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Synthetic Metals

Year: 2008  |  Volume: 158  |  Issue: 21-24  |  Page No.: 946 - 952

Scavenging of DPPH free radicals by polypyrrole powders of varying levels of overoxidation and/or reduction

Chyong Fang Hsu, Lijuan Zhang, Hui Peng, Jadranka Travas-Sejdic and Paul A. Kilmartin


Polypyrrole (PPy) powders were synthesized chemically using the oxidant ammonium persulfate (APS). The free radical scavenging properties were evaluated using a form of the α,α-diphenyl-β-picrylhydrazyl (DPPH) assay adapted for use with 1.0 mg amounts of conducting polymer powders. A lower scavenging capacity was obtained when a higher ratio of APS to pyrrole was used in the chemical synthesis which also led to a decrease in polymer conductivity and doping level as determined by the amount of (bi)sulfate present given by elemental analyses. The occurrence of overoxidation of polypyrrole at a higher oxidant level was confirmed in FTIR spectra by the presence of a carbonyl group. PPy prepared at a lower APS/pyrrole ratio contained more bipolaron charge carriers, which were converted to polarons upon initial reduction with hydrazine. More complete reduction with hydrazine led to a loss of (bi)sulfate dopant, but to improved DPPH radical scavenging, confirming that the conducting polymer is acting as a reducing agent in scavenging DPPH radicals.

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