The electrochemical polymerization of 1.2-methylenedioxybenzene (MDOB) in a room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmimPF(6)) has been investigated. Its polymer poly(1,2-methylenedioxybenzene) (PMDOB) showed good redox activitv and stability even in concentrated sulfuric acid. IR and H-1 NMR spectra confirmed that the polymerization occurred at the C-4 and C-5 positions on the benzene ring of MDOB, resulting in the main backbone of PMDOB similar to polyacetylene. In contrast to acetonitrile containing 0.1 mol[L Bu4NBF4, BmimPF6 serves as both the growth medium and an electrolyte. Hence, enhanced electrochemical stability of PMDOB can be easily obtained on repetitive redox cycling. As-formed PMDOB represented good electrochromic properties from green grass to opalescent between doped and dedoped states. Scanning electron microscopic results demonstrated that smooth and compact PMDOB films composed of ordered nanostructures were obtained, implying their possible utilizations in ion-sieving films, ion-selective. and matrices for catalyst particles. (C) 2007 Elsevier Ltd. All rights reserved.