The chemical oxidative copolymerization of 3,4-ethylenedithiathiophene (EDTT) with 3,4-ethylenedioxythiophene (EDOT) and 2-hydroxymethyl-3,4-ethylenedioxythiophene in a poly(styrene sulfonic acid) aqueous solution was successfully carried out to form stable, dark blue colloidal dispersions in water. Coating these dispersions onto polypropylene substrates led to the formation of free-standing copolymer films. The mechanical, electrical, and thermoelectrical properties of these films were investigated; the films showed superior properties in comparison with those of poly(3,4-ethylenedithiathiophene) (PEDTT)/poly(styrene sulfonate) (PSS). The copolymer film based on EDTT and EDOT achieved a high electrical conductivity (8.2 x 102 S cm1) at 298 K; this could be improved about 10 times through the addition of dimethyl sulfoxide (DMSO) or DMSO/isopropyl alcohol into the polymer dispersion with almost constant Seebeck coefficients of about 9 V K1. On the contrary, these additives had almost no effect on the conductivity of PEDTT/PSS. The structure and morphology of the polymer films were studied by X-ray diffraction and SEM analyses. (c) 2012 Wiley Periodicals, Inc.