Polypyrrole

Polypyrrole (PPy) is a type of organic polymer formed by the polymerization of pyrrole. It is a solid with the formula H(C4H2NH)nH. Upon oxidation, polypyrrole converts to a conducting polymer.[2]

Polypyrrole
Pyrrole can be polymerised electrochemically.[1]

History

Some of the first examples of polypyrroles were reported in 1963 by Weiss and coworkers. These workers described the pyrolysis of tetraiodopyrrole to produce highly conductive materials.[3]

The Nobel Prize in Chemistry was awarded in 2000 for work on conductive polymers including polypyrrole, polythiophene, polyaniline, and polyacetylene.[4]

Synthesis

Polypyrrole is prepared by oxidation of pyrrole:

n C4H2NH + 2n FeCl3 → (C4H2NH)n + 2n FeCl2 + 2n HCl

The process is thought to occur via the formation of the pi-radical cation C4H4NH+. This electrophile attacks the C-2 carbon of an unoxidized molecule of pyrrole to give a dimeric cation (C4H4NH)2]++. The process repeats itself many times.

Conductive forms of PPy are prepared by oxidation ("p-doping") of the polymer:

(C4H2NH)n + 0.2 X → [(C4H2NH)nX0.2]

The polymerization and p-doping can also be effected electrochemically. The resulting conductive polymer are peeled off of the anode. Cyclic voltammetry and chronocoulometry methods can be used for electrochemical synthesis of polypyrrole.[5]

Properties

Films of PPy are yellow but darken in air due to some oxidation. Doped films are blue or black depending on the degree of polymerization and film thickness. They are amorphous, showing only weak diffraction. PPy is described as "quasi-unidimensional" vs one-dimensional since there is some crosslinking and chain hopping. Undoped and doped films are insoluble in solvents but swellable. Doping makes the materials brittle. They are stable in air up to 150 °C at which temperature the dopant starts to evolve (e.g., as HCl).[2]

PPy is an insulator, but its oxidized derivatives are good electrical conductors. The conductivity of the material depends on the conditions and reagents used in the oxidation. Conductivities range from 2 to 100 S/cm. Higher conductivities are associated with larger anions, such as tosylate. Doping the polymer requires that the material swell to accommodate the charge-compensating anions. The physical changes associated with this charging and discharging has been discussed as a form of artificial muscle.[6] The surface of polypyrrole films present fractal properties and ionic diffusion through them show anomalous diffusion pattern.[7][8]

Applications

PPy and related conductive polymers have two main application in electronic devices and for chemical sensors.[9]

PPy is a potential vehicle for drug delivery. The polymer matrix serves as a container for proteins.[10]

Polypyrrole has been investigated as a catalyst support for fuel cells[11] and to sensitize cathode electrocatalysts.[12]

Together with other conjugated polymers such as polyaniline, poly(ethylenedioxythiophene) etc., polypyrrole has been studied as a material for "artificial muscles", a technology that offers advantages relative to traditional motor actuating elements.[13]

Polypyrrole was used to coat silica and reverse phase silica to yield a material capable of anion exchange and exhibiting hydrophobic interactions.[14]

Polypyrrole was used in the microwave fabrication of multiwalled carbon nanotubes, a rapid method to grow CNT's.[15]

A water-resistant polyurethane sponge coated with a thin layer of polypyrrole absorbs 20 times its weight in oil and is reusable.[16]

The wet-spun polypyrrole fibre can be prepared chemical polymerization pyrrole and DEHS as dopant.[17]

See also

References
  1. Yu, E.H.; Sundmacher, K. (2007). "Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B5): 489–493". Enzyme Electrodes for Glucose Oxidation by Electropolymerization of Pyrrole. 85 (5): 489–493. doi:10.1205/psep07031.
  2. Vernitskaya, Tat'Yana V.; Efimov, Oleg N. (1997). "Polypyrrole: a conducting polymer; its synthesis, properties and applications". Russ. Chem. Rev. 66 (5): 443–457. Bibcode:1997RuCRv..66..443V. doi:10.1070/rc1997v066n05abeh000261.
  3. McNeill, R.; Siudak, R.; Wardlaw, J. H.; Weiss, D. E. (1963). "Electronic Conduction in PolymersI. The Chemical Structure of Polypyrrole". Aust. J. Chem. 16 (6): 1056–75. doi:10.1071/CH9631056.
  4. MacDiarmid, A. G. (2001). "Synthetic metals: A novel role for organic polymers (Nobel Lecture)". Angew. Chem. Int. Ed. 40 (14): 2581–2590. doi:10.1002/1521-3773(20010716)40:14<2581::aid-anie2581>3.0.co;2-2.
  5. Sharifi-Viand, Ahmad (2014). "Determination of fractal rough surface of polypyrrole film: AFM and electrochemical analysis". Synthetic Metals. 191: 104–112. doi:10.1016/j.synthmet.2014.02.021.
  6. Baughman, Ray H. (2005). "Playing Nature's Game with Artificial Muscles". Science. 308 (5718): 63–65. doi:10.1126/science.1099010. PMID 15802593.
  7. Ahmad Sharifi-Viand, Diffusion through the self-affine surface of polypyrrole film Vacuum doi:10.1016/j.vacuum.2014.12.030
  8. Sharifi-Viand, Ahmad (2012). "Investigation of anomalous diffusion and multifractal dimensions in polypyrrole film". Journal of Electroanalytical Chemistry. 671: 51–57. doi:10.1016/j.jelechem.2012.02.014.
  9. Janata, Jiri; Josowicz, Mira (2003). "Progress Article: Conducting polymers in electronic chemical sensors". Nature Materials. 2 (1): 19–24. doi:10.1038/nmat768. PMID 12652667.
  10. Geetha, S.; Rao, Chepuri R.K.; Vijayan, M.; Trivedi, D.C. (2006). "Biosensing and drug delivery by polypyrrole" "Molecular Electronics and Analytical Chemistry". Analytica Chimica Acta. 568 (1–2): 119–125. doi:10.1016/j.aca.2005.10.011. PMID 17761251.
  11. Unni, Sreekuttan M.; Dhavale, Vishal M.; Pillai, Vijayamohanan K.; Kurungot, Sreekumar (2010). "High Pt Utilization Electrodes for Polymer Electrolyte Membrane Fuel Cells by Dispersing Pt Particles Formed by a Preprecipitation Method on Carbon "Polished" with Polypyrrole". The Journal of Physical Chemistry C. 114 (34): 14654–14661. doi:10.1021/jp104664t.
  12. Olson, Tim S.; Pylypenko, Svitlana; Atanassov, Plamen; Asazawa, Koichiro; Yamada, Koji; Tanaka, Hirohisa (2010). "Anion-Exchange Membrane Fuel Cells: Dual-Site Mechanism of Oxygen Reduction Reaction in Alkaline Media on Cobalt−Polypyrrole Electrocatalysts". The Journal of Physical Chemistry C. 114 (11): 5049–5059. doi:10.1021/jp910572g.
  13. http://atmsp.whut.edu.cn/resource/pdf/4987.pdf%5B%5D
  14. Ge, Hailin; Wallace, G.G. (1991-12-27). "High-performance liquid chromatography on polypyrrole-modified silica". Journal of Chromatography A. 588 (1–2): 25–31. doi:10.1016/0021-9673(91)85003-X.
  15. pubs.rsc.org/en/content/articlelanding/2011/CC/C1CC13359D
  16. Chemical and Engineering News, 26June2013 "Greasy Sponge Slurps Up Oil" http://cen.acs.org/articles/91/web/2013/06/Greasy-Sponge-Slurps-Oil.html
  17. Foroughi, J.; et al. (2008). "Production of polypyrrole fibres by wet spinning". Synthetic Metals. 158 (3–4): 104–107. doi:10.1016/j.synthmet.2007.12.008.
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