The Doping of Poly-P-Phenylene Sulfide and its Oligomers: a Spectroscopical Study
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THE DOPING OF POLY-p-PHENYLENE SULFIDE AND ITS OLIGOMERS: A SPECTROSCOPICAL STUDY P.PIAGGIO, D.GIRIBONE, C.CUNIBERTI AND G.DELLEPIANE UniversitA di Genova, Istituto di Chimica Industriale, Europa 30, 16132 Genova, Italy
Corso
ABSTRACT It is shown that the spectra of poly-p-phenylene sulfide doped at low doping level with different doping agents exhibit features similar to those already observed in polyacetylene and can be qualitatively interpreted in terms of the Amplitude Mode Theory.
INTRODUCTION Poly-p-phenylene sulfide (PPS) is a processable polymeric material with interesting properties of chemical, physical and thermal stability [1,21. The capability of this polymer to become conductive upon doping with strong oxidants has stimulated several studies on the physical and chemical modifications responsible of the change in its electrical conductivity [3-7]. Powerful tools for these studies are provided by electronic and vibrational spectroscopies, which also enable to compare the behaviors of different chemical classes of conducting
polymers
on the basis of the theoretical models developed for conjugated chains. Spectroscopical studies of PPS doping have been carried out mostly for the reaction with gaseous AsF 5 [3,4,6,8]. Less data are available for other dopants in the vapour phase like SbF5 , SOl [7] or for the doping reactions with AlCl 3 ,FeCl3,TaF 5 in solution [9]. These data ,often contradictory, have been explained by different models so that the origin of electrical conduction in PPS is still a controversial problem. It is our opinion that these difficulties derive from the following general problems connected with the spectroscopy of conducting polymers: - the best polymer samples for conductivity studies often are the worst ones for spectroscopy work; moreover they are always opaque in the conductive state - the reactivity of both dopants and doped polymers is very high and causes a great instability of the materials. Moreover in the case of PPS only very recently a reliable assignment of the vibrational spectrum and its dependence on the sample crystallinity has been proposed [10]. To reach a better understanding of all the problems connected with the doping of PPS selected samples of the polymer as well as of simple related molecules have been doped with TaF 5 and the spectral changes in the VIS,NIR and IR regions have been carefully analysed. Some comparative results from doping with other oxidizing agents are also reported. Mat. Res. Soc. Symp. Proc. Vol. 173. ©1990 Materials Research Society
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RESULTS The spectra of BPS films lightly doped in CH 3 NOý solutions 2 of TaF5 show a broad asymmetric band in the NIR with the maximum at 1250 nm (Fig.l) and less intense peaks in the IR around 1550 and 1040 cm-1 (Fig.2). 3.
~2. .0
Fig.l. Electronic absorption of BPS doped with TaF 5.
0
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.0
1600
nm
2200
3000
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Fig.2. Infrared spectra of pristine (a) and TaF53 doped (b) PPS.
o r-4000
3000
2000 ,r~ 1500
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All these bands disappear after exposure of the doped sample
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