Reactive groups on polymer covered electrodes 6-Copolymerization of 2,2 '-bithiophene with methyl thiophene-3-acetate and 3-methylthiophene

Polythiophene films at the surface of electrodes containing ester groups ar e interesting potential carrier materials for reagents. Methyl thiophene-3- acetate (2) can be copolymerized with 3-methylthiophene (1) by means of cyc lic voltammetry at potentials of 0-2.2 V. Higher potentials (0-2.4 V) lead to overoxidation of the copolymers. The ester groups were proved by FTIR sp ectra. Electrochemical investigations of 2,2'-bithiophene (4) and 2 at equi molar ratios shows no successful copolymerization at potentials of 0-1.3 V. If the copolymerization experiments of 4 with 1 or 2 were carried out at m olar ratios of 1:50 at 1.3 V 4 with its low oxidation potential can be poly merized without copolymerization of the other monomers. However, if the oxi dation potential is increased stepwise arising from 1.3 V the oxidation of 1 or 2 takes part forming copolymers containing both the monomer components . HPLC investigations of solutions containing mixtures of 4 and 2 and also 4 and 1 in acetonitrile/TEABF(4) shows after exhaustive oxidation at a pote ntial of 1.3 V the complete absence of 4. 1 and the ester 2 were not oxidiz ed and copolymerized at this potentials. From the results of the copolymeri zation experiments as well as the HPLC investigations, it can be concluded that the dominant mechanism of the electrochemical polymerization is the ra dical cation dimerization. (C) 1999 Elsevier Science Ltd. All rights reserv ed.