THIOL-MODIFIED PYRROLE MONOMERS - 4 - ELECTROCHEMICAL DEPOSITION OF POLYPYRROLE OVER 1-(2-THIOETHYL)PYRROLE

The electrochemical deposition of polypyrrole (PPy) potentiodynamicall y and potentiostatically over monolayers of 1-(2-thioethyl)pyrrole (1- TEP) is described. The relationship between monolayer oxidation and PP y growth depended strongly on the electrolyte. In propylene carbonate/ LiClO4, the PPy polymerization potential was higher than that for 1-TE P monolayer oxidation, and the monolayer oxidation peak was identical to that seen in monomer-free electrolyte. In water/LiClO4, the oxidati on and polymerization potentials were almost the same, with the result that the onset of polymerization was prevented until after the monola yer oxidation process had been completed. In water/(sodium dodecylbenz enesulfonate), an anionic surfactant, the PPy polymerization potential was lower than that in water/LiClO4, and polymerization apparently oc curred without monolayer oxidation. In all cases, PPy growth was found to be essentially the same on 1-TEP, oxidized 1-TEP, and clean gold a s evidenced by cyclic voltammograms, chronoamperograms, and film appea rance. These results show that the 1-TEP monolayers probably decompose d before PPy polymerization began or were, in the case of sodium dodec ylbenzenesulfonate, most likely inaccessible because they were covered by the surfactant. This indicates that 1-TEP cannot be used to covale ntly bind Pgr to gold. These results also demonstrate that the general approach to adhesion promotion through the use of thiol-modified pyrr oles has conditions and limits that must be recognized. The electroche mistry of PPy grafting to surface-bound pyrrole depends critically on the electrolyte, which is important for application of this technique in real devices. In addition, the oxidation reactions undergone by suc h a monolayer cannot be assumed to be different in the absence and pre sence of pyrrole. Finally, the technique will probably not work with s urfactant anions, which are of most practical interest.