Biomimetic Synthesis of Water-Soluble Conducting
Copolymers/Homopolymers of Pyrrole and
3,4-Ethylenedioxythiophene
山楂丸的功效
Ferdinando F.Bruno,*,†Stephen A.Fosy,†Subhalakshmi Nagarajan,‡
Ramaswamy Nagarajan,‡Jayant Kumar,‡and Lynne A.Samuelson†Nanotechnology Team,Natick Soldier Center,U.S.Army RDECOM,Natick,Massachutts01760,and Departments of Physics and Chemistry,Center for Advanced Materials,University of Massachutts
Lowell,Lowell,Massachutts01854
Received September6,2005;Revid Manuscript Received November15,2005
A novel biomimetic route for the synthesis of electrically conducting homopolymers/copolymers of pyrrole and 3,4-ethylenedioxythiophene(EDOT)in the prence of a polyelectrolyte,such as polystyrene sulfonate(SPS),is prented.A poly(ethylene glycol)-modified hematin(PEG-hematin)was ud to catalyze the homopolymerization of pyrrole and EDOT as well as copolymerization of EDOT and pyrrol
e in the prence of SPS to yield homopolymers of polypyrrole/SPS and PEDOT/SPS as well as a polypyrrole-co-poly(3,4-ethylenedioxythiophene)/ SPS complex.Spectroscopic characterization[UV-visible,Fourier transform infrared(FTIR),and X-ray photoelectron spectroscopy(XPS)],thermal analysis,(TGA),and electrical conductivity studies for the complexes indicated the prence of a stable and electrically conductive form of the polymers.Furthermore,the prence of SPS that rves as a charge-compensating dopant in this complex provides a unique combination of properties such as processability and water solubility.糖果简笔画
Introduction
The rising concern of hazardous chemical wastes has led to incread interest in exploring alternatives for the synthesis of electronic/photonic polymers.Oxidoreductas such as hor-radish peroxida(HRP),obtained from natural and renewable sources,have been known to catalyze the polymerization of aniline and phenol-bad monomers under benign conditions and in mixed solvent systems.1-3The mechanism for HRP-catalyzed polymerization requires the interaction of the heme-iron active group of the enzyme with the hydrogen peroxide, generating an oxidized heme-iron complex.4The oxidized heme-iron complex then reacts with the monomer,in a one-electron-transfer reaction,to yield a monomer radical and a modified iron-heme complex.The reaction of the monom
er radicals leads to the formation of the polymer.Nevertheless,to date this procedure,bad on“green chemistry”,could not be applied to polythiophenes or polypyrroles.5,6This is due to the higher oxidation potential of monomers such as3,4-ethylenedioxy-thiophene(EDOT)and pyrrole(PYR),compared to the catalyst HRP,thus proving to be inappropriate substrates for this enzymatic approach.The inactivity of HRP verely limits the prospects for the enzymatic synthesis of other conductive polymers such as polyethylenedioxythiophene(PEDOT),which exhibits important optical and electrical(antistatic/conductive) properties.Polymers bad on PYR,currently ud for organic batteries and display devices,6are also of great interest.A synthetic route,bad on green chemistry,for obtaining water-soluble electrically conducing polypyrrole(PPYR)or PEDOT has not been published.
Encouraged by a variety of reports bad on the potency and effectiveness of Fe2+catalysts,the u of cost-effective,“green”biomimetic catalysts,which would reproduce the action of enzymes while imparting greater stability and more versatility in an analogous ecofriendly mode,has been examined.The u of poly(ethylene glycol)-hematin(PEG-hematin)and Hematin, which rves as a catalytic center of redox enzymes such as catala,cytochrome c,etc.,was also investigated.Previous efforts describe the u of different forms of hematin for catalysis in aqueous c
onditions.However,the catalytic activity was obrved to be much lower than that reported for HRP.7-9 Moreover,Akkara10has reported the synthesis of polyaromatic compounds catalyzed by hematin in mixed solvent systems or in buffered systems under basic pH conditions.Also previously reported was the u of the chemically modified hematin,PEG-hematin,as a“syn-enzyme”to catalyze the synthesis of con-ducting polyaniline in the prence of polyelectrolytic tem-plates.11This synthetic enzyme has proved to be very appealing after being applied for the synthesis of polystyrene.12 Furthermore,a unique template-assisted approach for the synthesis of water-soluble polymers has been reported for the enzymatic polymerization of aniline and phenol with HRP as the catalyst in the prence of an anionic polyelectrolyte.13 Polyelectrolytes,such as SPS,performs veral functions in the systems.In the ca of anilines,the polyelectrolye enables the electrostatic alignment of the monomer to promote a para-directed coupling,providing counterions for charge compensa-tion in the doping process.The polyelectrolye also complexes with the polymer to maintain water solubility.The templates have been reported to rve as nanoreactors for the one-pot enzymatic synthesis of conducting polyanilines.14
In this paper a novel synthesis of water-soluble PEDOT, PPYR,and PEDOT-co-PPYR using PEGlyated hematin(PEG-hematin)as an effective catalyst in the prence of SPS as a template is re
ported.UV-visible,Fourier transform infrared (FTIR),and X-ray photoelectron spectroscopy(XPS),thermal
†U.S.Army RDECOM.
‡University of Massachutts Lowell.
586Biomacromolecules2006,7,586-589
10.1021/bm0506501CCC:$33.50©2006American Chemical Society
Published on Web12/20/2005
gravimetric analysis(TGA),and electrical conductivity studies were carried out to characterize the polymers.To our knowledge this is the first report of a green chemistry approach for the synthesis of PEDOT,PPYR,and PEDOT-co-PPYR.Further-more,the water-soluble copolymers showed an unusually high electrical conductivity in the range of0.1-1.0S/cm.This counterintuitive result indicates a possible synergic interaction between the two monomers.
Experimental Section
土槿皮的功效与作用
Hematin was purchad from Sigma Chemical Co.(St.Louis,MO). Pyrrole(PYR,purity99.5%),3,4-ethylenedioxythiophene(EDOT) monomer(purity99.5%),polystyrene sulfonate(SPS),and hydrogen peroxide(30%)were purchad from Aldrich Chemicals Inc.,Mil-waukee,WI,and were ud as received.All other chemicals were purchad from Aldrich and were of reagent grade or better.The esterification,yielding PEG-hematin,was carried out according a procedure published earlier.15
The polymerization and the copolymerization of PYR and/or EDOT, in the prence of SPS,was catalyzed by PEG-hematin at25°C with hydrogen peroxide under ambient conditions.SPS(36.8mg)was dissolved in deionized water(10mL)at pH1.0for the polymerization of EDOT(18mM)and at pH2.0for the polymerization of PYR(18 mM).A similar procedure was ud for the copolymerization of EDOT/ PYR(SPS/EDOT/PYR molar ratio1:1:1)in the prence of SPS at pH1.This was followed by the addition of5mg of PEG-hematin to this solution.The polymerization/copolymerization was initiated by the addition of veral aliquots of800µL of0.03%hydrogen peroxide added in small increments.The reactants were stirred for8h to complete the polymerization,followed by dialysis with Centricon concentrators (10000cutoff;Amicon Inc.,Beverly,MA).The samples were then dried under vacuum at60°C and ud for further analysis.The gravimetric yield was typically95%.
All UV-vis spectra were obtained on a Perkin-Elmer Lambda9 UV-vis-near-IR spectrophotometer.The FTIR measurements were carried out on films cast on a ZnSe disk by u of a Perkin-Elmer FTIR spectrophotometer.Thermal gravimetric analysis(TGA)was conducted on a TA instrument2950(New Castle,DE).TGA was carried out in a nitrogen atmosphere,and a heating rate of10°C/min was ud.To characterize the homo/copolymers catalyzed by the PEG-hematin,ESCA(electron spectroscopy chemical analysis)or X-ray photoelectron spectroscopy(XPS)was performed in a VG Escalab II with Al K R.Solid samples,after dialysis,were compresd in a disk and pasted on a sample holder.The copolymer does not charge during excitation since the C-C line appeared at285eV.The copolymer was highly conductive and maintained the C-C(cis)line at a binding energy of285eV.
创业的要素Molecular weights of PEDOT-co-PPYR were assd by matrix-assisted lar desorption ionization time-of-flight(MALDI-TOF)mass spectrometry(Waters MALDI-Micro MX MALDI-TOF)with dithranol as the matrix.
Conductivity measurements were performed on pellets by u of a standard linear four-point probe with a Keithley619electrometer/
multimeter.
Results and Discussion
The polymerization reaction of EDOT with PEG-hematin was monitored spectroscopically in an aqueous solution at pH1.0, and the spectral changes are reported in Figure1.As en in the figure,the monomer did not show significant absorption above300nm.However,initiation of polymerization by the addition of H2O2led to the appearance of absorption from600 to1200nm.This was also accompanied by the development of a dark blue color,with a simultaneous increa in the absorption intensity of the peaks over time.The broad band at700nm, with a large absorption tail around1200nm,was attributed to theπ-π*transition in the polymer chain.
The FTIR spectrum(Figure2)of the polymer showed absorptions at1342,1218,and976cm-1,all assigned to doping interactions of SPS.15The most significant feature,however, was the abnce of bands at the range of1600-1800cm-1, indicating that no overoxidation or ring opening had occurred. PEDOT is stable over a fairly high range of temperatures as en in Figure3.Significant degradation is obrved at110 and at250°C.The initial decrea in weight percent is due to evaporation of bound water.
Figure 1.UV-Vis spectra of monomers EDOT and PYR and polymers PEDOT,PPYR,and PEDOT-co-PPYR.
Figure2.FTIR spectra of(A)monomer EDOT and polymer PEDOT in the prence of SPS,(B)monomer PYR and polymer PPYR in the prence of SPS,and(C)PEDOT-co-PPYR.
Conducting Copolymers/Homopolymers of Pyrrole/EDOT Biomacromolecules,Vol.7,No.2,2006
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The electrical conductivity data for the PEDOT (1×10-3S/cm)is similar to the measured conductivity of the commercial PEDOT (Baytron).
The UV -vis spectrum of the water-soluble SPS/PPYR is also shown in Figure 1.The peak at 420nm is assigned to an electron transition from the valence band state to an antibonding bipolaron state.The high absorption (900nm and above)is related to an electron transition,to the valence band to the bonding bipolaron state.Moreover,conjugation was also confirmed by the FTIR spectrum of the polymer (Figure 2),wherein the peaks at 1480/1540cm -1are assigned to the symmetric and antisymmetric ring stretching modes,respec-tively.16
Similar to PEDOT,PPYR shows good thermal stability.The polymer exhibits two degradation temperatures.The first is due to bound water (115°C)and the cond is assigned to polymer degradation (273°C).Conductivity for the PYR polymerized with PEG-hematin was measured with a four-point probe and found to be 1×10-4S/cm.The low conductiv-ity for this polymer is not a surpri.It is known that electrochemical polymerization,in water,of PYR yields a polymer with poor electrical conductivity.16This is attributed to the formation of oxidized nonconjugated forms of PPYR
that significantly lower the conductivity of the polymer.14Neverthe-less,this is the first water-soluble PPYR synthesized via syn-enzyme.
手抄报元宵In addition,copolymerization of EDOT and PYR was also carried out with PEG-hematin.The UV -vis spectrum (Figure 1)of this copolymer showed a large absorbance in the 400-900nm range.Moreover,the conductivity of the copolymer was higher than that of the solitary homopolymers and was found to be in the range of 0.1-1.0S/cm.This unusual result generated an incread interest in a thorough analysis of this copolymer.The FTIR spectrum of the copolymer (Figure 2)shows two important peaks.The first,centered at 3894cm -1,is due to intramolecular H-bonding,and a broad peak (1384-1790cm -1)is due to extended conjugation in the polymer backbone.
Thermal gravimetric analysis shows remarkable thermal stability.This counterintuitive result can be explained only by a synergic interaction of the two different monomers.MALDI-TOF mass spectrometry shows a prominent peak at an m /z value of 3120.84g/mol.
Furthermore,ESCA studies were conducted on all polymers to further characterize this unique copolymer.It is evident from Figure 4that the copolymer is not a mix of the two homopoly-mers.The binding energies for S 1s (163.5and 167.5eV)are different from the binding energies reported for PEDOT (164.4
and 169.0eV)and PPYR (168.4eV).Similarly,the largest intensity peak for N 1s orbital for the PPYR is 399.7eV.In contrast,the copolymer has a peak at 398.0eV.
The propod structure is reported in Figure 5.This structure will justify the high conductivity due to planarity of the final copolymer.Furthermore,the significant thermal stability can be attributed to the intramolecular hydrogen-bonding absorption obrved in the FTIR that can ari only when PYR is adjacent to EDOT in the copolymer.Additionally,ESCA does not show prence of a block copolymer.Finally,modeling calculations show the lowest energies and a planar structure for the alternating copolymer.17This evidence does not eliminate the
Figure 3.TGA of the different monomers and polymers.
Figure 4.ESCA of N 1s orbital and S 2p orbital for PEDOT,PPYR,PEDOT-co -PPYR,and a mix of the two homopolymers.
Figure 5.Propod structure for the copolymer.
588Biomacromolecules,Vol.7,No.2,2006Bruno et
al.
possibility of a statistical copolymer but is strongly suggestive that any blocks of PYR or EDOT are very short.
Conclusions
In summary,a novel biomimetic method for the synthesis of conducting molecular complexes of polypyrrole and of PEDOT in the prence of a polyelectrolyte,such as polystyrene sulfonate(SPS)is prented.A poly(ethylene glycol)-modified hematin(PEG-hematin)was ud to catalyze the polymerization. UV-vis,FTIR,XPS,TGA,and electrical conductivity studies for all complexes indicate the formation of the electrically conductive form of the polymers.Copolymers of EDOT and pyrrole have also been synthesized and the novel materials have been shown to exhibit high electrical conductivity,with a unique combination of properties such as processability and water solubility.
Acknowledgment.We acknowledge Daniel Oblas and Dr. Julie Snook for their help in XPS measurements. References and Notes
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