Electrochromic properties of new methacrylate copolymers containing pendant terthiophene and oligo(ethyleneoxide) moieties, poly[(2,2＇:5＇,2 "-terthiophen-5-yl)methyl methacrylate-co-alpha-ethoxy-omega-methacryloyl-oligo(ethyleneoxide)] (poly(MA3T-co-MAEO)), in the presence of a polymer-gel electrolyte were studied. A polymer-gel electrolyte composed of poly(methylmethacrylate), lithium perchlorate, and propylene carbonate was sandwiched between two indium-tin oxide (ITO)-coated glass substrates, on one of which a film of poly(MA3T-co-MAEO) was coated. The device was found to undergo a color change from yellowish-orange to pale green and vice versa on electrochemical oxidation and reduction. The response times for green coloration and decoloration of a poly(MA3Tco-MAEO) 60/40 film in the presence of the polymer-gel electrolyte were estimated to be 5.3 and 5.5 s, respectively. (C) 2000 Elsevier Science Ltd. All rights reserved.