The structural properties of Poly(aniline)—Analysis via FTIR spectroscopy

Spectrochimica Acta Part A 74 (2009) 1229–1234

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The structural properties of Poly(aniline)—Analysis via FTIR spectroscopy A. Yelil Arasi a , J. Juliet Latha Jeyakumari b , B. Sundaresan b , V. Dhanalakshmi c , R. Anbarasan d,∗ a

Department of Physics, Kamaraj College of Engineering and Technology, Virudhunagar-626001, Tamil Nadu, India Department of Physics, Ayya Nadar Janaki Ammal College, Sivakasi-626124, Tamil Nadu, India c Department of Polymer Technology, KCET, Virudhunagar-626001, Tamil Nadu, India d Department of Mechanical Engineering, MEMS Thermal Control Lab, National Taiwan University, Taipei-10617, Taiwan, ROC b

a r t i c l e

i n f o

Article history: Received 16 December 2008 Received in revised form 7 September 2009 Accepted 25 September 2009 Keywords: Poly(aniline) FTIR TGA Relative intensity

a b s t r a c t Aniline was polymerized under different experimental conditions like variation in time, temperature, monomer and concentration of initiators. Relative intensity of the benzenoid and quinonoid forms were estimated and correlated with poly(aniline) (PANI) structure. TGA counseled the thermal stability of poly(aniline). Through FTIR study, the structure of poly(aniline) was recognized. Comparison of polymerized aniline with two different initiators was done. © 2009 Elsevier B.V. All rights reserved.

1. Introduction Poly(aniline) (PANI) has emerged as an important conducting polymer because of its good environmental, chemical and thermal stability and ease of synthesis. The conducting polymer that can be grown electrochemically or chemically from suitable oxidizable monomers have recently attracted much attention due to its applications like electrochromic windows [1], light emitting diodes [2,3], nonlinear optics based instrumentation [4], construction of solid state batteries [5–7] and photovoltaic cells [8]. Aniline can be easily oxidized in the presence of various supporting electrolytes. However, it should be taken into account that PANI has good conductivity only at low pHs. Hence, various acid media have been employed for electrochemical synthesis of PANI [9–12]. Conductive polymers show the electrical properties due to their conjugated double bonded chain structures, which derive both conducting and non-conducting forms. High quality conducting blends with conventional polymers by melt mixing [13] or by solution casting are still in a developing stage [14]. The reports are available for conducting polymers having conjugated pi bond on their backbone that is responsible for novel electrical and optical properties. The conjugation system consisted of alternating single and double bonds along the chain. The easy oxidation of the pi electron can induce the interesting characteristics such as electrical semiconductivity and variety of optical properties. Many research groups have investigated the functionalities of these materials and made numerous

∗ Corresponding author. Tel.: +886 2 3366 4945; fax: +886 2 2363 1755. E-mail address: anbu [email protected] (R. Anbarasan). 1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2009.09.042

applications [15,16]. PANI doped or protonated with acids like HCl, H2 SO4 or some organic sulphonic acid exhibited good electrical conductivity value. In addition, some reports were available on the use of polymeric acid dopants for PANI [17]. Cihaner and co-workers [18] did the electrochemical polymerization of para substituted halo aniline. In the present investigation we are concentrating only on ANI polymerization in the presence of two different chemical initiators. FTIR spectrometer is a useful tool for various science and engineering fields, because of its high sensitivity or detectivity toward trace amounts of sample, low noise to signal ratio and moreover this method is an easy and inexpensive one. FTIR spectroscopy is used for the determination of anti-oxidant efficiency in sunflower oil [19], characterization of nitrile rubber [20], textural properties of CuO thin films [21], food hydrocolloids in confectionary [22], cancerous tissues of esophagus [23] and in atmospheric applications [24]. Apart from those qualitative applications, the FTIR spectrophotometer is used in quantitative determination also. For example, quantitative application of FTIR spectrophotometer in Ibuprofen in pharmaceutical formulations [25], gypsum raw materials [26], OH populations in mineral grains [27], moisture in lubricants [28], characterization of polymer structure [29]. In the later 2002, Maillard et al. reported the applications of FTIR spectroscopy in the quantitative ester determination of ester functionalized polyolefins [30–32] followed by Anbarasan and coworkers [33,34] through thio ester functionalized HDPE. Currently our research team [35] has published a paper on FTIR based quantitative estimation of bio-degradable poly(glycolic acid) catalyzed by clay. By taking the above mentioned references as a model, we propose here a modified equation for the quantitative determina-

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tion of % amino and % imino forms in colored, rigid and amorphous PANI. Our recent publication proves that transmittance peak area is directly proportional to the concentration of the substance [35]. By thorough literature survey we could not find any report based on the determination of % amino and imino forms in PANI backbone through FTIR-RI method. The novelty of the present investigation is the determination of % amino and imino forms of PANI by FTIR-RI based kinetic method for the first time. 2. Materials 2.1. Methods Aniline (ANI), monomer was purchased from Merck, India. ANI was purified by distillation under vacuum. Hydrochloric acid (HCl, Reachem, India), Peroxy disulphate (PDS, Ottokemi, India), and Potassium dichromate (K2 Cr2 O7 , Reachem, UK) were used for further experimentation without subjecting them to any further purification process. Required amount of ANI (doped with 1 M HCl) has taken in a polymer tube and de-aerated for 30 min under nitrogen atmosphere. The polymerization reaction was initiated by the addition of calculated volumes of pre-aerated oxidizing agent such as PDS. The time of adding the oxidizing agent was the starting time of the reaction. The reaction mixture found to turn green in color and visible appearance of the polymer formation has noticed. Polymerization took place at 45 ◦ C for the reaction time of 2 h. At the end of the polymerization reaction air was blown into the polymer tube to freeze further chemical reactions. The formed PANI was filtered through already weighed G4 sintered crucible. The difference in weight gave the weight of the formed polymer. The same method was adopted for the polymerization of ANI using K2 Cr2 O7 as a chemical oxidizing agent. 2.2. Characterizations

Relative intensity of benzenoid form (RI) =

A1493 A801

Relative intensity of quinonoid form (RI) =

A1565 A801

Imino form =

RI[B/CH] × W1 W2 × 0.509 RI[Q/CH] × W1 W2 × 2.18

Structure of PANI = % amino form(benzenoid form) +% imino form(quinonoid form) The concentration of amino form can be determined from the ratio of the relative intensity of benzenoid structure (appears in the FTIR spectrum at 1493 cm−1 ) and C–H out of plane bending vibration (appears at 801 cm−1 , taken as an internal standard to nullify error). RI

(1)

A

1493



A801

∝ C and RI

A

1493



A801

= mC

Concentration of amino form = X = RI

A

1493



A801

×

W1 × 0.509 W2

where m is proportionality constant. Determination of m is given in Appendix A. Similarly the concentration of imino form can be determined as,

RI

Shimadzu 8400 S FTIR spectrophotometer instrument was used to record FTIR for the PANI samples. The baseline correction was made carefully and the corrected area of the peaks was determined using FTIR software. To confirm the corrected peak area values, the FTIR spectrum was recorded for three times at different places of the same sample. The measurements yielded the concordant corrected peak area values. Hence, for the corrected peak area determination, we need not fix the lower and upper wave number limits, the FTIR software will take care of the limits exactly. Because the corrected area peak values calculated by fixing the limits as well as without fixing the limits produced the same values. For the quantitative determination of % amino and imino forms of PANI, the following corrected areas of the peaks appeared at 1493, 1565 and 801 cm−1 was determined and the relative intensity was calculated as follows:

Amino form =

Our current publication proves that transmittance peak area is directly proportional to the concentration of the substance [35]. The relative intensities of aliphatic ester are proportional to the amount of substance and which can be equalized by the introduction of a proportionality constant. This can be written as, RI[A1745 /A1093 ] is proportional to C, RI[A1745 /A1093 ] = aC, where C is concentration of substance, a is a proportionality constant taken from Ref. [32]. The same principle is applied in the present investigation and the values are reported here. We know that PANI backbone is made up by benzenoid, quinonoid and semiquinonoid forms [36]. The amount of formation of semiquinonoid form is negligible because which can be readily oxidized or reduced. Hence we can write as,

A

1565

A801



∝ C and RI

A

1565

A801



= nC

Concentration of imino form = Y = RI

A

1565

A801



×

W1 × 2.18 W2

where n is a proportionality constant. Determination of n is given in Appendix A. W1 is the weight of polymer taken for FTIR study, W2 is the weight of the initiator used for polymerization, 0.509 and 2.18 are the proportionality constants or calibration coefficients. From the concentration of amino and imino forms of PANI, one can easily find out the % amino and % imino forms of PANI. % amino form =

X Y and % imino form = X +Y X +Y

(3)

Currently Anbarasan and co-workers [36] have published the results on the ratio of relative intensity of benzenoid and quinonoid forms, which predict the structure of poly(␣-naphthylamine), structurally similar to PANI. In the present investigation we are reporting about the order of reaction based on the FTIR-RI results for the first time. Let us see Section 3, dealing with the effect of different experimental kinetic parameters on the kinetics of polymerization one by one. TGA analysis was performed under air purge at the heating rate of 10 ◦ C/min by using SDT 2960 simultaneous TGA and DSC, TA instrument. The Standard Four Probe method determined the electrical conductivity value of polymer samples. 3. Results and discussion

(2)

where W1 is the weight of polymer taken for FTIR study, W2 is the weight of the initiator, 0.509 and 2.18 are the calibration coefficients.

3.1. FTIR spectroscopy The present investigation is mainly focusing on the FTIR spectroscopy based kinetic results and hence the polymer synthesized

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Fig. 1. FTIR spectrum of PANI–PDS–HCl system.

with the aid of PDS and K2 Cr2 O7 as a chemical initiator is explained first. Fig. 1 shows the FTIR spectrum of PDS initiated polymerization of ANI. A broad peak around 3500 cm−1 is responsible for the N–H stretching of PANI. A peak at 3229 cm−1 is accounting for the OH stretching of water molecules physisorbed the PANI backbone. A peak at 1563 cm−1 is due to the quinonoid structure of PANI. Another one sharp peak at 1487 cm−1 is corresponding to the benzenoid structure of PANI. The peak at 801 cm−1 is an evidence for C–H out of plane bending vibration. In the present investigation, even though the spectrum exhibits many peaks due to the structure of PANI, we are interested only on the peaks corresponding to quinonoid structure, benzenoid structure and C–H out of plane bending vibrations. Fig. 2 shows the FTIR spectrum of K2 Cr2 O7 initiated polymerization of ANI. Here also one can observe the same peaks as mentioned in PDS initiated polymerization of ANI. 3.2. Effect of time on the relative intensity (RI) of benzenoid and quinonoid forms of PANI ANI was polymerized under various time intervals with the help of an initiator PDS, while keeping other experimental con-

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Fig. 3. Effect of time on RI of PANI–PDS–HCl system: (A) [B/CH], (B) [Q/CH] and PANI–K2 Cr2 O7 –HCl system, (C) [B/CH], (D) [Q/CH], [ANI] = 0.25 M, [PDS] = 0.025 M, [K2 Cr2 O7 ] = 0.025 M, temperature = 45 ◦ C.

ditions as constant. Time interval was varied between 1 and 3.5 h. While increasing the reaction time, the RI of benzenoid form was increased from 0.4732 to 0.7115. The RI of quinonoid form was also increased with the increase in time. The longer reaction time permits ANI with different possible interactions leading to the formation of dimer, trimer and oligomer with different structures like pernigraniline, nigraniline, emeraldine, etc., Fig. 3A indicates the plot of time vs RI[B/CH] and Fig. 3B represents the plot of time vs RI[Q/CH] . These two plots confirmed that while ANI was subjected to longer polymerization time, the RI of both benzenoid and quinonoid forms of PANI was increased. Table 1 represents the % amino and imino forms of PANI, while varying the reaction time. Eqs. (1)–(3) were used for these calculations. ANI was polymerized with the help of another one initiator namely, potassium dichromate (K2 Cr2 O7 ) under the same experimental conditions as mentioned for PDS system. While increasing the reaction time, the RI of benzenoid form increased from 0.097 to 0.455. The RI of quinonoid form was also increased with the increase in time. Fig. 3C and 3D represents the plot of time vs RI[B/CH] and time vs RI[Q/CH] respectively for K2 Cr2 O7 initiated polymerization of ANI. 3.3. Effect of [ANI] on the RI of benzenoid and quinonoid forms of PANI The effect of various [ANI] on RI of [B/CH] and [Q/CH] was investigated. Concentration of ANI was varied between 0.15 and 0.35 M whereas the other experimental conditions were kept constant (ANI-PDS system). The RI of benzenoid structure increased from 0.0532 to 0.0852 while increasing the [ANI]. While increasing the [ANI], the RI[Q/CH] increased from 0.306 to 0.3583 and then it showed a decreasing trend. This is due to the following reasons: (1) while increasing the [ANI] the RI[B/CH] is increased up to Table 1 Effect of time on % amino and % imino forms of PANI. Time (s)

Fig. 2. FTIR spectrum of PANI–K2 Cr2 O7 –HCl system.

3,600 5,400 9,000 10,800 12,600

PDS

K2 Cr2 O7

% amino

% imino

% amino

% imino

83.3 92.5 92.6 92.9 93.2

16.7 7.5 7.4 7.1 6.7

71.3 77.1 82.8 80.9 79.0

28.7 22.9 17.2 19.1 21.0

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Fig. 4. Effect of [ANI] on RI of PANI–PDS–HCl system: (A) [B/CH], (B) [Q/CH] and PANI–K2 Cr2 O7 –HCl system, (C) [B/CH], (D) [Q/CH], time = 2 h, [PDS] = 0.025 M, [K2 Cr2 O7 ] = 0.025 M, temperature = 45 ◦ C.

[ANI]/[PDS] = 1, once all the free radicals were exhausted where there was no more free radicals to initiate the polymerization reaction. (2) At higher concentration of monomer, the autocatalytic effect plays a vital role, due to the surface effect of PANI lead to the formation of benzenoid structure and then decrement of quinonoid structure. These [B/CH] values are different from our earlier report [36]. In order to find out the order of benzenoid structure formation, the log–log plot was made between [ANI] and RI[B/CH] (Fig. 4A). The plot showed a straight line with the slope value of 0.36, which confirmed the 0.5 order of benzenoid structure formation with respect to [ANI]. Similarly, the effect of [ANI] on RI of quinonoid structure formation of PANI was determined. In order to find out the order of quinonoid structure formation, the log–log plot of [ANI] and RI[Q/CH] (Fig. 4B) was made and the slope value was determined as 0.32. This confirmed the 0.50 order of quinonoid structure formation of PANI with respect to [ANI]. Table 2 represents the % amino and imino forms of PANI, while varying the concentration of ANI. Similarly, when ANI was polymerized using K2 Cr2 O7 , the RI of the benzenoid structure increased from 0.0253 to 0.0402 and then it decreased. In order to find out the order of bezenoid structure formation, the log–log plot was made between [ANI] and RI[B/CH] (Fig. 4C). The plot exhibited a straight line with the slope value of 0.55. This declared the 0.50 order of benzenoid structure formation with respect to [ANI]. Similarly, the effect of [ANI] on RI of quinonoid structure of PANI was determined by plotting log[ANI] vs log(RI[Q/CH] ) (Fig. 4D). While increasing the [ANI], the RI[Q/CH] increased from 0.045 to 0.077. The log–log plot indicated that while increasing the [ANI] the RI[Q/CH] increased to a maximum efficiency and thereafter it showed a decreasing trend. The slope value was determined as 0.52, and confirmed the 0.50 order of quinonoid structure formation with respect to [ANI] while K2 Cr2 O7 was used as a chemical initiator.

Table 2 Effect of [ANI] on % amino and % imino forms of PANI. [ANI] (M)

0.15 0.20 0.25 0.30 0.35

PDS

Fig. 5. Effect of [I] on RI of PANI–PDS–HCl system: (A) [B/CH], (B) [Q/CH] and PANI–K2 Cr2 O7 –HCl system, (C) [B/CH], (D) [Q/CH], time = 2 h, [ANI] = 0.25 M, temperature = 45 ◦ C.

3.4. Effect of [PDS] or [K2 Cr2 O7 ] on the RI of benzenoid and quinonoid forms of PANI [PDS] was varied between 0.015 and 0.035 M by keeping the other experimental conditions as constant. While increasing the [PDS], the RI[B/CH] was increased. RI values increased up to 3.678 and then decreased, whereas RI[Q/CH] increased linearly with [PDS]. This is due to the following reasons: (1) at higher [PDS] all the monomer fractions were oxidized and there was no more free monomer to interact with free radicals generated from initiator. (2) The excess of free radical leads to secondary or over oxidation of ANI and hence the formation of quinonoid structure. The order of the reaction was invented at different [PDS]. A graph was drawn between log[PDS] and log(RI[B/CH] ) (Fig. 5A) and log[PDS] vs log(RI[Q/CH] ) (Fig. 5B) and the slope values were determined as 2.4 and 1.7 respectively with respect to [PDS]. While increasing [PDS], the % amino form was also increased linearly up to a maximum point and thereafter it showed a decreasing trend. The % imino form showed an increasing trend with [PDS]. Similarly, ANI was polymerized with the help of K2 Cr2 O7 and it was varied between 0.015 and 0.035 M, with the other experimental conditions as constant. RI[B/CH] values increased up to 0.4702 and then decreased, whereas RI[Q/CH] increased linearly with [K2 Cr2 O7 ]. The order of reaction was determined by drawing the plots log[K2 Cr2 O7 ] vs log(RI[B/CH] ) (Fig. 5C) and log[K2 Cr2 O7 ] vs log(RI[Q/CH] ) (Fig. 5D) and the slope values were calculated as 2.0 and 1.07 respectively with respect to [K2 Cr2 O7 ]. This confirmed the second order of benzenoid structure formation with respect to [K2 Cr2 O7 ] whereas the quinonoid structure formation followed the first order kinetic reaction with respect to [K2 Cr2 O7 ]. Table 3 represents the % amino and imino forms of PANI while varying the concentration of PDS or K2 Cr2 O7 .

Table 3 Effect of [PDS] or [PDC] on % amino and % imino forms of PANI. K2 Cr2 O7

[PDS] (M)

% amino

% imino

% amino

% imino

42.8 45.8 46.2 49.0 51.8

57.2 54.2 53.8 51.0 48.2

70.6 68.8 74.5 71.4 66.1

29.4 31.2 25.5 28.6 33.9

0.015 0.020 0.025 0.030 0.035

PDS

K2 Cr2 O7

% amino

% imino

% amino

% imino

93.7 93.1 92.5 90.1 87.5

6.3 6.9 7.5 9.9 12.5

86.5 93.2 92.5 90.7 91.3

13.5 6.8 7.5 9.3 8.7

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Fig. 6. Effect of temperature on RI of PANI–PDS–HCl system: (A) [B/CH], (B) [Q/CH] and PANI–K2 Cr2 O7 –HCl system, (C) [B/CH], (D) [Q/CH], time = 2 h, [ANI] = 0.25 M, [PDS] = 0.025 M, [K2 Cr2 O7 ] = 0.025 M.

3.5. Effect of temperature on the RI of benzenoid and quinonoid forms of PANI The effect of temperature was studied on the RI of benzenoid and quinonoid forms of PANI. While increasing the temperature from 283 to 343 K, the RI[B/CH] was increased up to 328 K and then it showed a decreasing trend, whereas RI[Q/CH] showed a linear increasing trend. This is due to the thermal oxidation of monomer at higher temperature leads to the secondary oxidation of monomer with simultaneous oxidative diffusion reaction. Hence, at higher temperature, RI[B/CH] was found to be decreased. From the Arrhenius plot, the energy of activation was determined for both benzenoid and quinonoid structure formation. Fig. 6A shows a plot of 1/T vs log(RI[B/CH] ) and Fig. 6B represents a plot of 1/T vs log(RI[Q/CH] ) for ANI-PDS system. The slope values were determined and the energy of activation (Ea ) was calculated as 100 kJ/mol and 138 kJ/mol respectively for benzenoid and quinonoid structure formation while PDS was used as a chemical initiator. This indicated that the formation of quinonoid structure consumed more amount of heat energy than the benzenoid structure formation. Table 4 indicates the % amino and imino forms of PANI synthesized at different temperatures. Similarly, the effect of temperature was studied on the RI of benzenoid and quinonoid forms of PANI using K2 Cr2 O7 as an initiator. Fig. 6C shows a plot of 1/T vs log(RI[B/CH] ) and Fig. 6D reveals a plot of 1/T vs log(RI[Q/CH] ). The Ea values were determined for both benzenoid and quinonoid structures as 110 kJ/mol and 142 kJ/mol, respectively. The later Ea values indicated that K2 Cr2 O7 system consumed such a higher amount of heat energy for the polymerization of ANI. However, due to the three electron transfer reaction, the K2 Cr2 O7 system produced higher RI values for both benzenoid and quinonoid forms. This value is parallel with the Ea value determined by Rp (not included here) method. Hence, the determination of Ea value based on the FTIR-RI method for polymer-

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Fig. 7. TGA of (A) PANI–PDS–Hcl and (B) PANI–K2 Cr2 O7 –Hcl.

ization reaction for particular oxidative system is exactly suitable. In such a way one can cross-check the Ea values calculated for the same system. 3.6. TGA profile The thermal stability of PANI synthesized by PDS and K2 Cr2 O7 as chemical initiators was analyzed by TGA method. Fig. 7A represents the TGA of PANI–PDS system. The thermogram showed a multi-step degradation processes. The first minor weight loss step up to 200 ◦ C was due to the removal of moisture and physisorbed water molecules. The second minor weight loss step was ascribed to the degradation of undoped benzenoid form. The degradation was extended up to 300 ◦ C. The third major weight loss step up to 800 ◦ C was due to the degradation of HCl doped quinonoid form of PANI. Above 700 ◦ C, it showed that 42.6% weight of residue remained. Fig. 7B blinks the TGA of PANI–K2 Cr2 O7 system. This system also represented a multi-step degradation processes similar to that of PANI–PDS system. Above 700 ◦ C, it showed 36.8% weight residue remained. On critical comparison, the thermal stability of PDS initiated polymerization of ANI yielded higher thermal stability than the K2 Cr2 O7 initiation. This accounted that the PDS was not only acting as an initiator but also acted as a chemical dopant, which can be further confirmed by conductivity measurements. Due to the doping nature of PDS anion, the thermal stability of PANI was increased. The TGA results are in good agreement with FTIR spectral data. The TGA inferred that one minor weight loss step below 200 ◦ C was observed due to the loss of water molecules. The presence of water molecules in the PANI backbone can be further supported with the FTIR spectrum of PANI. A broad peak around 3229 cm−1 accounted for the OH stretching of water molecules. In such a way the TGA results can be correlated with FTIR spectrum of PANI. 3.7. Conductivity measurements

Table 4 Effect of temperature on % amino and % imino forms of PANI. Temperature (K)

283 305 328 338 343

PDS

K2 Cr2 O7

% amino

% imino

% amino

% imino

96.3 96.7 96.2 95.8 95.4

3.7 3.3 3.8 4.2 4.6

84.2 81.8 81.5 80.6 77.1

15.8 18.2 18.5 19.4 22.9

The d.c. conductivity of PANI, which was synthesized by two different initiators, is discussed here. When the PDS concentration is 0.025 M the conductivity value is 4.25 × 10−4 S/cm whereas at the same concentration of K2 Cr2 O7 it shows the electrical conductivity value as 4 × 10−4 S/cm. The slight increase in electrical conductivity of PANI–PDS system proves that PDS is not only acting as a free radical initiator but also acting as a chemical dopant during the chemical polymerization of ANI.

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4. Conclusions ANI was chemically polymerized with the help of two different chemical initiators. The RI from FTIR spectroscopy inferred that during the variation of ANI concentration, both the benzenoid and quinonoid structure formation showed 0.5 order of reaction in the presence of both PDS and K2 Cr2 O7 as chemical initiators. While varying the [PDS], the benzenoid structure formation followed the 2.5 order of reaction whereas the quinonoid structure formation followed the 1.75 order of reaction. However, during the variation of [K2 Cr2 O7 ], the system showed 2.5 and 1.0 order of reaction for benzenoid and quinonoid structure formation, respectively. Temperature variation concluded that quinonoid structure (142 kJ/mol) formation consumed more amount of heat energy than the benzenoid structure formation (110 kJ/mol). The TGA confirmed that PDS initiated polymerization of ANI showed higher thermal stability than the K2 Cr2 O7 initiation. Similarly, PDS initiated system represented higher electrical conductivity than the K2 Cr2 O7 initiator. This recommended that utilizing PDS as a chemical initiator for the chemical polymerization of ANI. Appendix A. Determination of m and n The values of m and n can be determined by FTIR kinetics method. m and n are proportionality constants for amino and imino forms of PANI respectively. In order to find out the value of m, structurally similar compound to amino form, o-phenylene diamine (OPDA), has taken and FTIR spectrum was recorded for different amounts of OPDA. By using FTIR software the corrected peak area of a peak appeared between 1400 and 1500 cm−1 corresponding to the benzenoid structure of OPDA was noted after proper base line correction. The peak area was determined without fixing the lower and upper wave number limits manually because the peak area was determined by manual calculation and by using FTIR software provided the same value. A graph was drawn by plotting log(weight of OPDA) in the X-axis and log(RI[B/CH] ) in the Y-axis and the slope value was determined from the straight line. The slope value is proportionality constant m. The value of m was determined as 0.509.

The relative intensity (RI) of benzenoid structure can be determined by measuring the corrected peak area of benzenoid peak

(appeared between 1400 and 1500 cm−1 ) and a peak corresponding to C–H out of plane bending vibration (720–820 cm−1 ) and their ratio gave the RI of benzenoid structure (i.e.) area of benzenoid peak/area of C–H out of plane bending vibration. The same procedure was adopted for the determination of n, corresponding to the quinonoid structure. For that we need structurally similar compound (i.e.) p-benzo quinine (PBQ) was selected as a structurally similar compound. Here also for different amounts of PBQ, FTIR spectrum was recorded and the corrected peak area was noted for peaks appeared at 1600 cm−1 and (720–820 cm−1 ) corresponding to the quinone structure and C–H out of plane bending vibration. The slope value obtained from the log(weight of PBQ) vs log(RI[Q/CH] ) plot provided the value of n. In the present investigation the value of n was determined as 2.18. The RI of quinonoid structure is A(Q) /A(C–H) . References [1] M.A. De Paoli, A.F. Noguerira, D.A. Machado, C. Longo, Electrochim. Acta 46 (2001) 4243. [2] Q. Pei, Y. Yong, G. Yu, Y. Cao, A.J. Heeger, Synth. Met. 85 (1997) 1229. [3] K. Tada, M. Onada, H. Nakayama, J. Appl. Phys. 238 (1999) L833. [4] Y.D. Zhang, L.M. Wang, T. Wada, H. Sasabe, Macromol. Chem. Phys. 197 (1996) 667. [5] S. Neves, C.P. Foonseea, J. Power Sources 107 (2002) 13. [6] N. Oyama, O. Hatozaki, Macromol. Symp. 156 (2000) 171. [7] H. Uemachi, Y. Mitani, Electrochim. Acta 46 (2001) 2305. [8] K. Tada, M. Onoda, H. Nakayama, K. Yoshino, Synth. Met. 102 (1999) 82. [9] S.J. Choi, S.M. Park, J. ElectroChem. Soc. E 149 (2002) 26. [10] A. Eftelhari, Synth. Met. 145 (2004) 211. [11] M.V. Kulkarni, A. Viswanath, J. Polym. Sci. A: Polym. Chem. 42 (2004) 2043. [12] L. Duic, J. Mandie, E. Kovacieek, J. Polym. Sci. A: Polym. Chem. 32 (2003) 105. [13] M. Zilberman, A. Siegmann, Y. Haba, M. :Narkis, J. Appl. Polym. Sci. 66 (1997) 243. [14] G.I. Titeman, A. Seigmann, Y. Haba, M. Narkis, J. Appl. Polym. Sci. 66 (1997) 2199. [15] M. Situmorang, J. Gooding,.J.D. Hibbert, B. Barnett, D. Biosense, Bioelectronics 13 (1998) 953. [16] P.N. Barlett, P. Cooper, J. Electroanal. Chem. B 105 (1993) 362. [17] J.M. Liu, S.C. Yan, Chem. Commun. (1991) 1529. [18] A. Cihaner, M. Ahmet, J. Onal, J. Macromol. Sci. A: Pure. Appl. Chem. 43 (2006) 153. [19] S.F. Hameed, M.A. Allam, J. Appl. Polym. Sci. 2 (2006) 27. [20] S. Chakraborty, S. Bandyopadhyay, A.S. Durei, Polym. Test 26 (2007) 38. [21] F. Svegl, B. Orel, Mater. Technol. 37 (2003) 29. [22] J. Copikova, A. Synytsya, M. Novethna, Czech. J. Food Sci. 19 (2001) 51. [23] J.S. Wang, J.S. Shi, J.G. Wu, World J. Gastroenterol. 9 (2003) 1897. [24] I. Xueref, F. Domine, Atmos. Chem. Phys. 3 (2003) 1779. [25] S.M. Matkovic, G.M. Valle, L.E. Briand, Latin Am. Appl. Res. 35 (2005) 189. [26] K. Schwendner, E. Libowitsky, S. Koss, Geophys. Res. Abs. 5 (2003) 06826. [27] P.D. Asimow, L.C. Stein, G.R. Rissman, Am. Miner. 91 (2006) 278. [28] F.R. van De Voort, J. Sedman, C. Mucciardi, Appl. Spectrosc. 58 (2004) 193. [29] J.R. Parker, W.H. Waddell, J. Elast. Plast. 28 (1996) 140. [30] M. Saule, S. Navarre, O. Babot, B. Maillard, Macromolecules 36 (2003) 7469. [31] M. Saule, S. Navarre, O. Babot, B. Maillard, Macromolecules 38 (2005) 77. [32] S. Navarre, B. Maillard, J. Polym. Sci. A: Chem. Ed. 38 (2000) 2957. [33] R. Anbarasan, O. Babot, M. Dequiel, B. Maillard, J. Appl. Polym. Sci. 97 (2005) 761. [34] R. Anbarasan, O. Babot, M. Dequiel, B. Maillard, J. Appl. Polym. Sci. 97 (2005) 766. [35] K. Duraimurugan, S. Rathiga, I. Baskaran, R. Anbarasan, Chin. J. Polym. Sci. 26 (2008) 393. [36] R. Anbarasan, R. Anandhakrishnan, G. Vivek, Polym. Compd. 29 (2008) 949.