Chemical Polymerization of Hydroxymethyl and Chloromethyl Functionalized PEDOT:PSS

Poly(3,4-ethylenedioxythiophene) (PEDOT) conducting polymer synthesized via oxidative chemical polymerization in the presence of polyelectrolyte poly(styrenesulfonate) (PSS) can form water-dispersible conductive ink and has broad applications. However, the lack of functionality of PEDOT hinders the broader application of PEDOT:PSS. In this work, we introduced a hydroxymethyl (−MeOH) and a chloromethyl (−MeCl) functional group to the oxyethylene ring of EDOT to obtain hydroxymethylated 3,4-ethylenedioxythiophene (EDOT–MeOH) and chlorylmethylated 3,4-ethylenedioxythiophene (EDOT–MeCl) monomer, respectively. We applied oxidative chemical polymerization to synthesize PEDOT–MeCl:PSS and PEDOT–MeOH:PSS as well as PEDOT:PSS. For EDOT, we found that adding base to neutralize acidic PSS has a significant effect on the dispersibility, surface morphology, and electrical conductivity (9.06 × 10–4–1.17 × 10–1 S/cm) of PEDOT:PSS. For functionalized EDOT, the repulsive force between EDOT–MeCl monomer and PSS counterion strongly hinders the oxidation and doping process, resulting in a product with well-dispersed PSS-doped PEDOT–MeCl and nondispersible sulfate-doped PEDOT–MeCl clusters, rough thin film, and electrical conductivity of 1.68 × 10–3 S/cm. The hydrogen bonding between EDOT–MeOH monomer and PSS counterion as well as among EDOT–MeOH monomers makes the polymerization and doping processes easy, yielding a well-dispersed, homogeneous product, smooth thin film, and electrical conductivity of 1.17 × 10–3 S/cm. This study sheds light on the polymerization of PEDOT with functional groups and provides a guideline for the synthesis of functionalized PEDOT conducting polymers with polyelectrolyte counterions using oxidative chemical polymerization.