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4.3 Modification of the Oxidation State of the Conducting Polymer

Since the electrical properties of conducting polymers like polypyrrole can be modified by controlling the oxidation state of the polymer, oxidation and reduction are performed to alter the electrical conductivity.  Chemical methods of oxidation and reduction can be used to alter doping levels within the polymer.  Vapor phase exposure of the conducting polymer to iodine is a common method used for oxidation.  Upon oxidation, the polymer becomes positively charged and the electrons along the backbone of the polymer get delocalized, allowing conduction.  Negatively charged I₃^- is then inserted into the polymer matrix.  Removal of these anions will then reduce the oxidation state of the polymer and localize the electrons, preventing conduction. 

Oxidation and reduction can also be accomplished electrochemically.  A polypyrrole coated YBa₂Cu₃O_7-x electrode can be placed in an electrolyte solution such as tetraethylammonium tetrafluoroborate, Et₄NBF₄, in acetonitrile where it can be oxidized at a potential of ~0.0 V vs. SCE.²³  Here, BF₄^- anions are incorporated into polymer matrix to compensate the positive charge of polypyrrole as seen in Figure 3.3.