SYNTHESIS, PROPERTIES and APLICATIONS of

JORNADAS SAM/ CONAMET/ SIMPOSIO MATERIA 2003

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SYNTHESIS, PROPERTIES and APLICATIONS of FUNCTIONALIZED CONDUCTIVE POLYMERS. César A. Barbero, Diego F. Acevedo, Horacio J. Salavagione, María C. Miras Departamento de Química, Universidad Nacional de Río Cuarto, Agencia postal N° 3- 5800- Río Cuarto (ARGENTINA). E-mail: [email protected] Novel functionalized conductive polymers are synthesized using modification reactions of polyaniline: combinatorial diazonium coupling, nucleophilic addition and N-nitrosation. To perform combinatorial modification, azo dyes, bearing terminal aromatic amino groups, are synthesized combinatorially using commercially available aromatic amines. The dyes are then diazotized and coupled with polyaniline. The properties of the conductive polymer is altered, making the products soluble in common solvents, albeit with a relatively small decrease in conductivity. It is also shown that nucleophilic addition to oxidized polyaniline could be controlled, chemically or electrochemically, by the oxidation state of the polymer. Reversible nitrosation reaction is used to design lithographic and photolithographic processes to deposit PANI patterns. Keywords : conductive polymers, combinatorial chemistry, lithography, conductivity, processability 1. INTRODUCCIÓN Polymers have been traditionally considered as insulators[1]. However, since the discovery by Shirakawa et al that the conductivity of polyacetylene increases significantly upon doping with electron acceptors[2], a large effort has been devoted to making new intrinsically conductive polymers (ICP) and/or improving the properties of those materials[3]. Conductive polymers could have a variety of applications: corrosion protection coatings and conductive coatings for antistatic and/or RF shielding purpouses[3] An obvious requirement to produce such coatings is processability trough solubility of the conductive polymers in common solvents, including aqueous solutions. The usual way to produce new ICP involves the synthesis or acquisition of a monomer, homopolymerization or copolimerization, followed for detailed study of the polymer properties. Another, less explored, route to produce materials with varying properties involves post modification of already synthesized, and well characterized, conducting polymers. This can be done by covalent bonding to the polymer backbone[4], formation of organic-inorganic hybrids or incorporation of functionalized counterions. Examples of two novel reaction pathways: nucleophillic addition and nitrosation will be discussed in the present paper. An alternative approach involves the combinatorial synthesis, coupled to high throughput screening of compounds. The method was initially developed to accelerate the discovery of pharmaceutical compounds[5], and has then been extended to the search of other organic compounds[6], materials[7] and polymers[8]. Several compounds are produced through the reaction of several substrates with several reactants by the same reaction. The method will be illustrated using the reaction of

combinatorially synthesized diazonium salts with polyaniline. 2. RESULTS and DISCUSSION Subsequently, different methods of polyaniline modification will be discussed. 2.1 Combinatorial with polyaniline

coupling of diazonium salts

The reaction for the synthesis of the azo dyes, its conversion into diazonium salts and subsequent reaction with polyaniline is given by Scheme 1:

Ar-NH2

NO2-/H+

Ar-N2+

Ar´-N H2

Ar-N=N-Ar´-N H2

NO 2-/H+ Ar-N=N-Ar´-N2+

PAN I

Ar-N=N-Ar´-N=N Modified PANI

Scheme 1: Reaction pathway of diazonium coupling to polyaniline The proposed reaction requires the coupling of a diazonium salt, produced by diazotization of an

JORNADAS SAM/ CONAMET/ SIMPOSIO MATERIA 2003 aromatic amine (A), with another aromatic amine (B). The later have to be activated for electrophilic substitution. Taking this into account, the following aromatic amines were chosen: NH 2

NH 2

NH 2

SO3 H

COOH

NO 2

A1

A2

NH 2

A3

NH 2

NH 2 O

B1

CH 3

B2

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(activated) to produce azo dyes terminated in –NH2 , which could be then diazotized and coupled with PANI. The effectiveness of the diazonium salts coupling to PANI was tested using FTIR spectroscopy on the products. Beside the bands due to PANI backbone, -1 new bands (e.g. 1650 & 1310 cm for –COOH and -OCH3 characteristic vibrations)[9] are observed in the spectrum, due to the presence of incorporated groups. As it can be seen in Table 1, while PANI is insoluble in common solvents, modification of the polymer by azo coupling renders the modified polymer soluble in some solvents, including water aqueous solutions (Table 1), depending on the functional group incorporated[10]. Additionally, the UV-visible absorption and fluorescence spectra of the solutions were measured and the maxima evaluated (Table 1).

B3

As it can be seen, it is possible to couple type A amines (non activated) with type B amines

Polymer

NH3 /H2 O

Acetone

Toluene

NH3 /iPrOH

CHCl3

PANI

I

I

I

I

I

A1*

VS

-

-

-

-

A2

VS 261,349,217

I

I

I

I

A3

I

S 398,540,970

I

I

I

B1

I

S 340,413

S 288, 354

S

I

B3

I

S 342,428,510

I

I

I

B2

I

S 356,505

S 284, 375

S

VS 240, 378

A1B1

VS 261,327,449

I

I

S 253, 398

I

A1B3

VS 213,285,485

S 427,550

I

I

I

A1B2

I

I

I

I

I

A2B1

S

S 347,490

I

I

I

A2B3

I

S 342,375,527

I

S 220, 280, 388

I

A2B2

S 213,247,338

I

I

I

I

A3B1

I

S 397,513

I

I

I

A3B2

I

S 350, 560

I

I

I

A3B3

I

S 359,526,972

I

I

I

Table I. Solubilities (VS = 1 % w/v, S = 0.1 % w/v, I = insoluble) and UV-visible spectral maxima (the maximum of fluorescence is underlined) of modified polyanilines. * This polymer is highly soluble in water, being impossible to isolate.

While solubility is acceptable for most applications, an important factor is the conductivity of the polymer. Using a two point method, the conductivity of polymer films deposited onto PE

was evaluated (Figure 1). It seems that the most important factor in the conductivity change is the size of the group, except for strongly electron


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withdrawing groups (e.g. –NO2 ) that lower the conductivity by electronic effects

6 4

2

1 0.8 0.6 0.4

PANI

B3

A1

B1

A2

A2B2

A3B2

A2B1

A1B2

B2

A3B3

A3B1

A3

A1B1

0.1

A1B3

0.2

A2B3

log(conductivity) / log(S/cm)

10 8

Polymer

Figure 1. Conductivity of modified polyanilines.

2.2 Nucleophilic addition to oxidized PANI

An alternative way to modify polyaniline involves addition of nucleophiles to the oxidized polymer (Scheme 2) [11].

R H N

NH H N

NH RNH 2

O OR2 NH

O

Amines

O

(-)

H

OR1

NH

R1 O

R S

OR 2

R SH

O

Carbanions

Thiols

CN -

NH

NH

N

so2-

N Arylsulfinate

Cyanide

NH

CN NH

SO2 SO3

2-

Sulfite

NH

SO3H N

H N

Scheme 2: reaction pathways of nucleophilic addition to polyaniline.


In that way, polyaniline could be easily modified by nucleophilic addition giving polymers containing different moieties linked to the polymer backbone. The modification changes the properties of the polymer increasing the solubility in common organic solvents[12] and miscibility with common polymers (e.g. PMMA)[13]. The reaction follows the mechanism: H+ N

N H+

Nucleophilic addition

- H+ + Nu Nu

H NH+

NH +

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As it can be seen, only the oxidized species reacts, and the product is reduced during the reaction. Therefore, the reactivity could be controlled by the oxidation state of the polymer. In Figure 2 is shown the mass increase of a polyaniline film during in-situ addition of sulfite ion while the potential is stepped from the reduced to the oxidized state. The mass of the film is measured using Electrochemical Electroacustic Quartz Crystal Microbalance (EEQCM)[14]. Ex-situ FTIR of the films confirm that sulfonate groups are incorporated to the film. Up to 50 % sulfonation can be achieved, under potential control. The redox coupled ion exchange of the film is also modified, from a dominant anion process towards a dominant cation exchange. This change is due to the incorporation of anionic (sulfonate) groups to the polymer backbone, which compensate for the positive charges created during oxidation.

H

Scheme 3: mechanism of nucleophilic addition

E/V 0.30

∆XLf / Ω = f(Mass)

120

∆XLf / Ω

100

0.25 0.20 0.15

80

0.10 60

E/V

0.05 0.00

40

-0.05 20

∆R f / Ω -0.10 0

-0.15 0

100

200

300

400

500

Time / sec

Figure 2: Electrochemical Electroacoustic Quartz Microbalance (EEQCM) parameters (∆ Rf , ∆ XLf ) of EQCM -2 while aplying potential (E) pulses during PANI nucleophilic sulfonation. Mass of PANI = 1.86 mg cm . Solution = 4 M NaHSO3 (pH = 2).

JORNADAS SAM/ CONAMET/ SIMPOSIO MATERIA 2003 2.3 Lithography of polyaniline via reversible nitrosation.

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Reversible nitrosation on PANI produce a olymer soluble in common solvents[15] (Scheme 4).

PANI base N N H

NH Synthesis

N NO2-/H +

PANI-NO N N N

- HCl

N

O

N O

NH 4OH

Hydrolisis

HCl H N Cl-

N

N+.

NH .+N Cl H

H PANI salt

Scheme 4: nitrosation reaction of polyaniline and hydrolysis

The reaction could be used to devise a lithographic process of polyaniline[16] (Figure 3).

A

B

C

Figure 3. Lithography of PANI using reversible nitrosation

First a PANI-NO coating was deposited onto a plastic plate (Fig. 3.A) from its solution in CH2 Cl2 . Then, the red film was covered with a metal mask and an image of a protective layer was produced by spraying a solution of an inert polymer (PMMA) through the mask.

The plate was then exposed to HCl vapors. The PANI-NO layer hydrolyzes into PANI except in the protected region, leaving a positive image of the mask in PANI-NO surrounded by a PANI salt region (Fig. 3.B).

JORNADAS SAM/ CONAMET/ SIMPOSIO MATERIA 2003 The plate is then washed with CH2 Cl2 removing the protective layer together with the unexposed PANINO leaving a negative image of the mask (Fig. 3.C) in PANI salt. The exposed region is conductive while the unxeposed region shows high resistivity (> 100 M Ω ), suggesting that PANI-NO has been completely removed. The process is easily extend to photolithography since the inert polymer image could be created by conventional photolithography or an acid photogenerator used to promote PANI-NO hydrolysis.

A

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It is known that poly(vinylchloride) (PVC) suffers degradation under UV irradiation, releasing HCl. Therefore a photolithographic process was devised. In Fig. 4 are shown the images of a plastic plate covered with nitrosated polayniline and PVC (Fig. 4A). After irradiation with UV light (250 nm) trough a mask (letter U), the PVC degrades and releases HCl which hydrolyze the PANI-NO film (Fig.4B) leaving a positive image of PANI. After separation from the PVC film and washing with CH2 Cl2 , the PANI-NO is removed and only the positive image of PANI reamains (Fig. 4.C). An FTIR spectrum of the layer has the same spectrum that of emeraldine salt.

B

C

Figure 4: Photolithography of PANI-NO into PANI using PVC as acid pghotogenerator.

3. EXPERIMENTAL DETAILS 3.1 Polyaniline synthesis Polyaniline (PANI) was prepared by chemical oxidation of aniline (0.1 M) with ammonium persulfate (equimolar) in 1 M HCl solution. The o temperature was maintained below 5 C by continuous agitation in an ice bath. The polymerization was monitored potentiometrically to detect reaction completion[17]. The polymer was washed with 1 l of 1 M HCl and then agitated for 48 hrs in 0.1 M NH4 OH solution to deprotonate and form the emeraldine base form. After washing with water, it was dried for 48 hrs under dynamic o vacuum at 50 C.

The dye precipitate and was washed with distilled water. All dyes were then diazotized with sodium nitrite and concentrated HCl in an ice bath. PANI was suspended in TRIS buffer (pH=8) and mixed with the diazonium salt solution in an ice bath. The solid is filtered under vacuum and washed first with 1 l of 1 M HCl solution and then with 1 l distilled water. The products were filtered out of the mixture under vacuum and dried (dynamic vacuum for 48 hs). PANI films supported on LDPE were also treated with the diazonium salts, washed with acidic (1 M HCl) solution and water and dried under vacuum. 3.3 Nucleophilic addition

3.2 Combinatorial modification The azo dyes were synthesized in solution. The amines were diazotized with sodium nitrite and concentrated HCl in an ice bath. The coupling amine was dissolved in TRIS buffer (pH=8) and mixed with the diazonium salt solution in an ice bath.

Nucleophilic addition of bencensulfinic acid to PANI: 50 ml of a solution 0.5 M of bencensulfinic acid in buffer (pH 4) are mixed and heated in a water bath during 2 hs. The reaction mixture is left to cool, filtered and washed with successive portions (500 ml) of H2O, NH4OH 1 M and ClH 1

JORNADAS SAM/ CONAMET/ SIMPOSIO MATERIA 2003 M: Then, the product is dried under dynamic vacuum for 24 hs. 3.4 N-nitrosation reaction N-nitrosated polyaniline (PANI-NO) was prepared reacting PANI (emeraldine base) with sodium nitrite (1 M) in 1.1 M HCl solution[18]. Up to 43% of N-nitrosation is obtained. FTIR spectrum of the product shows bands characteristic of polyaniline (emeraldine base) and new bands occurring at 1508 -1 -1 cm (str. -N=O), 1034 cm (str. -N-N-) and 757 -1 cm (def. -N-N=C)[9], indicating formation of Nnitrosated polyaniline PANI-NO is soluble in common solvents (CHCl3 , CH2 Cl2 , C2 H4 Cl2 , secondary amines, DMSO, DMF), giving deep red solutions.

FTIR spectra were measured using an Impact 400 (Nicolet) spectrometer. UV-visible spectra were determined in quartz cells using a HP8453 spectrophotometer. Fluorescence spectra were measured with and Hitachi F2500 fluorimeter, exciting at the lowest wavelength absorption maxima. 3.6 Electrochemical characterization

real ground. This Au-coated quartz electrode was simultaneously one of the quartz polarizing contacts at 10 MHz and the electrochemically 2 working electrode (active area 0.196 cm ). Two vinyl o-rings were used for sealing the quartz crystal with only one face of the crystal in contact with the electrolyte. The reference electrode was a Ag/AgCl/Cl electrode and all potentials herein are quoted with respect to this electrode. A platinum mesh was used as counter electrode. 4. CONCLUSIONS -

-

3.5 Polymer characterziation

modification

and

AT-cut quartz crystals (10 MHz) of 14 mm diameter with Au electrodes deposited over a Cr adhesion layer (ICM, Oklahoma, US) were used for EQCM measurements. A standard three-electrode electrochemical cell made of Teflon® was used with an LM11 operational amplified potentiostat with the working electrode (Au-coated quartz) at

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-

It has been shown that it is possible to combinatorially synthesize diazonium salts, which are used to modify PANI to produce conductive and soluble polymers. Polyaniline could be easily modified by nucleophilic addition giving polymers with increased solubility in common organic solvents and miscibility with common polymers. Reversible nitrosation could be used to develop lithographic processes to deposit polyaniline patterns.

5. ACKNOWLEDGEMENTS D.F.A. and HJ.S. thank Agencia Córdoba Ciencia and FONCYT for fellowships. C. Barbero is a permanent research fellow of CONICET. The work presented here was funded by FONCYT, Agencia Córdoba Ciencia, CONICET and SECYT-UNRC. The donation of chemical reactants by Vilmax S.A. is most gratefully acknowledged.

6. REFERENCES th

[1] “Seymour/Carraher´s Polymer Chemistry”, 4 Edition, C.E. Carraher, M. Dekker, New York, 1996. [2] H. Shirakawa, Angew. Chem. Int. Ed., 40(2001)2575; A.G. McDiarmid, Angew. Chem. Int. Ed., 40 , 2001,p 2581; A.J. Heeger, Angew. Chem. Int. Ed., 40 ,2001,p 2591. [3]”Handbook of Conducting Polymers”, T.A. Skotheim, R.L. Elsenbaumer, J.R. Reynolds, Eds., nd 2 Ed. Marcel Dekker, New York, 1998. [4] J. Yue, Z.H. Wang, K.R. Cromack, A.J. Epstein, A.G. MacDiarmid, J. Am. Chem. Soc., 113,1991,2665; X-L. Wei, Y.Z. Wang, S.M. Long, C. Bobeczko, A.J. Epstein, J. Am. Chem. Soc., 118 ,1996,p 2545. [5] “Combinatorial Chemistry”, S.R. Wilson, A.W. Czarnik, Eds., J. Wiley & Sons, Inc., New York, 1997.

[6] “Solid-Supported Combinatorial and Parallel Synthesis of small-Molecular-Weight Compound Libraries”, D. Obrecht, J.M. Villalgordo, Pergamon, Oxford, 1998. [7] B. Jandeleit, D.J. Schaefer, T.S. Powers, H.W. Turner, W.H. Weinberg, Angew. Chem. Int. Ed., 38 ,1999,p 2494. [8] S. Brocchini, K. James, V. Tangpasuthadol, J. Kohn, J. Am. Chem. Soc., 119,1997, p 4553. [9] “The Handbook of Infrared and Raman Frequencies of Organic Molcules”, D.Lin-Vien, N.B. Colthup, W.G. Fateley, J.G. Grasselli, Academic Press, Boston, 1991. [10] D.F. Acevedo, G.A. Planes, M.C. Miras, C. Barbero, Argentine Patent App., P020104989, 2002.


[11] G.M. Morales, M.C. Miras, C. Barbero, Synth. Metals, 101 ,1999,p 678; C. Barbero, G.M. Morales, D. Grumelli, G. Planes, H. Salavagione, C.R. Marengo, M.C. Miras, Synth. Metals, 101 ,1999, p 694. [12] H. Salavagione, G. M. Morales, M.C. Miras, C. Barbero, Acta Polymerica, 50 ,1999, p 40. [13] C.A. Barbero, M.C. Miras, G.M. Morales, H.J. Salavagione, D.E. Grumelli, Argentine Patent App., P990106154, 1999, [14] C. Barbero, E.J. Calvo, R. Etchenique, G.M. Morales, L. Otero, Electrochim. Acta., 45 , 2000, pp 3895-3906. [15] C.A. Barbero, M.C. Miras, H.J. Salavagione, Argentine Patent App., P020100570, 2002. [16] H.J. Salavagione, M.C. Miras, C. Barbero, J. Am. Chem. Soc.; 125 ,2003, pp 5290-5291 [17] G.M. Morales, M. Llusa, M.C. Barbero, Polymer, 38 , 1997, p 5247.

Miras, C.

[18] H.J. Salavagione, M.C. Miras, C. Barbero, Argentine Patent App., P020100570, 2002.

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