The structure and protonation level of the chemically synthesized 2-chloroaniline and 2-iodoaniline homopolymers and their copolymers with aniline have been studied. the results indicate there is no elimination of the substituent group and the polymerization probably occurs at the para-position. the protonation level of the copolymers decreases substantially when the fraction of substituted aniline units is above 0.5, and the electrical conductivity of the copolymers decreases rapidly with an increase in the fraction of substituted aniline units. the protonation level is also lower when HCl rather than H2SO4is used as the protonating acid species, and a significant fraction of the chlorine incorporated is covalently bonded to the polymer. the Nls core-level spectra of the copolymer and the haloaniline homopolymer bases reveal that their imine/amine ratio is substantially lower than that of the polyaniline base. the copolymers show partial solubility in chloroform, but the electrical conductivity of the chloroform-treated samples is not significantly different from that of the pristine sample. When the copolymers synthesized in HCl are heated to 150°C, a fraction of the ionic chlorine is converted to covalently bonded species, resulting in a substantial decrease in the electrical conductivity.