A series of poly(o-/m-toluidine-co-o-/m-chloroaniline) copolymers of different compositions were synthesized by an emulsion method with ammonium persulfate as the oxidant. The conductivity of the copolymers was two to five orders of magnitude higher than that of the homopolymers poly(o-toluidine) and poly(m-chloroaniline). Among the copolymers, the copolymer of o-toluidine and m-chloroaniline exhibited a maximum conductivity of 0.14 S cm(-1). The conductivity of these copolymers was also higher than that of poly(aniline-co-chloroaniline). The properties of the copolymers were greatly influenced by the positions of the substituents and the concentrations of the individual monomers in the feed. All the copolymers were completely soluble in polar solvents such as dimethyl sulfoxide and showed higher heat stability as the chloroaniline concentration increased. These effects could be interpreted in terms of extensive hydrogen bonding and interchain linking and, therefore, higher electron delocalization in these copolymers due to the presence of electron-rich toluidine rings adjacent to electron-deficient chloroaniline. (c) 2005 Wiley Periodicals, Inc.