Editing Polypyrrole

{{Short description|Conductive polymer}}
[[Image:Polypyrrol.svg|thumb|Polypyrrole]]
[[Image:Pyrrole Electro-polymerisation.png|thumb|Pyrrole can be polymerised electrochemically.<ref name="Pyrrole Electrochem">{{cite journal
 | title=Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B5): 489–493
 | journal=Enzyme Electrodes for Glucose Oxidation by Electropolymerization of Pyrrole
 | doi=10.1205/psep07031
 | volume=85
 | issue=5
 | pages=489–493| year=2007
 | last1=Yu
 | first1=E.H.
 | last2=Sundmacher
 | first2=K.
 }}</ref>]]
'''Polypyrrole''' ('''PPy''') is an organic polymer obtained by oxidative  polymerization of [[pyrrole]]. It is a solid with the formula H(C<sub>4</sub>H<sub>2</sub>NH)<sub>n</sub>H. It is an intrinsically [[conducting polymer]], used in electronics, optical, biological and medical fields.<ref name=RussChemRev>{{cite journal | year = 1997 | title = Polypyrrole: a conducting polymer; its synthesis, properties and applications | journal = Russ. Chem. Rev. | volume = 66 | issue = 5| pages = 443–457 | doi=10.1070/rc1997v066n05abeh000261| last1 = Vernitskaya | first1 = Tat'Yana V. | last2 = Efimov | first2 = Oleg N. | bibcode = 1997RuCRv..66..443V | s2cid = 250889925 }}</ref><ref name=":0">{{Cite journal|last1=Müller|first1=D.|last2=Rambo|first2=C.R.|last3=D.O.S.Recouvreux|last4=Porto|first4=L.M.|last5=Barra|first5=G.M.O.|date=January 2011|title=Chemical in situ polymerization of polypyrrole on bacterial cellulose nanofibers|url=https://linkinghub.elsevier.com/retrieve/pii/S0379677910004583|journal=Synthetic Metals|language=en|volume=161|issue=1–2|pages=106–111|doi=10.1016/j.synthmet.2010.11.005|url-access=subscription}}</ref>

==History==
Some of the first examples of PPy were reported in 1919 by Angeli and Pieroni, who reported the formation of pyrrole blacks from pyrrole magnesium bromide.<ref>A. Angeli and A. Pieroni, Qazz. Chim. Ital. 49 (I), 164 (1919)</ref>  Since then pyrrole oxidation reaction has been studied and reported in scientific literature.

Work on conductive polymers including polypyrrole, [[polythiophene]], [[polyaniline]], and [[polyacetylene]] was awarded the [[Nobel Prize in Chemistry]] in 2000 to Alan J. Heeger, Alan G. MacDiarmid and Hideki Shirakawa .<ref>{{cite journal | last1 = MacDiarmid | first1 = A. G. | year = 2001 | title = Synthetic metals: A novel role for organic polymers (Nobel Lecture) | journal = Angew. Chem. Int. Ed. | volume = 40 | issue = 14| pages = 2581–2590 | doi = 10.1002/1521-3773(20010716)40:14<2581::aid-anie2581>3.0.co;2-2 }}</ref>

==Synthesis==
Different methods can be used to synthesize PPy, but the most common are electrochemical synthesis and chemical oxidation.<ref>{{Cite journal|last1=Sabouraud|first1=Guillaume|last2=Sadki|first2=Saïd|last3=Brodie|first3=Nancy|date=2000|title=The mechanisms of pyrrole electropolymerization|url=http://xlink.rsc.org/?DOI=a807124a|journal=Chemical Society Reviews|volume=29|issue=5|pages=283–293|doi=10.1039/a807124a|url-access=subscription}}</ref><ref name=":0" /><ref>{{Cite journal|last1=Rapi|first1=S.|last2=Bocchi|first2=V.|last3=Gardini|first3=G. P.|date=1988-05-01|title=Conducting polypyrrole by chemical synthesis in water|url=https://dx.doi.org/10.1016%2F0379-6779%2888%2990259-7|journal=Synthetic Metals|language=en|volume=24|issue=3|pages=217–221|doi=10.1016/0379-6779(88)90259-7|issn=0379-6779|url-access=subscription}}</ref>

Chemical oxidation of pyrrole:
:n C<sub>4</sub>H<sub>4</sub>NH  +  2n FeCl<sub>3</sub>   →   (C<sub>4</sub>H<sub>2</sub>NH)<sub>n</sub>  +  2n FeCl<sub>2</sub>  +  2n HCl

The process is thought to occur via the formation of the pi-[[radical cation]] C<sub>4</sub>H<sub>4</sub>NH<sup>+</sup>.  This electrophile attacks the C-2 carbon of an unoxidized molecule of pyrrole to give a dimeric cation [(C<sub>4</sub>H<sub>4</sub>NH)<sub>2</sub>]<sup>++</sup>.  The process repeats itself many times.

Conductive forms of PPy are prepared by oxidation ("p-doping") of the polymer:
:(C<sub>4</sub>H<sub>2</sub>NH)<sub>n</sub>  +  0.2 X   →    [(C<sub>4</sub>H<sub>2</sub>NH)<sub>n</sub>X<sub>0.2</sub>]

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.<ref>{{cite journal | last1 = Sharifi-Viand | first1 = Ahmad | year = 2014 | title = Determination of fractal rough surface of polypyrrole film: AFM and electrochemical analysis | journal = Synthetic Metals | volume = 191 | pages = 104–112 | doi=10.1016/j.synthmet.2014.02.021}}</ref>

Most recent micro and nano droplet researches have been conducted in the synthesis of polypyrrole microstructures using various fluid templates formed on different solid surfaces.<ref>{{cite book|title=Creating microstructures using conducting polypyrrole|last=Johan|first=Albert|date=2010|publisher=GRIN Verlag |url=https://www.grin.com/document/506250|isbn=9783346068415}}</ref>

==Properties==
Films of PPy are yellow but darken in the 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 the air up to 150&nbsp;°C at which temperature the dopant starts to evolve (e.g., as HCl).<ref name=RussChemRev/>

Doping the polymer requires that the material swell to accommodate the charge-compensating anions. The physical changes associated with this charging and discharging have been discussed as a form of artificial muscle.<ref>{{cite journal | last1 = Baughman | first1 = Ray H. | year = 2005 | title = Playing Nature's Game with Artificial Muscles | journal = Science | volume = 308 | issue = 5718| pages = 63–65 | doi = 10.1126/science.1099010 | pmid=15802593| s2cid = 180181717 }}</ref> The surface of polypyrrole films present [[fractal]] properties and ionic diffusion through them show [[anomalous diffusion]] pattern.<ref>Ahmad Sharifi-Viand, [http://www.sciencedirect.com/science/article/pii/S0042207X15000032 Diffusion through the self-affine surface of polypyrrole film] ''Vacuum'' doi:10.1016/j.vacuum.2014.12.030
</ref><ref>{{cite journal | last1 = Sharifi-Viand | first1 = Ahmad | year = 2012 | title = Investigation of anomalous diffusion and multifractal dimensions in polypyrrole film | journal = Journal of Electroanalytical Chemistry | volume = 671 | pages = 51–57 | doi=10.1016/j.jelechem.2012.02.014}}</ref>

==Applications==
PPy and related conductive polymers have two main application in electronic devices and for chemical sensors and electrochemical applications.<ref>{{cite journal | last1 = Janata | first1 = Jiri | last2 = Josowicz | first2 = Mira | year = 2003 | title = Progress Article: Conducting polymers in electronic chemical sensors | journal = Nature Materials | volume = 2 | issue = 1| pages = 19–24 | doi = 10.1038/nmat768 | pmid = 12652667 | s2cid = 1250380 }}</ref>

==Research trends==
PPy is a potential vehicle for [[drug delivery]]. The polymer matrix serves as a container for proteins.<ref>{{cite journal | last1 = Geetha | first1 = S. | last2 = Rao | first2 = Chepuri R.K. | last3 = Vijayan | first3 = M. | last4 = Trivedi | first4 = D.C. | year = 2006 | title = Biosensing and drug delivery by polypyrrole" "Molecular Electronics and Analytical Chemistry | journal = Analytica Chimica Acta | volume = 568 | issue = 1–2| pages = 119–125 | doi = 10.1016/j.aca.2005.10.011 | pmid = 17761251 }}</ref>

Polypyrrole has been investigated as a [[catalyst support]] for fuel cells<ref>{{cite journal|last1=Unni|first1=Sreekuttan M.|last2=Dhavale|first2=Vishal M.|last3=Pillai|first3=Vijayamohanan K.|last4=Kurungot|first4=Sreekumar|title=High Pt Utilization Electrodes for Polymer Electrolyte Membrane Fuel Cells by Dispersing Pt Particles Formed by a Preprecipitation Method on Carbon "Polished" with Polypyrrole|journal=The Journal of Physical Chemistry C|pages=14654–14661|year=2010|doi=10.1021/jp104664t|volume=114|issue=34}}</ref> and to sensitize cathode electrocatalysts.<ref>{{cite journal|last1=Olson|first1=Tim S.|last2=Pylypenko|first2=Svitlana|last3=Atanassov|first3=Plamen|last4=Asazawa|first4=Koichiro|last5=Yamada|first5=Koji|last6=Tanaka|first6=Hirohisa|title=Anion-Exchange Membrane Fuel Cells: Dual-Site Mechanism of Oxygen Reduction Reaction in Alkaline Media on Cobalt−Polypyrrole Electrocatalysts|journal=The Journal of Physical Chemistry C|volume=114|pages=5049–5059|year=2010|doi=10.1021/jp910572g|issue=11}}</ref>

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.<ref>{{cite web |url=http://atmsp.whut.edu.cn/resource/pdf/4987.pdf |title=Archived copy |website=atmsp.whut.edu.cn |access-date=30 June 2022 |archive-url=https://web.archive.org/web/20111121003707/http://atmsp.whut.edu.cn/resource/pdf/4987.pdf |archive-date=21 November 2011 |url-status=dead}}</ref>

Polypyrrole was used to coat silica and reverse phase silica to yield a material capable of anion exchange and exhibiting hydrophobic interactions.<ref>{{cite journal | doi=10.1016/0021-9673(91)85003-X | volume=588 | issue=1–2 | title=High-performance liquid chromatography on polypyrrole-modified silica | journal=Journal of Chromatography A | pages=25–31| date=1991-12-27 | last1=Ge | first1=Hailin | last2=Wallace | first2=G.G. }}</ref>

Polypyrrole was used in the microwave fabrication of multiwalled carbon nanotubes, a rapid method to grow CNT's.<ref>pubs.rsc.org/en/content/articlelanding/2011/CC/C1CC13359D</ref>

A water-resistant polyurethane sponge coated with a thin layer of polypyrrole absorbs 20 times its weight in oil and is reusable.<ref>Chemical and Engineering News, 26June2013 "Greasy Sponge Slurps Up Oil" http://cen.acs.org/articles/91/web/2013/06/Greasy-Sponge-Slurps-Oil.html</ref>

The wet-spun polypyrrole fibre can be prepared chemical polymerization pyrrole and DEHS as dopant.<ref>{{cite journal | last1 = Foroughi | first1 = J. | display-authors = etal   | year = 2008 | title = Production of polypyrrole fibres by wet spinning | journal = Synthetic Metals | volume = 158 | issue = 3–4| pages = 104–107 | doi=10.1016/j.synthmet.2007.12.008}}</ref>

==See also==

*[[Organic semiconductor]]
*[[Tetrapyrrole]]s

==References==
<References/>

[[Category:Organic polymers]]
[[Category:Molecular electronics]]
[[Category:Pyrroles]]
[[Category:Organic semiconductors]]
[[Category:Biology of bipolar disorder]]
[[Category:Conductive polymers]]