Characterization of thiophene-based conducting polymers by pyrolysis-gas chromatography-mass spectrometry

Tang, Shu (1999) Characterization of thiophene-based conducting polymers by pyrolysis-gas chromatography-mass spectrometry. Masters thesis, Memorial University of Newfoundland.

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Abstract

Conducting polymers have attracted great attention since their discovery at the end of the 70's due to their high conductivity, versatility and structural flexibility. Various methods have been developed for their structural characterization but few are useful for microstructure elucidation. This study demonstrates the ability of Pyroiysis-Gas Chromatography-Mass Spectrometry to examine both the thermal degradation behavior and microstructure of thiophene-based conducting polymers. -- Unsubstituted polythiophenes, i.e., polythiophene, poly(2,2'-bithiophene), and poly(2,2':5',2"-terthiophene) were prepared by galvanostatical electropolymerization. β-substituted polythiophenes, i.e. poly (3-alkylthiophene)s (alkyl = methyl, hexyl, octyl), poly(3-methoxythiophene) and poly(3,4-ethylenedioxy-thiophene), were synthesized either electrochemicaliy or chemically. Optimum pyrolysis temperatures for high yields of structurally-important fragments were established by investigating pyrolysis temperatures from 300 to 1400°C. Comparison of polythiophenes shows that the yield of H₂S decreases, while the yield of thiophene oligomer fragments increases, as the chain length of the precursor oligomer increases. These results reflect decreasing the conjugation length from polythiophene to poiyterthiophene. The predominant polymeric linkage in unsubstituted polythiophenes is α-α' along with non-negligible amounts of α-β' linkage. Evidence of partial overoxidation of polythiophene during electropolymerization was also obtained from the pyrograms. Structural analysis of oligomer fragments obtained from pyrolysis of poly(3-alkylthiophene)s gave useful stereoregularity information (i.e., head / tail configurations). Furthermore, based on the pyrolysis products, possible degradation pathways of poly(3-alkylthiophene)s were established.

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