Manipulating the Polymerization of 3,5-Diaminobenzoic Acid with a Bromate Oscillator

Abstract

Manifestation of the properties of 3,5-diaminobenzoic acid polymer film was explored by polymerizing 3,5-diaminobenzoic acid in the presence of bromate. Depending on the initial concentration of bromate, the 3,5diaminobenzoic acid solution was observed to transit from steady to oscillatory evolution in a batch reactor. The thus-fabricated film on Au electrodes exhibited different activities toward the electrochemical oxidation of pyrocatechol. The film synthesized at nonoscillatory conditions has a primary oxidation peak of pyrocatechol at about 0.20 V (vs Hg/Hg 2 SO 4 electrode), as opposed to 0.0 V with the film that was prepared under oscillatory conditions. A phase diagram in the bromate−sulfuric acid phase was constructed to demonstrate the influence of each parameter on the emergence of oscillatory behavior in the 3,5-diaminobenzoic acid system. Experiments showed that an increase in the concentrations of sulfuric acid and bromate greatly increased the frequency and reduced the induction period of these transient oscillations. Unlike the systems that used ortho-and para-disubstituted organic substrates, this 1,3,5-trisubstituted compound did not evolve through the dihydroxy intermediate (pyrocatechol/hydroquinone) as no peak for resorcinol (110 m/z) was found in any of the mass spectrometry results.