Polypyrrole (PPy) is a chemical compound formed from a number of connected pyrrole ring structures. For example a tetrapyrrole is a compound with four pyrrole rings connected. Methine-bridged cyclic tetrapyrroles are called porphyrins. Polypyrroles are conducting polymers of the rigid-rod polymer host family, all basically derivatives of polyacetylene. Polypyrrole was the first polyacetylene-derivative to show high conductivity.
In a series of papers in 1963, DE Weiss and coworkers reported [2] high-conductivity (up to 1 S/cm) in iodine-doped oxidized polypyrrole. While too early and thus eventually "lost", this anticipated by many years the Nobel-prize-winning discovery of high-conductivity in similarly iodine-doped and oxidized polyacetylene, as well as John McGinness' et al.s report of a high-conductivity "ON" state in the putative first organic electronic device.[3]
Polypyrroles are also called pyrrole blacks or polypyrrole blacks. Polypyrroles also exist naturally, especially as part of a mixed copolymer with polyacetylene and polyaniline in some melanins.
In 2006, scientists from Brown University published work on a fast-charging and discharging battery chemistry based on polypyrroles.[4]
There are current studies into the medical applications of polypyrroles: A current study suggests that polypyrroles may be used for testing the blood lithium levels of patients being treated for bipolar disorder.
Polypyrrole is also being investigated in low temperature fuel cell technology to increase the catalyst dispersion in the carbon support layers [5] and to sensitize cathode electrocatalysts as it has been inferred that the metal electrocatalysts (Pt, Co, etc) when coordinated with the nitrogen in the pyrrole monomers show enhanced oxygen reduction activity.[6]
Polypyrrole (together with other conjugated polymers such as polyaniline, poly(ethylenedioxythiophene) etc.) has been actively studied as a material for "artificial muscles", a technology that would offer numerous advantages over traditional motor actuating elements.[7]
Polypyrrole was used to coat silica and reverse phase silica to yield a material capable of anion exchange and exhibiting hydrophobic interactions.[8]
Polypyrrole was used in the microwave fabrication of multiwalled carbon nanotubes, a new method that allows to obtain CNTs in a matter of seconds.[9]