Enzymatically synthesized conducting polyaniline

A novel strategy for the enzymatic synthesis of a water-soluble, conducting polyaniline (PANI)/sulfonated polystyrene (SPS) complex is presented. The enzyme horseradish peroxidase (HRP) is used to polymerize aniline in the presence of a polyanionic template, sulfonated polystyrene. The synthesis is simple, and the conditions are mild in that the polymerization may be carried out in a 4.3 pH buffered aqueous solution, with a stoichiometric amount of hydrogen peroxide and a catalytic amount of enzyme. UV-visible absorption, FTIR, GPC, elemental analysis, and conductivity measurements all confirm that the electroactive form of PANI, similar to that which is traditionally chemically synthesized, is formed and complexed to the SPS. The reversible redox activity of the polyaniline displays a unique hysteresis loop with pH change. Cyclic voltammetry studies show only one set of redox peaks over the potential range of -0.2 to 1.2V, which suggests that the PANI/SPS complex is oxidatively more stable. The conductivity of the complex is found to increase with the molar ratio of PANI to SPS. Conductivities of 0.005 S/cm are obtained with the pure complex and may be increased to 0.15 S/cm after additional doping by exposure to HCl vapor. This enzymatic approach offers unsurpassed ease of synthesis, processability, stability (electrical and chemical), and environmental compatibility.