Investigation On Electro-Copolymerization Of Aniline And Its Derivatives, And Characterization And Application For Copolymer

For more than 30 years,Polyaniline,as a very hopeful conducting polymers withmany potential advanced applications,have attracted considerable attention due to itsrelatively easy preparation,excellent environmental stability,good acidic and electricdopability.The conductivity of polyaniline comes from its delocalizedÏ€-conjugatedbond,but the structure of polyaniline also leads to its lack of solubility in organicsolvents and its poor processible properties,which have restricted its practical utility.In order to overcome these difficulties,there are two important approaches employedto improve the properties of polyaniline conductive polymers:one is to polymerizesubstituted anilines such as N-substitued and aromatic ring substituted anilines usingchemical and electrochemical methods;the other is to produce some specialcopolymers between different aniline derivatives through the two methods mentionedabove.In particular,not only could the copolymerization approach tune the propertiesof copolymers by changing the ratio of different monomer concentration incopolymerization system bath;but also the structural information of copolymers andhomopolymers might be acquired through comparing the characteristics,i.e,FTIRspectra,Raman spectra,SEM images and UV-vis spectra,of copolymers with that ofhomopolymers.Further,the studies on copolymerization get more knowledge aboutthe reactivity of monomers and the mechanism of homo/copolymerization using insitu FTIR spectra,in situ UV-vis spectra,etc..For this reason,the copolymerizationbetween different aniline derivatives is being paid more and more attentionincreasingly.In this thesis,the main studies are focused on the following six topics1,Study on Electropolymerization of Aniline with in situ UV-VISSpectroelectrochemistryThe mechanism of the electro-polymerization of aniline in 0.5M sulfuric acidwas studied in detail by in situ UV-vis spectrometry.Spectroelectrochemicalexperiments were done in a three electrode cell built with a quartz cuvette of lcmpath length.the work electrode was ITO(indium-tin oxide) conductive glassperpendicular to light path,and the counter electrode was platinum wire.OneAg/AgCl with saturated KCl served as reference electrode.All potential values in thearticle were against to the reference.The acquired in situ UV-vis spectra showed thatpolyanilines could be electropolymerized at aniline concentrations 0.01 mol·dm^-3,0.05 mol·dm^-3 and 0.2 mol·dm^-3 in sulfuric acid by cyclic voltammetry.Based onin situ UV-Vis spectra corresponding to cylic potential sweep at three differentconcentration of aniline above,the plots of the relationship between absorbance at350nm and 750nm and elctrolysis time was made,which showed that the obviousinductive period in electropolymerization of aniline by cyclic voltammetry was seen for 0.01 mol·dm^-3 aniline in 0.5 mol·dm^-3 sulfuric acid water solution.In order tostudy how the concerntration of aniline in 0.05 mol·dm^-3 sulfuric acid and potentialapplied ITO conductive glass electrodes effected the polymerization of aniline,In situUV-Vis spectra was recrded during electrolysis of solution by potentiostaticmethod at different concentrations of aniline in 0.5 mol·dm^-3 sulfuric acid.Thesein situ UV-vis spectra indicated that the polymerization of aniline occurred byelectrolysis of aniline at potential 0.8V,1.0V and 1.3V when the concentration ofaniline was greater than 0.05mol/L,however at potential 0.8V,the polymerization ofaniline did not happen in 0.01mol/L of aniline.In situ UV-vis spectra at the earlierphase of aniline electropolymerization by potentiostatic way showed that the 350nmabsorbance band appeared before 750nm absorbance band.This fact proposed thatlower molecular weight oligomer intermediates during electrochemicalpolymerization of aniline might be existed and that the intermediate was brought outprior to the production of polyaniline on ITO electrode.When ITO conductive glasselectrode was placed parallel to light path,no absorbance bands were observed duringelectrolyzing 0.05 mol/L of aniline at potential 0.8V,which showed that intermediateand polymer mainly were produced on ITO conductive glass electrode.Thesephenomena was not reported up to now.When aniline concentration was 0.01mol/Land the potential applied on ITO glass conductive was 0.8V,there were onlyabsorbance band at 350nm in corresponding in situ UV-vis spectra,which showedthat the intermediates such as low molecular oligomers could be produced and existedon ITO electrode,but did not lead to form polyaniliane because of lowerconcentration of intermediate.After aniline of 0.05 mol/L in 0.5mol/L sulfuric acidwas electropolymerized by potentiostatic electrolysis at potential 0.8V for 70 minutes,the electrolysis was stopped,but in situ UV-Vis spectra were recorded continually.The red shift of absorbance band in spectra was seen,which indicated that polyanilineproduced on ITO electrode was of oxidized state and could react with anilinemonomer in solution to form polyaniline toward reduced state.2,Study on Electrochemical copolymerization of aniline withp-phenylenediamine on ITO electrode by in situ UV-visSpectroelectrochemistry and Characterization of the copolymerIt was observed by in situ UV-vis spectrometry that the polymerization ofp-phenylenediamine and the electrocopolymerization between aniline andp-phenylenediamine happened by cyclic voltammetry.Experimental results showedthat the absorbance band at 430nm in in situ UV-Vis spectra disappeared because ofthe presence of p-phenylenediamine.It was a direct evidence which indicated theaddition of p-phenylenediamine changed the mechanism of theelectro-polymerization of aniline on ITO electrode in 0.5 mol/L sulfuric acid solution.FTIR spectra of films deposited on ITO electrode was obtained and showed that 1,2or 1,2,3 substituted modes could exist in the copolymer films.The SEM images of the films showed the additional p-phenylenediamine could changed markedlymorphology of films and promoted the growth of fibrous morphology with large area.The diameter of fiber in film grown on ITO electrode might reach 50nm.Theelectrochromic behaviors of polymer films were studied in detail.At the potentialranged from 0.0v to 0.6v,the in situ UV-Vis spectra of copolymer film deposited onITO electrode was obviously different from that of polyaniline film on ITOelectrode.The electrochromic reversibility of copolymer was better than that ofpolyaniline.Furthermore,SEM morphology images indicated that electrolyzingpolyaniline and copolymer on ITO electrode at 0.8V in 0.5 mol/L H2SO4 madethem aggregate.3,Study on Electrochemical Copolymerization of o-Toluidine withp-Phenylenediamine on ITO Electrode by in situ UV-VisSpectroelectrochemistryOn the condition of potentiostatic electrolysis,the electropolymerization ofo-toluidine and p-phenylenediamine,and the electrocopolymerization betweeno-toluidine and p-phenylenediamine on indium-tin oxide(ITO) conductive glasselectrode was studied in detail by in situ UV-Vis spectrometry in a 0.5 mol/L sulfuricacid media.It was showed that both o-toluidine and p-phenylenediamine could beelectropolymerrized on ITO electrode,which depended on the applied electrolysispotential and the concentration of monomer.At 20 mmol/L of o-toluidine and 0.9V(vs saturated Ag/AgCl) of electrolysis potential,the polymerization did not happenwhereas the low molecule weight oligomer such as dimers could be produced on ITOelectrode.The obvious induction period was observed when elctropolymerization ofo-toluidine was performed on the 200 mmol/L o-toluidine at 0.7 V (vs saturatedAg/AgCl).At low concentration of p-phenylenediamine,in situ UV-Visspectrometry showed that the elctropolymerization of p-phenylenediamine did nothappen,but the low molecule weight oligomers such as dimers,etc could be createdon the surface of ITO electrode through C-C,C-N and N-N coupling.Theelctropolymerization of p-phenylenediamine,however,was carried out by C-Ncoupling at higher concentration of p-phenylenediamine.Furthermore,in situ UV-Visspectra indicated that the electrocopolymerization between o-toluidine andp-phenylenediamine could happen.The presence of p-phenylenediamine was not onlypromote polymerization but also accelerated polymerization.In addition,p-phenylenediamine could be incorporated into copolymer to make the copolymerhave phenazine or phenazine like cyclic structure,which was proved by thereflectance FTIR spectra of polymer and copolymer.The SEM morphology image ofpolymers obtained showed that beside accelerating polymerization,p-phenylenediamine also could change the way of nucleation for polymer to makecopolymer possess fibrous surface morphology.The diameter of copolymer fibre isabout 100 nm and the length of that reachs about 1000 nm 4,Study on Electrocopolymerization of o-Toluidine and AnthranilicAcid,the Electochromism of Copolymers,and Characterization of theCopolymersThe copolymers of o-Toluidine(OT) with anthranilic acid(AA) waselectrochemically synthesized on indium tin oxide (ITO) conducting glass electrodeby potentiostatic method at a potential of 0.9 V in sulfuric acid of 0.5 mole.dm-3.Theelectropolymerizaitons in the present study was followed by in situ UV-visspectrometry,which showed the rate of elecctropolymerization decreased as theconcerntration of anthranilic acid in reaction solution.The current-time transientcurve during electropolymerization indicated that poly(o-Toluidine) and copolymersmight be deposited on ITO electrode in three-dimensional progressivenucleation(3DPN).The resultant homo/copolymers was characterized using FTIR,SEM and spectroelectrochemistry.The SEMs of the copolymers from 200mmol·dm^-3OT/50 mmol·dm^-3 AA and 150mmol·dm^-3 OT/50 mmol·dm^-3 exhibit thatcopolymers have a smaller granular compact morphology.the resultant Copolymerfilms has more distinct electrochromic properties than poly(o-Toluidine).Especially,the response time of copolymers is shorter than that of poly(o-Toluidine).5,Study on Copolymerization of o-Toluidine with p-Phenylenediamineon Platium Electrode by Cyclic Voltammetry,and Charatrization andApplication of Platinum Nano Particles Loaded on CopolymersThe electrocopolymerization of o-toluidine and p-phenylenediamine occurred onplatinum electrode in the solution of 0.5 mol·dm^-3 H₂SO₄ using cyclic voltammetry,during which the cyclic voltamgrams for different feed ratio of systems witho-toluidine and p-phenylenediamine showed the addition of p-phenylenediamine tothe solution of o-toluidine in 0.5 mol·dm^-3 H₂SO₄ might lead to formation of morereactive intermediates.They accelerated the electrocopolymerization of o-toluidineand p-phenylenediamine.in comparison with the elctro-homopolymerization ofo-toluidine.Through FTIR and UV-vis spectra for polymer and copolymer,it wasindicated that the unit of p-phenylenediamine should be integrated into thebackbones of copolymers to form phenazine-like ring structures in the copolymers ofo-toluidine and p-phenylenediamine.These spectra also showed the delocalization ofelectron in copolymer might be better than homopoymer of toluidine.The SEMimages for copolymers clearly implied that the morphologies of copolymers wouldbecome more porous and smaller particles as the concentrations ofp-phenylenediamine in reaction system increased.By dynamic-potential scanningpolymers in 0.5 M H₂SO₄ in absence of monomers,the acquired cyclicvoltammgrams proved that the copolymers have more kinds of electrochemical activesites due to the presence of the unit of p-phenylenediamine in the backbone ofcopolymers.Both poly(o-toluidine) and copolymers could catalyzed the redox of hydroquinone electrochemically,but the cyclic voltammgrams for the electrochemicalredox of hydroquinone on polymers suggested that the active sites relative to the unitofp-phenylenediamine in the backbone of copoplymers seemed not to catalyze thisredox reaction due to steric hindrance arising from the unit ofp-phenylenediamine.Furthermore,oxygen can easily oxidized both reduced poly(o-toluidine) andcopolymers;the later were oxidized by oxygen faster than the former sincecopolymers had a more porous and rough morphology with smaller particles.It wasproved through SEM,EDAX and TEM that Nano platinum particles could be loadedon poly(o-toluidine) and the copolymer of o-toluidine and p-phenylenediamine.Inparticular,the size of nano platinum particles on the copolymer was much smallerthan on poly(o-toluidine) to reach below 25 nm,which showed that unlike onpoly(o-toluidine),the platinum particles can not aggregated easily to form largerparticles on copolymers.The nano platinum particles loaded on poly(o-toluidine) andcopolymers had better electrochemical catalytic activity toward electro-oxidation ofmethanol than bare platinum.Due to much smaller platinum particles on copolymers,they had better ability to resist poison during their electrocatalytic oxidation ofmethanol than the larger nano platinum particles on poly(o-toluidine).6,In situ UV-Vis Spectroelectrochemistry for Electropolymerization ofm-Toluidine and Electrocopolymerization of m-Toluidine withp-PhenylenediamineIn a 0.5 mol·dm^-3 sulfuric acid medium,cyclic voltammograms of m-toluidineand its corresponding in situ UV-Vis spectra indicate that the poly(m-toluidine) filmwas produced on the surface of the electrode.Under the condition of potentiostaticelectrolysis,the electropolymerization of m-toluidine on an indium-tin oxide(ITO)conductive glass electrode was studied in detail by in situ UV-Vis spectrometry.Itwas showed that m-toluidine could be electropolymerized on the ITO electrode onlyunder the condition of higher electrolysis potential and lager concentration of themonomer.At 0.2 mol·dm-3 of m-toluidine,0.7V(vs.saturated Ag/AgCl) and 20mmol·dm-3 of m-toluidine,0.9 V(vs.saturated Ag/AgCl),in situ UV-Visspectrometry indicated the polymerization did not happen whereas the low moleculeweight oligomer such as dimers could be produced on the ITO electrode.The obviousinduction period was observed when elctropolymerization of m-toluidine wasperformed in the 200 mmol·dm-3 m-toluidine at 0.8 V (vs.saturated Ag/AgCl).Furthermore,in situ UV-Vis spectra showed that the electrocopolymerizationbetween m-toluidine and p-phenylenediamine was performed.Thep-phenylenediamine might react with m-toluidine to yield more active intermediates,which not only promote polymerization but also accelerate polymerization.Inaddition,through that p-phenylenediamine could be incorporated into copolymer tomake the copolymer have a phenazine or phenazine like cyclic structure,which wasproved by the FTIR of polymers.