- Email: [email protected]
base indicator
Synthetic Metals, 36 (1990) 209 - 215
209
POLYANILINE: REACTION STOICHIOMETRY AND USE AS AN IONEXCHANGE POLYMER AND ACID/BASE INDICATOR AKHEEL A. SYED* and MARAVATTICKALK. DINESAN Department of Chemistry, University of Mysore, Manasagangotri, Mysore 570 006 (India) (Received March 28, 1988; accepted January 8, 1990)
Abstract An iodometric m e t h o d has been used to establish that in the synthesis of polyaniline by the oxidative polymerization of aniline with a m m o n i u m peroxydisulfate, ~ 2 . 5 electrons are involved per (CeHd)N repeat unit. It is also demonstrated that polyaniline can act as an ion~xchange polymer and as an acid/base indicator.
Introduction During recent years there has been a marked resurgence of interest in the conducting polymer polyaniline, as indicated by extensive chemical, electrochemical and physics studies [ 1 - 7 ] . Although several elemental analytical studies of the protonated and non-protonated emeraldine oxidation state of polyaniline have been described, there have been no reports on the oxidative stoichiometry of the most c o m m o n m e t h o d of chemical synthesis of polyaniline, viz., the oxidative polymerization of aniline with a m m o n i u m peroxydisulfate. We report here the first study of this t y p e and also give an evaluation of polyaniline (PANI) as an ionexchange polymer and as an acid/base indicator.
Experimental Reagents All reagents were AnalaR grade and were purchased from Glaxo Laboratories (India) Ltd. Aniline was doub!e
0379-6779/90/$3.50
© Elseveir Sequoia/Printed in The Netherlands
210
Determination o f reaction stoichiometry Polyaniline was chemically synthesized from 0.04 moles of aniline in a solution of 100 ml sulfuric acid containing 0.5 M sodium sulfate (pH = 1). A known number of equivalents of a m m o n i u m peroxydisulfate oxidant were added and the reaction mixture was stirred for 60 min. The precipitate was separated by filtration through a sintered glass crucible (porosity 2) and washed with a copious m o u n t of sulfuric acid solution (pH = 1). The filtrate (containing small quantities of oligomers) was collected and made up to the mark in a 500-ml standard flask using sulfuric acid solution (pH = 1). The estimation of unconsumed a m m o n i u m peroxydisulfate was carried out for different sets of polymerization conditions wherein we varied the ratio of aniline to peroxydisulfate keeping the number of moles of aniline constant. An aliquot (5 ml) of the filtrate solution was transferred to an iodine flask and the determination of unreacted a m m o n i u m peroxydisulfate was effected by a standard iodometric m e t h o d [8]. In comparative studies, polymerization of aniline and determination of unreacted a m m o n i u m peroxydisulfate was also carried out in 1 M sulfuric acid and in 1 M hydrochloric acid media. The results are presented in Table 1. Polyaniline as an ion-exchange polymer Polyaniline sulfate was synthesized as described in the previous section. After the filtration and washing step, it was air dried and the lower molecular weight species were extracted with CHaCN until the extract was colourless. It was then dried under vacuum for ~ 2 4 h. About 4 g of this polyaniline sulfate (50-mesh material) was transferred to a column of 1.2 cm TABLE 1 Number of electrons, X, involved per molecule of aniline polymerizeda Ammonium peroxydi~ulfate employed (equivalents x l 0 -2)
X b'¢
H2SO4 + 0.5 M Na2SO4 (pH = 1) 11 12 16 20
2.57 2.52 2.56 2.67
1 M H2SO4 12
2.60
1MHC1 12
2.60
a4 × 10 -2 moles of aniline in 100 ml of solution. bCalculated from the number of equivalents of ammonium peroxydisulfate consumed during polymerization, assuming that all the aniline employed underwent polymerization. CAverage of five experiments.
211
internal diameter and 12.5 cm height. It was then washed with a 0.25 M NaNO 3 solution until the effluent was sulfate-free. A KC1-KBr mixture (2 ml; 0.1 to 0.6 mmol of C1- and 0 . 0 5 - 0.5 mmol of Br-) was placed quantitatively on the top of the column and was eluted with a 0.25 M NaNO3 solution. Effluents were collected in fractions of 2 ml. Each fraction was collected in a conical flask and was titrated against standard silver nitrate solution using 1% (wt./vol.) potassium chromate as indicator. When the titre value reached a minimum, the elution was carried out with a 0.5 M NaNO3 solution. The results are presented in Table 2. Polyaniline as an acid~base indicator
Approximately 200 mg of polyaniline sulfate, synthesized as described above, was deprotonated by equilibration with 250 ml of 1 M NH4OH for ~ 1 0 h. The powder was separated by filtration through a sintered glass crucible (porosity 4) and rinsed with acetonitrile, followed by drying under dynamic vacuum for ~ 2 4 h. A sample (20 mg) of this base form of polyaniline was transferred to a 25-ml beaker containing 5 ml DMF and stirred for "~1 h. The solution was filtered and the filtrate (saturated solution)was used as an acid/base indicator. Aliquots (20 ml) or 0.5 to 0.05 N sulfuric, hydrochloric, nitric or perchloric acid were transferred to an Erlenmeyer flask; 2 - 3 drops of the above polyaniline solution were added and the mixture was titrated with sodium hydroxide solution until a blue colour appeared. The values are in full agreement with the potentiometric end-points (Table 3). TABLE 2 Determination of weights of chloride and bromide ions in a mixture using polyaniline as an anion-exchange polymer Weight used a (mg)
Weight found after separation b (mg)
Standard deviation (mg)
Relative error (%)
CI-
Br-
Cl-
Br-
CI-
Br-
CI-
Br-
3.10 7.26 12.13 14.73 19.31 13.26 12.17 12.18 11.04 10.88 14.70
34.67 32.25 34.45 32.03 32.01 29.72 26.58 21.23 23.65 17.31 4.09
3.10 7.56 11.78 14.22 18.72 13.15 11.73 12.50 10.82 10.79 15.06
33.06 33.22 34.52 32.68 32.87 28.65 25.51 20.84 24.29 17.48 3.82
0.19 0.18 0.33 0.23 0.37 0.22 0.07 0.20 0.11 0.19 0.31
0.67 0.37 0.04 0.19 0.09 0.23 0.23 0.12 0.19 0.11 0.38
--0.1 +4.0 --2.9 --3.4 --3.0 --0.8 --3.6 +2.6 --2.0 --0.8 +2.4
--4.6 +3.0 +0.1 +2.1 +2.7 --4.0 --4.0 --1.9 +2.7 +1.0 --6.7
aWeight refers to the weight of the halide ion in the corresponding potassium salt. b Average of five determinations.
212 TABLE 3 Determination of sulfuric acid, hydrochloric acid, nitric acid and perchloric acid using polyaniline as acid/base indicator Acid
Normality of acid (potentiometric method)
Normality a of acid (polyaniline indicator)
Standard deviationb×10 -4
HC1
0.5073 0.2542 0.1019 0.0509
0.5062 0.2536 0.1015 0.0507
16.0 3.5 1.6 1.3
HNO3
0.5116 0.2568 0.1016 0.0510
0.5113 0.2562 0.1021 0.0512
24.0 5.2 1.3 1.3
HC104
0.5073 0.2547 0.1021 0.0510
0.5086 0.2543 0.1017 0.0508
7.8 3.7 2.8 1.6
H2S04
0.5169 0.2595 0.1040 0.0516
0.5180 0.2590 0.1036 0.0518
6.3 4.9 2.8 1.4
aAverage of five determinations. bStandard deviation observed for the five separate determinations.
Results and discussion
Reagent analysis: stoichiometry of the reaction The standard r e d u c t i o n potential of the peroxydisulfate ion (S2Os) 2is estimated to be 2.01 V versus NHE in aqueous solution [9]. Under mild conditions ($208) 2- undergoes decomposition t o yield the radical anion, SO4"-, which appears t o be a very effective electron-transfer agent [10]. The peroxydisulfate determination in t he filtrate solution containing oligomers did n o t pose any interference to the iodometric m e t h o d , as shown b y the following experiment. A m m o n i u m peroxydisulfate solution (20 ml; 4 0 - 400 mg) was transferred t o each o f t w o stoppered conical flasks containing ~ 4 g o f KI. To one flask 20 ml o f t he filtrate solution (obtained in a reaction where < 2 . 5 equivalents o f p e r o x y d i s u l f a t e / m o l e o f aniline was e m p l o y e d ) was added. The mixtures were allowed t o stand for ~ 1 5 rain. The liberated iodine was titrated with standard sodium thiosulfate solution. Near the end-point 1 ml o f 1% (wt./vol.) starch solution was added and the titration was continued until the blue colour disappeared. The same titre value was obtained in each sample. A relative error of 0.8% was observed fo r six determinations. Hence, oligomers did n o t interfere with the iodometric titration.
213
The data (Table 1) demonstrate that the oxidation of aniline is consistent with the stoichiometry: --2ne-
--0.5ne-
n(C6HsNH2)
> [(C6H4)NH--ln --2nil
> [(C(~T-I4)NH--°'S+]n
+
Thus ~ 2 . 5 electrons are removed from each molecule of C6HsNH2 during polymerization.
80
CI"
!I 70
P
~
'CI- I
:
I
(a)
I I |
60
~0
t" I I
CI"
~E
40
!
;p"~\ Br-
\
i
(b}
Nr"
I I
3oi
~ A f
/\ I
,
II
\
20
I0
;j
~.
I
\
\
"\\
~
o,
•
/I
/
I
i
i
"x
\
i
0
I0
d.~" 2o
~ VOLUME OF N o N O 3
40
50
'-
F i g . 1. Elution graphs of chloride-bromide mixtures. Eluents: chloride (0.25 M NaNO3); bromide (0.50 M NaNO3). (a) Large concentrations of chloride and small amounts of bromide; (b) equimolar concentrations of chloride and bromide; (c) optimum concentrations of chloride and bromide.
214
Anion-exchange chromatography The elution graphs of mixtures of chloride and bromide of different concentrations are shown in Fig. 1. At lower concentrations of bromide, almost all the chloride appeared in the first 34 ml of the eluate and all the bromide in the next 20 ml (a in Fig. 1), while at equimolar chloride-bromide concentrations, the resolution is poor (b in Fig. 1). This is understandable as both anions have the same charge. However, good separation is seen, as shown in c in Fig. 1. Similar results were observed for chloride-iodide (0.2 0.4 mmol of CI- and 0.1 - 0 . 4 mmol of 1-) and bromide-iodide (0.1 - 0 . 4 mmol of Br- and 0.08 - 0.3 mmol of V) mixtures. The theoretical specific capacity, Qo, of the polymer is 4.60 milliequivalents of chloride per gram of the dry polymer. The volume capacity, Qv, has been determined as 1.24 milliequivalents per cm 3 (sulfate form of the polymer in 0.25 M NaNO3 solution). Polyaniline as an acid/base indicator Change in colour upon addition/elimination of protons is the basis for the use of polyaniline as an acid/base indicator. This indicator gives a sharp end-point in the titration of 0 . 5 - 0.05 N sulfuric, hydrochloric, nitric or perchloric acids with sodium hydroxide solution. At lower acid concentrations sluggish end-points are observed. Late end-points are seen in the reverse titration (acid in the burette and base in the Erlenmeyer flask). This may be due to a kinetically slower rate of protonation of the undoped polyaniline solution. A simple titration of the polyaniline salt powder in water with sodium hydroxide displayed equilibrium constants pK 1 = 6.5 and pK2 = 2.7.
Conclusions
We have used a volumetric m e t h o d to establish the number of electrons per repeat unit in the peroxydisulfate oxidative polymerization of aniline to polyaniline. The use of this polymer as an anion~exchange polymer and as an acid/base indicator is encouraging.
Acknowledgement One of us (M.K.D.) gratefully acknowledges the University Grants Commission for the award of a Junior Research Fellowship.
References 1 R. Willstatter and S. Dorogi, Ber., 42 (1909) 2147. 2 A. G. Green and A. E. Woodhead, J. Chem. Soc., 97 (1910) 2388; 101 (1912) 1117.
215
3 E. M. Geni~s, A. A. Syed and C. Tsintavis,Mol. Cryst. Liq. Cryst., 121 (1985) 181; E. M. Geni~s and C. Tsintavis,J. Electroanal. Chem., 195 (1985) 109; 200 (1986) 127. 4 W. S. Huang, B. D. Humphrey and A. G. MacDiarmid, J. Chem. Soc., Faraday Trans. I, 82 (1986) 2385; A. G. MacDiarmid, J. C. Chiang, A. F. Richter and A. J. Espstein, Synth. Met., 18 (1987) 285; A. G. MacDiarmid and A. J. Epstein, Trans. Faraday Soc., (Discuss.), (1989) in press. 5 N. Mermilliod, J. Tanguy, M. Hoclet and A. A. Syed, Synth. Met., 18 (1987) 359. 6 H. Kuzmany, E. M. Geni~s and A. A. Syed, Springer Series in Solid-State Sciences, Vol. 63, Springer, Berlin, 1985, p. 223. 7 S. Kaplan, E. M. ConweU, A. F. Richter and A. G. MacDiarmid, J. Am. Chem. Soc., 110 (I 988) 7647, and refs.therein. 8 I. M. Kolthoff and R. Belcher (eds.), Volumetric Analysis, Vol. Ill, Interscience, N e w York, 1957, pp. 287 - 289. 9 W. M. Latimer, Oxidation States o f the Elements and their Potentials in Aqueous Solution, Prentice-Hall, New York, 1952, p. 78. 10 F. Minisci, A. Citterio and C. Giordano, Acc. Chem. Res., 16 (1983) 27.
209
POLYANILINE: REACTION STOICHIOMETRY AND USE AS AN IONEXCHANGE POLYMER AND ACID/BASE INDICATOR AKHEEL A. SYED* and MARAVATTICKALK. DINESAN Department of Chemistry, University of Mysore, Manasagangotri, Mysore 570 006 (India) (Received March 28, 1988; accepted January 8, 1990)
Abstract An iodometric m e t h o d has been used to establish that in the synthesis of polyaniline by the oxidative polymerization of aniline with a m m o n i u m peroxydisulfate, ~ 2 . 5 electrons are involved per (CeHd)N repeat unit. It is also demonstrated that polyaniline can act as an ion~xchange polymer and as an acid/base indicator.
Introduction During recent years there has been a marked resurgence of interest in the conducting polymer polyaniline, as indicated by extensive chemical, electrochemical and physics studies [ 1 - 7 ] . Although several elemental analytical studies of the protonated and non-protonated emeraldine oxidation state of polyaniline have been described, there have been no reports on the oxidative stoichiometry of the most c o m m o n m e t h o d of chemical synthesis of polyaniline, viz., the oxidative polymerization of aniline with a m m o n i u m peroxydisulfate. We report here the first study of this t y p e and also give an evaluation of polyaniline (PANI) as an ionexchange polymer and as an acid/base indicator.
Experimental Reagents All reagents were AnalaR grade and were purchased from Glaxo Laboratories (India) Ltd. Aniline was doub!e
0379-6779/90/$3.50
© Elseveir Sequoia/Printed in The Netherlands
210
Determination o f reaction stoichiometry Polyaniline was chemically synthesized from 0.04 moles of aniline in a solution of 100 ml sulfuric acid containing 0.5 M sodium sulfate (pH = 1). A known number of equivalents of a m m o n i u m peroxydisulfate oxidant were added and the reaction mixture was stirred for 60 min. The precipitate was separated by filtration through a sintered glass crucible (porosity 2) and washed with a copious m o u n t of sulfuric acid solution (pH = 1). The filtrate (containing small quantities of oligomers) was collected and made up to the mark in a 500-ml standard flask using sulfuric acid solution (pH = 1). The estimation of unconsumed a m m o n i u m peroxydisulfate was carried out for different sets of polymerization conditions wherein we varied the ratio of aniline to peroxydisulfate keeping the number of moles of aniline constant. An aliquot (5 ml) of the filtrate solution was transferred to an iodine flask and the determination of unreacted a m m o n i u m peroxydisulfate was effected by a standard iodometric m e t h o d [8]. In comparative studies, polymerization of aniline and determination of unreacted a m m o n i u m peroxydisulfate was also carried out in 1 M sulfuric acid and in 1 M hydrochloric acid media. The results are presented in Table 1. Polyaniline as an ion-exchange polymer Polyaniline sulfate was synthesized as described in the previous section. After the filtration and washing step, it was air dried and the lower molecular weight species were extracted with CHaCN until the extract was colourless. It was then dried under vacuum for ~ 2 4 h. About 4 g of this polyaniline sulfate (50-mesh material) was transferred to a column of 1.2 cm TABLE 1 Number of electrons, X, involved per molecule of aniline polymerizeda Ammonium peroxydi~ulfate employed (equivalents x l 0 -2)
X b'¢
H2SO4 + 0.5 M Na2SO4 (pH = 1) 11 12 16 20
2.57 2.52 2.56 2.67
1 M H2SO4 12
2.60
1MHC1 12
2.60
a4 × 10 -2 moles of aniline in 100 ml of solution. bCalculated from the number of equivalents of ammonium peroxydisulfate consumed during polymerization, assuming that all the aniline employed underwent polymerization. CAverage of five experiments.
211
internal diameter and 12.5 cm height. It was then washed with a 0.25 M NaNO 3 solution until the effluent was sulfate-free. A KC1-KBr mixture (2 ml; 0.1 to 0.6 mmol of C1- and 0 . 0 5 - 0.5 mmol of Br-) was placed quantitatively on the top of the column and was eluted with a 0.25 M NaNO3 solution. Effluents were collected in fractions of 2 ml. Each fraction was collected in a conical flask and was titrated against standard silver nitrate solution using 1% (wt./vol.) potassium chromate as indicator. When the titre value reached a minimum, the elution was carried out with a 0.5 M NaNO3 solution. The results are presented in Table 2. Polyaniline as an acid~base indicator
Approximately 200 mg of polyaniline sulfate, synthesized as described above, was deprotonated by equilibration with 250 ml of 1 M NH4OH for ~ 1 0 h. The powder was separated by filtration through a sintered glass crucible (porosity 4) and rinsed with acetonitrile, followed by drying under dynamic vacuum for ~ 2 4 h. A sample (20 mg) of this base form of polyaniline was transferred to a 25-ml beaker containing 5 ml DMF and stirred for "~1 h. The solution was filtered and the filtrate (saturated solution)was used as an acid/base indicator. Aliquots (20 ml) or 0.5 to 0.05 N sulfuric, hydrochloric, nitric or perchloric acid were transferred to an Erlenmeyer flask; 2 - 3 drops of the above polyaniline solution were added and the mixture was titrated with sodium hydroxide solution until a blue colour appeared. The values are in full agreement with the potentiometric end-points (Table 3). TABLE 2 Determination of weights of chloride and bromide ions in a mixture using polyaniline as an anion-exchange polymer Weight used a (mg)
Weight found after separation b (mg)
Standard deviation (mg)
Relative error (%)
CI-
Br-
Cl-
Br-
CI-
Br-
CI-
Br-
3.10 7.26 12.13 14.73 19.31 13.26 12.17 12.18 11.04 10.88 14.70
34.67 32.25 34.45 32.03 32.01 29.72 26.58 21.23 23.65 17.31 4.09
3.10 7.56 11.78 14.22 18.72 13.15 11.73 12.50 10.82 10.79 15.06
33.06 33.22 34.52 32.68 32.87 28.65 25.51 20.84 24.29 17.48 3.82
0.19 0.18 0.33 0.23 0.37 0.22 0.07 0.20 0.11 0.19 0.31
0.67 0.37 0.04 0.19 0.09 0.23 0.23 0.12 0.19 0.11 0.38
--0.1 +4.0 --2.9 --3.4 --3.0 --0.8 --3.6 +2.6 --2.0 --0.8 +2.4
--4.6 +3.0 +0.1 +2.1 +2.7 --4.0 --4.0 --1.9 +2.7 +1.0 --6.7
aWeight refers to the weight of the halide ion in the corresponding potassium salt. b Average of five determinations.
212 TABLE 3 Determination of sulfuric acid, hydrochloric acid, nitric acid and perchloric acid using polyaniline as acid/base indicator Acid
Normality of acid (potentiometric method)
Normality a of acid (polyaniline indicator)
Standard deviationb×10 -4
HC1
0.5073 0.2542 0.1019 0.0509
0.5062 0.2536 0.1015 0.0507
16.0 3.5 1.6 1.3
HNO3
0.5116 0.2568 0.1016 0.0510
0.5113 0.2562 0.1021 0.0512
24.0 5.2 1.3 1.3
HC104
0.5073 0.2547 0.1021 0.0510
0.5086 0.2543 0.1017 0.0508
7.8 3.7 2.8 1.6
H2S04
0.5169 0.2595 0.1040 0.0516
0.5180 0.2590 0.1036 0.0518
6.3 4.9 2.8 1.4
aAverage of five determinations. bStandard deviation observed for the five separate determinations.
Results and discussion
Reagent analysis: stoichiometry of the reaction The standard r e d u c t i o n potential of the peroxydisulfate ion (S2Os) 2is estimated to be 2.01 V versus NHE in aqueous solution [9]. Under mild conditions ($208) 2- undergoes decomposition t o yield the radical anion, SO4"-, which appears t o be a very effective electron-transfer agent [10]. The peroxydisulfate determination in t he filtrate solution containing oligomers did n o t pose any interference to the iodometric m e t h o d , as shown b y the following experiment. A m m o n i u m peroxydisulfate solution (20 ml; 4 0 - 400 mg) was transferred t o each o f t w o stoppered conical flasks containing ~ 4 g o f KI. To one flask 20 ml o f t he filtrate solution (obtained in a reaction where < 2 . 5 equivalents o f p e r o x y d i s u l f a t e / m o l e o f aniline was e m p l o y e d ) was added. The mixtures were allowed t o stand for ~ 1 5 rain. The liberated iodine was titrated with standard sodium thiosulfate solution. Near the end-point 1 ml o f 1% (wt./vol.) starch solution was added and the titration was continued until the blue colour disappeared. The same titre value was obtained in each sample. A relative error of 0.8% was observed fo r six determinations. Hence, oligomers did n o t interfere with the iodometric titration.
213
The data (Table 1) demonstrate that the oxidation of aniline is consistent with the stoichiometry: --2ne-
--0.5ne-
n(C6HsNH2)
> [(C6H4)NH--ln --2nil
> [(C(~T-I4)NH--°'S+]n
+
Thus ~ 2 . 5 electrons are removed from each molecule of C6HsNH2 during polymerization.
80
CI"
!I 70
P
~
'CI- I
:
I
(a)
I I |
60
~0
t" I I
CI"
~E
40
!
;p"~\ Br-
\
i
(b}
Nr"
I I
3oi
~ A f
/\ I
,
II
\
20
I0
;j
~.
I
\
\
"\\
~
o,
•
/I
/
I
i
i
"x
\
i
0
I0
d.~" 2o
~ VOLUME OF N o N O 3
40
50
'-
F i g . 1. Elution graphs of chloride-bromide mixtures. Eluents: chloride (0.25 M NaNO3); bromide (0.50 M NaNO3). (a) Large concentrations of chloride and small amounts of bromide; (b) equimolar concentrations of chloride and bromide; (c) optimum concentrations of chloride and bromide.
214
Anion-exchange chromatography The elution graphs of mixtures of chloride and bromide of different concentrations are shown in Fig. 1. At lower concentrations of bromide, almost all the chloride appeared in the first 34 ml of the eluate and all the bromide in the next 20 ml (a in Fig. 1), while at equimolar chloride-bromide concentrations, the resolution is poor (b in Fig. 1). This is understandable as both anions have the same charge. However, good separation is seen, as shown in c in Fig. 1. Similar results were observed for chloride-iodide (0.2 0.4 mmol of CI- and 0.1 - 0 . 4 mmol of 1-) and bromide-iodide (0.1 - 0 . 4 mmol of Br- and 0.08 - 0.3 mmol of V) mixtures. The theoretical specific capacity, Qo, of the polymer is 4.60 milliequivalents of chloride per gram of the dry polymer. The volume capacity, Qv, has been determined as 1.24 milliequivalents per cm 3 (sulfate form of the polymer in 0.25 M NaNO3 solution). Polyaniline as an acid/base indicator Change in colour upon addition/elimination of protons is the basis for the use of polyaniline as an acid/base indicator. This indicator gives a sharp end-point in the titration of 0 . 5 - 0.05 N sulfuric, hydrochloric, nitric or perchloric acids with sodium hydroxide solution. At lower acid concentrations sluggish end-points are observed. Late end-points are seen in the reverse titration (acid in the burette and base in the Erlenmeyer flask). This may be due to a kinetically slower rate of protonation of the undoped polyaniline solution. A simple titration of the polyaniline salt powder in water with sodium hydroxide displayed equilibrium constants pK 1 = 6.5 and pK2 = 2.7.
Conclusions
We have used a volumetric m e t h o d to establish the number of electrons per repeat unit in the peroxydisulfate oxidative polymerization of aniline to polyaniline. The use of this polymer as an anion~exchange polymer and as an acid/base indicator is encouraging.
Acknowledgement One of us (M.K.D.) gratefully acknowledges the University Grants Commission for the award of a Junior Research Fellowship.
References 1 R. Willstatter and S. Dorogi, Ber., 42 (1909) 2147. 2 A. G. Green and A. E. Woodhead, J. Chem. Soc., 97 (1910) 2388; 101 (1912) 1117.
215
3 E. M. Geni~s, A. A. Syed and C. Tsintavis,Mol. Cryst. Liq. Cryst., 121 (1985) 181; E. M. Geni~s and C. Tsintavis,J. Electroanal. Chem., 195 (1985) 109; 200 (1986) 127. 4 W. S. Huang, B. D. Humphrey and A. G. MacDiarmid, J. Chem. Soc., Faraday Trans. I, 82 (1986) 2385; A. G. MacDiarmid, J. C. Chiang, A. F. Richter and A. J. Espstein, Synth. Met., 18 (1987) 285; A. G. MacDiarmid and A. J. Epstein, Trans. Faraday Soc., (Discuss.), (1989) in press. 5 N. Mermilliod, J. Tanguy, M. Hoclet and A. A. Syed, Synth. Met., 18 (1987) 359. 6 H. Kuzmany, E. M. Geni~s and A. A. Syed, Springer Series in Solid-State Sciences, Vol. 63, Springer, Berlin, 1985, p. 223. 7 S. Kaplan, E. M. ConweU, A. F. Richter and A. G. MacDiarmid, J. Am. Chem. Soc., 110 (I 988) 7647, and refs.therein. 8 I. M. Kolthoff and R. Belcher (eds.), Volumetric Analysis, Vol. Ill, Interscience, N e w York, 1957, pp. 287 - 289. 9 W. M. Latimer, Oxidation States o f the Elements and their Potentials in Aqueous Solution, Prentice-Hall, New York, 1952, p. 78. 10 F. Minisci, A. Citterio and C. Giordano, Acc. Chem. Res., 16 (1983) 27.