We report the synthesis of a water-soluble diblock copolymer composed of polysulfonic diphenyl aniline (PSDA) and poly(ethylene oxide) (PEO), which was prepared by reacting an amine-terminated PSDA and tosylate PEO (PEO-Tos). First, a HCl-mediated polymerization of sulfonic diphenyl aniline monomer with the formation of HCl-doped PSDA was carried out. After its neutralization and reduction, a secondary amine-functionalized PSDA was obtained. Second, PEO-Tos was synthesized via the tosylation of the monohydroxyl PEO methyl ether with tosylol chloride. Diblock copolymers with various PEO segment lengths (PSDA-b-PEO-350 and PSDA-b-PEO-2000) were obtained with PEO-350 [number-average molecular weight (M-n) = 350] and PEO-2000 (M-n = 2000). The prepolymers and diblock copolymers were characterized by Fourier transform infrared spectroscopy, NMR, mass spectrometry, and ultraviolet-visible light. They had relatively low conductivities, ranging from 10(-6) to 10(-3) S/cm, because of the withdrawing effect of the sulfonic group as well as the steric effects of the bulky aromatic substitutuents at the N sites of the polyaniline backbone and of the PEO block. These polymers were self-doped, and an intermolecular self-doping was suggested. The external doping was, however, more effective. The self-doping induced aggregation in water among the PSDA backbones, which was also stimulated by the presence of hydrophilic PEO blocks. Furthermore, the electrical conductivities of the diblock copolymers were strongly temperature-dependent. PSDA-b-PEO-2000 exhibited about one order of magnitude increase in conductivity upon heating from 32 to 57 degreesC. (C) 2004 Wiley Periodicals, Inc.