REACTIVE GROUPS ON POLYMER COVERED ELECTRODES .1. ELECTROCHEMICAL COPOLYMERIZATION OF THIOPHENE-3-ACETIC ACID WITH 3-METHYLTHIOPHENE

Cyclic voltammetry (cv) experiments at Pt electrodes were carried out to produce ethyl-2,5-thiophenediyl-2,5-thiophenediyl-3-acetic acid) (3 a) from the monomers 3-methylthiophene (1) and thiophene-3-acetic-acet ic acid (2a), and to study the mechanism of electrocopolymerization. I t was found by means of esterification and amidation and further chemi cal reactions of the copolymers thus obtained that the COOH groups are covalently bound to the copolymer structure. The charge/discharge rev ersibility and the overoxidation (irreversible redox process occurring when the covered electrode is scanned beyond the positive potential l imit) of 3a and some of its derivatives are demonstrated by representa tive cyclic voltammograms. In a series of copolymerization experiments the positive potential limit (E(pos)) was lowered step by step from 2 .20 to 1.70 V (vs. s Ag/AgCl) below the potential for the oxidation of 2a (E(mox) = 2.11 V vs. s Ag/AgCl) and, yet, the copolymer 3a was obt ained. The results of the examination are discussed with the aid of da ta from cv, MS, FTIR-GIR (Fourier-Transform-Infrared-Grazing Incidence Infrared) spectroscopy, H-1 NMR/C-13 NMR spectroscopy, and elementary analyses.