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					                                                                                                                                  Abstract No. 3
NATO Advanced Research Workshop
on Electrochemistry of Electroactive Polymer Films WEEPF-2000

                                     A combined way of production of modified sulphonated polyaniline

                                                                              E. Binkauskiene

                                                Institute of Chemistry, A. Gostauto 9, LT-2600 Vilnius, Lithuania

          Polyaniline has been widely investigated because of its practical applications. However, polyaniline is
unsoluble and shows a redox activity only in acidic solution. Polyaniline becomes electrochemically inactive at pH > 4.
When polyaniline had been synthesized with sulphonic groups, the influence of redox activity and conductivity occurred
at pH units higher than 5 in the case of usual polyaniline. A combined way of production of modified self-doped
polyaniline electrode, which is electrochemically active in neutral aqueos solutions, is shown in this work.
          Modified polyaniline films were synthesized by the cyclic voltammogram method in the range of – 0.1 and 1.1
V in aqueous 1.0 M HCl baths containing 0.1 M aniline. A platinum electrode covered with electrochemically
synthesized polyaniline was directly chemically sulphonated in 1.3-propanesultone solution. 1.3-propanesultone solution
in dioxane ( 0.1 g/ml ) was used.
          The incorporation of a sulphonated monomer into the copolymer shows a strong depressing effect on the
deposition rate of the copolymer. It is noted that suppression of the first cycle effect by applying a potential cycling for
degradation studies in acidic solution in self-doped polyaniline is compared with polyaniline. One of the explanations of
this difference is a process of an inner anion doping in the copolymer.
          Reaction of electrochemically synthesized polyaniline with excess of 1.3-propanesultone was carried out under
different conditions: changing temperature and duration. It is possible that 1.3-propanesultone molecules are preferably
adsorbed at the electrode surface [1]. Redox properties of the sulphonated polyaniline were tested with the method of
the first cycle effect. In comparison with polyaniline for the sulphonated polyaniline, the peak current of polyaniline
oxidation decreased and the peak potential shifted to more positive potentials.
          The synthesis of a self-doped polyaniline was optimised as follows. The reaction of polyaniline with excess of
1.3-propanesultone proceeded under different conditions: changing temperature and duration. After that, the first cycle
investigations were performed. Temperature was found be the most essential factor.
          If a chemical synthesis had been carried t = 90 oC for 50 minutes, no dependence of anodic peak in the first
potential scan was on the waiting time at potentials E = 0.0 V. It means that these conditions are the best for
sulphonation of polyaniline. Under other conditions, the effect of the first anodic peak increase was observed. This may
explained by a lower extent of sulphonation and participation of doping anions in the redox process.
          The influence of synthesis temperature on changes of the first anodic peak in the first potential should have
scan at potential E= 0.00 V is shown in Fig. The value of relative anodic peak current I a(t)/Ia(o) does not exceed 1.28.
Small values of a relative anodic peak current were characteristic of N-substituted polyanilines. Ring-substituted
polyanilines showed higher Ia(t)/Ia(o) values [2]. Where Ia(t) represents an anodic peak current obtained at the waiting
time of 500 s, and Ia(o) represents anodic peak current, obtained at zero waiting time.

                     1 ,3
                                                                                      Fig. Dependence of a relative anodic peak current
                                                                                      on temperature at E = 0,00V (electrochemically
                     1 ,2
   Ia (t)/Ia ( 0 )

                                                                                      synthesized polyaniline + 1,3-propanesultone, T
                                                                                      = 90oC,  = 50 min).
                     1 ,1

                            0   10    20   30    40       50   60   70   80    90
                                                  T, C

         A self-doped polyaniline shows its redox activity in neutral 0.1 M CH 3COONa and phosphate buffer solutions.
The redox activity of the self-doped polyaniline in neutral solutions has shown that doping anions do not participate in
the redox process.

1. H. Tang, A. Kitani and S. Ito, Electrochim. Acta 42, 3421(1997).
2. A. Malinauskas, Ber. Bunsenges. Phys. Chem. 102, No. 7, 972(1998).

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