Reactive groups on polymer-covered electrodes 11. Copolymerization of methyl thiophene-3-acetate with 3-alkylthiophenes

Polythiophene films containing ester groups on the surface of electrodes ar e interesting potential carrier materials for reagents. Methyl thiophene-3- acetate (3) can be copolymerized with 3-methylthiophene (1) and 3-butylthio phene (2) by means of cyclic voltammetry (CV) at potentials of 0-2.2 V. Hig her potentials (0-2.4 V) lead to overoxidation of the copolymers. The eater groups were confirmed by FTIR spectra. Electrochemical investigations of 2 ,2'-bithiophene (6) and 3 at equimolar ratios showed no successful copolyme rization at potentials of 0-1.3 V, If the copolymerization experiments of 6 with 1 or 3 were carried out at molar ratios of 1:50 at 1.3 V, 6 with its low oxidation potential was polymerized without copolymerization of the oth er monomers. However, if the oxidation potential was increased stepwise fro m 1.3 V, the oxidation of 1 or 3 occurred, forming copolymers containing bo th monomer components. HPLC investigations of solutions containing mixtures of 6 and 3 and also 6 and 1 in acetonitrile/TEABF(4) showed, after exhaust ive oxidation at a potential of 1.3 V, the complete absence of 6. 1 and the eater 3 were not oxidized and copolymerized at these potentials. From the results of the copolymerization experiments, as well as the HPLC investigat ions, it can be concluded that the dominant mechanism of the electrochemica l polymerization is radical cation dimerization.