A copolymer based on 1,4-bis(2-thienyl) benzene (BTB) and 3,4-ethylenedioxythiophene was electrochemically synthesized in acetonitrile containing sodium perchlorate (NaClO4). Cyclic voltammetry, ultravioletvisible spectroscopy, and Fourier transform infrared analyses confirmed that the resulting polymer was a copolymer rather than a blend or a composite of the respective homopolymers. Poly(1,4-bis(2-thienyl) benzene) has only two colors; it switches between yellow in the neutral state and green in the oxidized state, whereas the poly[1,4-bis(2-thienyl) benzene-co-3,4-ethylenedioxythiophene] (PBTBE) film exhibited five different colors (brownred, orangeyellow, yellowish green, green, and blue). This revealed distinct electrochromic properties from that of the BTB homopolymer film. The maximum optical contrast (?T %) and response time of the copolymer film were measured to be 27.8% and 0.51 s, respectively, at 780 nm. An electrochromic device (ECD) based on PBTBE and poly(3,4-ethylenedioxythiophene) was also constructed and characterized. This ECD showed a ?T % value of 22.2% in the visible region with a response time of 0.43 s at 616 nm. The coloration efficiency of the device was calculated to be 129 cm2/C at 616 nm. (C) 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012