Poly(3,4-ethylenedithiathiophene). A New Soluble Conductive Polythiophene Derivative

A new polythiophene derivative has been synthesized by both chemical and electrochemical oxidative polymerization of the monomer 3,4-ethylenedittdathiophene (EDTT). Both methods produce a polymer which is completely soluble in 1-methyl-2-pyrrolidinone (NMP) and partly soluble in tetrahydrofuran (THE) and chloroform. The FT-IR spectra of the neutral polymer indicate a regular structure formed via α,α coupling of thiophene rings. The new polymer shows two absorption bands at 341 nm and 413-419 nm in NMP solution in the UV-vis region. Photoexcitation of the polymer in dilute NMP solution results in a broad band luminescence with peak at ca. 552 nm. The redox behavior of the polymer was studied by cyclic voltammetry in 0.1 M (Bu₄N)ClO₄ acetonitrile solution. The average molecular weights have been determined by gel permeation chromatography (GPC) to be M_n ~ 3.03 x 10³ and M_n ~ 4.75 x 10³ for the chemically and electrochemically synthesized polymer, respectively. Electron spin resonance data are reported. Thermal gravimetric analysis studies show that the new polymer is stable in nitrogen up to 276 °C. The chemically doped (with FeCl₄^-) polymer and the electrochemically doped (with ClO₄^-) polymer show electrical conductivity of 0.1 and 0.4 S/cm at room temperature, respectively. These results are compared to some previously characterized polythiophenes.