Synthesis and optical and electrical properties of self-doped copolymers consisting of N -4-sulfopropylaniline and 3,4-ethylenedioxythiophene units

Polymerization of aniline with 3,4-ethylenedioxythiophene (EDOT) in several molar ratios using ammonium persulfate yielded copolymers consisting of p-aminophenylene (unit A) and 3,4-ethylenedioxythiophene-2,5-diyl (unit B). The content of units A and B in the copolymers depended on the monomer feed ratio. Treatment of the copolymers with sodium hydride deprotonated the NH groups to give polyanions. Subsequent treatment of these polyanions with 1,3-propanesultone yielded copolymers with sodium N-propylsulfonate side groups, which were converted into N-propylsulfonic acid moieties by treatment with diluted hydrochloric acid. The copolymers exhibited absorption peaks at approximately 330 and 650 nm, which can be ascribed, respectively, to the benzenoid π–π* and quinoid n–π* transitions of unit A. The copolymers were subjected to electrochemical oxidation, which was dependent on the contents of units A and B. The electrical conductivity of copolymers with N-propylsulfonic acid side chains was found to be higher than that of copolymers bearing sodium N-propylsulfonate groups.