At

Fa

b

c

a

ARRAA

KOSK

1

ahmpctwvhpmmamp

0d

Synthetic Metals 161 (2011) 79–86

Contents lists available at ScienceDirect

Synthetic Metals

journa l homepage: www.e lsev ier .com/ locate /synmet

zomethine-based phenol polymer: Synthesis, characterization andhermal study

atih Dogana,∗, Ismet Kayab, Ali Bilici c

Canakkale Onsekiz Mart University, Faculty of Education, Secondary Science and Mathematics Education, 17100 Canakkale, TurkeyCanakkale Onsekiz Mart University, Department of Chemistry, 17020 Canakkale, TurkeyControl Laboratory of Agricultural Ministry, Senliköy, Florya, Istanbul, Turkey

r t i c l e i n f o

rticle history:eceived 19 July 2009eceived in revised form 25 August 2010ccepted 2 November 2010vailable online 10 December 2010

eywords:xidative polymerizationchiff base polymer

a b s t r a c t

Azomethine-based phenol polymer, poly-2-{[(6-aminopyridin-2-yl)imino]methyl}-phenol (PAPIMP),was synthesized through the combination of condensation reaction and oxidative polymerization. Poly-mer isolated from aqueous solution was characterized by UV–vis, FT-IR, NMR and TG, SEC analysis.According to the SEC chromatograms, the number-average molecular weight (Mn), weight-averagemolecular weight (Mw) and polydispersity index (PDI) values of PAPIMP were determined to be 33,550,78,900 g mol−1 and 2.352, respectively. Also, optical band gaps (Eg) of APIMP and PAPIMP calculatedfrom cyclic voltammetry (CV) measurements. Also, electrical conductivities of each component mea-sured with four-point probe technique. TG analysis showed that PAPIMP was stable up to 300 ◦C. The

inetic parameter thermal decomposition kinetics of PAPIMP was investigated by means of thermogravimetric analysis indynamic nitrogen atmosphere at four different heating rates: 5, 10, 15 and 20 ◦C min−1. The apparentactivation energies for thermal decomposition of PAPIMP were obtained by Tang, Flynn–Wall–Ozawa(FWO), Kissenger–Akahira–Sunose (KAS) and Coats–Redfern methods (CR) were 96.97, 105.33, 97.28and 88.60 kJ mol−1, respectively; the mechanism function and pre-exponential factor were determinedby master plots method. The most likely decomposition process was a Dn Deceleration type in terms ofthe Coats–Redfern and master plots results.

. Introduction

The oxidative polymerization of phenol derivatives constitutesclass of interesting research topic [1]. Oligophenols/polyphenolsave been received much more attention because of their ther-al and mechanical properties [2–6]. Oligophenols are used to

repare composites, graphite materials, epoxy polymers and blockopolymers adhesives, and antistatic materials which are resistableo high temperature. Thermogravimetric analysis (TGA) has beenidely used to investigate the thermal stability characteristic of

arious substances, including polymer pyrolyses. Several papersave shown that nonisothermal thermogravimetric analysis is aowerful tool to characterize the thermal degradation of poly-ers. With proper experimental procedures, information about the

echanism function and kinetics of decomposition can be obtained

nd the kinetic data obtained from thermogravimetric analysisay be used as criteria for the choice of a polymer. The kinetic

arameters of degradation processes, such as the rate constants,

∗ Corresponding author. Tel.: +90 286 218 00 18; fax: +90 286 218 05 33.E-mail address: fatihdogan@comu.edu.tr (F. Dogan).

379-6779/$ – see front matter © 2010 Elsevier B.V. All rights reserved.oi:10.1016/j.synthmet.2010.11.001

© 2010 Elsevier B.V. All rights reserved.

activation energies, reaction orders, and Arrhenius pre-exponentialfactors, can be assessed in light of data recorded from thermo-grams. The study of thermal degradation of oligophenol systemsis of great interest since it can, in many cases; determine theupper temperature limit of use for these materials [8]. Numerousinvestigations employ thermogravimetric analysis to evaluate thethermal behavior of several polymeric materials, at different heat-ing rates in nitrogen. Dogan et al. investigated the thermal behavior,kinetic and thermodynamic parameters of azomethine-based phe-nol polymer–metal complexes using different methods based onthe single heating rate in a nitrogen atmosphere with TG/DTG andDTA [7]. Also, the synthesis and thermal properties of various semi-conducting polymeric materials was reported by Kaya et al. [9–11].On the other hand, El-Shekeil et al. studied the thermal decompo-sition processes of some polymer–metal complexes [12].

In this study, a new polyphenol derivate, poly-2-{[(6-aminopyridin-2-yl)imino]methyl}-phenol (PAPIMP), was synthe-

1 13

sized and characterized using FT-IR, UV–vis, H NMR, C NMR,TG–DTA and SEC techniques. The kinetics of the thermal degra-dation mechanism and the apparent activation energy of poly-2-{[(6-aminopyridin-2-yl)imino]methyl}-phenol were investigatedin different heating rates.

80 F. Dogan et al. / Synthetic Metals 161 (2011) 79–86

ynthe

2

2

wSr

2

(hampd

11(d–

2

at

baat

Scheme 1. S

. Experimental

.1. Materials

Salicylaldehyde, 2,6-diaminopyridine along with all solventsere supplied by Merck Chem., Co. (Germany) and used as received.

odium hypo chloride (NaOCl) (30% aqueous solution), used aseceived was supplied by Paksoy Chem., Co. (Turkey).

.2. Preparation of APIMP

The synthesis of APIMP was adapted from the literatureScheme 1) [13]. The procedure as follows: 2-hydroxy benzalde-yde (0.1 mmol), 2,6-diaminopyridine (0.1 mmol) and catalyticmount of acetic acid were solved in 20 ml absolute ethanol. Thisixture was refluxed for 5 h and cooled to room temperature. The

recipitate formed was filtered, washed with ethanol and thenried under reduced pressure.

IR (KBr) (�max: cm−1): 3470, 3370 and 3210 (–OH and –NH2),614 (–C N), 1479 (–C C-aromatic), 1454 (–C C-aromatic), 1280,230, 1152, 1114, 1085, 752. 1H NMR (400 MHz d6-DMSO): ı 6.221H, d), ı 6.75 (1H, d), ı 7.07 (1H, d), ı 7.08–7.42 (4H, m), ı 7.87 (1H,), ı 8.23 (2H, br., –NH2), ı 8.52 (1H, br., –N CH–), ı 11.0 (1H, br.,OH).

.3. Preparation of PAPIMP with NaOCl

The oxidative polymerization of APIMP was carried out in anqueous alkaline medium using NaOCl as oxidant [14]. The syn-hetic strategy for PAPIMP is outlined in Scheme 2.

Polymerization was carried out in 50 ml three-necked round-ottom flasks which fitted with a condenser, a thermometer andmagnetic stirrer. The APIMP (0.001 mol) was dissolved in an

queous KOH solution (10%, 0.001 mol). After heating the reac-ion mixture to 40 ◦C, NaOCl solution was added drop by drop

Scheme 2. Synthetic procedure and th

sis of APIMP.

within about 20 min. When APIMP interacted with NaOCl solutionin alkaline medium, phenoxy radicals precipitated immediatelywith brown colour.

The mixture was neutralized with 0.001 mol HCl solution atroom temperature. Unreacted monomer was separated from thereaction products by washing with methanol. For the separation ofmineral salts, the mixture was filtered and washed with 25 ml ofhot water for three times and then dried in an oven at 105 ◦C.

IR (cm−1): 3500, 3395, and 3270 (–OH and –NH2), 1622 (–C N),1507 and 1442 (C C-aromatic), 1278, 1181, 1080 (–C–OH andC–O–C), 868, 802, 756 (out-of-plane CH bend). 1H NMR (DMSO):ı ppm, 5.8–8.6 (aromatic protons), 4.1–5.8 ppm (–NH–, –NH2),9.5–11.5 (–CH N and –OH) and 13.2 ppm (intramolecular hydro-gen bonding). 13C NMR (DMSO): ı ppm, 160–145 ppm (C–OH, and–CH N–), 110–145 ppm aromatic carbon signals.

2.4. Characterization techniques

Infrared spectra were measured by Perkin Elmer Spectrum OneFT-IR system and recorded using universal ATR sampling acces-sory within the wavelengths of 4000–550 cm−1. UV–Vis spectraof APIMP and PAPIMP were determined in DMSO. 1H NMR and13C NMR measurements were performed using a Bruker AvanceDPX at 400 and 100.6 MHz, respectively at ambient tempera-ture in deuterated DMSO as solvent. Tetramethylsilane was usedas internal standard. Thermal data were obtained using PerkinElmer Diamond Thermal Analysis. The TG–DTA measurementswere made between 15 and 1000 ◦C (in N2, rate 10 ◦C min−1). SECanalyses were performed at 30 ◦C using a Shimadzu 10AVp seriesHPLC-SEC system with DMF/methanol (v/v, 4/1) as eluent at a

flow rate of 0.4 ml min−1. Polystyrene samples were used as stan-dards. Macherey-Nagel GmbH & Co. (100 A and 7.7 nm diameterloading material) 3.3 mm i.d. × 300 mm column was used. Conduc-tivity was measured on a Keithley 2400 Electrometer. The pelletwas pressed on hydraulic press developing up to 1700 kg/cm2.

e proposed structure for PAPIMP.

F. Dogan et al. / Synthetic Metals 161 (2011) 79–86 81

Table 1Algebraic expression for the most frequently used mechanisms of solid state process.

No. Mechanisms Symbol Differential form, f(˛) Integral form, g(˛)

Sigmoidal curves1 N and G (n = 1) A1 (1 − ˛) [−ln(1 − ˛)]2 N and G (n = 1.5) A1.5 (3/2)(1 − ˛)[−ln(1 − ˛)]1/3 [−ln(1 − ˛)]2/3

3 N and G (n = 2) A2 2(1 − ˛)[−ln(1 − ˛)]1/2 [−ln(1 − ˛)]1/2

4 N and G (n = 3) A3 3(1 − ˛)[−ln(1 − ˛)]2/3 [−ln(1 − ˛)]1/3

5 N and G (n = 4) A4 4(1 − ˛)[−ln(1 − ˛)]3/4 [−ln(1 − ˛)]1/4

Deceleration curves6 Diffusion, 1D D1 1/(2˛) ˛2

7 Diffusion, 2D D2 1/(ln(1 − ˛)) (1 − ˛)ln(1 − ˛) + ˛8 Diffusion, 3D D3 1.5/[(1 − ˛)−1/3 − 1] (1 − 2˛/3) − (1 − ˛)2/3

9 Diffusion, 3D D4 [1.5(1 − ˛)2/3][1 − (1 − ˛)1/3]−1 [1 − (1 − ˛)1/3]2

10 Diffusion, 3D D5 (3/2)(1 + ˛)2/3[(1 + ˛)1/3 − 1]−1 [(1 + ˛)1/3 − 1]2

11 Diffusion, 3D D6 (3/2)(1 − ˛)4/3[[1/(1 − ˛)1/3] − 1]−1 [[1/(1 − ˛)]1/3 − 1]2

12 Contracted geometry shape (cylindrical symmetry) R2 3(1 − ˛)2/3 1 − (1 − ˛)1/3

13 Contracted geometry shape (sphere symmetry) R3 3(1 − ˛)2/3 1 − (1 − ˛)1/3

Acceleration curves14 Mample power law P1 1 ˛15 Mample power law (n = 2) P2 2˛1/2 ˛1/2

16 Mample power law (n = 3) P3 (1.5)˛2/3 ˛1/3

3/4 1/4

/2

/3

/4

Ivid0pPTwa

2

acii

i

Rt

g

w

2

aaf

l

17 Mample power law (n = 4) P4

18 Mample power law (n = 2/3) P3

19 Mample power law (n = 3/2) P2

20 Mample power law (n = 4/3) P3

odine doping was carried out by exposure of the pellet to iodineapor at atmospheric pressure and room temperature in a des-ccator. Electrochemical properties of APIMP and PAPIMP wereetermined using CH instruments 660 C cyclic voltammetry using.1 M tetrabutylammonium hexafluorophosphate (TBAPF6) as sup-orting electrolyte. The voltametric measurements of APIMP andAPIMP were carried out in acetonitrile and DMSO, respectively.he HOMO and LUMO energy levels of the APIMP and PAPIMPere determined from the onset potentials of the n-doping (�

′n)

nd p-doping (�′p), respectively.

.5. Kinetics methods

The application of dynamic TG methods holds great promises a tool for unraveling the mechanisms of physical and chemi-al processes that occur during polymer degradation. In this paper,ntegral isoconversional methods were used to analyze the non-sothermal kinetics of PAPIMP.

The rate of solid-state non-isothermal decomposition reactionss expressed as

d˛

dT=

(A

ˇ

)exp

(−E

RT

)f (˛) (1)

earranging Eq. (1) and integrating both sides of the equation leadso the following expression:

(˛) =(

A

ˇ

)∫ T

T0

exp(−E

RT

)dT =

(AE

ˇR

)(u) (2)

here p(u) =∫ u

∞ −(e−u/u2)du and u = E/RT.

.5.1. Flynn–Wall–Ozawa (FWO) method [15,16]This method is derived from the integral method. The technique

ssumes that the A, f(˛) and E are independent of T while A and E

re independent of ˛, then Eq. (2) may be integrated to give theollowing in logarithmic form:

og g(˛) = log(

AE

R

)− log ˇ + log p

(E

RT

)(3)

4˛ ˛2/3(˛)−1/2 ˛3/2

3/2(˛)1/3 ˛2/3

4/3(˛)−1/3 ˛3/4

Using Doyle’s approximation [17] for the integral which allows forE/RT > 20, Eq. (3) now can be simplified as

log ˇ = log(

AE

R

)− log g(˛) − 2.315 − 0.4567

E

RT(4)

2.5.2. Coats–Redfern method (CR) [18]Coats–Redfern method is also an integral method, and it

involves the thermal degradation mechanism. Using an asymptoticapproximation for resolution of Eq. (2), the following equation canbe obtained:

ln(

g(˛)T2

)= ln

(AR

Eˇ

)− E

RT(5)

The expressions of g(˛) for different mechanism have been listed inTable 1 [19,20], and activation energy for degradation mechanismcan be obtained from the slope of a plot of ln[g(˛)/T2] versus 1000/T.

2.5.3. Tang method [21]Taking the logarithms of sides and using an approximation

formula for resolution of Eq. (2), the following equation can beobtained:

ln

(ˇ

T1.894661

)= ln

(AE

Rg (˛)

)+ 3.635041

−1.894661 ln E − 1.001450E

RT(6)

The plots of ln(ˇ/T1.894661) versus 1/T give a group of straight lines.The activation energy E can be obtained from the slope −1.001450E/R of the regression line.

2.5.4. Kissenger–Akahira–Sunose method (KAS) [22,23]This method is integral isoconversional methods as FWO

ln

[ˇ

]= ln

[AR

]− E

(7)

T2 Eg(˛) RT

The dependence of ln(ˇ/T2) on 1/T, calculated for the same ˛ val-ues at the different heating rates ˇ can be used to calculate theactivation energy.

82 F. Dogan et al. / Synthetic Metals 161 (2011) 79–86

Ft

2

g

g

we

PteiiPtaek

3

3

up7sAaccpcP

tdFoo–hcsafa

ig. 1. FT-IR spectrum of PAPIMP (the region 2800–1900 cm−1 is not shown sincehere are no characteristic bands in this region).

.5.5. Determination of the kinetic model by master plots methodUsing a reference at point ˛ = 0.5 and according to Eq. (2), one

ets

(˛) =(

AE

ˇR

)p(u0.5) (8)

here u0.5 = E/RT. When Eq. (2) is divided by Eq. (8), the followingquation is obtained:

g(˛)g(0.5)

= p(u)p(u0.5)

(9)

lots of g(˛)/g(0.5) against ˛ correspond to theoretical mas-er plots of various g(˛) functions [21,22]. To draw thexperimental master plots of P(u)/P(u0.5) against ˛ from exper-mental data obtained under different heating rates, an approx-mate formula [24,25] of P(u) with high accuracy is used(u) = exp(−u)/[u(1.00198882u + 1.87391198)]. Eq. (9) indicateshat, for a given ˛, the experimental value of g(˛)/g(˛0.5) are equiv-lent when an appropriate kinetic model is used. Comparing thexperimental master plots with theoretical ones can conclude theinetic model [26].

. Results and discussion

.1. Structure of PAPIMP

According to the SEC analysis, the number-average molec-lar weight (Mn), weight-average molecular weight (Mw) andolydispersity (PDI) values of PAPIMP were found to be 33,550,8,900 g mol−1 and 2.351, respectively. The UV–vis spectroscopictudies carried out with DMSO solutions of the APIMP and PAPIMP.ccording to UV–vis measurements, PAPIMP showed absorptionsnd onset position at longer wavelengths than those of APIMP. Thisan be attributed to co-existence of both long and short effectiveonjugation in the polymer chains [27]. Relatively high PDI value ofolymer also confirms the presence of both long and short effectiveonjugation in polymer structure. Fig. 1 shows FT-IR spectrum ofAPIMP.

The spectrum of PAPIMP was different in terms of a reduction ofhe band strength and wavenumber from the spectrum of APIMPue to the increase molecular weight after polymerization. In theT-IR spectra of APIMP and PAPIMP, the bands of azomethine werebserved at 1614 and 1622 cm−1, respectively. The broad signalsbserved between 2900 and 3500 cm−1 for polymer are due toNH2 and –OH vibrations in addition to inter and/or intramolecularydrogen bonding formed between these functional groups. The

−1

arbonyl vibration (1730 cm ) possibly arising from quinonoidegments (oxidation of phenolic hydroxyl groups) is marked by anrrow in Fig. 1. The broad peaks centered at 1507 and 1442 cm−1

or polymer are due to aromatic carbon vibrations and the signalsppeared at 1278 and 1080 cm−1 should attribute to the presence

Fig. 2. 1H NMR-spectra of PAPIMP.

of both phenylene and oxyphenylene units in polymer chains [28]and the resulting polymer should be a complex structure consistinga mixture of these couplings as given in Scheme 2. A significantlyincrease in the peak intensity observed at 802 cm−1 for polymerindicates phenylene type couplings (C–C) are dominant in polymerstructure.

As seen from Scheme 2, APIMP has two reactive groups (–NH2and –OH). Therefore, many coupling sites are available for poly-merization of APIMP and this monomer can be polymerized viaboth C–C couplings (Scheme 2a) and/or C–O–C, C–N–C couplings(Scheme 2b).

The possible existence of a multitude of coupling modes withinone single polymer chain makes it difficult to predict a model repeatunit. For this reason, the determination of precise structure forresulting polymer is extremely hard [29]. Similar spectral complica-tions were also seemed for the other –NH2 and –OH functionalizedaromatic polymers [30,31].

However, to follow the spectral changes after polymerizationand understand the proposed polymer structure, 1H NMR spec-trum of monomer (not shown) should be took into account. Thebroad –NH2 and –OH proton signals were observed centered at8.23 ppm and 11.0 ppm, respectively. The azomethinic proton sig-nal was appeared at 8.52 ppm. The aromatic proton signals wereobserved at between 6.22 and 7.87 ppm.

After polymerization, the all proton signals were become quitebroad as shown in Fig. 2. The broad 1H NMR signals assign the pres-ence of protons with the different chemical surroundings on theother hand, the presence of high integration ratios for hydroxyland amine protons in 1H NMR spectrum suggest that the polymer-ization should take place via mainly phenylene units as shown inScheme 2a. IR spectrum of polymer also confirms this finding (thepeak at 756 cm−1).

1H NMR spectrum of PAPIMP showed multiplets in the5.8–8.6 ppm and 4.1–5.8 ppm range are attributed to signals ofaromatic hydrogens and –NH– and –NH2 hydrogens, respectively.The broad signals between 9.5 and 11.5 ppm are attributed to –OHand –CH N signals of PAPIMP (Fig. 1) and again, the broad sig-nal centered at 13.2 ppm should attribute to inter/intramolecularhydrogen bondings in polymer backbone [32]. It is well known,oxidative polymerization of –NH2 and –OH functionalized aromaticmonomers in aqueous alkaline medium should produce branched(ortho and para) constitutional units.

The duplets observed at 6.22 and 6.75 ppm for monomer spec-trum belong to proton signals of pyridine rings. However, theproton signals observed lower aromatic field indicate proton sig-nals of phenol rings. As examined the 1H NMR spectrum ofpolymer, it can be clearly seen, the peak intensity between 6.22 and6.75 ppm are still high, although the peak intensities of proton sig-

nals observed at lower aromatic field (phenol rings) are relativelyreduced (Fig. 2). These indicate that the aromatic dehydrogenation(couplings for polymerization) should mainly via phenol rings notpyridine rings.

F. Dogan et al. / Synthetic Metals 161 (2011) 79–86 83

1bTo

3a

alwa

b[g−

oped

f

�

wi

Fig. 3. Cyclic voltammograms of APIMP and PAPIMP.

13C NMR studies of PAPIMP indicated that the multiplets in00–145 ppm and 145–160 ppm range are attributed aromatic car-on signals and C–OH, –C–NH, –CH N carbon signals, respectively.he FT-IR spectral data and the results of the 1H–13C NMR spectraf the PAPIMP confirmed together.

.2. Electrochemical and conductivity measurements of APIMPnd PAPIMP

The voltammograms of APIMP and PAPIMP were carried out incetonitrile and DMSO, respectively. The HOMO and LUMO energyevels and electrochemical energy gaps (E

′g) of APIMP and PAPIMP

ere determined from oxidation and reduction onset values andre shown in Fig. 3.

The onset potentials of the n-doping (�′n) and p-doping (�

′p), can

e used to determine HOMO and LUMO energy levels of component33]. The HOMO, LUMO energy levels and electrochemical energyaps (E

′g) of APIMP and PAPIMP were found to be between −5.41,

5.24; −2.71, −3.13; 2.67 and 2.54 eV, respectively.The conductivity measurements were taken on pressed pellets

f the solids via a four-point probe method after drying the solidellets in a vacuum oven for 24 h. The monomer and polymer werexposured to iodine vapors with varying doping times from 0 to 7ays.

Conductivity of the samples was then calculated according toollowing equation [34]:

= ln 2� × t

here � is the conductivity in S cm−1, t the thickness of the pelletn cm, and R is the resistance obtained from the four-point probe

Fig. 5. The typical dynamic TG/DTG and DTA curves

Fig. 4. Electrical conductivities changes of I2-doped APIMP and PAPIMP versus dop-ing time at 25 ◦C.

current versus voltage profile. The results are illustrated in Fig. 4.The undopped the conductivity values of AIPMN and PAIPMN werefound to be about 10−l2–10−11 S/cm, respectively. As monomer andpolymer doping with iodine up to 3 days, the conductivity values ofAIPMN and PAIPMN were sharply increased by three or four magni-tude and then reached a maximal level after 7 days. This maximumconductivity level assigns the presence of iodine-saturated com-pounds and therefore, extra doping with iodine did not significantlyincrease their conductivity values. We assume that the fast increas-ing in conductivity values of monomer and polymer for first 3 daysshould attribute to the presence of azomethine and free –NH and–NH2 moieties in their structures. These groups can be interactedin polymer chains and therefore, led to increased conductivity val-ues. As expected, PAIPMN exhibits the higher conductivity thanthat of AIPMN possibly due to the conjugated structure. In addi-tion, the lower electrochemical band gap of PAIPMN consistent withits the higher conductivity value. The doping with the FeCI3 andSbCI5 were also conducted. However, the lower increase in the con-ductivity values were obtained for synthesized compounds. This isprobably due to lower interaction of these doping agents with thecompounds. However, the obtained values assign the semiconduc-tor natures of synthesized compounds.

3.3. Thermal decomposition process

The thermal decomposition of PAPIMP was selected for thekinetic study. The activation energy of the decomposition pro-cess was determined by multiple heating rate kinetics. The typicaldynamic TG thermograms of PAPIMP in a dynamic nitrogen

of PAPIMP in a dynamic nitrogen atmosphere.

84 F. Dogan et al. / Synthetic Metals 161 (2011) 79–86

ad1Pit

3a

oimtvomcfimr

Kfsewov

oeptpetttF

tAietc

Fig. 7. Activation energy (E) as a function of degree of conversion for the decompo-sition process of PAPIMP calculated by Tang, KAS and FWO methods.

tal data of the thermal decomposition of PAPIMP under different

Fig. 6. FWO plots of PAPIMP at varying conversation in N2.

tmosphere were shown in Fig. 5, where the TG curves for theecomposition of 8–10 mg PAPIMP sample were shown with 5, 10,5 and 20 ◦C min−1 under 60 ml min−1 nitrogen gas. All TG curves ofAPIMP showed that the thermal decomposition took place mainlyn one stage and the curves shifted to the right-hand side with theemperature.

.4. Determination of activation energy Ea, kinetic model g(˛),nd pre-exponential factor A

Several techniques using different approaches have been devel-ped for solving the integral of Eq. (2). The four methodsnvestigated in this work were those of FWO, KAS, Tang and CR

ethod. CR method was based on a single heating rate, whilehe other methods were based on multiple heating rates. Isocon-ersional methods were firstly employed to analysis the TG dataf PAPIMP, because it is independent of any thermal degradationechanisms. Eq. (6) used to obtained the activation energy which

an be calculated from the plot of ln(ˇ/T1.894661) versus 1000/T andtting to a straight line. The mean value of activation energy of ther-al degradation of PAPIMP in N2 was 96.97 kJ mol−1. The calculated

esults were summarized in Table 2.Another isoconversion method used in this paper was that of

AS. Eq. (7) utilized to determine the values of activation energyrom plots of ln(ˇ/T2) against 1000/T over a wide range of conver-ation. In this case ˛ = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 were chosen tovaluate E values of PAPIMP. The determined activation energiesere listed in Table 2 and the average value was 97.28 kJ mol−1

ver the range of ˛ given. This result agrees better with the meanalue of activation energy obtained by Tang method.

The FWO method is an integral method also being independentf the degradation mechanism. Eq. (4) has been used and the appar-nt activation energy of PAPIMP can therefore be obtained from alot of log ˇ against 1000/T for a fixed degree of conversion sincehe slope of such a line given by −0.456E/RT. Fig. 6 illustrated thelots of ln ˇ versus 1000/T at varying conversions. The activationnergies calculated from the slopes were tabulated in Table 2 andhe mean value of activation energy was 105.33 kJ mol−1. Compara-ively, the E value of PAPIMP was very close to ones obtained by thewo methods. The E values of PAPIMP obtained by Tang, KAS andWO methods were 96.97, 97.28 and 105.33 kJ mol−1, respectively.

Constant mass loss lines were determined by measuring theemperature at a given mass percent for each rate. In Fig. 7, therrhenius type plots of dynamic TG runs were shown for mass rang-

ng from ˛ = 0.1 to 0.70 in N2. Table 3 summarizes the activationnergy and correlation coefficient on the overall mass loss from 10o 70 mass% in N2. The results indicated an acceptable correlationoefficient always superior to 0.98551.

Fig. 8. Master plots of theoretical g(˛)/g(0.5) against ˛ for various reaction models(solid curves represent 20 kinds of reaction models given in Table 1) and experi-mental data (�) of PAPIMP at the heating rates 5, 10, 15 and 20 ◦C min−1.

The thermal decomposition of PAPIMP in N2 presented a samebehavior for Tang, KAS and FWO method. The initial activationenergy required to initial decomposition was about 80.61 kJ mol−1.When 90% mass of PAPIMP was loss the activation energy increasedto a maximum value of about 127.46 kJ mol−1. In order to findout the degradation mechanism of PAPIMP, CR method has beenchosen as it involves the mechanisms of solid-state process. Accord-ing to Eq. (5), activation energy for every g(˛) function listed inTable 1 can be calculated at constant heating rates from fitting ofln(g(˛)/T2) versus 1000/T plots. The activation energies and the cor-relations at constant heating rates such as 5, 10, 15 and 20 ◦C min−1

were tabulated in Table 3 for thermal degradation of PAPIMP. Inorder to determine the mechanism the degradation of PAPIMP, wehave compared the activation energies obtained by methods above.According to Table 1, it was found that the E values of PAPIMP inN2 corresponding to mechanism D6 had best agreement with thevalues obtained by Tang, KAS and FWO methods.

Especially at the heating rate in 20 ◦C min−1, the activationenergy corresponding to mechanism D6 is 88.60 kJ mol−1, whichwas very close to the value of 96.97 kJ mol−1 obtained by Tangmethod. The correlation coefficient was also much higher thanother values. In order to confirm the conclusions, the experimentalmaster plots P(u)/P(u0.5) against ˛ constructed from experimen-

heating rates and the theoretical master plots of various kineticfunctions are shown in Fig. 8.

The comparisons of the experimental master plots with the-oretical ones indicate that the kinetic process of the thermal

F. Dogan et al. / Synthetic Metals 161 (2011) 79–86 85

Table 2Activation energies and correlation coefficient of PAPIMP obtained by KAS, FWO and Tang methods.

Conversion KAS method Tang method FWO method

Activation energy,E (kJ mol−1)

Correlationcoefficient, r

Activation energy,E (kJ mol−1)

Correlationcoefficient, r

Activation energy,E (kJ mol−1)

Correlationcoefficient, r

0.05 78.65 0.98551 79.14 0.98965 84.06 0.985370.1 91.62 0.98751 92.11 0.98462 99.02 0.989710.2 96.35 0.99474 96.85 0.99320 101.0 0.989800.3 99.51 0.99832 100.1 0.99684 105.6 0.993150.4 98.77 0.99276 99.35 0.99565 105.4 0.995430.5 94.19 0.99627 94.84 0.99205 101.6 0.997850.6 95.61 0.99739 96.19 0.99522 102.5 0.994320.7 93.53 0.99311 94.28 0.99864 104.0 0.991140.8 120.3 0.99833 121.1 0.99617 129.4 0.998360.9 127.3 0.99143 117.7 0.99009 137.4 0.995120.95 74.07 0.98755 74.99 0.98641 8831 0.98721

Mean 97.281 96.97 105.33

Table 3Activation energies of PAPIMP obtained by CR method in N2 atmosphere.

5 ◦C min−1 10 ◦C min−1 15 ◦C min−1 20 ◦C min−1

E (kJ mol−1) r E (kJ mol−1) r E (kJ mol−1) r E (kJ mol−1) r

A1 45.79 0.98321 46.48 0.98341 46.68 0.98422 47.23 0.98431A1.5 34.40 0.98675 35.02 0.98154 35.23 0.99634 35.71 0.98163A2 28.70 0.99187 29.30 0.99361 29.51 0.99422 29.95 0.99466A3 23.00 0.98862 23.57 0.98331 23.78 0.98574 24.19 0.98433A4 20.16 0.99653 20.71 0.99431 20.92 0.99648 21.31 0.99811D1 63.73 0.99287 64.51 0.99371 64.68 0.99292 65.52 0.99341D2 68.22 0.99123 69.02 0.99231 69.20 0.99073 70.02 0.99121D3 70.08 0.99321 70.89 0.99151 71.07 0.99386 71.89 0.99278D4 73.87 0.99232 74.71 0.99361 74.90 0.99443 75.69 0.99431D5 59.53 0.99344 60.30 0.99211 60.47 0.99432 61.30 0.99521D6 86.77 0.99521 87.66 0.99451 87.91 0.99611 88.60 0.99834R2 41.35 0.98678 42.02 0.98411 42.21 0.98123 42.79 0.98462R3 42.74 0.98875 43.41 0.98765 43.61 0.98634 44.18 0.98412P1 37.67 0.99282 38.32 0.99422 38.50 0.99622 39.10 0.98765P2 24.64 0.99341 25.33 0.99365 25.41 0.99851 25.88 0.97667P3 20.30 0.99423 20.85 0.99432 39.58 0.99234 21.48 0.97432P4 18.13 0.98242 18.67 0.98654 18.87 0.98242 19.28 0.98602P3/2 50.70 0.97412 51.41 0.97343 51.59 0.97635 52.31 0.97600P2/3 28.98 0.98422 29.59 0.98443 29.78 0.98472 30.29 0.98838P3/4 31.15 0.98861 31.77 0.98643 31.96 0.98542 32.04 0.98772

Table 4Activation energies and correlation coefficients obtained by plottingln[ˇR/E] − ln[P(u)] against −ln[1/(1 − ˛)1/3 − 1]2.

ˇ (K mol−1) ln A (s−1) r

5 11.89 0.9982110 11.68 0.9973115 11.35 0.9966720 11.22 0.99573

dBDi

l

Aapl

conductivity measurements show that obtained compounds are

Mean 11.53

ecomposition of PAPIMP agrees well with the D6 master curve.y assuming a Dn law, experimental data, the expression of then model, and the average reaction energy predetermined were

ntroduced into Eq. (2), the following expression was obtained:

n

[ˇR

E

]− ln[p(u)] = ln A − ln

[1

(1 − ˛)1/3− 1

]2

(10)

group of lines were obtained by plotting ln[ˇR/E] − ln[P(u)]

gainst −ln[1/(1 − ˛)1/3 − 1]2. As shown in Fig. 9 and Table 4, there-exponential factor was calculated from the intercepts of the

ines corresponding to various heating rates.

Fig. 9. Plotting ln[ˇR/E] − ln[P(u)] against −ln[1 − (1 − ˛)1/3]2 for PAPIMP at heatingrates.

4. Conclusion

A new polyphenol derivate, PAPIMP, was synthesized by anoxidative polymerization process in alkaline medium. Resultingpolymer was characterized by spectral and thermal studies. The

semiconductor. The activation energies of thermal degradation ofPAPIMP in nitrogen obtained by Tang, KAS, FWO and CR meth-ods were 96.97, 97.28, 105.33 and 88.60 kJ mol−1, respectively. The

8 tic Me

rwmP

R

[[[[

[[[

[[[[[[[

[

[

[[[

[

[[31] C.H. Lim, Y.J. Yoo, Process Biochem. 36 (2000) 233–241.

6 F. Dogan et al. / Synthe

esulting logarithmic value of the pre-exponential factor ln A (s−1)as 11.53. The analysis of the results obtained by CR method andaster plots method showed that the degradation mechanism of

APIMP in N2 is a Dn mechanism.

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