Electrochemically Induced Substitution of Polythiophenes and Polypyrrole

The electrochemically induced substitution of thin films of polypyrrole, polythiophene, poly(3-methylthiophene), and poly(2,2‘-bithiophene) with the nucleophiles Cl -, Br -, methanol, and 3-bromopropanol has been investigated by cyclic voltammetry, electron microprobe analysis, IR spectroscopy, and NMR spectroscopy. The degree of substitution obtained is potential dependent and varies between nucleophile/polymer combinations. Thus, reaction of polythiophene, poly(3-methylthiophene), or polypyrrole with Cl - at 1.4 V vs SSCE results in chlorination of approximately 80% of the rings, while for poly(2,2‘-bithiophene) only 20% substitution is obtained. Reaction with 3-bromopropanol, results in 25−35% substitution for both poly(3-methylthiophene) and polypyrrole. The substituted polymers are electroactive and conductive. However, for substitution of the polythiophenes by Cl -, electrochemically deactivated intermediates with low conductivity can be isolated. Reaction of poly(3-methylthiophene) with methanol results in solubilization of the polymer in acetonitrile.