Indian Journal of Chemistry Vol. 38A, February 1999, pp. 141-149

Oxidatiye synthesis and properties of poly(2-ethylaniline)

R A Misra* , S Dubey, B M Prasadt & Dan Singh

Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005 , India

Received 17 March 1998; revised 21 August 1998

Poly(2-ethylaniline), a n-electron conjuga ted conducting polymer, has been prepared under different polymeriza tion conditions in nitrogen atmosphere. The structure of the prepared polymer has been elucidated by infrared spectra and elemental analyses . The electrochemical studies of the polymerization of 2-ethylaniline and its film at a platinum electrode have been performed in 1,2-dichloroethane using different dopants . The electrical conducti vi ti es of these polymers are found to be in the range of 10'4 to 10'7 Scm'l. Thermal studies of

the polymer were carried out by thermogravimetric analysis. The DTG curves of CI 0 ~ and SbCI ~ doped

polymer revea l the maximum weight loss at 400 and 500°C respectively. The magnetic susceptibility of the prepared polymer shows paramagnetic behaviour. Surface morphology of the polymer film is also described.

Research on highly conducting polymers has increased exponen tia ll y in the last twenty years l' ll. In

the series of conduct ing orgamc po lymers,

polyaniline and polypyrro le have been recogni zed as interesting and unu sual members of the class of TC-conjugated conduc tin g polymers'2"4. Pol y;m iline

has shown potential for large scale applicati ons due

to its simple synthes is, good environmenta l stab ility and adequate level s of elec trica l conducti vity. In vicw

of the above, it was thought worthwhile to study in

detail the synthesis of poly(2-ethylaniline) by oxidative polymeri za tion usi ng some nove l dopants

like SnC l ~ and SbC I;, . T he present paper a lso

emphasizes the electroc hemical properties of the

polymeriza ti on process and the polymer film. The thermal , morphol og ica l and electrical properti es of

the prepared pol ymer have a lso been studied.

Materials and Methods 2-Ethylaniline (A ldri ch, b.p. 210°C) was )Juri Cied

by di stillati on under reduced pressure. 1,2-

Dichloroethane (Glaxo) and water were used arter two distillations. Tetra-n-butylammonillm penta­

chlorostannate 15 (TBAPCS, m .p. 206C C), tet ra-Il­butylammonium perchlorate (TBAP, Fluka, m .p. 2 lOOC), te tra-Il-bllty lammonium tetratlllornborate (TBATFB , Aldrich, l11 .p . 244°C), tetra-Il - buty l-

'Government Post Gradu;](c Co llege, Gopheswar, Chamoli , 24(, 40 1. Imlia

ammonium hexachloroantimonate '6 (TBAHCA, m .p .

200°C), tetra-n-butylammonium chloride (TBAC, m .p. 74°C) and tetra-n-butylammonium hexafluoro­

phosphate (TBAHFP, m.p . 244°C) were used as

supporting electrolytes. All other chemicals used

were of A.R. grade.

(a) Electrochemical polymerization In a typical electrolysis, a solution of 2-ethyl­

aniline (O.IM) and tetra-n-butylammonium

perchlorate (O . IM) in 1,2-dichloroethane (100 ml) was taken in one-compartment cell -containing platinum foil (6.25 cm2) as anode and cathode. The

solution was purged with nitrogen and electrolysis

was carried out under constant current (/=20 rnA, c.d .=3.2 rnA cm'2) with D.C. regulated power supply.

The temperature of the reaction mixture was

maintained at 15±2°C. At the time of electrolysis the

anode got heavily covered with black coloured polymer mass which was removed at the interval of

25-30 minutes by a sharp blade. After obtaining

sufficient amount of product (about 5 hr) the electrolysis was terminated.

(b) Chemical polymerization

Chemical polymerization was performed by peroxodisulphate oxidation. A solution (0.12M) of

K2S20 g in O.IM acid (HCI, HCI04, CH)COOH, H2C20 4, CCI)COOH, 5-sulphosalicylic acid, p-toluene sulphonic acid or sulphamic acid)7 was

142 INDIAN J CHEM, SEC. A, FEBRUARY 1999

added to solution of the monomer (0 .1M) in the same acid. The reaction mixture was stirred for 4-5 hr utider nitrogen atmosphere to get the polymer mass.

The polymer mass obtained by the above method was filtered, washed thoroughly with distilled water and methanol and dried under controlled temperature at 70°C for 5-6 hr. For measuring conductivity the dried polymer mass was pressed in the form of a pellet and conductivity was measured with the help of a Keithly electrometer. The presence of dopant anion was confirmed by the usual analytical methods. Magnetic susceptibility of polymer samples was determined by Gouy's method at room temperature usmg mercury (tetrathiocyanatb)cobaltate (II), Hg[C{)(CNS)4] as reference material. Cyc lic voltammogram was recorded using an EG & G Parc Model-362, scanning pote~tiostat and Servogor 733, x-yet) recorder; scanning electron micrograph was recorded with a JSM 840-A SEM unit with the film deposited on plat inum foil. IR spe,ctrum of the poly(2-ethylaniline) was recorded with a JASCO­FTIR-5300 infrared spectrophotometer using KBr pellet. The IR spectral data of some polymer samples are given below.

Poly(2-ethylaniline) CIO ~ , IR (KEr, cm·I): 3450-

3350, 2950, 2880, 1600, 1520, 1310, 1230, 1140, 1080, 840, 640; Poly(2-ethylaniline) CI-, IR (KEr, cm-I): 3475-33 80, 2950, 2880, 1600, 1510, 1480, 131 0, 1222, 11 70, 838, 638; Poly(2-ethybniline)

BF ;, [R (KEr, cm-I): 3450-3370, 2950, 2880, 1600,

1520, 1480, 1300, 1225, 1180, 1040, 940, 838; Poly(2-ethylanili ne) CH}COO- IR (KEr, cm-I): 3500-3400, 2950, 2880, 1600, 1560, 1525, 1478 , 1350, 1305, 1240, 11 70,840, 680; Poly(2-ethylaniline) CCI)COO-, IR (KBr, cm-I): 3500-3400, 2950, 2880, 1600, 1560, 1508 , 1480, 1360, 1305, 1220, 11 70,

840, 680; Poly(2-ethylaniline) NH)SO ~, IR KEr, cm-I): 3500-3400, 2950, 2880, 1600, 151 8, 1480, 1310, 1225, 1137, 835, 635 ; Poly(2-ethylaniline) p-

CH)C6H4SO ~, IR (KBr, cm-I): 3500-3400, 2950,

2880,1 600,1 520, 1480, 1310, 1250, 1170,83 8,640; Poly(2-ethylanili ne) salicylic acid-5-sulphonate, IR (KEr, cm-Ih 3325-3250, 2950, 2880, 1600, 1518, 1390, 1305, 1240, 1222, 1139,840,612; Poly(2-

ethylaniline) SnCI ~ , IR (KBr, cm-I) : 3375 -3200, 2960, 1600 , 1495, 1285, 1060, 820; Poly(2-

ethylaniline) SbCI ~, IR (KEr, cm-I): 3430-3390,

2925,1600,1510,1280,1150,810.

Results and Discussion

The anodic polymerization of 2-ethylaniline was carried out in different supporting electrolytes and solvents (Table 1). The results suggest that the solvent and electrolyte have pronounced effect on the yield as well as conductivity of polymer possibly due to variation of the chain length of the polymer. Magnetic susceptibility of the polymer per two ring unit mole of samples is also given in Table 1 which shows that the polymers are paramagnetic. The origin of the magnetic properties has been an unsolved problem in the study of conducting polymers. Earlier studies and theoretical calculations l 7

.18 applied to

conjugated chains have suggested that for such polymers,. oxidation creates hole defect state in the band gap. Such a hole defect or charge state is localized to form a polaron. This is the: main species generated by p-type doping in the polymer chain. A polaron has a localized energy level occupied by one electron and has a spin of 112. TIle interaction between polarons in the polaron lattice would lead to the formation of a half-filled band. This would change spin concentration in the sample and hence the magnetic susceptibility. The dopant oxidation level and method of synthesis may produce the variation in electrical conductivity of 1t-electron conjugated polymers. Polymers derived from 2-ethylaniline may be considered as a mixture of repeat units characterized by the redox state of N-atom such

+ + + + as NH, NH2, N =, NH= and N or (=N=); the relative coricentrations of these species depend on the nature, percentage of doping and the oxidation state of N atom which may affect the concentration of polaron and bipolaron and so the electrical conductivity of the polymer. Structural studies

These polyaniline derivatives obtained by chemical and electrochemical mdhods were characterized by IR. TI1e IR spectra of polymers with various dopants show a weak band between 3500 and 3250 cm· l

; characteristic of NH2 and NH stretching

vibrations. Presence of the dopant CIO ~ anion was confirmed by absorption peak at 1110 or 1080 cm-I

and the presence of sulphamate anion was confirmed

•

MiSRA et aJ.: OXIDATIVE SYNTHESIS OF POLY (2-ElHYLANILINE) 143

Table I- Yield, clectrical conductivity and magnetic susceptibility ofpoly(2-ethylaniline) fonned in different electrolytic media by electrochemical [c.d. = 3.2 rnA cm'l, t = 15±2°C, volume of reaction mixture (100 ml), electrolysis time = 5 hr at

Pt (6.25 cm2) electrOde] and chemical methods

No. Solvent Electrolyte Mag.netic J-Ieft' Yield Conductivity susceptibility (8M) (mg) (Scm" ) (emu/two ring

unit)

A Electrochemical method I 1,2-Dichlorocthane TBAP (O. IM) 2.270xI0·) 2.347 276 0.48x I 0.7

2 1,2-Dichloroethane TBAP' (0.1 M) 4.789xI0·) 3.38 360 1.28x 10.7

3 1,2-Dichloroethane TBAPCS (0.05M) 3.486xlO·) 2.90 270 3.80x 10-6 4 1.2-Dichloroethane TBA TFB (0.02M) 0.220xI0·) 0.73 300 2.08xlO·7

5 1,2-Dichloroethane TlJA TFBa (0.02M) 11.604x I 0') 5 .27 390 7.60xlO·7

6 1,2-Dichloroethane TlJAC (0.1 M) 0.647xI0·) 1.24 330 2 .70xI0·~

7 1.2-Dichlorocthane TlJAHCA (0.005M) 3.59IxI0·) 2.19 280 6.38x I 0-4

8 1.2-Dichloroethane TlJAHFP (0.05M) 9 Aqueous HCIO ~ b

B Chemicalmcthod 10 Aqueous HCIO. (0. 1 M) II Aqueous CH,COOH (0. I M) 12 Aqueous HCI (0. 1 M) 13 Aqueous H1Cp. (0.1 M) 14 Aqueous-5-sulphosalicylic acid (0.1 M) 15 Aqueous sulpha111ic acid (0.1 M) 16 Aqueous p-Io luene sulphonic acid (0.1 M) 17 Aqueous CCI ,COOH (0. I M)

a=at Ni e lectrode, b=at stainless steel electrode

by the absorption bands at 1310 and 1137 cm· l. The

other dopants like acetate and p-toluene sulphonate anion were observed to absorb at 1560 and 1250 cm· 1

respectively. The peak at 1525 cm-I is attributed to C=N bonds of the benzenoid units, and the peak at 1600 cm·1 is attributable to C=N bonds of quinoid units . The absorption peak around 840 is assignable to 1 ,2,4-trisubstituted benzene .

The elemental data of carbon, hydrogen and nitrogen in the poly(2-ethylaniline) are presented in

Table 2. The empirical formula of these polymers are

(2 - EtC 6 H J NH-)4 2A - suggesting the presence of

two dopant anions in most of the cases for every four aromatic ring units . The presence of differcnt counter ion levels poss ibly causes the discrepancy observed in the calculated and experimental values. The percent doping levels pf poly(2-ethylaniline) with

different anion are given as P2-EtAnCI 0 ~ (26.4(%),

P2-EtAnSnCI ~ (51.2%), P2-EtAnCl' (11.7%) , P2-

EtAnSbC l ~ (52 .7'10), P2-EtAn P-CH3C6H~S O ~

(15.3% ). The proposed structure for the polymcr c'hain is shown in Scheme 1.

8.754xI0·) 4.60 230 5.60xI0·7

4.168x 10') 3 .18 410 1.43x I 0.7

6.219x I 0') 3.88 480 0.37xI0·7

9.423x I 0') 4.75 210 1.00x I 0.7

1.535x 10') 1.91 630 0.3IxI0·7

1.916x 10') 2. 14 210 0. llxI0·7

0.764x I 0') 1.33 1260 0.63x 10-6 7.042x 10') 4 .05 150 0.18xI0-6 3.69IxI0·) 2.94 300 0.3IxI0-6 4.922xI0·) 3.43 340 0.78xI0·7

A9

a:tV~a!~~/ Et A9 Et

A~ Dopant anion

Scheme

Cyclic vo/twllll1C'lric studies

In the CV run , all studies were carri ed out us ing platinum microelectrode (0. 16 cm2

) very cautiously avoiding the potential values beyond the range of £ =-0.4 to 1.0 V vs SeE under nitrogen atmosphere. The cyclic voltammogral11 of 2-ethylaniline obtained in 0.02 M Bu4NSnC I5 at scan rates, 20, 50, 100 and 200 mV/s are shown in fig , 1. The first potential sweep is characteri zed by a strong narrow anodic peak at approximately 580 mV with the corresponding cathodic peak at 420 mY, The oxidation reaction involves a charge of 151 mC/cm2 at 20 m V Is, During different scan sweeps (Fig. 1) the anodic CUITent peak is increased and shifted towards positive potent ia ls and the corresponding cathodic current peak shift ed

144 INDIAN J CHEM, SEC. A, FEBRUARY 1999

Table 2-Analytical data ofpoly(2-ethylaniline)

No. Polymer

Poly (2-ethylaniline) perchlorate

2 Poly(2-ethylanilinc) pentachlorostannate

3 Poly(2-cthylaniline) tetratluoroborate

4 Poly(2-ethylaniline) chloride

5 Poly(2-ethylanilinc) hexachloroantimonate

6 Po ly(2 -cth ylanilinc) he.xatluorophosphate

7 Poly(2-ethylanilinc) acetate

8 Poly (2-cth ylaniline) oxalate

9 Poly(2-cthylaniline) p-toluene sulphonate

10 Poly(2-cthylaniline) sulph31llate

II Poly(2-cthylan ilinc) sa licyl ic acid-5-sulphonate

12 Po ly(2-C' thylani linc) trichl oroacetate

towards · negati ve ·potentials. The Ipa values vary linearly with sweep rate and Ip/ Ipc ratio is round to be unity between 20 and 200 mV/s as expected for the react ion of s urf~1ce locali zed material. The linear plot of anodic peak current vs scan rate appears to show that the polymeri zation is reversible and diffusion con tro \I ed .

The cyel ic ml ta ll1mogram for 2-ethy Ian iI ine in 0.1 M BujNCIO.j is depleted in Fig. 2 and has two anodic peaks wi th corresponding cathodic peaks. The broad current peaks for the redox reaction of the polymerization process were centered at E,.=680 mV and Epc= 180 m V vs SCE and the coulombic charge passed during the reaction was calculated as 207 and 190 mC/cm2 respectively at 20 mV/s.· The plot of anodic peak current vs scan rate is linear and peak current ratio found to be unity. Although the redox reaction must involve the electrons in the extended 1t­

system of the polymer, the broadness of the peaks together with the fact that Epa does not equal Epe suggests that the reaction has some kinetic limitation. The polymer deposited on the electrode surface was found to be quite stable and could be cycled repeatedly without any evidence of decomposition of

Found (Calc) % C H N

58.24 5.12 8.14 (56.88) (5 .33) (8.29} 36.35 3.24 5.14

(35 .98) (3.37) (5 .24) 61.37 5.76 7.73

(59.07) (5 .53) (8.61) 71.76 6.59 9.36

(70 .20) (6.58) (IO.~) 35.13 3.58 4.9

(33.56) (3.14) (4.89) 54.63 4.85 6.93

(50.13) (4.69) ("7.31 ) 75.38 7.82 8.28

(72.72) (7.07) (9.42) 68.56 5.60 8.32

(66.05) (5 .81) (8.52) 69.06 6.32 6.95

(67.48) (6. 11 ) (6.84) 58.86 6.42 11.69

(57.48) (5 .98) ( 12.50) G3.11 5.76 6.53

(60.65) (5.05) (6."15) 54.31 4.64 6.16

(53 .93) (4.49) (6.99)

the material. As expected, the reaction is slow with thicker film and peaks broaden considerably.

The cyclic voltammetry of 2-ethylaniline in 0.05 M Bu4NBF4 (Fig. 3) shows anodic peak at 460 mV (8.8 mC/cm2

) with the corresponding cathodic peak at 380 m V (6.5 mC/cm2

). 111e Ip. values vary linearly with sweep rate between 10 and 200 mY/so The Ip/Ipc values obtained are approximately uni!'! revealing the process to be diffusion controlled. The cyclic voltammogram of 2·-ethylaniline with 0.005 M Bu4NSbCI6 in 1,2-dichloroethane (Fig. 4) shows oxidation peak at 760 m V (257 mC/clT~2) vs SCE at 20 mY/sec. The oxidation peaks are shifted towards positive potentials at higher scan rates. The comprehensive CV data of 2-ethylaniline with Bu4NSnCIs, Bu4NCI04 and Bu4NBF, are given in Table 3.

The poly(2-ethylaniline) film deposited on platinum microelectrode from the solution containing 2-ethylaniline (O.OIM) and Bu4NSnCls (0.02M) in 1,2-dlchloroethane was washed thoroughly with 1,2-dichloroethane and then immersed 10 1,2-dichloroethane containing Bu4NSnCIs (O.02M) and its cyclic voItammogram was recorded (Fig. 5). The CV curve of the polymer film shows electtoactive

...

MISRA et ol. : OXIDA llVE SYNTI-IESIS OF POLY (2-ETHYLANlLINE) 145

Anodic

;: .. .. '-:> u

- 0·2 E IV Y5· SeE

Fig. I-Cyclic voltammogram of 2-ethylaniline (0.01M) on a platinum microelectrode in 1,2-dichloroethene contammg Bu.NSnCI, (O.02M) wi th diffe rent scan rates of (a) 20 mVs·I, (b) 50 mVs·I, (c) 100 mVs·I and (d) 200 mVs·I.

c .. .­... :> u

Anodic

Cathodic

0·4 0.6 0·8 1.0 EN YS . SCE

Fig. 2- Cycl ic vo lt:lJ1lJ1logram of 2-ethylanili ne (0.0 I M) on a plati num mieroeleetrode In 1.2.-d iehloroethene containing Bu.NCIO, (0 .1 A1) \Vll h different scan rates of (a) 20 mVs·I, (b) 50 mVs·I. (el 100 mVs·1 and (d) 200 mVs·I.

-c .. '-... :> u

Anodic

Cathodic

0·0 0·2 0·4 0 ·6 0·8 EN Ys· SCE

Fig. 3-Cyelic vo ltammogram of 2-ethylaniline (0.0 1M) on a pl atinum Ill icroe leetrode in 1,2-d ichloroeth enc containi ng Bu.NBF. (0.05M) wit h differcnt scan rates of (a) 10 IllVs· I, (b) 20 mVs·I, (c) 50 IllVs·l

. (d) 100 mVs·I and (e) 200 mVs·I .

c .. L L :> u

Anod ic

}O)J.A

Cot hod ic

- 0·4 - 0 ·2 0 ·0 0·2 0·4 0·6 0·8 ' ·0 EN vs s e E

Fig. 4- Cyelic l'ol t ~1Il 1 1ll0gm lll of 2-ethylan il ine (O .OIAf) 011 a platinum 11lIeroeicct rodc In 1.2-dichl oroethcne containing Bu4 NSbCI" (O.OOSAI) Wit h different scan rates of (a) 20 nN s" , (b) 50 mVs·1 and (el 100 J1l Vs·l

•

Tablc 3-Cyclic vo ltammctric rcsults: Pol ymcri zation of 2-ethylani line (0.01 M) on platinum microelectrode in 1,2-dichloroethane containing II -BlI,NSnCI; (0.02 Afl, II -Bu,NCIO, (0.0 1 M) or II -Bu,NBF, (0.05 M), as a supporting electrol yte at different scan rates

No . Scan rate II -Bu.NSnC I; (0 .02 M) ' l n-Bu.NCIO. (0 .0 I M) Il-Bu.NBF. (0.05 M)

mYs·1 Epa Epc fpa fpc fpaJfpc Epa Epc fpa fpc /paJ/pc Epa

(mY) (mY) (mA) (mA ) (mY) (mY) flA flA mY

10 440

2 20 580 420 0.007 0.006 1.1 680 180 7.0 7.0 1.0 460

3 50 620 380 0.012 00 12 1.0 700 160 14.5 14 .5 1.0 470

4 100 660 320 0 .020 0 .025 0.8 740 140 23 .2 23.0 1.01 480

5 200 700 260 0.032 0 .035 0 .9 800 100 35 .5 34.0 1.04 490

Table 4- Thermogravimetric analysis of poly(2-ethylaniline)

S. No . Polymeri zation

Monomer Solvent Electrolyte Percentage loss at 300°C

Percentage loss at

Electrochemical method I 2-Ethylaniline

2 2-Ethylaniline

1,2-Dichloroethane

1,2-Dichloroethane

TBAP' (0. I M)

TBAHCAb (0.005 M)

34.04

8.80

a = Measurement performed at 5°C/min under nitrogen atmosphere b = Measurement performed at 10°C/min under air c = Weight percentage ofresidue at 900°C ci. = High rate of decomposition of polymers

400°C

84.90

25.00

Epc /pa fpc /paJ/pc mY flA flA

380 0 .25 0.20 1.2

380 0.45 0 .35 1.2

360 0 .85 0 .65 1.3

350 1.35 1.00 1.3 340 2.20 1.60 1.3

PolymerTGA Residue percentageC DTGd (l"C)

9 .93 400

17.50 500

..... ~ 0\

I .... (j

.~ ~ }» "T1 tTl tIl

~ -< -'I:> 'I:> 'I:>

c .. .. .. " u

:M]SRA et 01. : OXIDATIVE SYNTIIESIS OF POLY (2-ETHYLANILINE)

'inodlc

lOot "'"

Cathodit

-O.S ().o o·s ' ·0 ' .S 2·0 ElY vs . SCE

;F-

...

.c;

. r:!' .. ~

100

80

60

40

20

0 0 200 400

147

0·0 c 'E

2'() .... ;F-

4·0 '; .~ ...

6·0 CI .~

8·0 ... .. .,

to-O ~

12·0

600 800

Fig. 5-Cyclic vo italllillogram of poly(2-ethylanil.ine) fi lJ11 on a platinum l11icroclcct rodc In 1,2-dic hl oroethcne containing Bu4 NSnCI , (O.02M) <It 50 mVs·'.

Fig. 6a--TGA and DTG curves of CI O~ doped poly(2-ethyl­

ani l.ine) with a heating rate of IO°C/min.

v

110 NDfT TM eo TI

~ I ~ - . 100 -~ ... ~ .. :) .~ ell •

110 .0

10 !~

" .. .. ... c: 70 30 0 a > u 0 Co 110 is

Co a u II. ..

1: 110 20

40 111

30 10

20 ., 10

100 200 ! 0 .00 eoo tOO 0 1000 eag C

Fig. 6b-TGA and DTA curves of Sb Cl ~ doped poly(2- ethylani line) with a heating rate of IO°C/min .

-I' •

Q"~+ ~r::e.~~~ -Q l . t

~ j ~ ~.-. NH2 ~~. \ ~r) ~ /; ~) n + (n -1) H

Et Et Et Et

Scheme 2

148 INDIAN J CHEM. SEC. A. FEBRUARY 1999

0-0

C 2·0

1 4·0 :: '" 6·0 > .

~ 8 ·0 >

~ 10·0

~ 12·0 .

200 600

Fig. 7a- DTG curves of Sb CI;; doped poly(2-ethylaniline) with a heating rate of 10'C/min .

;; 6

~ 4

100 300 500 700 900

TEMPERATUREOC

Fig. 7b- DTA curves ofCI O~ doped poly(2-ethyl aniline) with a

heating rate of 10°C/min .

properties which cycles at 1150 m V vs SCE. The

redox peak current of this film at multiple scanrt (Fig. 5) is constant wh ich shows that the electrochemically

prepared P2-EtAnSnC I ~ film 15 stable.. under

experimental condition.

Thermogravimetric (TG) analysis

The TG analysis of CIO ~ (Fig. 6a) and SbCI ;

(Fig. 6b) doped e lectrochemically synthesised

po lymer Crab le 4) sho\Vs that about 34 and 10 percent weight o/" the po lymer sample gets lost at 300 and 333°C respec ti ve ly. Thi s loss may be due to the

evolu tion o/" a lo\V molecu lar weigh t compound , li ke the dopant anion. The weight lost at 400 and GOO"C indicated about :-: 5 percent loss either by evaporation

and/or by degrad at ion on hea ting the C IO ~ and

SbC I ~ doped pol ymer. The derivati ve thermo­

gravimetry (OTG) curvc o/" CIO 4" (Fi g. Ga) and

SbC I ;' (Fig. 7a) doped polymer suggested that the

maximum rate of decompos ition is· at 400 and 500"C

respectivel y . The different ial thermal analys is (OT 1\)

curve or poly(2-ct hy laniline) C IO ~ (Fi g. 7b) sho\Vs

Fi g. ,-SEM picture of pol y(2-ethylaniline with different dopant

(a) Sn C I ~ , magnifi cation x I 000, (b) C I 0 ~ , magnificat ion xSOO

and (c) Sb C I ~, magnificati on XSOO.

one exotherm hump around 150uC and another [\'·0

exotherm around 250 ami 350"C. The SbCI ;' (Fi g.

6b) doped pol ymer sys tem a lso shows onc exotherm hump at 324"C and othe r two exot herrn s observed at 456 and 593"(". This exothermic deco mposit ion

possibl y correspo nds to the bra nc hin g and/or cross linkin g o /" the po lymer at thi s point (Table 4).

MISRA et al.: OXIDATIVE SYNTHESIS OF POLY (2-ETHYLANllJNE) 149

Morphology SEM photograph of poly(2-ethylaniline) doped

with SnCI ~ (Fi g. 8a) shows regular pattcrn of

deposition with pctal like morphology k1\'ing minute

cracks. On the other hand ClO ~ dopcd (Fig. 8b)

poly(2-ethy lanilinc) shows chain li ke fibrous

structure with broader crac ks . The SbC I ;' doped (Fig.

8c) poly(2-ethy laniline) represents regular pattcrn of

deposition with granular morphology wi thout any

cracks. Furthe r, corroboration is provided by the fac t

that conductivity is affected by thc pattern of

deposi tion or pol ymers s ince pol y(2-cthylaniline)

ShCI ~ doped pol ymer w ith no cracks ha s a hi ghcr

conductivity than SnCI ~ doped pol ymcr and the

conductivity o f SnC I ~ doped polymer is hi gher than

that of CIO : doped one which is al so co nlirmcd by

the conductivity mea surement presented in Table 1.

MechaJll.\'/I/ The chemi ca l and electrochemical pol Y11leri zation

of 2-ethy lanilinl' to ]Jol y( 2-ethy lanilinc) is a strai ght forward reac tion. The anodic oxidatiun o f 2-

ethylanilllle in nonaqueou s so lution allord s a rad ica l

cation which then dimerizes with the expulsion of 2W. The process is repeated with involvement of 2e­

and 2H+ in each step favouring the polymerization

process (Scheme 2).

Acknowledgement One of the authors (RAM) thanks the Head,

Chemistry Department for laboratory f(lcility and CSIR New Delhi for the award of an emeritus

sc ientist position. OS and SO are thankful to the

CSIR, New Delhi, for the award of Senior Research

Fellowships.

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