Living polytetrahydrofuran (PTHF) was terminated with sodium thiophenemethonate to yield a polymer with thiophene groups at both ends. Copolymerizations of PTHF with pyrrole and thiophene were achieved in water-p-toluene sulfonic acid (PTSA) and acetonitrile (AN)tetrabutylammonium tetrafluoroborate (TBAFB) solvent-electrolyte couples via constant-potential electrolysis. The electrical conductivities were measured by the four-probe technique. The PTHF/PTh film,, which was deposited on indium tin oxide (ITO) glass in a dichloromethane-TBAFB solvent-electrolyte couple, was found to be anodically coloring copolymers that electrochemically switch between the green oxidized and red reduced states, exhibiting the electrochromic behavior. Spectroelectrochemical analysis was run in the ultraviolet-visible region to reach a better understanding of the band structure of the PTHF/PTh electrochromic copolymer. (c) 2004 Elsevier B.V. All rights reserved.