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We synthesize poly-3-alkylthiophene with different side
chain length by applying chemical and electrochemical
polymerization of the corresponding monomer. The regioregularity
and solubility of the polymer prepared from chemical
polymerization are better than those from electrochemical
polymerization. After primary doping (partial oxidation) of the
neutral polymer (chemically prepared), the conductivity
increases 105~108 times. The longer the side chain, the lower
the conductivity of doped polymer. For the polymer film at ca.
5000 A, regardless the side chain length, the maximum
conductivity was obtained after doping for 20 to 30 minutes. We
also demostrate that the primary doping reaction produces
polarons and bipolarons by cyclic voltammetry experiment. The
oxidation potentials of the polymers depend on the structure
regioregularity but not on the side chain length. The secondary
doping (rearrangement of polymer chain) of the doped poly-3-
alkylthiophene is performed with the vapor-transfer method. It
was found that most solvents have the tendency to increase the
dedoping rate of doped poly-3-alkylthiophene. The higher the
polarity of the solvent, the faster the dedoping rate.
Interestingly, when toluene is used as a secondary dopant,
although slightly dedoping phenomenon also occurs, the
conductivity increases. It implied that the secondary doping
effect of FeCl3 doped poly-3-alkylthiophene may occur when
toluene is used as a secondary dopant.
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