Probing Polymer–Pendant Interactions in the
Conducting Redox Polymer Poly(pyrrol-3-ylhydroquinone)
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Abstract
Conducting
polymers with redox active pendant groups show properties typical
of both conducting polymers (i.e., capacitive charging and intrinsic
conductivity) and redox polymers (i.e., electrochemical surface response
at the formal potential of the pendant groups). The two components
can also exert significant interaction on each other during their
separate electrochemical reactions. In poly(pyrrol-3-ylhydroquinone),
a polypyrrole derivative functionalized with hydroquinone units, the
redox conversion of the pendant groups has a large impact on the polymer
backbone. This interaction is manifested by a loss of bipolaron states
during the hydroquinone oxidation, leading to a decreasing p-doping
level with increasing potential, something which, to the best of our
knowledge, has never been observed for a conducting polymer. Another
effect is a contraction of the polymer film, and subsequent mass loss
due to solvent expulsion upon hydroquinone oxidation, which counteracts
the normal swelling of polypyrrole with increased potential. The conducting
redox polymer under investigation has been synthesized via two routes,
leading to different fractions of subunits bearing redox active hydroquinone
groups. While the redox potentials are unaffected by the synthesis
route, the backbone/pendant group interaction varies notably depending
on the degree of quinone functionalization. This type of polymers
could find use in, e.g., organic energy storage materials, since the
polymer backbone both increases the electronic conductivity and prevents
dissolution of the active material, as well as in actuator application,
due to polymer contraction over the relatively narrow potential region
where the pendant group redox chemistry occurs