ISSN 15600904, Polymer Science, Ser. B, 2011, Vol. 53, Nos. 11–12, pp. 586–594. © Pleiades Publishing, Ltd., 2011.
FUNCTIONAL POLYMERS
Electrochemical and Chemical Synthesis of Nanostructure Copoly(AnilineoAnisidineoToluidine) and Study of Its Electrochemical Behavior in Organic Sulfonic Acid Media1 Bakhshali Massoumia, Fatemeh Ghashangpour Peivastia, Mahnaz Saraeia, and Ali Akbar Entezamib b
a Department of Chemistry, Payame Noor University, Tabriz, Iran Department of Organic Chemistry, Faculty of Chemistry, University of Tabriz, Tabriz, Iran email:
[email protected]
Received January 22, 2011; Revised Manuscript Received June 18, 2011
Abstract—Terpolymerization of aniline, oanisidine and otoluidine was carried out by electrochemical and interfacial chemical polymerization. All homopolymers and terpolymer thin films have been synthesized through electropolymerization at room temperature in aqueous solutions containing 0.5 M of organic sul fonic acid, such as ptoluene sulfonic acid, methane sulfonic acid, sulfosalicylic acid, dodecylbenzene sul fonic acid, and 0.1 M of aniline, oanisidine and otoluidine monomers, using cyclic voltammetry method, applying a sequential linear potential scan at a rate of 25 mV s–1 between –0.1 and 0.9 V. The electrochemical terpolymerization has been performed at various mole ratios of monomers. Nanoparticles obtained from conjugation of homo and terpolymer with organic sulfonic acids, were prepared by a chemical oxidation via interfacial chemical polymerization. SEM micrographs, FTIR spectra and conductivity measurements using fourprobe method were applied for the characterization of the products. Terpolymer was characterized by higher conductivity than polyotoluidine and lesser than polyaniline and polyoanisidine. The solubility of terpolymers was dependent on the monomers mole ratio. DOI: 10.1134/S1560090411110054 1
INTRODUCTION
A large amount of researches have been carried out in the field of conducting polymers since 1975 when the conjugated polymer – polyacetylene was discov ered to conduct electricity through a halogen doping [1–3]. The 2000 Nobel Prize in Chemistry recognized the discovery of conducting polymers passing 25 years of progress in the field [4, 5]. In recent years, there has been a growing interest in research on conducting polymer nanostructures (i.e., nanorods, tubes, wires, and fibers) since they combine the advantages of organic conductors with lowdimensional systems and therefore create interesting physicochemical properties and potentially useful applications [6–11]. Traditionally, an outstanding advantage of polymeric materials is that they could be synthesized and pro cessed on a large scale at relatively low cost. Conduct ing polymers could be prepared by chemical and/or electrochemical polymerization. Although the chemi cal method offers a mass production at a reasonable 1 The article is published in the original.
cost, the electrochemical method involves the direct formation of conducting thin films of polymer with better control of thickness and morphology, which is suitable for applying in electronic device such as or ganic LEDs. Although it is established that the con ducting properties of the polymer films depend greatly on the method of synthesis and also on the number of parameters such as type of counterion, type and pH of electrolyte, synthesis temperature [12, 13]. The studies on the preparation and characterization of the conducting polymers are still continuing. Thus, in or der to improve conducting properties of polymer films tailored for a desired application, it is necessary to control and optimize the various synthesis parameters, critically. Electrochemical and chemical syntheses of co polymers are the most convenient methods to pre pare a new conducting material with desired proper ties different from individual homopolymers. Syn thesis of polyaniline and its derivatives thin films with excellent electrical properties, coupled with good en vironmental stability, boosted the research to tailor
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physical and chemical properties of different con ducting polymers suitable for particular applications [14]. Wei and coworkers have been prepared various copolymers of aniline [15, 16]. They have shown that aniline could be copolymerized with otoluidine in such a way that the conductivity could be controlled in a broad range. A successful copolymerization of aniline with Nmethylaniline [17], 3aminophenyl boric acid [18] and terpolymerization of aniline with oanisidine and otoluidine [19] have also been re ported. Borol and coworkers have reported terpoly mer electrosynthesis of aniline, oanisidine and otoluidine using platinum substrate as working elec trode with good conductivity [20]. The optical and electrical properties of the soluble terpolymers of pyrrole, thiophene and 3decylthiophene have also been studied [21]. In present communication, we report about terpo lymerization of aniline, oanisidine and otoluidine via cyclic voltammetry and characterization of elec trodeposited thin films in three molar ratios of mono mers on the glassycarbon as working electrode. Nanostructured terpolymers have been also synthe sized by an interfacial chemical polymerization proce dure in aqueous medium using ptoluene sulfonic ac id, sulfosalicylic acid and methane sulfonic acid as electrolytes. We have compared the conductivity and solubility of obtained terpolymer with homo polymers. EXPERIMENTAL Materials The monomers, aniline (ANI), oanisidine (OA), and otoluidine (OT), were all purchased from Fluka and were distilled under a reduced pressure before use. Ptoluene sulfonic acid (PTSA), methane sulfonic acid (MSA), sulfosalicylic acid (SSA), dodecylben zene sulfonic acid (DBSA), ammonium persulfate (APS) and chloroform were obtained from Merck, and were used as received without further treatment. Electrochemical Deposition of Poly (ANIcoOAcoOT) Films The thin films of polyaniline (PANI), poly(oanisi dine) (POA), poly(otoluidine) (POT) and the ter polymer were synthesized electrochemically on a 0.07 cm2 glassy carbon working electrode using cyclic voltammetry in a simple onecompartment three elec trode glass cell. A platinum rode was used as counter and an Ag/AgCl electrode as reference electrodes. The films were electropolymerized in a solution containing 0.1 M monomers and 0.5 M supporting electrolyte by applying a sequential linear potential scan at a rate of 25 mV s–1 between –0.1 and 0.9 V. The homopolymer and terpolymer films were deposited after 30 consecu tive cycles for the polymerization in all supporting POLYMER SCIENCE
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electrolytes and their voltammograms were recorded. Throughout the studies anaerobic conditions were maintained with nitrogen gas purging. The mole ratios of ANI : OA : OT in monomer mixtures were 1.0 : 0.5 : 1.5, 1.0 : 1.0 : 1.0 and 0.5 : 1.5 : 1.0, respectively. Preparation of Nanostructured Terpolymer by Interfacial Chemical Polymerization Standard synthetic process of interfacial chemical polymerization for the preparation of PANI, POA, POT and a nanostructured terpolymer was as follows. In a 500 ml beaker, 0.1 mol of each monomer or monomer mixture with mole ratios of 1.0 : 0.5 : 1.5 ANI : OA : OT were dissolved in 100 ml of chloroform. In another beaker 0.025 mol APS was dissolved in 100 ml of supporting electrolyte (PTSA, MSA and SSA) (0.5 M), to form aqueous solution. The aqueous solution was gently added to the organic solution. The resulting twophase system was left undisturbed at 5°C for 24 h. The precipitated polymer was filtered and washed first with water, then with methanol to remove oligomers until the filtrate became colorless. When most of the product precipitated out, black powder was obtained. Black powder was dried in a vacuum ov en at 60°C for 48 h. They were labeled as PANI, POA, POT and terpolymer. Characterization of Polymer Structure The FTIR spectra of the samples were recorded by Bruker Tensor 27 Fourier Infrared spectrophotometer (FTIR) using KBr pellet technique. The conductivity was measured by fourprobe technique (Suzho Baish en SZ 82), for which the polymer pellets were obtained applying a pressure of 100 kPa. Before measurements, the pellets were dried in a vacuum oven at 50°C during 8 h. The morphologies of the nanoparticles were in vestigated by a field emission gun scanning electron microscopy LE440I. To prepare a specimen, a drop of the nanoparticle suspension was placed on a graphite surface and dried by lyophilization. After drying, the sample was coated with platinum/palladium using an Ion Sputter (12–15 mA for 80 s). Finally, the observa tion was performed at 5 kV. The UVvis spectra of the samples were recorded by UV1601PC spectropho tometer Shimadzu. RESULTS AND DISCUSSION In this research, we have prepared homo and ter polymers through electrochemical and interfacial chemical polymerization in organic sulfonic acids. 2011
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BAKHSHALI MASSOUMI et al. I, mA 3
(a)
2 1 0 −1 −2 −0.25 I, mA 2
0
0.25
0.50
0.75
1.00 E, V
I, mA 0.05
(b)
1
(c)
0.01
0
−0.01
−1 −0.25
0
0.25
0.50
0.75
1.00 E, V
−0.05 −0.25
0
0.25
0.50
0.75
1.00 E, V
Fig. 1. Cyclic voltammograms recorded during the synthesis of (a) PANI, (b) POA and (c) POT films in aqueous solution of PTSA at 25 mV s–1 scan rate.
The morphology, conductivity and solubility of ter polymer NH2
NH2 +
–e–
NH2 OMe +
CH3
H N
H N
OMe
CH3
(1) The electrochemical polymerization character istics of these monomers in different supporting elec trolytes on the glassycarbon electrode are almost the same during the first positive cycle. (2) In the presence of the supporting electrolytes 2–3 peaks are observed in repetitive cycling. The redox potentials and current densities corresponding to these peaks for different supporting electrolytes are summarized in Table 1.
H N
(3) The cyclic voltammogram curve peaks grew with the number of cycles for all supporting electro lytes, indicating the formation of conducting polymer films in each case.
n
have been investigated. Cyclic Voltammetric Study of Terpolymers Figures 1(a–c), 2(a–d), 3(a–d) and 4(a–d) show the cyclic voltammograms recorded continuously dur ing polymerization of individual monomers and their ternary mixture with different ratios in aqueous solu tions and in the presence of various organic sulfonic acids at room temperature. Overall conclusions based on analysis of cyclic voltammograms obtained are as follows:
(4) Three redox peaks were observed for the po lymerization of aniline in pTSA, SSA, MSA and DBSA. Three redox peaks were observed in the case of oanisidine polymerization in MSA, two peaks in PTSA, SSA and DBSA. Three peaks were ob served for the polymerization of otoluidine in DBSA, while there were two peaks in PTSA, SSA and MSA. Similarly, three redox peaks were observed in the case of terpolymerization in MSA, SSA and PTSA, while there were two redox peaks in DBSA. Different redox
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I, mA
(a)
0.10
0.03
0.05
0.02
0
0.01
−0.05
0
−0.10 −0.25
0.25 0.50 0.75 1.00
0
(c)
−0.01 −0.25
(b)
0.25 0.50 0.75 1.00
0
(d)
0.10
0.014
589
0.07
0.009
0.05
0.004
0.02 0
0 −0.25
0
0.25 0.50 0.75 1.00 E, V
−0.02 −0.25
0
0.25 0.50 0.75 1.00 E, V
Fig. 2. Cyclic voltammograms recorded during the synthesis of PANIcoPOAcoPOT films in ratios 1.0 : 0.5 : 1.5 in aqueous solutions of (a) PTSA, (b) SSA, (c) MSA and (d) DBSA at 25 mV s–1 scan rate.
I, mA 0.4
I, mA (a)
(b) 0.03
0.2 0.02 0
0.01
−0.2 −0.4 −0.25
0
0
0.25
0.50
0.75
1.00
(c)
−0.01 −0.25
0
0.25
0.50
0.75
1.00
0.75
1.00
(d)
0.10
0.04 0.05 0.02
0
0 −0.02 −0.25
−0.05
0
0.25
0.50 E, V
0.75
1.00
−0.10 −0.25
0
0.25
0.50 E, V
Fig. 3. Cyclic voltammograms recorded during the synthesis of PANIcoPOAcoPOT films in ratio 1.0 : 1.0 : 1.0 in aqueous solutions of (a) PTSA, (b) SSA, (c) MSA and (d) DBSA at 25 mV s–1 scan rate. POLYMER SCIENCE
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BAKHSHALI MASSOUMI et al. I, mA 1.0
I, mA (a)
(b) 0.04
0.5
0.02
0
0
−0.5
−0.02
−0.25
0
0.25
0.50
0.75
−0.25
1.00
0
0.25
(c) 0.12
0.04
0.02
0
−0.07 0
0.25
0.75
1.00
0.75
1.00
(d)
0.09
−0.25
0.50
0.50 E, V
0.75
−0.25
1.00
0
0.25
0.50 E, V
Fig. 4. Cyclic voltammograms recorded during the synthesis of PANIcoPOAcoPOT films in ratio 0.5 : 1.5 : 1.0 in aqueous solutions of (a) PTSA, (b) SSA, (c) MSA and (d) DBSA at 25 mV s–1 scan rate.
peaks were obtained for PANI, POA, POT and ter polymer in various sulfonic acids. This indicates that the electrochemical behavior of PANI, POA, POT and PANIcoPOAcoPOT depends on the electro
lytic medium, i.e., the size and type of the anion present [22]. (5) The cyclic voltammogram clearly revealed the formation of electroactive polymer films in all sup
Table 1. Redox potentials of PANI, POAM, POT and PANIcoPOMAcoPOT(1 : 0.5 : 1.5) films in various supporting electrolytes Redox potential (mV) No.
Supporting electrolyte
PANI A
POA
POT
PANIcoPOAcoPOT
B
C
A
B
C
A
B
C
A
B
C
1
pToluene sulfonic acid (PTSA) 315
569
869
328
–
536
323
–
595
245
455
642
2
Sulfosalicylic acid (SSA)
172
481
738
185
434
–
240
–
603
222
411
–
3
Methane sulfonic acid (MSA)
178
468
766
250
450
585
274
–
591
263
407
673
4
Dodecylbenzene sulfonic acid (DBSA)
271
515
735
206
429
–
224
416
620
213
379
598
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UVvis Spectroscopy
Absorbance 2.5
The peak values of optical absorption spectra of PANI, POA, POT and PANIcoPOAcoPOT pre pared by chemical oxidation in presence of support ing electrolyte, PTSA, MSA and SSA under identi cal experimental conditions were summarized in Ta ble 2 and the spectrum of terpolymer was depicted in Fig. 5. The UVvis spectra were obtained in DMSO and peaks appearing at about 817–890 nm with a shoulder at 416–433 nm which were related to the emeraldine salt (ES) phase of PANI, POA, POT and terpolymer in organic sulfonic acid. According to the UVvis spectra (Fig. 5), it may be concluded that all three organic acids have similar effect on the proper ties of terpolymer. The difference in the electronic spectra may also be attributed to a fewer quinoneimine moieties in the polymer synthesized in the presence of organic sulfon ic acid [24]. From Table 2, it could be seen that an av erage absorption for the polymerized products ob tained using the monomers indicates the formation of terpolymer, i.e., absorption peaks for (ANIOAOT) terpolymer are different from individual polymers PANI, POA and POT.
2.0
1.5
a b
1.0 c 0.5 0 300
400
591
600
800
1000 1100 Wavelength, nm
Fig. 5. Optical absorption spectra of PANIcoPOAco POT films in ratio 1.0 : 0.5 : 1.5 synthesized under chemi cal oxidation conditions by interfacial chemical polymer ization (a) SSA, (b) PTSA and (c) MSA.
porting electrolytes. The anodic peak A can be as signed to the oxidation of polymer deposited on the electrode surface, which corresponds to the conver sion of amine units to radical cations [20]. Peak C is assigned to radical cationquinoid transition (emeral dinepernigraniline). Peak B in the cyclic voltammo grams is due to the absorption of quinone/hydro quinone, generated during the growth of polymer film which is strongly absorbed in the polymer matrix [23]. The appearance and intensity of peak B is highly de pendent on the electrolytic medium. The cyclic volta mmogram of the terpolymer differs from that of an in dividual homopolymer, which clearly supports the for mation of a terpolymer.
Conductivity Measurements The conductivity of PANI, POA, POT and PANI coPOAcoPOT films prepared in a solution contain ing 0.5 M SSA was equal to 1.732, 0.526, 0.072 and 0.120 S cm–1, respectively. However, the conductivity of these films prepared in the presence of MSA was 0.397, 0.093, 0.035 and 0.048 S cm–1, respectively. The conductivity of the films prepared in a solution con taining PTSA and MSA is observed to be lower than those prepared in SSA. The electrical conductivity of these films is shown in Table 2.
Table 2. Influence of organic supporting electrolytes on electrical conductivity and UV/Vis spectra for PANI, POA, POT and PANIcoPOAcoPOT (1 : 0.5 : 1.5) films Electrical conductivity (S/cm) Support No. ing elec trolyte PANI POA
UV/Vis spectroscopy (nm) PANI
POT
POA
POT
PANIco POAcoPOT Peak
Shoul Shoul Peak Peak der der
PANIcoPOA coPOT
Shoul Shoul Peak der der
1
(PTSA)
1.475 0.432 0.069
0.104
884
429
854
424
826
418
829
423.5
2
(SSA)
1.732 0.526 0.072
0.120
890
433
836
427.5
825
425
833
425
3
(MSA)
0.397 0.093 0.035
0.048
882
427
827
422
817
416
833.5
420
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BAKHSHALI MASSOUMI et al. Transmittance, % 120 80 40
(a)
0 4000
3500
3000
2500
2000
1500
1000
500
3500
3000
2500
2000
1500
1000
500
3500
3000
2500
2000
1500
1000
500
3500
3000
1500
1000
500
120 80 40 (b) 0 4000 120 80 40
(c)
0 4000 120 40 (d) 0 4000
2500 2000 Wavenumber, cm−1
Fig. 6. FTIR spectra of (a) POA, (b) PANI, (c) POT and (d) PANIcoPOAcoPOT in SSA.
FTIR Spectra The IR band positions of PANI, POA, POT and PANIcoPOAcoPOT films prepared with chemi cal oxidation conditions (interfacial chemical poly merization) in the presence of SSA as electrolyte
were shown in Fig. 6. The main FTIR characteristic bands are: 1494–1585 cm–1 (benzenoid–quinoid), 1295–1300 cm–1 (C–N stretching), 1106– 1121 cm–1 and 1142–1204 cm–1 (C–H bending), 797–800 cm–1 (C ⎯ H outof plane), 1020 cm–1
Table 3. Solubility of homo and terpolymers in commune solvent No. 1 2 3 4 5 6 7 8 9 10 11
Solvent NMP (Nmethyl2pyrrolidone) DMSO (Dimethyl sulfoxide) DMF (N,Ndimethylformamide) THF (Tetrahydrofuran) H2O Dichloromethane Toluene Chloroform CH3COOH Acetonitrile Acetone
PANI
POA
POT
PANIcoPOAcoPOT
++ ++ + – – – – – – – –
+++ +++ ++ ++ – ++ – ++ + + +
+++ +++ ++ ++ – + + ++ – + ++
+++ +++ +++ ++ – ++ + ++ + + ++
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300 nm (b)
(a)
200 nm (c)
593
300 nm
Fig. 7. Optical microscopy photographs of PANIcoPOAcoPOT in (a) SSA, (b) MSA, (c) PTSA.
(alkyl C–O stretching), 3200–3350 cm–1 (single N–H stretching vibration), 1375–1380 cm–1 ( ⎯ CH3 group bending) [25]. Solubility The solubility of the prepared by interfacial chem ical polymerization powdery PANI, POA, POT and terpolymer was tested in some solvents (0.01 g of ter polymer or homopolymer in 3 ml solvent) as shown in Table 3.
showed that the best ratio of monomers among studied ratios in the formation of terpolymers was ANI : OA : OT = 1.0 : 0.5 : 1.5 in PTSA, SSA, MSA and DBSA. The nanostructured terpolymers were prepared by an interfacial chemical polymerization. In general, the electrical conductivity depends on the mole ratio of monomers and also on the organic sulfonic acid spe cies. Conductivity measurements showed that higher conductivity is observed for SSA followed by PTSA and then MSA. The solubility of terpolymer depends on the mole ratio of monomers. The morphology of terpolymers obtained by an interfacial method is nanoscale.
Morphology Studies The morphology of the terpolymer obtained using interfacial chemical polymerization (organic phase, CHCl3, APS 0.5 M in aqueous solution and 1 M for each one or monomer mixtures) with organic solution acids as electrolyte was shown in Figs. 7(a–c). Diameter of obtained polymer particles was about 100–150 nm. From the micrographs (Fig. 7), it is clear that terpolymer nanostructure could be formed via sim ple interfacial nucleation mechanism and the nanostruc tures could be formed by a competing process between the interfacial and aqueous nucleation. The polarity of the organic phase, the concentration of APS and the type of dopant influence the distribution of monomer in aque ous and organic phase, and in turn affect the diffusion of monomer from organic to aqueous phase. Our work proved that it is possible to obtain ter polymer with nanoparticle morphology and higher conductivity by tuning the preparation conditions in a two phase medium. CONCLUSIONS The cyclic voltammetric investigations clearly indi cate the formation of electroactive PANI, POA, POT and PANIcoPOAcoPOT films in PTSA, SSA, MSA and DBSA. It was observed that the anodic cur rent densities during polymerization of monomers are strongly influenced by the presence of organic sulfonic acid. An overall study of the cyclic voltammograms POLYMER SCIENCE
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