymerisation of PANI-DBSA (dodecylbenzene sulfonic acid doped polyaniline) were evaluated and a new process was formulated. The doping on heating of polyaniline base (EB) with two dopants DBSA and toluene sulfonic acid (TSA) was studied using differential scanning calorimetry (DSC). Polymers with a molar ratio of base unit/dopant of 1 presented the good thermal stability and solubility expected from sulfonic acid doped polyanilines. The conductivity of the samples obtained was up to 15 Scm[sup]-1 and was improved by annealing polymer films, which led to conductivities of up to 25 Scm[sup]-1. Finally, a comprehensive study of the thermal stability of the various polyanilines produced is presented. The good stability of polyaniline was demonstrated by DSC and thermogravimetric (TGA) studies. The initial degradation stages were allocated to the loss or decomposition of dopants. Some degradation products were identified by gas chromatography coupled with mass spectrometry (GC-MS) and correlate with loss and decomposition of the dopants. The kinetic parameters of the decomposition of the polymers were calculated using a computer package and a tailored logarithmic method. Those parameters were then used in mathematical models of the TGA decomposition curves. They showed good agreement with the experimental results therefore proving the accuracy of the kinetic parameters. Attempts at stabilisation of the polymer using commercially available antioxidants showed that it is possible to enhance polyaniline stability even further. The secondary antioxidants used (trivalent phosphorus and divalent sulphur containing compounds) demonstrated a more positive effect on the stability of the polymers than the primary antioxidants (hindered phenols). However, even in the best conditions only a minor reduction in weight loss of the polymers can be obtained.

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