Kinetics and mechanism of pyrrole chemical polymerization

Proton NMR spectroscopy was used to study the kinetics of the chemical polymerization of pyrrole in water using ferric chloride as an oxidant. A kinetics model was proposed in which the consumption of pyrrole is due to a fast oxidation reaction, and a relatively faster reaction with the oxidized oligomers of pyrrole. This suggests the commonly used mechanism for polymerization of pyrrole to polypyrrole, which is an important conductive polymer, is not correct for polymerization in water. Instead the polymerization is based on a mechanism where the pyrrole monomer is attacked by a radical cation, leading directly to the pyrrole reacting with the oxidized oligomer. We conducted kinetics studies as a function of temperature and determined the activation energy, activation entropy and enthalpy for each step of the polymerization process for the first time. The activation enthalpy and activation entropy are respectively 77,091 ± 17 J and 24.25 ± 0.06 J/K for the initial step, and 70,971 ± 14 J and 24.25 ± 0.06 J/K for the propagation step.