Radiation-chemical behaviour of 4,4'-bipyridinium salts in solid polymeric matrices

The radiation induced reduction mechanism of alkyviologens in a number of polymers was studied by means of pulse and steady-state radiolysis with spectrophotometric and ESR registration of radiolysis products. It was found that the formation of reduced molecules (viologen radical-cations) occurred in reactions of bipyridinium salts with free electrons and long lived polymer radicals. The reaction time of the first process was much shorter than the electron pulse duration (2.5 μs). The mean time of the second reaction exceeded several seconds. Simultaneously with radical-cations of viologens a number of transient species, including OH-adduct (λmax = 570 nm) and protonated form (λmax = 595 nm), were produced during the action of electron pulse. The effective rate constant of reaction between hepthyl-viologen dibromide and poly(vinyl alcohol) radicals was obtained. The influence of temperature, viologen concentration, absorbed dose and polymer structure on radical-cation formation was also studied. (author)