Conducting Polymer with Improved Long-Time Stability: Polyaniline-Polyelectrolyte Complex
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167 Mat. Res. Soc. Symp. Proc. Vol. 328. 91994 Materials Research Society
Synthesis of the Complex: The Template-Guided Synthesis The polymeric molecular complex of polyaniline and polyelectrolyte was synthesized by a non-traditional synthetic method7 . The synthesis consists two key steps: (1) A polyelectrolyte (Poly(E)) is used as a macromolecular template to bind aniline monomers to form an anilinetemplate adduct (Poly(E):(An),), (2) An oxidant is used to polymerize the aniline monomers in Poly(E):(An), to form a molecular complex (Poly(An):Poly(E)). This method is called templateguided synthesis. As an example, polyaniline-poly(styrenesulfonic acid) molecular complex (Poly(An):PSSA) was synthesized from 3.5 ml distilled aniline and 30 gram of 30% poly(styrenesulfonic acid) aqueous solution (Polysciences, MW= 70,000) in 3 M HCl solution by oxidation with 25 ml of 3.0 M ferric chloride and 8 ml 15% hydrogen peroxide. The dark green powders of Poly(An):PSSA complex were obtained after the reaction product was purified and dried in a rotary evaporator under vacuum at 65 °C7",Th.Elemental analysis results indicated that the chemical composition and formula of the synthetic products were consistent with that of the complex of polyaniline and poly(styrenesulfonic acid)7""7. The complex could be controlled to be soluble in water and polar organic solvents by varying the amount of free solvable functional groups in the polyelectrolyte8 '. Other polyelectrolytes, e.g. poly(acrylic acid) (PAA) may be used to further adjust the properties of the complex7' 8 . Poly(An):Poly(E) Complexes Resist Dedoping by Water We examine a comparative 0.8test in which a sample of 0.7conventional polyaniline is compared with several 0.6Poly(An):Poly(E) complexes when 0.5C: 2 they were immersed in water (c 0.4buffered at pH 7. When chloride(n n -0 doped polyaniline was immersed in 0.3water (pH 7), the color of the 0.2sample changed from green to blue, and the electrically conductive 0.1material changed into an insulator. This transformation was caused by 400 500 600 700 800 900 1000 1100 the loss of dopant (HCl) from Wavelength in nm polyaniline. The doped and undoped films have optical absorption bands Fig. 1 Optical spectra of the water solutions of with X. = 800 nm (curve #3) and polyaniline-polyelectrolyte complexes and polyaniline ý,. = 630 nm (curve #4) film. respectively as shown in Fig. 1. In 1: Poly(An):PAA, 2: Poly(An):PSSA, contrast, the polymeric complexes 3: Poly(An) conductive film, remained in its green and 4: Poly(An) film immersed in water conductive state (curve #1 and #2) when they were in pH 7 water, indicating that Poly(An):Poly(E) is not dedoped. The results of
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a series of such comparative tests are shown in Fig. 2 in which the absorption band at 800 nm (the 0 polaron band) is used as an 0.4SO indicator for the presence of the Ec 0.5'S doped form. It can be seen that the S0.3-2 chloride-doped polyaniline dedoped for pH > 3, while the complexes S0.2-73 resisted dedoping until pH 9. This 0 resistance to dedoping n
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