Synthesis and properties of Polyaniline

Polyaniline which is regarding kind of Inherently Conducting Polymers (ICPs), was prepared by
either chemical and electricchemical polymerization in acidic medium. Such solvents were used
and compared the affecting on the conductivity between EB solution in DMF and mcresol solvents by using UVvis spectrum. UVvis
spectra and cyclic voltametry were used to generate
and analyze the spectrum for the polymer films

1. Synthesis and properties of Polyaniline 
by Awad Albalwi 
 
Abstract  
PolyanilinewhichisregardingkindofInherentlyConductingPolymers(ICPs),waspreparedby                    
eitherchemicalandelectric­chemicalpolymerizationinacidicmedium.Suchsolventswereused                  
andcomparedtheaffectingontheconductivitybetweenEBsolutioninDMFandm­cresol                     
solventsbyusingUV­visspectrum.UV­visspectraandcyclicvoltametrywereusedtogenerate                     
and analyze the spectrum for the polymer films  
 
 
Introduction   
Inrecentyear,polyaniline(PANI)isconsideredoneofthemostwidelyusedfortheapplicationin                        
electricdevices.ThatisbecausePANIhasagreatelectricalconductivity,highchemicalstabilityand                      
easysynthesisthatitcanbeabletocontroloxidationstateanddegreeofprotonation[1,2].Inaddition,                        
theproductofthepolymerization(PANI)hasbeenlookingforwardtodeveloptheapplicationin                      
differentfieldsincludingsensors,chargestoragesystemsandprotectionagainstcorrosion[1].PANI                       
canbeusedtoundergoformingdielectricofemeraldinebase(EB)withasignificantfilmforming                      
solvent(N­methyl­2pyrrolidone(NMP)intoconductiveformofemeraldinesalt(ES)byprotonicacid                  
[2].PANI­ESisduetobesolubilitywithlargenumberoforganicsolventdependingupon                       
functionalities of protonic acid such as camphorsulfonic acid (HCSA).  

2.  
Themainpropertiesofpolyanilinesuchascrystallinity,conductivity,molecularweightand                    
electrochemical behavior rely on the processes and conditions of preparation [3].  
​Inherentlyconductingpolymers(ICPs)areconjugationofπ­electronsextendingalloverthelength                       
ofpolymerbackbonewhichtheyarepreparedbychemicalorelectrochemicaloxidationwithlargeof                      
appropriate ​monomeric materials.  ​The unique properties of ICPs might be included:
1­Tuningtheconductivitycanpossiblyemployedbyadjustingtheamountofdopantincorporated                      
within the polymer,  
2­ Doping and undoping are reversible process. 
3­BothofthecharacteristicsfortheopticalandelectromagneticabsorptionintheUV,visibleandnear                      
infrared are involved [4]. 
There are three of the most studied ICPs are defined below: 
 
Theformationofentirelyorganicconductingpolymersdependsupontheoxidationstateofthe                     
polymer.Theprocessofthatformation(oxidationorreduction)whichiscalled‘doping”,causes                       
changing in the electronic structure in order to provide conducting electricity.  
Inthisexperiment,thepolyanilinewaspreparedbypotentiodynamicpolymerization(cyclic                 

3. voltammetry).Moreover,thechangeofpolyanilinewerealsoexaminedandcomparedtotheirredox                    
and acid/base chemistry via using a sample of emeraldine base which was provided. 
 
 
Experiment: 
Preparation of stock polyaniline solution  
Polyanilinestocksolutionwaspreparedbyadding4gofaniline&20mlofHClinto200mL                       
water in 1L beaker and then stirred for 10 min.  
Potentiodynamic synthesis of polyaniline 
The parameters of using cyclic voltammetry for 10 mL of the stock polyaniline solution were : 
●Initial potential = final potential= ­0.2 v 
●Lower potential limit= ­0.2v 
●Upper potential limit= +0.9v 
●Number of growth cycles = 10 
●Scan rate = 100 m Vs​
­1
  
●Current = 1 mA/ cm​
2 
Chemical and spectroscopic properties of emeraldine base: 
For more details about the procedure refer back to the lab manual. 
 
Result and discussion  
Question 1: 
From adding different solvent or changing PH of the solvent, the color of the EB solution was 
reported as shown in Table 1 below: 
Table1.​ the difference color to EB with different solvent. 
Samples  color   
EB solution + DMF  Dark blue  Prepared 
(EB+DMF)+ HCSA  Light green   Prepared 

4. (EB+DMF)+ Hydrazine  Blue light (clear)  Prepared 
(EB+DMF)+Ammonium persulfate  Violet   Prepared 
EB+ m­cresol  Blue  Provided 
(EB+ m­cresol) + HCSA  Green   Provided 
 
 
Figure1.​TheUV­VisspectrumofEBdissolveinDMF,thesolutionwasdarkblueandgives                     
wavelength in between 327­ 626 nm.  
 
Figure2​.ThelowconductivitywasconfirmedwhileEBinDMFwhichaddedtoHSCA                     

5. obtaininggreenlightandthreebands354nm(​π­π*),410nm(polaron–π*)and789nm(π­polaron                        
band).Thepollaronsofeachtetranericunitareisolatedfromeachotherinordertothetwistdefect                      
between aromatic rings. Because of that the conductivity of the polymer has little energy.  
 
 
 
Figure3.ThespectrumshowedthatEBinDMFwithaddinghydrazineweregivencolorexchange                      
wherewasfromdarkbluetolightblue(clear)solution.Also,therewasonlyoneabsorptionoccurred                     
by 342nm which due to (π­ π*) transition​. 
 

6.  
Figure4​. The spectrum illustrated EB in DMF with ammonium persulfate was converted from 
dark blue to give violet color (form pernigraniline state). Moreover, there were two peaks 
occurred by 323nm (​π ­ π*) and 592nm (π­ polaron band).  
 
Question2. 
Electrochemicalpolymerizationofanilinewasusedcontainingathreeelectrodeelectrochemical                
cell as shown below: 
 
Figure​ .A three­ electrode electrochemical cell [3]. 

7.  
Thematerialandsizeoftheworkingelectrode(WE)whichPANIfilmwasgrowndependedon                        
using ITO coated glass electrode  
Auxiliaryelectrodes(AE)whichmadefromplatinumorstainlesssteel,haslargesurfacearea                     
therefore they don’t have limit the passage of current. 
Referenceelectrode(RE)usedAg/AgClelectrodeinconjunctionwithNaClsaltbridgeasa                    
reference in aqueous solution. 
The procedure of electrochemical polymerization of polyaniline can be concluded by: 
1.Radical cation of aniline was formed by oxidation on electrode surface. 
2.CouplingofradicalsisoccurredultimatelybetweenN­andC­onthecycleandthen                    
subsequent elimination of two protons.  
3.The dimmer will be formed by rearomatization step resulting in propagation of the chain. 
4.Oxidation and Doping the polymer were occurred by adding acid (HA). 
 
 
 
 
Question 3 
Usingm­cresolasasolvent,thepolymerbackbonehaspositivechargewithnegativecounterions                      
thataresittingintheproximityofpolymerchains.Incaseofremovingcounterionsfromthe                      
polymerchain,theinteractionofpositivechargesonthepolymerbackbonewillheadtoextend                      
thepolymerchainfromacoillikeconformationtoanexpandedcoillikeconformation.                    
Therefore,theexistenceofm­cresolwillchangetheconfirmationbecausethetwistsanddefects                     
betweenaromaticringsareremoved.Ontheotherhand,withusingDMFasasolvent,the                        
polymerchainshaveacoillikeconfirmationandthepolaronsofeachtetramericunitareisolated                     
andpolaron­π*transitionpossiblyoccurred.Moreover,half­filled‘polaroneband’thatformedby                       
interactionofseparatingpolarononthefullyprotonatedforPANIemeradlinesaltthereforethepolaron                      

8. band has a little dispersion energy. 
Basedonthat,theinteractionofm­cresolbetweentheadjacentisolatedpolaronhasincreasedand                      
strongerandthatledtomorescatteredinenergy.Hence,theobservationpeak626nmforEBinDMF                       
wascorrespondedtoπ­polarontransitionsdisappearforEBinm­cresolandthenreplacedbyabroad                       
free­ carrier tail associated with the intraband transitions among the half filled polaron band. 
 
Conclusion: 
Inconclusion,itcanbeenseenthattheconductivityofpolyanilinehasmainlyinfluencedby                    
usingandchangingtheaciditywithdifferentelectronicstructuresindifferentsolvents.Thiskind                     
ofchangingcanleadtoattributetothedifferencesingeometricstructure(conformation)forthe                     
polymerchainofpolyaniline.So,theconductivityofm­cresolwasgreaterthanDMFsolvent                     
where they were used in this experiment.  
 
Reference 
1.Moraes, S. R.; Huerta­Vilca, D.; Motheo, A. J., Characteristics of polyaniline synthesized in 
phosphate buffer solution. ​European Polymer Journal ​2004, ​40​ (9), 2033­2041. 
 
2. Xia, Y., et.al., Camphorsulfonic Acid Fully Doped Polyaniline Emeraldine Salt: Conformations in 
Different Solvents Studied by an UltravioletNisiblel Near­Infrared Spectroscopic Method, chem. 
Mater, 1995, 7, 443­445. 
 
3. pornputtkul, Y., Development of chiral conducting polymers for asymmetric electrosynthesis, 
intelligent polymer research institute,  2005,  475 
 
4. ​http://www.conductivepolymers.com/general.htm