REDOX CHEMISTRY OF BIPYRROLES - FURTHER INSIGHTS INTO THE OXIDATIVE POLYMERIZATION MECHANISM OF PYRROLE AND OLIGOPYRROLES

The oxidation of 2,2'-bipyrrole, 5-methyl-2,2'-bipyrrole, and 5,5'-dim ethyl-2,2'-bipyrrole has been investigated by means of electrochemistr y, flash photolysis, and pulse radiolysis. The bipyrrole cation radica l was found to give polypyrrole or oligopyrrole under electrochemical and chemical oxidation and also under UV-light irradiation of the solu tion in the presence of CCl4 as an electron acceptor, The cation radic als have been characterized by their optical absorption spectra, and t heir decay processes have been followed. In all processes (chemical, e lectrochemical, and photochemical), the first step involves the reacti on between two cation radicals. The cation radical does not react on s tarting bipyrrole nor on pyrrole monomer, Depending on pH, the cation radical can deprotonate to form a neutral radical. It was found that o nly the cation radicals, but not the neutral radicals, produce higher oligomers, which explains the inhibition of polymerization by strong b ases.