Doctor of Philosophy (PhD)
This research focused on elucidation of structural information for conducting polymer systems using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The structure of conducting polymer systems has been found to directly influence their physical properties. Poly(pyrrole) and poly(thiophene) are two of the most widely studied conducting polymers due to their high electrical conductivity, stability in the doped state, low toxicity, and current/potential applications. The purpose of this research was to apply MALDI-TOF MS to heterocyclic conducting polymers, specifically those of pyrrole and thiophene, to investigate structural properties of these polymers, with the specific aim of determining end group and molecular weight dependence on polymerization conditions. The common synthesis route of chemical oxidation was used for the production of poly(3-hexylthiophene) and it was demonstrated that solvent and monomer-to-oxidant ratio strongly influence the composition of the polymer, specifically halogen content and size. More specifically, it was demonstrated that the end groups of the polymer synthesized in nitromethane could be changed from hydrogen to chlorine by simply changing the monomer-to-oxidant ratio. This is important because studies on 3-hexylthiophene oligomers indicate that chlorine substituents do affect their optical properties. A red shift in the Î»max was observed for thiophene oligomers with chlorine substituents versus pristine thiophene oligomers. A proposed mechanism was outlined to further describe the polymerization as well as chlorine substitution process in these polymers, during oxidative polymerization with FeCl3. For the first time, MALDI-TOF MS was successfully used to characterize soluble pyrrole polymers. The pyrrole polymers studied were much more structurally complicated than the thiophene polymers. One reason for this is that they are more susceptible to nucleophilic substitution than the thiophene systems. Unlike the thiophene polymers, manipulation of the polymerization parameters did not lead to formation of pristine pyrrole polymer lacking chlorine and/or oxygen substitution, under the conditions used here. Also, it was observed from the MALDI-TOF MS analysis that hydrogen loss is a characteristic of these substituted pyrrole polymers, and it occurs regardless of the location of the side chain.
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Brauch, Rebecca Marie, "Structural Characterization of Poly(heterocycles) Formed Using Oxidative Methods" (2006). LSU Doctoral Dissertations. 2101.