- Email: [email protected]
Synthesis and Characterization of Organically Soluble Polyaniline and Polyaniline Block Copolymers
ELSEVIER
Synthetic Metals 101 (1999) 758-76 1
Synthesis and Characterization of Organically Soluble PoIyaniline and Polyaniline Block Copolymers P. J. Kinien*, B. G. Frushour, Y. Ding and V. Menon Monsanto
Company,
St. Louis,
Missouri
63167
Abstract An emulsion process has been developed for the direct synthesis of the emeraldme salt of polyaniline (PANI) that is soluble in organic solvents. The process entails forming an emulsion composed of water, a water soluble organic solvent {e.g., 2-butoxyethanol), a water insoluble organic acid (e.g., dinonylnaphthalene sulfonic acid) and aniline. The resulting product is truly soluble in organic sohents such as xylene and toluene, of high molecular weight (Mw >22,000) and film forming. The emulsion polymerization process was also employed to synthesize ABA triblock polymers of polyaniline where the 3 block is a diamine terminated polymer and the A block is polyaniline. As casf PANI films were only moderately conductive (1 O-5 S/cm). However, PANI conductivity could be enhanced by up to five orders ofmagnitude by treatment of the films with surfactants or low molecular weight alcohols and ketones. Blends of PANI. and plasticizers such as toluenesulfonamide were found to exhibit conductivities up to 100 S/cm. X-ray diffraction studies of cast PAN1 films help to explain the conductivity enhancement by showing that surfactant and solvent treatments significantly increase the crystallinity and long range ordering of the polymer. Kep~ordr:
coupling reactions, X-my diffraction, stmctural phase transitions, polyaniline and derivatives.
1. Introduction Synthesis of polyaniline is commoniy performed by chemical oxidative polymerization in an aqueous solution (see e.g., Cao, et al. l), however the material synthesized by this approach is predominately amorphous, intractable and insoluble in most organic solvents2. Emulsion polymerization processes for preparing polyaniline salts have been reported374536, however the products of the above reactions were not isolatable directly, since the polyaniline salt remained entrained in the emulsion at completion of the reaction along with by-products of the reaction. This paper describes an emulsion polymerization process for polyaniiine which yields a soluble, conducting emeraldine salt directly without the need for a post-doping process step. The reaction is unique since the emulsion flocculates during the course of reaction to form a two phase system, the poIyaniline remaining as a soluble component in the organic phase. When employing diionylnaphthalene sulfonic acid (DNNSA) as the dopant organic acid the polyaniline produced has a high molecular weight (722,000), moderate conductivity (IO-5 S/cm), and exhibits high solubility in low dielectric constant solvents, When using diamine polymers as precursors, ABA triblock conductive polymers are formed where the 3 block is a diamine terminated polymer of choice (e.g. PPO or PEO) and the A block is polyaniline. Conductivity of thin films of the polymer was enhanced two to three orders of magnitude by treatment with quaternary ammonium salts or solvents such as methanol or acetone. Further enhancement in conductivity to 100-200 S/cm was obtained through addition of plasticizers to the film. TEM images show tie self-assembly of PANIDNNSA molecules into an interconnected network morphology for the polymer-quaternary salt treatment or plasticizer addition which appears to explain the observed conductivity enhancement. In the case of methanol or acetone treatment, conductivity increases due to removal of excess dopant, densification of the polymer and a resultant increase in Cl-ptdliity.
2. ExperimentalSection Polpner Synthesis Polyaniline Dinonylnaphthalene sulfonic acid was prepared as described previously.7 Copolymers were synthesized starting with diamine polymers of polyethyleneoxide (PEO), polypropylene oxide (PPO), polydimethylsiloxane (PODMSiOj and polyacryloninile-co-butadiene (PANBD) obtained from Aldrich and used as received. These polymers were added to the standard aniline-DNNSA emulsion7 prior to ammonium peroxydisulfate addition at mole ratios (starting polymer/aniline) ranging from 1120 to 6/I. Molecular weight distribution averages determined by size-exclusion chromatography (SEC)‘. UVMSMIR measurements were made on a Car-y 5E spectrophotometer. TEM experiments were carried out using a JEOL 2000FX instmment Conduefivity Measurements A 6 mil wet coating of PAN-DNNSA concentrate (ca 50% solids in xylene) was applied across a pattern of four gold contacts using a draw down blade. Resistance measurements between two adjacent gold contacts was taken using a Keithly Model 2001 Multimeter in the two point resistant mode.
Samples were prepared in film form and analyzed using a Scintag-Seifert PAD V diffractometer that produced a record of scattering intensity as a function of 28, where 8 is the Bragg angle. The spacing corresponding to any value of 0 was calculated from the Bragg equation, nh = 2dsin9, where h, the wave length of the Cu-K, x-nys, was equal to 1.54 Angstroms. 3. Resultsand Discussioo Emulsion Prowess The emulsion polymerization process utilizes a water soiuble organic solvent(Zbutoxyethanol) that facilitates the polymerization of poiyaniline salts of hydrophobic organic acids such as DNNSk When synthesizing copolymers, the diamlne terminated polymer is added to the emulsion prior to
0379~6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: .80379-6779(98)00280-X
PJ. Kinlen
et d. i Synthetic
addition of ammonium peroxydisulfate. Since the diamine polymer is more easily oxidized than aniline we believe the first step in the reaction is the formation of a short lived amine radical cation which nucleophilically attacks aniline at the para position. Subsequent polymerization then occurs through the terminal end groups of the growing block copolymer, as depicted in Figure 1. H2N-pEO-l\nl,
( Q@z%
I&N-PEO-N&f
Metals
101 (1999)
758-761
759
film isshownin Figure2, curve A. A strongpolaron absorptionat 720nm is observedwith a “free carriertail” commencing at ca. 1000nm. Similarspectrahavebeen observedfor PANI-camphorsulfonicacidexposedto mcresol.8After treatmentof the PANI-DNNSA filmsin 0.05or 0.5 M BTEAC solutionsat 22 or 58oC,conductivitieswere foundto increaseby 3 to 4 ordersof magnitude.Figure2, curveB, showsa decrease in the polaronabsorptionbandat 720nmwith a concomitantdecrease or “flattening”of the free carriertail absorption.
f
H2N-PEO-+MJL
I
-2P
4 Copolymer
-
H2N-PEO-N
H +NH2
Figure 1. Block CopolymerPolymerizationMechanism Molecular
Weight
The SECNISC chromatograms for deprotonatedpolyaniline saltsweretypically unimodalandnearlybaselineresolutionof the PANI andits sulfonicacidcomponentwasobserved. In generalthe polyanilinesaltstestedproducedbroadsize exclusionchromatograms, with Mw/Mn (polydispersity)21.5. Molecularweightsandpolydispersities of ABA block copolymersaresummarized in Table 1. Electrical
Conductivit#pectroscopy/X-ray
Diffraction
Filmsof PANI-DNNSA ca. 0.15 mmthick castfrom xylene solutionsanddriedat 700Cat lo-20 mmHg for 7 hours yieldedconductivitiesrangingfrom 6.5x10-6to 63 x10-6 S/cm.The WNisMear IR spectraof a driedPANI-DNNSA
Figure2. WNisibleMIR spectra of PANI-DNNSA tilms(curveA “ascast”film, curveB treatedwith0.5M BTEAC) Webelievethe BTEAC treatmentresultsin morphological changefrom discontinuous (PANI-DNNSA) conducting domainsto multipleconnectedpathwaysof PANT-DNNSAin anamorphous dopant(DNNSAIBTEAC) matrix9. As shown in Table2, PANI-DNNSA films treatedwith methanol,MEK, 2-propanolandethanolexhibitedincreases in conductivity up to 5 ordersof magnitude.
Table 1.MolecularWeightsof ABA Copolymers(Mole Ratioof DNNSA to aniline= 1.7) D&nine Polymer
Mw DiaminePolymer
Mole RatioDiaminePolymerto Aniline
Mw(PolystyreneEquivalent)
MwIMn
PEO
4,960
0.010
113,000
1.4
PEO
4,900
0.0050
126,000
1.5
PEO
4,900
0.025
112,400
1.5
PEO
4,900
0.10
91,600
1.6
PPO
4,000
0.12
73,600
1.9
PPO
400
1.2
46,100
2.1
PDMSiO
5,~
0.093
139,000
1.3
PDMSiO
w@J
0.47
117,000
1.5
PANBD
4,900
0.0063
30,700
2.9
P.J. Kinlen
760
et al. I Synthetic
Metals
10
20
30
40
50
758-761
degrees,Especiallynoteworthyis the appearance of a strong low-anglepeakat a 29valueof 4.9 degrees,which corresponds to a Braggspacingof 18Angstroms.The methanoltreatment significantlyincreases thecqstallinity. Peaksbeginto emerge from the amorphous scatteringpeak,while the low anglepeak hasshifteddownto a 20 valueof 3.35degrees,andthe corresponding spacinghasincreased from 18to 26 Angstroms. The diffraction patternof polyanilinesalthaspreviouslybeefi analyzed by Pougetet al.11, who assigned two strongpeaksto the (100) and(110)reflectionsin a pseudo-orthorhombic cell. The low anglepeakhasbeenobservedby Zhenget al,12in emeraldinebasedopedwith sulfonicacidswith long tails,such asdodecylbenzenesulfonicacid(DDBSA), and isattributed to the interlayerrepeat.Thepolymerformsa layeredstructure in whichthe alkyl tailsof the counterions,in this caseDDNSA, functionasspacers betweenparallelplanesor sheetsstackedby polymerbackbones.FollowingZhenget al., we haveusedthe Scherrerequationto calculatethe crystallitesizeof the methanolprecipitatedpolymerusingthe sharppeakat 4.9 degrees,andweobtaina valueof 110Angstroms.This compares favorablywith the resultsobtainedby the lattergroup usingDDBSA asthe dopantwith alkylatedPANI.
No effects were noted with water or heptane treatment. The rate at which resistance dropped was very rapid, and substantial increases in conductivity were observed with as little as 5 seconds contact with the solvent. During the treatment process, the coating underwent shrinkage and became insoluble in solvents like dichloromethane and xylene (these solvents readily dissolve dried PANI-DNNSA coatings as well as the BTEAC treated coatings discussed above). As in the case of the BTEAC treated film, the UVNisJNear IR spectra exhibits both a decrease in the polaron absorption and free carrier absorption after treatment with methanol.
0
101 (1999)
We alsoexaminedthe diffractionpatternbeforeand after soakinga film of the PANI-DNNSA in anaqueoussolutionof benzyltriethylammonium chloride(BTEAC). We observeda slightincrease in crystallinity asevidencedby an increasein the intensityof the reflectionat 26 degrees.
80
20 dqrm
Figure 3. X-ray diffractometerscansshowing the increasein crystallinity upongoing from the emeraldinebaseto the driedPAMDNNSA, and the latter after treatmentwith methanol.The Bragg spacingfor the prominentreflectionsare given in Angstroms (A).
of Phsth’zers m Conductivity/X-ray scattering Table3 showstheeffect of plasticizeron PANI-DNNSA conductivity. Thebestresultswereobtainedwith blendson PANI-DNNSA with 4,4’-dihydroxydiphenylsuifone whichgave a humidity independent conductivity of 30S/cm after heat treatmentat 1oOoC.W/VisJNear IR spectrashowformation of a strongfreecarrierabsorptionbandand total loss of the localizedpolaronband(Figure4). This heattreatmentaffects the low-angleX-ray scattering,ascanbeseenin Figure5, wherethe low-anglecurvesfor the PANI-DNNSA without plasticizeris compared to the plasticizedmaterial,beforeand afterthe heattreatment Thewide-angleregionisnot shownbecauseit is obscuredby the scattering,ofplasticizercrystallites.Two peaksare observedin theplasticizedmaterialwith Braggspacingsof 31 and24 Angstroms.Uponactivationthe two peakscoalesce Influence
Thex-ray diffractometerscansfor threepolyaniline-based materialsarecomparedin Figure 3. Includedarethe emeraldme basein powderform, a film of the solublePANIDNNSA castonto glassanddried in a vacuumoven for three daysat 40°C andthe latter film after immersionin methanol for severalminutesfollowedby vacuumdrying. The level of crystallinity andthedegreeof crystallineperfectiondiffer amongthesematerials.The emeraldine baseis essentially amorphous asindicatedby the singlebroadscatteringcentered at a 29 valueof 20 degrees,which corresponds to a Bragg spacingof approximateiy4.5 Angstroms.This is a typical scatteringpatternfor anamorphous polymer,andis described by AlexanderlO. The PANI-DNNSA film isslightly more crystallineasevidencedby the sharpening of the 4.5 Angstrom peakandthe appearance of a shoulderpeakat a 29 valueof 26 Table2. Effect of SolventTreatmenton PANI-DNNSA Conductivity Solvent
Conductivity Before Treatment
ImmersionTime(s)
4 1800 20
0.9
1x105 4x104
MEK
2.2x10-5 2.4x10-5 3.7x10-7
8.lxlO.3
2xl~4
2-propanol
3.4x10-7
20
2.4x10-2
7x104
Ethanol
4.8x10-7
20
2.4x10-2
5x104
m-cresol
4.5x10-5
60
2.9~10-3
6x101
Methanol
ConductivityAfter Immersion andking at8OW (S/cm) 2.3
Fold Increasein Conductivity
3
?‘_I. Kin/m
Table 3. Effects of Plasticizer on PANI-DNNSA
et al. / Synthetic
Merals
101
(1999)
758-761
761
Conductivity
Plasticizer/Aniline Mole ratio
As Cast Conductivity, Sicm (50% RI-I)
Dry Film Conductivity, S/cm (0% RI-I)
N-butylbenzenesulfonamide
0.75
2.5
5 x 10-3
N-ethyl o/p-toluenesulfonamide
0.81
IO
5 x IO-4
1.5
12
IO-2
o/p-toluenesulfonamide dioctylsulfosuccinic acid, sodium salt
1.9 0.18
100 4 x 10-z
100 5 x IO-4
4,4’-dihydroxydiphenylsulfone
0.645
30
30
Plasticizer
dodecylbenzenesulfonic acid
/ 0.6
x Cum
I -Cum8
A. Eefoce Heat Treabnert 8, After Heat Treabnerd
I / I
0.1 Oi
I
300
6w
1300
1800
2300
Wavolrngth,
2600
),
3300
nm
L Figure 4. WNisiblelNJR spectra of PANI-DNNSA film containing4: 4’-dihydroxydiphenylsulphone(curve A before heattreatmcnf curve B after heattreatmentat 1oO’C).
4. Summary A new emulsion process has been discovered for the direct synthesis of the emeraldine salt of polyaniline (PANI) that is soluble in organic solvents. As the reaction proceeds, the reaction mixture changes from an emulsion to a two phase system. the soluble PANI remaining in the organic phase. Thus, organically soluble polyaniline is formed directly. Using diamine terminated polymers as precursors, the emulsion process was also utilized to synthesize triblock copolymers of polyaniline. Thin films of PANI-DNNSA are readily cast from xylene and have relatively low conductivities due to low crystallinity and poor aggregation of conducting domains. Treatment of thin films of PANI-DNNSA with surfactants or low molecular weight alcohols and ketones significantly enhances the polymer conductivity by changing the morphology from predominately amorphous to highly ordered crystalline. 1.
YCao, A. Andreatta,A.J. Heegerand P. Smith,Polyner, 30,2305(1989).
2.
B.K. Annis, A.H. Nat-ten,A.G. MacDiarmid,andA.F. Richter,SynthericMetals, 22, 191(1986).
3.
Y. Cao andJ.-E. Osterholm,WO94/03528,1994.
4.
Y. Cao and J.-E. Osterholm, CIS.PatentNo. 5,324,453, 1994.
5.
J.-E. Osterholm,Y. Cao, F. Klavetter andP. Smith,Q&I. Mel.,55, 1034(1993).
6.
J.-E. Osterholm,et al., Polymer,35, 2902(1994).
7.
PJ. Kinlen, J. Liu, Y. Ding, CR. GrahamandE.E. Remsen,Macromolecules, 31, 1735 (1998).
8.
Y. Min, Y Xia, A. G. MacDiannid andA.J. Epstein,Synrh. Met.,69, 159(1995).
9.
J. Liu andP.J. Kinlen,Proceedings
I
4xc
“1
AA
I 2
3
4
5
5
7
28dqrus Figure 5. X-ray small-anglescatteringof plasticizedPANI-DNNSA before andafter thermalactivation(120-C for 10 minutes). into a single peak with a spacing of 25 Angstroms, but this peak is not nearly as sharp as the peak observed at 26 Angstroms in the methanol treated film PANI-DNNSA shown in Figure 3. We conclude that the heat activation does not induce a high degree of crystallinity, but there is some reorganization leading to an increase in conductivity.
a
1997 MRS Fail
Meeting.
10.
L.E. Alexander,X-ray Diffraction Methods Science,Wiley-Interscience, 1969,p.43.
11.
J.P.Pouget,et al. Macromolecules,21, 79 (1991).
12.
W-Y Zheng,et al., Polymer
28,412
in Po/ymer
(1996).
Synthetic Metals 101 (1999) 758-76 1
Synthesis and Characterization of Organically Soluble PoIyaniline and Polyaniline Block Copolymers P. J. Kinien*, B. G. Frushour, Y. Ding and V. Menon Monsanto
Company,
St. Louis,
Missouri
63167
Abstract An emulsion process has been developed for the direct synthesis of the emeraldme salt of polyaniline (PANI) that is soluble in organic solvents. The process entails forming an emulsion composed of water, a water soluble organic solvent {e.g., 2-butoxyethanol), a water insoluble organic acid (e.g., dinonylnaphthalene sulfonic acid) and aniline. The resulting product is truly soluble in organic sohents such as xylene and toluene, of high molecular weight (Mw >22,000) and film forming. The emulsion polymerization process was also employed to synthesize ABA triblock polymers of polyaniline where the 3 block is a diamine terminated polymer and the A block is polyaniline. As casf PANI films were only moderately conductive (1 O-5 S/cm). However, PANI conductivity could be enhanced by up to five orders ofmagnitude by treatment of the films with surfactants or low molecular weight alcohols and ketones. Blends of PANI. and plasticizers such as toluenesulfonamide were found to exhibit conductivities up to 100 S/cm. X-ray diffraction studies of cast PAN1 films help to explain the conductivity enhancement by showing that surfactant and solvent treatments significantly increase the crystallinity and long range ordering of the polymer. Kep~ordr:
coupling reactions, X-my diffraction, stmctural phase transitions, polyaniline and derivatives.
1. Introduction Synthesis of polyaniline is commoniy performed by chemical oxidative polymerization in an aqueous solution (see e.g., Cao, et al. l), however the material synthesized by this approach is predominately amorphous, intractable and insoluble in most organic solvents2. Emulsion polymerization processes for preparing polyaniline salts have been reported374536, however the products of the above reactions were not isolatable directly, since the polyaniline salt remained entrained in the emulsion at completion of the reaction along with by-products of the reaction. This paper describes an emulsion polymerization process for polyaniiine which yields a soluble, conducting emeraldine salt directly without the need for a post-doping process step. The reaction is unique since the emulsion flocculates during the course of reaction to form a two phase system, the poIyaniline remaining as a soluble component in the organic phase. When employing diionylnaphthalene sulfonic acid (DNNSA) as the dopant organic acid the polyaniline produced has a high molecular weight (722,000), moderate conductivity (IO-5 S/cm), and exhibits high solubility in low dielectric constant solvents, When using diamine polymers as precursors, ABA triblock conductive polymers are formed where the 3 block is a diamine terminated polymer of choice (e.g. PPO or PEO) and the A block is polyaniline. Conductivity of thin films of the polymer was enhanced two to three orders of magnitude by treatment with quaternary ammonium salts or solvents such as methanol or acetone. Further enhancement in conductivity to 100-200 S/cm was obtained through addition of plasticizers to the film. TEM images show tie self-assembly of PANIDNNSA molecules into an interconnected network morphology for the polymer-quaternary salt treatment or plasticizer addition which appears to explain the observed conductivity enhancement. In the case of methanol or acetone treatment, conductivity increases due to removal of excess dopant, densification of the polymer and a resultant increase in Cl-ptdliity.
2. ExperimentalSection Polpner Synthesis Polyaniline Dinonylnaphthalene sulfonic acid was prepared as described previously.7 Copolymers were synthesized starting with diamine polymers of polyethyleneoxide (PEO), polypropylene oxide (PPO), polydimethylsiloxane (PODMSiOj and polyacryloninile-co-butadiene (PANBD) obtained from Aldrich and used as received. These polymers were added to the standard aniline-DNNSA emulsion7 prior to ammonium peroxydisulfate addition at mole ratios (starting polymer/aniline) ranging from 1120 to 6/I. Molecular weight distribution averages determined by size-exclusion chromatography (SEC)‘. UVMSMIR measurements were made on a Car-y 5E spectrophotometer. TEM experiments were carried out using a JEOL 2000FX instmment Conduefivity Measurements A 6 mil wet coating of PAN-DNNSA concentrate (ca 50% solids in xylene) was applied across a pattern of four gold contacts using a draw down blade. Resistance measurements between two adjacent gold contacts was taken using a Keithly Model 2001 Multimeter in the two point resistant mode.
Samples were prepared in film form and analyzed using a Scintag-Seifert PAD V diffractometer that produced a record of scattering intensity as a function of 28, where 8 is the Bragg angle. The spacing corresponding to any value of 0 was calculated from the Bragg equation, nh = 2dsin9, where h, the wave length of the Cu-K, x-nys, was equal to 1.54 Angstroms. 3. Resultsand Discussioo Emulsion Prowess The emulsion polymerization process utilizes a water soiuble organic solvent(Zbutoxyethanol) that facilitates the polymerization of poiyaniline salts of hydrophobic organic acids such as DNNSk When synthesizing copolymers, the diamlne terminated polymer is added to the emulsion prior to
0379~6779/99/$ - see front matter 0 1999 Elsevier Science S.A. All rights reserved. PII: .80379-6779(98)00280-X
PJ. Kinlen
et d. i Synthetic
addition of ammonium peroxydisulfate. Since the diamine polymer is more easily oxidized than aniline we believe the first step in the reaction is the formation of a short lived amine radical cation which nucleophilically attacks aniline at the para position. Subsequent polymerization then occurs through the terminal end groups of the growing block copolymer, as depicted in Figure 1. H2N-pEO-l\nl,
( Q@z%
I&N-PEO-N&f
Metals
101 (1999)
758-761
759
film isshownin Figure2, curve A. A strongpolaron absorptionat 720nm is observedwith a “free carriertail” commencing at ca. 1000nm. Similarspectrahavebeen observedfor PANI-camphorsulfonicacidexposedto mcresol.8After treatmentof the PANI-DNNSA filmsin 0.05or 0.5 M BTEAC solutionsat 22 or 58oC,conductivitieswere foundto increaseby 3 to 4 ordersof magnitude.Figure2, curveB, showsa decrease in the polaronabsorptionbandat 720nmwith a concomitantdecrease or “flattening”of the free carriertail absorption.
f
H2N-PEO-+MJL
I
-2P
4 Copolymer
-
H2N-PEO-N
H +NH2
Figure 1. Block CopolymerPolymerizationMechanism Molecular
Weight
The SECNISC chromatograms for deprotonatedpolyaniline saltsweretypically unimodalandnearlybaselineresolutionof the PANI andits sulfonicacidcomponentwasobserved. In generalthe polyanilinesaltstestedproducedbroadsize exclusionchromatograms, with Mw/Mn (polydispersity)21.5. Molecularweightsandpolydispersities of ABA block copolymersaresummarized in Table 1. Electrical
Conductivit#pectroscopy/X-ray
Diffraction
Filmsof PANI-DNNSA ca. 0.15 mmthick castfrom xylene solutionsanddriedat 700Cat lo-20 mmHg for 7 hours yieldedconductivitiesrangingfrom 6.5x10-6to 63 x10-6 S/cm.The WNisMear IR spectraof a driedPANI-DNNSA
Figure2. WNisibleMIR spectra of PANI-DNNSA tilms(curveA “ascast”film, curveB treatedwith0.5M BTEAC) Webelievethe BTEAC treatmentresultsin morphological changefrom discontinuous (PANI-DNNSA) conducting domainsto multipleconnectedpathwaysof PANT-DNNSAin anamorphous dopant(DNNSAIBTEAC) matrix9. As shown in Table2, PANI-DNNSA films treatedwith methanol,MEK, 2-propanolandethanolexhibitedincreases in conductivity up to 5 ordersof magnitude.
Table 1.MolecularWeightsof ABA Copolymers(Mole Ratioof DNNSA to aniline= 1.7) D&nine Polymer
Mw DiaminePolymer
Mole RatioDiaminePolymerto Aniline
Mw(PolystyreneEquivalent)
MwIMn
PEO
4,960
0.010
113,000
1.4
PEO
4,900
0.0050
126,000
1.5
PEO
4,900
0.025
112,400
1.5
PEO
4,900
0.10
91,600
1.6
PPO
4,000
0.12
73,600
1.9
PPO
400
1.2
46,100
2.1
PDMSiO
5,~
0.093
139,000
1.3
PDMSiO
w@J
0.47
117,000
1.5
PANBD
4,900
0.0063
30,700
2.9
P.J. Kinlen
760
et al. I Synthetic
Metals
10
20
30
40
50
758-761
degrees,Especiallynoteworthyis the appearance of a strong low-anglepeakat a 29valueof 4.9 degrees,which corresponds to a Braggspacingof 18Angstroms.The methanoltreatment significantlyincreases thecqstallinity. Peaksbeginto emerge from the amorphous scatteringpeak,while the low anglepeak hasshifteddownto a 20 valueof 3.35degrees,andthe corresponding spacinghasincreased from 18to 26 Angstroms. The diffraction patternof polyanilinesalthaspreviouslybeefi analyzed by Pougetet al.11, who assigned two strongpeaksto the (100) and(110)reflectionsin a pseudo-orthorhombic cell. The low anglepeakhasbeenobservedby Zhenget al,12in emeraldinebasedopedwith sulfonicacidswith long tails,such asdodecylbenzenesulfonicacid(DDBSA), and isattributed to the interlayerrepeat.Thepolymerformsa layeredstructure in whichthe alkyl tailsof the counterions,in this caseDDNSA, functionasspacers betweenparallelplanesor sheetsstackedby polymerbackbones.FollowingZhenget al., we haveusedthe Scherrerequationto calculatethe crystallitesizeof the methanolprecipitatedpolymerusingthe sharppeakat 4.9 degrees,andweobtaina valueof 110Angstroms.This compares favorablywith the resultsobtainedby the lattergroup usingDDBSA asthe dopantwith alkylatedPANI.
No effects were noted with water or heptane treatment. The rate at which resistance dropped was very rapid, and substantial increases in conductivity were observed with as little as 5 seconds contact with the solvent. During the treatment process, the coating underwent shrinkage and became insoluble in solvents like dichloromethane and xylene (these solvents readily dissolve dried PANI-DNNSA coatings as well as the BTEAC treated coatings discussed above). As in the case of the BTEAC treated film, the UVNisJNear IR spectra exhibits both a decrease in the polaron absorption and free carrier absorption after treatment with methanol.
0
101 (1999)
We alsoexaminedthe diffractionpatternbeforeand after soakinga film of the PANI-DNNSA in anaqueoussolutionof benzyltriethylammonium chloride(BTEAC). We observeda slightincrease in crystallinity asevidencedby an increasein the intensityof the reflectionat 26 degrees.
80
20 dqrm
Figure 3. X-ray diffractometerscansshowing the increasein crystallinity upongoing from the emeraldinebaseto the driedPAMDNNSA, and the latter after treatmentwith methanol.The Bragg spacingfor the prominentreflectionsare given in Angstroms (A).
of Phsth’zers m Conductivity/X-ray scattering Table3 showstheeffect of plasticizeron PANI-DNNSA conductivity. Thebestresultswereobtainedwith blendson PANI-DNNSA with 4,4’-dihydroxydiphenylsuifone whichgave a humidity independent conductivity of 30S/cm after heat treatmentat 1oOoC.W/VisJNear IR spectrashowformation of a strongfreecarrierabsorptionbandand total loss of the localizedpolaronband(Figure4). This heattreatmentaffects the low-angleX-ray scattering,ascanbeseenin Figure5, wherethe low-anglecurvesfor the PANI-DNNSA without plasticizeris compared to the plasticizedmaterial,beforeand afterthe heattreatment Thewide-angleregionisnot shownbecauseit is obscuredby the scattering,ofplasticizercrystallites.Two peaksare observedin theplasticizedmaterialwith Braggspacingsof 31 and24 Angstroms.Uponactivationthe two peakscoalesce Influence
Thex-ray diffractometerscansfor threepolyaniline-based materialsarecomparedin Figure 3. Includedarethe emeraldme basein powderform, a film of the solublePANIDNNSA castonto glassanddried in a vacuumoven for three daysat 40°C andthe latter film after immersionin methanol for severalminutesfollowedby vacuumdrying. The level of crystallinity andthedegreeof crystallineperfectiondiffer amongthesematerials.The emeraldine baseis essentially amorphous asindicatedby the singlebroadscatteringcentered at a 29 valueof 20 degrees,which corresponds to a Bragg spacingof approximateiy4.5 Angstroms.This is a typical scatteringpatternfor anamorphous polymer,andis described by AlexanderlO. The PANI-DNNSA film isslightly more crystallineasevidencedby the sharpening of the 4.5 Angstrom peakandthe appearance of a shoulderpeakat a 29 valueof 26 Table2. Effect of SolventTreatmenton PANI-DNNSA Conductivity Solvent
Conductivity Before Treatment
ImmersionTime(s)
4 1800 20
0.9
1x105 4x104
MEK
2.2x10-5 2.4x10-5 3.7x10-7
8.lxlO.3
2xl~4
2-propanol
3.4x10-7
20
2.4x10-2
7x104
Ethanol
4.8x10-7
20
2.4x10-2
5x104
m-cresol
4.5x10-5
60
2.9~10-3
6x101
Methanol
ConductivityAfter Immersion andking at8OW (S/cm) 2.3
Fold Increasein Conductivity
3
?‘_I. Kin/m
Table 3. Effects of Plasticizer on PANI-DNNSA
et al. / Synthetic
Merals
101
(1999)
758-761
761
Conductivity
Plasticizer/Aniline Mole ratio
As Cast Conductivity, Sicm (50% RI-I)
Dry Film Conductivity, S/cm (0% RI-I)
N-butylbenzenesulfonamide
0.75
2.5
5 x 10-3
N-ethyl o/p-toluenesulfonamide
0.81
IO
5 x IO-4
1.5
12
IO-2
o/p-toluenesulfonamide dioctylsulfosuccinic acid, sodium salt
1.9 0.18
100 4 x 10-z
100 5 x IO-4
4,4’-dihydroxydiphenylsulfone
0.645
30
30
Plasticizer
dodecylbenzenesulfonic acid
/ 0.6
x Cum
I -Cum8
A. Eefoce Heat Treabnert 8, After Heat Treabnerd
I / I
0.1 Oi
I
300
6w
1300
1800
2300
Wavolrngth,
2600
),
3300
nm
L Figure 4. WNisiblelNJR spectra of PANI-DNNSA film containing4: 4’-dihydroxydiphenylsulphone(curve A before heattreatmcnf curve B after heattreatmentat 1oO’C).
4. Summary A new emulsion process has been discovered for the direct synthesis of the emeraldine salt of polyaniline (PANI) that is soluble in organic solvents. As the reaction proceeds, the reaction mixture changes from an emulsion to a two phase system. the soluble PANI remaining in the organic phase. Thus, organically soluble polyaniline is formed directly. Using diamine terminated polymers as precursors, the emulsion process was also utilized to synthesize triblock copolymers of polyaniline. Thin films of PANI-DNNSA are readily cast from xylene and have relatively low conductivities due to low crystallinity and poor aggregation of conducting domains. Treatment of thin films of PANI-DNNSA with surfactants or low molecular weight alcohols and ketones significantly enhances the polymer conductivity by changing the morphology from predominately amorphous to highly ordered crystalline. 1.
YCao, A. Andreatta,A.J. Heegerand P. Smith,Polyner, 30,2305(1989).
2.
B.K. Annis, A.H. Nat-ten,A.G. MacDiarmid,andA.F. Richter,SynthericMetals, 22, 191(1986).
3.
Y. Cao andJ.-E. Osterholm,WO94/03528,1994.
4.
Y. Cao and J.-E. Osterholm, CIS.PatentNo. 5,324,453, 1994.
5.
J.-E. Osterholm,Y. Cao, F. Klavetter andP. Smith,Q&I. Mel.,55, 1034(1993).
6.
J.-E. Osterholm,et al., Polymer,35, 2902(1994).
7.
PJ. Kinlen, J. Liu, Y. Ding, CR. GrahamandE.E. Remsen,Macromolecules, 31, 1735 (1998).
8.
Y. Min, Y Xia, A. G. MacDiannid andA.J. Epstein,Synrh. Met.,69, 159(1995).
9.
J. Liu andP.J. Kinlen,Proceedings
I
4xc
“1
AA
I 2
3
4
5
5
7
28dqrus Figure 5. X-ray small-anglescatteringof plasticizedPANI-DNNSA before andafter thermalactivation(120-C for 10 minutes). into a single peak with a spacing of 25 Angstroms, but this peak is not nearly as sharp as the peak observed at 26 Angstroms in the methanol treated film PANI-DNNSA shown in Figure 3. We conclude that the heat activation does not induce a high degree of crystallinity, but there is some reorganization leading to an increase in conductivity.
a
1997 MRS Fail
Meeting.
10.
L.E. Alexander,X-ray Diffraction Methods Science,Wiley-Interscience, 1969,p.43.
11.
J.P.Pouget,et al. Macromolecules,21, 79 (1991).
12.
W-Y Zheng,et al., Polymer
28,412
in Po/ymer
(1996).