Thiophene capped poly(ethylene oxide) (PEO) was synthesized. Copolymerisations of PEO with pyrrole (Py) and thiophene (Th) were achieved in water-sodium dodecyl sulfate (SDS) and acetonitrile (AN)-tetrabutylammonium tetrafluoroborate (TBAFB) solvent electrolyte couples via constant potential electrolyses. Characterisations of the samples were performed by NMR, cyclic voltammetry (CV), FT-IR, scanning electron microscopy (SEM). Electrical conductivities were measured by the four-probe technique. PEO-co-PTh film which was synthesized on ITO-glass in boron fluoride-ethyl ether (BFEE) found to exhibit electrochromic behaviour and it electrochemically switches between blue oxidized and red reduced states. Optical analyses were carried out to investigate the electronic structure of PEO-co-PTh electrochromic copolymer. (c) 2005 Elsevier B.V. All rights reserved.