Recent developments in the polymerization of 3-alkylthiophenes

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Synthetic Metals, 55-57 (1993) 1204-1208

RECENT DEVELOPMENTS IN THE POLYMERIZATION OF 3-ALKYLTHIOPHENES

J. LAAKSO and H. J,ARVINEN Neste Oy, Technology Centre, P.O.B. 310, SF-06101 Porvoo (Finland) B. SKAGERBERG ASTRA Pharmaceutical Production (Sweden)

ABSTRACT We have optimized the polymerization conditions of 3-octylthiophene. In the reactions the varying parameters were polymerization time, monomer addition speed, temperature and molar ratio FeCl~:monomer. As a summary we can say that the parameters mentioned above affect the yield, molar mass and quality (crosslinking etc.) of the resulting polymer.

INTRODUCTION Poly(3-alkylthiophenes) are melt and solution processable conducting polymers. They can be blended with other processable polymers using conventional melt processing [1] or solution processing [2] methods. Normally poly(3-alkylthiophenes) have been synthesized using 3-alkylthiophenes as a monomer and ferric chloride as an oxidant [3,4]. Changing the reaction time, reaction temperature, etc. we can vary the characteristics of the resulting polymer. In this paper we report some notes which affect the quality of the polymer.

RESULTS The starting monomer 3-octylthiophene was synthesized by coupling of octylmagnesiumbromide with 3-bromothiophene in the presence of Ni(dppp)C12 according to the method of Kumada et al. [5]. 3-Octylthiophene has been polymerized using FeC13 as an oxidant in a chloroform solution [3]. The crude product is precipitated in ethanol and washed several times with ethanol and water and dried under vacuum. Elsevier Sequoia

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Experiments were carried out using a factorial design with four variables which have values +1 and -1 (i.e. a 2' factorial). The factorial was completed with an experiment at the centre of values. The four manipulated variables were reaction temperature (x0, polymerization time (x2), monomer addition time (x~) and relative amount of oxidant (x,) (Table 1).

TABLE 1 Experimental domain

Variable

low

high

X~ Temperature (°C) X2 Polymerization time (h) X~ Addition time (min) X, Amount of oxidant (ratio to amount of monomer)

-5

10

1

2

15 3

45 5

TABLE 2 A two-level factorial design in four variables augmented with one centre point

X~

X2

X3

X,

-1 1

-1 -1

-1 -1

-1 -1

-1

1

-1

-1

1

1

-1

-1

-1 1 -1 1 -1 1

-1 -1 1 1 -1 -1

1 1 1 1 -1 -1

-1 -1 -1 -1 1 1

-1

I

-1

1

1 -1 1 -1 1

1 -1 -1 1 1

-1 1 1 1 1

1 1 1 I 1

0

0

0

0

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The purpose of this study was to perform a screening, i.e. to investigate the linear effect of these manipulated variables with respect to four responses, yield in grams (y,), yield in % (y~), solubility in chloroform (Y3) and molecular weight (y,). Tables 2 and 3 show the experimental setups.

TABLE 3 Design table in natural units X-BLOCK DATA

Exp #

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Temp. ( ° C )

-5 10 -5 10 -5 10 -5 10 -5 10 -5 10 -5 10 -5 10 2.5

Polym. time (h)

1 1 2 2 1 1 2 2 1 1 2 2 1 1 2 2 1.5

Add. time (min)

15 15 15 15 45 45 45 45 15 15 15 15 45 45 45 45 30

Oxid/mon

3 3 3 3 3 3 3 3 5 5 5 5 5 5 5 5 4

Table 4 shows the experimental results. There is no clear correlation between molar mass and solubility. On the other hand, when the yield increases solubility decreases. That means there might be some kind of crosslinking between the polymer chains. Low polymerization temperature, short reaction time, low oxidant/monomer ratio and short monomer addition time result polymer with low yield, low molar mass and high solubility (Exp. 1). If the reaction temperature is increased (Exp. 2) the yield is higher but the solubility in chloroform is still complete. The same happens with long polymerization time (Exp. 3-4). Long monomer addition time affects the solubility negatively (Exp. 5-8). This might result from different polymerization system which results crosslinking and mislinking. The situation is the same when we increase oxidant/monomer ratio (Exp. 9-12) or monomer addition time (Exp. 13-16).

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It can be concluded that temperature does not have any major influence on the four investigated responses. A short monomer addition time seems to be favourable. However, there also seems to be a conflict between the effect of amount of oxidant on yield together with molar mass and solubility, respectively. Niemi et al. [6] have noticed that the FeCI~ must be solid to be active as a polymerization oxidant for 3-alkylthiophenes. The soluble part of the oxidant seems to be inert. The solubility of FeCI~ in chloroform and the consuming effect of evolved HC1 gas explain the extra portion of FeCI~ that is needed initially to get high conversion in polymerization.

TABLE 4 Data from experimentation Y-BLOCK DATA

Exp #

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17

Yield (g)

4.5 5.5 5.0 5.8 4.8 5.4 5.7 5.4 8.6 8.0 9.6 10.0 8.0 7.9 9.5 8.4 7.1

Yield (%)

36.2 44.3 40.2 46.7 38.6 43.4 45.9 43.4 69.2 64.4 77.2 80.5 64.4 63.6 76.4 67.6 57.1

Solubilility"

5 5 5 5 4 4-5 4-5 4-5 4-5 4 2 4 4-5 4-5 4-5 3-4 5

Mw

D

36850 39750 35100 43250 52600 58100 46650 52300 67500 84700 49050 80750 58450 55250 82100 75500 46400

2.3 2.2 2.5 2.3 2.6 2.5 2.5 2.5 4.1 5.0 3.7 3.1 3.3 3.1 3.4 3.4 2.5

" 5 = completely soluble in chloroform, 1 = nonsoluble in chloroform

ACKNOWLEDGEMENTS We are indebted to Mrs Irma Auvinen for assisting in the polymer syntheses and preparation of the samples. We also thank the Analytical Department for analyzing our samples.

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REFERENCES 1 J. Laakso, J.-E. 0sterholm and P. Nyholm, Svnth. Met.. 28 (1989) C467. 2 A. Fizazi, J. Moulton, K. Pakbaz, S.D.D.V. Rughooputh, P. Smith and A.J. Heeger, Phys. Rev. Lett., 64 (1990) 2180. 3 R. Sugimoto, S. Takeda, H.B. Gu and K. Yoshino, Chem. Exp., 1 (1986) 635. 4 J.-E. Osterholm, J. I_aakso, P. Nyholm, H. Isotalo, H. Stubb, O. Ingan~is and W.R. Salaneck, Synth. Met.. 28 (1989) C435. 5 K. Tamao, S. Kodama, I. Nakajima and M. Kumada, Tetrahedron, 38 (1982) 3347. 6 V.M. Niemi, P. Knuuttila, J.-E. Osterholm and J. Korvola, Polymer, 33 (1992) 1559.