Synthesis and self-limited electrochemical doping of polyacetylene ionomers

The synthesis, electrochemical characterization, and self-limited electrochemical doping of a family of soluble polyacetylene ionomers are reported. The conjugated ionomers (also known as conjugated polyelectrolytes) are synthesized by the ring-opening metathesis copolymerization of ionically functionalized cyclooctatetraenes with the nonionic trimethylsilylcyclooctatetraene. Sulfonate and alkylammonium derivatized polyacetylenes are reported with functional group densities ranging from 1 per 5 double bonds to 1 per 65 double bonds and weight-average molecular weights of 10-20 kDa. Electrochemically, the copolymers can be reversibly n- and p-doped, although not sequentially on the same polymer film, and their voltammetric behavior appears as a superposition of their constituent homopolymers. The extent of electrochemical doping becomes self-limited by the ion density built into the polymer when it is carried out in an appropriately charged polyelectrolyte-based electrolyte. More specifically, the extent of electrochemical p-doping for the anionic polyacetylene derivatives scales linearly with the density of ionic functional groups when carried out in tetrabutylammonium polystyrenesulfonate/CH3CN. Similar results are seen for the n-doping of the cationic polyacetylene derivatives in poly(N,N-dimethyl-3,5-dimethylene piperidinium) hexafluorophosphate/CH3CN. The self-limiting nature of the oxidation in the polystyrenesulfonate-based electrolyte greatly extends the potential stability window (to as much as 1.4 V vs SCE) of the polyacetylene anionomers without the same irreversible degradation observed in more conventional small ion electrolytes.