Electrochemical characteristics and stability of poly(1,5-diaminoanthraquinone) in acidic aqueous solution

The electrochemical characteristics and stability of poly(1,5-diaminoanthraquinone) (P15DAAQ) has been investigated in different acidic aqueous solution by electrochemical methods and Fourier transform infrared spectroscopy (FTIR). Cyclic voltammetry (CV) analysis suggests,that electropolymerization consists of two phases-the deposition of P15DAAQ from the oxidation of 15DAAQ monomers and the polymer growth process. The CV and chronoamperometry (CA) data provide the evidence that ion transfers are different between oxidation and reduction processes and are profoundly influenced by the sizes of ion radius during the redox process of P15DAAQ in acid solution. The H+ transfer is diffusionless, while the insertion/expulsion of large aqua anions is controlled by diffusion. A model is proposed to describe these ion transfer processes. In further CA research, the calculated diffusion coefficients of aqua anions in P15DAAQ are in the order of Cl- > SO42- > NO3- > PO43-. As a result of stability research, it can be seen that degradation of the polymer 4 4 exists not only in overoxidation but also in the stable redox reaction. The degradation rates of P15DAAQ in the reversible potential region from -0.2 to 0.75 V obey the apparent first-order kinetic, and the degradation rate constants are 2.04, 4.93, 2.59, and 3.03 x 10(-5) s(-1) in HCl, H2SO4, HNO3, and H3PO4, respectively. According to FTIR and CV, the quinone-like structure is destroyed, accompanied with conjugation length of the polymer's pi-bond being decreased and chains in the polymer being broken and recombined with anions combined to the polymer, when P15DAAQ is potentiodynamically overoxidized at 1.5 V.