Synthesis of polypyrrole with fewer structural defects using enzyme catalysis

Abstract

Enzymatic polymerization is an environmentally friendly alternative route for the synthesis of advanced π-functional materials. Until recently, synthetic methods for production of polypyrrole (PPy) were confined to the use of chemical oxidants or electrochemical methods. Here, we report the low temperature, oxidative polymerization of pyrrole using soybean peroxidase as the catalyst in aqueous non-toxic media. In addition to the benefits of the mild synthetic conditions, enzyme catalysis also affords PPy with fewer structural defects. Poly(sodium 4-styrenesulfonate) (PSS) was used as a charge-balancing dopant and dispersant for PPy to monitor changes in the absorption spectra of the polymer over time. However, the polymerization methodology is amenable to other dopants, including small molecule dopants like 10-camphor sulfonic acid. Spectroscopic characterization indicated that the PPy was conductive, and was produced in higher yields and at faster rates at lower temperatures. Careful temperature control combined with the appropriate choice of dopant ensured production of more electrically conductive PPy with conductivities that exceeded 3 S/cm. UV–Vis spectroscopy was used to provide evidence of favorable interactions between pyrrole and the dopant that may have facilitated the reaction. These interactions, combined with a low synthesis temperature and controlled enzyme-catalyzed radical generation, synergistically favored the formation of PPy with fewer defects and a more linear structure.