Changes of the properties of poly-phenylene-vinylene-ether and C1–4 poly-phenylene-vinylene-ether with iodine pressure and annealing

Changes of the properties of poly-phenylene-vinylene-etherand C1�4 poly-phenylene-vinylene-ether with iodine

pressure and annealing

B. Zaidia, S. Ayachia, A. Mabrouka, P. Molinieb, K. Alimia,*aLaboratoire des Materiaux, Faculte des Sciences de Monastir, 5000 Monastir, Tunisia

bInstitut des Materiaux Jean Rouxel, CNRS-UMR 6502, 2 Rue de la houssiniere, BP 32229, 44322 Nantes Cedex 3, France

Received 11 July 2002; accepted 16 August 2002

Abstract

It is shown by X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR), infrared absorption (IR) and optical

density (OD), that a charge transfer (CT) complex is formed between poly-phenylene-vinylene ether (PPV-ether) or C1�4PPV-etherand iodine. New more stable CT complexes are obtained with annealing at 463 K for PPV-ether and 353 K for C1�4PPV-ether.From IR, XPS and ESR analysis, we deduced that the doping mechanism of both co-polymers is a grafting of the iodine to the

ether links. ESR analysis reveals that at this annealing temperature, 433 K for iodine doped PPV-ether and 463 K for iodine dopedC1�4PPV-ether, a new radical center appears, added to the first radical centre.# 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Charge transfer; PPV; Iodine; ESR; Radical

1. Introduction

A number of investigations undertaken in the past tostudy organic semi-conducting polymers, from the pointof view of doping polymers with the aim of electronicdevice fabrication, have attracted attention. Manyexperiments have been done using iodine as a dopant[1–5]. Iodine doping of polymers results in the forma-tion of charge-transfer complexes. Although the stabi-lity of semiconducting polymers is especially importantfor applications, chemically doped polymers oftenappear to be unstable at room temperature. As shownin the case of poly(N-Vinylcarbazole) (PVK) there is acharge transfer complex between PVK and iodine [6]which ameliorates its photocondutive properties, andannealing at 370 K can stabilize the properties of thecharge transfer complex [7,8].In parallel many studies show the performance of

poly-para-phenylene (PPV) in fabrication of electro-

luminescent components [9]. Recently it has been shownthat iodine can improve the performance of light emit-ting diodes [10]. Furthermore, it appears that iodine isthe most promising dopant because it does not induceany degradation of the polymer [11] used to makeorganic light emitting diodes. The idea described in thispaper is to study, by X-ray photoelectron spectroscopy(XPS), thermogravimetric analysis (TGA), infraredabsorption, optical density (OD) and electron spinresonance (ESR), the effect of iodine on two co-poly-mers derived from PPV after doping at room tempera-ture, but also after annealing at different temperaturesto stabilize the properties of the CT-complexes.

2. Experimental

The PPV-ether and C1�4PPV-ether syntheses havebeen previously described and their structures (Scheme4a and b) are supported by infrared measurements,raman scattering, XPS and optical density analysis [12–13]. To make this paper easy to read, we briefly recallthe main stages of the syntheses of these co-polymers.The first copolymer, derived from PPV and referred to

0141-3910/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.

PI I : S0141-3910(02 )00271-9

Polymer Degradation and Stability 79 (2003) 183–192

www.elsevier.com/locate/polydegstab

* Corresponding author. Tel.: +216-73-500-274; fax: +216-73-

500-278.

E-mail address: [email protected] (K. Alimi).

as PPV-ether, is obtained by homopolycondensation of1-chloromethyl, 4-methoxylbenzene (Scheme 1).The synthesis of the second co-polymer, referred as

C1�4PPV-ether, was performed in two steps, prepara-tion of the monomer followed by a copolymerisationreaction. The molecular synthesis was also carried outin two stages. First, an O-alkylation reaction consistingof addition of bromobutane on 4-methoxylphenol(Scheme 2) was performed. A chloromethylationreaction then followed (Scheme 3).

2.1. Doping PPV-ether and C1�4PPV-ether powders

The classical method [14] was used for doping co-polymer powders by iodine. The powders were placed in

a separate glass cup with iodine in an isolated bell jar.The doping was done at room temperature over 72 h toachieve the saturation state. After room temperaturedoping, the powders thus obtained were introduced intoa Pyrex tube. The tube was sealed and heated at differenttemperatures: 353, 393, 433 and 463 K for 24 h.

2.2. Experimental techniques of measurements

The resulting powders were characterized by XPSanalysis using a Leybold LHS-12 spectrometer. Thedata were obtained with a magnesium radiation source(1253.6 eV) operating at 10 kV and 10 mA. The passenergy was set at 50 eV. High resolution scans withgood signal to noise ratios were obtained in the C1s,Cl2p, O1s and I3d regions of the spectrum. In order todecrease the charge effect, the powder was fixed to thesubstrate holder by pressing it onto an indium sheet.The quantitative analysis was based on the determina-tion of the C1s, Cl2p, O1s and I3d peak areas with sen-sitivity factors of 0.2, 0,58, 0.6 and 6.4, respectively. The

Scheme 4. (a) Structure of PPV-ether; (b) structure of C1�4PPV-ether.

Scheme 1.

Scheme 2.

Scheme 3.

184 B. Zaidi et al. / Polymer Degradation and Stability 79 (2003) 183–192

sensitivity factors of the spectrometer were provided bythe manufacturer. The vacuum in the analysis chamberwas around 10�6 Pa. All spectra were recorded underidentical conditions. The deconvolution of the XPSpeaks into different components and the quantitativeinterpretations were made after subtraction of thebackground using the Shirley method [15]. The devel-oped curve-fitting programs permitted the variation ofthe parameters such as the Gaussian/Lorentzian ratio,the full width at half maximum (FWHM), the positionand the intensity of the contribution. These parameterswere optimized by a curve-fitting program in order toobtain the best fit.Infrared and UV–Vis spectra were measured at room

temperature using a Brucker Vector 22 spectro-photometer and a Cary 2300 spectrophotometer,respectively. For optical measurements, band positionsare expressed in wave numbers (cm�1) from 400 to 4000for the infrared. The wavelengths, expressed in nm foroptical density vary from 200 to 1500 nm. The sampleswere pellets of KBr mixed with the organic compoundunder study.Dynamic thermogravimetric analysis was carried out

in a Perkin-Elmer TGS-1 thermobalance with a Perkin-Elmer UV:1 temperature program controller. Sampleswere placed in a platinum sample holder and the ther-mal degradation measurements were carried out attemperatures ranging from room temperature to 973 Kat a rate of 5 K min�1 in air.Electron spin resonance (ESR) experiments were per-

formed at temperatures varying from 110 to 523 K on aBruker ER200D spectrometer operating in the X band.

The deconvolution of the ESR spectrum and the inter-pretation was made using the pole method describedelsewhere [16–18].

3. Physical and chemical analysis of the doped

copolymers

3.1. XPS analyses

We start this study with the XPS quantitative analy-sis (Table 1) which shows the presence not only of theelements constituting the co-polymers (C, O, Cl) butalso of iodine which reveals that the co-polymers weremixed with iodine. The relative intensity of iodine inthe case of PPV-ether doped at room temperature is17%, whereas it is 6.6% for C1�4PPV-ether dopedunder the same conditions. According to the quantita-tive XPS analyses, we notice an increase of the oxygencontent in the doped co-polymers after annealing,probably due to the increased influence of the specificsurface area of the co-polymers as a consequence of theiodine doping. A decrease of the relative iodine atomicconcentration according to the annealing temperature isalso observed.Deconvolution of the oxygen peaks in the qualitative

XPS analyses (Table 2) shows two contributions. Thecomponents corresponding to the highest binding ener-gies can be assigned to C–O–C. The peak appearing atlower energy originates from the indium (In2O3) used asa support. The deconvolution of the carbon peak showsthe a new line attributed to COOR bonds in the case of

Table 1

Quantitative (at.%) analysis of different elements in pure and doped with iodine and annealed PPV-ether and C1�4PPV-ether

Etching time Annealing temperature PPV-ether C1�4PPV-ether

C1s O1s C12p I3d C1s O1s C12p I3d

pure 87.0 11.0 2.0 84.4 15.4 0.2

0 mn T=289 K 61.6 19.4 2.0 17.0 77.9 15.1 0.4 6.6

T=353 K 79.6 20.0 0.2 0.2 78.4 17.2 0.5 3.9

T=393 K 74.6 21.1 1.3 3.0 67.3 27.4 1.0 4.3

T=433 K 76.5 20.5 1.0 2 77.5 20.8 1.3 0.4

T=463 K 85.3 13.5 0.4 0.8 74.8 24.2 0.6 0.4

1 mn T=289 K 59.4 13.0 1.7 25.9 77.0 15.0 1.7 6.3

T=353 K 72.7 22.5 0.5 4.3 81.8 9.3 0.7 8.2

T=393 K 84.7 7.8 1.4 6.1 78.0 12.1 2.6 7.3

T=433 K 82.5 12.0 1.0 4.5 88.2 8.7 2.0 1.1

T=463 K 90.8 4.0 0.8 4.4 87.0 11.4 1.2 0.4

3 mn T=289 K 68.5 9.8 1.8 19.9 77.9 14.6 0.4 7.1

T=353 K 68.2 26.0 0.8 5.0 86.3 7.4 0.9 5.7

T=393 K 88.5 6.1 1.2 5.2 83.5 9.2 2.6 4.7

T=433 K 89 8.0 1.0 2.5 87.7 8.8 2.2 1.3

T=463 K 92.6 2.7 0.4 4.3 90.0 7.7 1.8 0.5

B. Zaidi et al. / Polymer Degradation and Stability 79 (2003) 183–192 185

Table 2

XPS qualitatitive analysis of PPV-ether and C1�4PPV-ether powders pure or doped with iodine

Annealing

temperature

PPV-ether C1�4PPV-ether

C1s O1s C12p I3d C1s O1s C12p I3d

C–C C–O–C

C–O–H

C–Cl

COOH In2O3 C=O C–O–C C–O–H I5 C–C C–O–H COOH In2O3 C=O C–O–C C–O–H I5

Pure 285.0a 286.5 – 530.0 531.2 533.0 – 200.2 – 285.0 286.5 288.5 529.0 531.5 533.1 – 200.2

86.5b 13.5 13.5 21.6 65.0 100 73.0 23.5 23.5 10.0 29.0 65.0 100

T=289 K 285.0 286.0 287.5 530.4 – 532.6 – 199.0 620.0 284.8 286.3 288.5 530.7 – 532.6 534.2 – 620.0

76.5 18.5 5.0 22.0 78.0 100 100 77.0 19.0 4.0 12.0 79.0 9.0 100

T=353 K 285.0 285.7 288.6 530.15 – 532.3 – – 619.8 385.0 286.7 288.6 530.5 – 532.2 – 198.9 619.6

75.0 19.5 5.5 37.5 62.5 100 91.0 4.5 4.5 15 85.0 100 100

T=393 K 285.0 286.8 289.0 530.0 – 532.3 – 198.9 619.6 285.0 286.4 288.9 530.5 – 532.3 – – 619.9

85.0 8.0 7.0 3.0 97.0 100 100 75.5 17.5 7.0 16.5 83.5 100

T=433 K 285.0 287.2 288.9 530.2 – 532.2 – 199.0 619.7 285.0 287.2 288.8 530.0 – 532.1 – 198.5 619.1

91.0 4.5 4.5 19.0 81 100 100 92.0 2.5 5.5 9.0 91.0 100 100

T=463 K 285.0 285.6 288.9 – – 532.2 – 199.2 619.9 285.0 286.3 288.5 – – 531.9 – 198.5 619.0

66.5 28.3 5.0 100 100 100 82.5 10.0 7.5 100 100 100

a First line, binding energy.b Second line, relative concentration (at.%).

Fig. 1. Infrared absorption of PPV-ether powders: (a) undoped, (b)

doped at room temperature, annealed at (c) 353 K, (d) 393 K, (e) 433

K and (f) 463 K.

Fig. 2. Infrared absorption of C1�4PPV-ether powders: (a) undoped,

(b) doped at room temperature, annealed at (c) 353 K, (d) 393 K, (e)

433 K and (f) 463 K.


iodine doping. The other contributions are due to car-bon in an environment with C–C links (285 eV) used asa reference [19]. The second component (at 286.5 eV)corresponds to a C–O–H or C–O–C environment butsome C–Cl links can also be present. The chlorine ispresent in a covalent form and the iodine in ionic form(I5�) which can be related to the charge exchange

between the co-polymer and iodine.

3.2. Infrared spectroscopy measurements

Comparison of the infrared spectra is essentiallybased on the PPV and ether characteristic peaks (Figs. 1and 2, Table 3). The latter two are present in all spectra(Fig. 1, Table 2). However, some modifications areobvious. In fact, the peak intensity at about 1080 cm�1

identified as CH2–O–CH2 has diminished compared to

Table 3

Infrared assignments of iodine-doped co-polymers (PPV-ether and C1�4PPV-ether) at various annealing temperature

Assignment PPV-ether C1�4PPV-ether

Pure Doped T=353 K T=393 K T=433 K T=463 K Pure Doped T=533K T=393 K T=433 K T=463 K

F I F I F I F I F I F I F I F I F I F I F I F I

C–I stretch – – 420 vw 420 vw 420 vw 420 vw 420 vw – – 590 vw 590 vw 590 vw 590 vw 590 vw

Aliphatic C=C stretch 828 m 826 s 826 m 828 vs 828 vs 828 vs 860 m 860 m 860 s 863 s 866 m 868 m

Aromatic C–C stretch 1512 s 1506 s 1510 s 1508 s 1506 s 1504 s 1501 s 1497 s 1499 s 1500 s 1501 s 1501 s

1608 m 1606 m 1606 m 1608 m 1609 m 1605 m 1604 m 1604 m 1608 m 1614 m 1617 m 1619 m

CH2–O–CH2 stretch 1080 s 1076 m 1075 m 108 w 1072 w 1076 w 1066 s 1062 m 1063 w 1063 w 1064 w 1064 w

O–CH3 – – – – – – – – – – – – 1462 s 1495 s 1461 s 1462 s 1462 s 1462 s

O–H 3440 vs 3430 s 3420 s 3440 m 3420 m 3440 m 3440 s 3389 w 3200 vw 3270 w 3300 m 3304 m

C–Cl stretch 625 s 630 s 623 m 633 m 628 w 628 vw 678 m 672 w 663 w 675 w 675 vw 675 vw

F, frequency (cm�1); s, strong; vs, very strong; m, mean; w, weak; vw, very weak.

Fig. 3. Optical density of PPV-ether powders: (a) undoped, (b) doped

at room temperature, annealed at (c) 353 K, (d) 393 K, (e) 433 K and

(f) 463 K.

Fig. 4. Optical density of C1�4PPV-ether powders: (a) undoped, (b)

doped at room temperature, annealed at (c) 353 K, (d) 393 K, (e) 433

K and (f) 463 K.


the same peak in pure powders (spectra are normalizedaccording to C¼C peak intensity). We could also statethat the intensity of the peak located at 3440 cm�1 andattributed to O–H (the terminal of co-polymers asmentioned in Scheme 4a and b) decreased with anneal-ing temperature. Also, in the case of C1�4PPV-ether thislatter is shifted towards 3200 cm�1. The OH bandintensity decrease is probably due to the absorption ofwater by the co-polymers or to the KBr used for IRanalyses. We also note that the peaks characteristic ofPPV (Table 3) in both co-polymers are not affected byannealing and iodine doping. Furthermore, new weakabsorption bands appear at about 420 cm�1 for PPV-ether and at 590 cm�1 in the case of C1�4PPV-etherwhich can be ascribed to C–I links [20].

3.3. Optical density measurements

The optical density measurements show that the opti-cal properties of the PPV-ether and C1�4PPV-ether areprofoundly modified by annealing and iodine doping(Figs. 3 and 4). The results show a threshold decreasewith annealing temperature and iodine doping. On theother hand, three possible optical transitions wereobserved in the pure state from the two co-polymers[12,13] [3 (420 nm), 4.25 (290 nm) and 5.6 eV (220 nm)].After iodine doping of PPV-ether, only the transition athigh energy persists. In addition, the thermal annealingcarried out at 353, 433, and 463 K revealed new transi-tions at 2.5 eV (500 nm) which is fixed. On the contrary,in the case of the iodine doped C1�4PPV-ether, only thetransition at weaker energy has disappeared indepen-dently of the annealing temperatures. Moreover we notethe disappearance of the intermediate transition atannealing carried out at 393 and 433 K. At 463 K a newband centred at 800 nm (1.5 eV) appears.

3.4. ESR studies

For the electronic spin resonance (ESR) measure-ments, we note, that no ESR signal was observed beforedoping for PPV-ether and C1�4PPV-ether. After dopingand annealing treatment, a well-resolved ESR signal isobserved in all cases (Figs. 5 and 6), which is certainlyattributed to the charge transfer (CT) between the co-polymers and iodine. The observed line, centred atg=2.0026, at room temperature in the case of C1�4PPV-ether (Fig. 8a and Table 4) is isotropic while it is aniso-tropically centred at 2.0019 in the case of PPV-ether(Fig. 7a and Table 4). Although the shape of ESR signalof PPV-ether is identical to that of C1�4PPV-ether, theirevolution according to the annealing temperature,shown in Table 4, Figs. 5 and 6, is different. In fact, inthe case of C1�4PPV-ether, and after annealing at 353K, we note a decrease in the room temperature ESRsignal when the annealing temperature increases(Table 5). In the case of PPV-ether the ESR intensityafter annealing at 393 K increases with annealing tem-perature. The evolution of the ESR spectra according tothe annealing temperature shows that in both casesbesides the initial structure a new wider isotropic g lineappears. Indeed in the case of C1�4PPV-ether this line iscentred at 2.0030 and appears from 393 K (Fig. 8) whilein the case of the PPV-ether this line, centred at 2.0040,appears from 433 K (Fig. 7). This new paramagneticcentre could correspond to a localized radical carried bythe carbon chain, in particular the C¼C link, or couldresult from the replacement of the ether by a doublebond.

Fig. 5. ESR spectra as a function of annealing temperature of PPV-

ether.Fig. 6. ESR spectra as a function of annealing temperature of

C1�4PPV-ether.


3.5. Thermogravimetric analysis (TGA)

For PPV-ether the TGA results (Fig. 9) show twoplateaus. The first appears in all cases at 450 K andrepresents a weight loss of 4.5% in mass and the secondis at 550 K and can be seen only for the annealed sam-ples. The second mass loss decreases according to theannealing temperature i.e. at 353 K: 12%, at 393 K: 7%,

at 433 K: 3% and at 463 K: 0%. In the case ofC1�4PPV-ether (Fig. 10), if we consider only theannealed samples there is only a single plateau whichappears towards 525 K showing a mass loss of about 20,27, 10 and 0% for annealing temperatures of 353, 393,433 and 463 K respectively. In all cases we think thatthe weight loss observed between 300 and 450 K can beattributed to the loss of labile species (air, water). Up to

Fig. 7. ESR spectra of iodine doped PPV-ether as a function of annealing temperature: experimental (-^-^-), theoritical curve (-&-) and different

components (-) at: (a) 298 K, (b) 353 K, (c) 393 K, (d) 433 K and (e) 463 K.


525 K the observed weight losses, which are greater,probably result from the evaporation of small molecules(monomer or dimer).

4. Discussion and conclusion

The quantitative XPS analyses show the presence notonly of the elements constituting the co-polymers (C, O,

Cl) but also the iodine, which reveals that the co-poly-mers were mixed with iodine. The IR absorption ana-lyses shows the existence of PPV band characteristics, aswell as those of the ether function after doping, whichindicates that the structures of the two co-polymers didnot decompose during doping and annealing. Therefore,new peaks attributed to the iodine (C–I) appear. Theoptical density measurements show that the opticalproperties of both co-polymers are affected by iodine

Fig. 8. ESR spectra of iodine doped C1�4PPV-ether as a function of annealing temperature: experimental (-^-^-) theoretical curve (-&-) and differ-

ent components (-) at: (a) 298 K, (b) 353 K, (c) 393 K, (d) 433 K and (e) 463 K.


doping and annealing. It has been shown by qualitativeXPS that iodine exists as an anionic species (I5

�) whichdemonstrates that the iodine has exchanged a chargewith the co-polymers. On the other hand, we show thatco-polymers exhibit an ESR signal after iodine doping.So, we could deduce through XPS, IR, AO and ESRstudies, that there is a charge transfer (CT) complexformed between the co-polymers and iodine.The observed anisotropy in the case of PPV-ether and

isotropy in the case of C1�4PPV-ether can correspond toa sigma radical carried by a carbon situated out of theplane of the polymer or to the p radical carried by acarbon of the phenyl ring. We think that the iodinedoping mechanisms are the same for PPV-ether andC1�4PPV-ether. On the other hand, the absorption band

at 1081 cm�1 decreases in intensity, showing that hydro-gen atoms in ethylic-ether disappear upon reaction withiodine. As a consequence, we can deduce that there is agrafting of the iodine onto the ether groups (Scheme 5).The iodine ionization shown by qualitative XPS and

the optical spectra changes lead us to believe that the I5�

anion introduces polaronic and/or bipolaronic levels

Table 4

ESR signal deconvolution at 300 K for iodine doped co-polymers PPV-ether and C1�4PPV-ether as a function of annealing temperature

Annealing temperature (K) C1�4PP V-ether PPV-ether

g(xyz) �Hpp I% g(xyz) �Hpp I% g(xyz) g(z) �Hpp I% g(xyz) �Hpp I%

300 2.0026 7.0 100 – – – 2.0013 2.0030 4.75 100

313 2.0020 4.9 100 – – – 2.0013 2.0030 5 100

353 2.00235 3.9 100 – – – 2.0013 2.0030 4.8 100

393 2.0018 3.2 77 2.0026 6.0 23 2.0013 2.0035 7.0 100

433 2.0023 5.75 63 2.0032 8.25 37 2.0010 2.0040 6.0 72 2.0044 9.0 28

463 2.0023 5.8 70 2.0040 6.8 30 2.0003 2.0027 6.0 74 2.0032 8.5 26

Fig. 9. TGA of PPV-ether powders: (a) undoped, (b) doped at room

temperature, annealed at (c) 353 K, (d) 393 K, (e) 433 K and (f) 463 K.

Fig. 10. TGA of C1�4PPV-ether powders: (a) undoped, (b) doped at

room temperature, annealed at (c) 353 K, (d) 393 K, (e) 433 K and (f)

463 K.

Table 5

Evolution of threshold and ESR intensity under iodine process and annealing temperature

PPV-ether C1–4PPV-ether

Threshold (eV) ESR intensity Threshold (eV) ESR intensity

Pure 2.42 (511.5 nm) 0 2.05 (603.8 nm) 0

T=298 K 2.22 (558.8 nm) 200 1.86 (665.3 nm) 272

T=353 K 2.22 (555.8 nm) 16 1.42 (807.1 nm) 101

T=393 K 2.66 (465.3 nm) 41 2.08 (596.1 nm) 20

T=433 K 2.80 (442.3 nm) 217 2.15 (576.9 nm) 6

T=463 K 2.58 (480.7 nm) 277 1.33 (930.7 nm) 1

Scheme 5. Iodine doping.


within the optical gap. After doping at room tempera-ture, an optical transition was suppressed in all samples.The ESR intensity decrease (Table 5) may be due to therecombination of polarons into bipolarons suggestingthat the inter polaronic level transitions are favoured.After annealing PPV-ether at 463 K and C1�4PPV-etherat 353 K, although there is a decrease in the iodineconcentration with annealing temperature, there are nolarge optical changes. Furthermore, the deconvolutionof the ESR spectrum after annealing at high tempera-ture indicates the appearence of two paramagneticradical centres (Table 4). Beyond these temperatures, wenote that the two transitions at weaker energies dis-appear in all cases. However, a decrease of the ESRsignal was observed in the case of C1�4PPV-ether,whereas the observed results were the complete oppositein the case of PPV-ether. We think that the radicalscreated in the case of C1�4PPV-ether do not exist asstable species. On the contrary, the created radicals aremore stable in the case of PPV-ether which explains theESR signal increase. This fact is confirmed by quantita-tive XPS, when samples are annealed at 463 and 393 K.In fact, the iodine content introduced into the C1�4PPV-ether powder is greater than that of PPV-ether. As aconsequence, the states induced within the band gap aremore populated in the first case, which allows the mostpossible radical recombinations.If we take the average iodine percentage, obtained

before and after etching (table 1), we can deduce thatannealing at high temperature (463 K) favours theiodine fixation in the case of the PPV, in contrast toC1�4PPV-ether where a temperature less than 353 K isneeded for this iodine fixation. Therefore Iodine dopingof co-polymers generates charge transfer (CT) com-plexes whose properties evolve with annealing tempera-ture. It seems that an optimal annealing temperature(463 K for PPV-ether and less than 353 K for C1�4PPV-ether) stabilises the CT complexes thus formed.

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Documents

Changes of the properties of poly-phenylene-vinylene-ether and C1–4 poly-phenylene-vinylene-ether with iodine pressure and annealing