Ion Charge Compensation upon Electrochemical Doping of Redox Polymer Films with Tunable Crosslinking Density

ABSTRACT The electrochemical doping behavior of thin films of redox‐active copolymers of vinyl(triphenylamine, (TPA)) and styrene (S) with differing ratios from 100:0 (PVTPA) to 20‐80 (PVTPA‐ co ‐PS) is reported. The presence of TPA units in the polymers allows for electrochemical dimerization into tetraphenylbenzidine (TPB) units which act as redox‐active π‐systems in the crosslinked films. By changing the copolymer ratio, the degree of crosslinking can be tailored which has direct influences on the electrochemical behavior, e.g., visible in the cyclic voltammetry profiles and accompanying in situ conductance measurements. The crosslinked films show reversible oxidation and reduction behavior and are therefore ideal model systems to study mixed conductivity characteristics for mixed conducting polymers. Electrochemical Quartz Crystal Microbalance (EQCM) and ac ‐electrogravimetry are used to monitor the ion charge compensation process and associated gravimetric changes of the crosslinked films upon electrochemical doping. Our data clearly show that PF 6 − anion (hexafluorophosphate) transfer presents the major contribution in the charge compensation process along with concomitant acetonitrile solvent contributions. Crosslinked copolymer films show overall lower anion concentrations, which coincides with lower redox‐active moieties, and overall lower swelling ratios due to solvent contributions which we assign to the high amount of non‐redox‐active styrene units compared to the crosslinked homopolymer films.