The conductive composites of polyaniline (PAn) and chlorosulfonated poly ethylene (CSPE) were prepared by polymerization of aniline in the presence of CSPE, using a direct, one-step in situ emulsion polymerization method. The polymerization of aniline was performed in an emulsion comprising water and xylene containing CSPE in the presence of dodecylbenzene sulfonic acid, which acts both as a surfactant and a dopant for PAn. The composites can be processed by either melt method (MP) or solution method (SP). Conductivity of the composites obtained by different processing methods shows different percolation thresholds: 14 wt % for MP samples and 22 wt % for SP samples. At the same content of PAn, the conductivity of MP composites is higher than that of SP composites. The relationships between mechanical properties and PAn content obtained by the two different processing methods were also investigated. When PAn content of MP samples is between 12 and 18 wt %, the composites behave like a thermoplastic elastomer with tensile strength at 6-8 MPa, ultimate elongation > 400% and permanent set < 30%. The conductivity of composites obtained by SP method after secondary doping with m-cresol is about 6 orders of magnitude higher than the original at below 18 wt % PAn content and the percolation threshold for conductivity is lowered to 3 wt % PAn content. The composite shows no electrochromic activity in acidic solution of LiClO4 in propylene carbonate, but after secondary doping exhibits electrochromic activity even in neutral electrolyte. (C) 2000 John Wiley & Sons, Inc.