The commercial use of polyaniline has been impeded by its intractable nature and insolubility. The use of substituted polyaniline has been attempted mainly to increase the processibility of polyaniline, but this approach usually results in the lowering of the conductivity. This study reports the synthesis of poly(l-naphthylamine), a fused ring derivative of polyaniline, and its copolymers with aniline and o-toluidine via a chemical polymerization method. Spectral, thermal, morphological, and conductivity studies were carried out to elucidate the influence of the incorporation of aniline and o-toluidine units into poly(l-naphthylamine). (C) 2008 Wiley Periodicals, Inc.