Vapor-phase polymerization of 3,4-ethylenedioxythiophene: A route to highly conducting polymer surface layers

A new synthetic route to poly-3,4-ethylenedioxythiophene (PEDT) with a conductivity exceeding 1000 S/cm is described. The method is based on base-inhibited vapor-phase polymerization, where a surface covered with ferric p-toluenesulfonate as oxidant mixed with a volatile base (pyridine) is exposed to 3,4-ethylenedioxythiophene (EDT) vapors. The base is added to suppress an acid-initiated polymerization of EDT, leading to a product with little or no conjugation. The product of the base-inhibited vapor-phase polymerization is confirmed to be virtually identical to PEDT obtained by wet chemical oxidation by both spectroscopic and electrochemical methods. A possible reaction scheme for the acid-initiated polymerization is discussed.