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SzcmmaryThe electrochemical polymerization of pyrrole on platinum produces a strongly adhered, durable film with enhanced conductivity and good electrode properties.MANY workers have been interested in the modification of electrode surfaces by covalently attaching organic monolayers or depositing polymer films.1 While the electrochemical preparation of films on a surface could conceivably produce superior material, this approach has not been pursued rigorously. Our interest in the preparation of durable, conducting organic electrode surfaces led us to this approach. We now present the preliminary results on the electrochemical polymerization of pyrrole2 under controlled conditions. The polypyrrole films were synthesized galvanostatically on a platinum surface in a two-electrode cell containing 0-1 M Et4NBF4 and 0.06 M pyrrole in 99% aqueous MeCN. The films strongly adhere to the surface. These films can be prepared in a variety of aprotic solvents. The yield of deposited film is 0-5 mol F-1 but can be less if the nucleophilic character of the solvent or electrolyte is enhanced. For example, no film is produced in the presence of 0-1 M Et4NBr in MeCN.A polypyrrole film (0.8,um thick) on platinum was used as an electrode in cyclic voltammetry measurements. In MeCN and Me,SO containing Et4NBF,, only a broad background current is observed in the range + 1.0 to -2.0 V.The voltammogram of M ferrocene in MeCN resembles that obtained on platinum. The E" value equals $0.450 us. NaCE (sodium chloride calomel electrode) (0.450 V on Pt3), ip,/ipa equals unity, and I Ep, --E.pcI equals 90 mV a t 2OmVs-l scan rate, with ca. 70% zR compensationFor the reduction of tetracyanoquinodimethane (TCNQ) the signals appear a t +0.260 and -0-290 V vs. NaCE (+0-265 and -0.300 V on Pt). I values equal 70mV a t 2OmVs-l scan rate and ipa/zpc values equal unity for both reaction steps.The I E,, --E PC

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The electrooxidation of , -coupled thiophene oligomers with terminal a-(CH3)3Si groups ( -TMS) and i8-CH3 groups was studied in methylene chloride at room temperature. The oligomers with four, five, six, seven, and eight thiophene rings undergo two stepwise oxidations to produce the radical cation and dication, respectively, as confirmed by the ESR spectra. The redox waves are chemically reversible and separated by 180 mV for the hexamer, heptamer, and octamer, suggesting that the same electrochemical behavior should be observed with the next higher oligomers or with the «--conjugated segments of polythiophene. Thus it is proposed that the broad, featureless voltammogram observed with films of polythiophene is not an inherent property of the polymer segments but may reflect complications from the solid-state nature of the film. Radical cations and dications of some of the oligomers were succesively generated with stoichiometric amounts of FeCl3 in CH2C12 and characterized by vis-near-IR. The energies of the sharp absorption bands in the visible and near-infrared of the neutral and oxidized oligomers are found to scale linearly with the inverse of the oligomer size. Extrapolation of the absorption energy to infinite chain length leads to excellent agreement with the values for neutral poly(methylthiophene), but significant differences are observed with those for the oxidized forms. The implications of this difference on the delocalization length of the polymer radical cation and dication are discussed. Some of the electronic transition assigments for the oxidized thiophene oligomers which appear i:

Highly stable, flexible films of polypyrrole with p-type conductivities of 100 Q-1 cni-l have been prepared by electrolytic oxidation of the appropriate pyrrole monomers; similarly prepared films of mixtures of pyrrole and N -m e t h y l p~~r o l e have conductivities between 5 xand 100 Q-l cm-1 depending upon the composition. ~~ THE discovery of metallic properties in polymers such as polysulphur nitride, (SN) .,l and doped polyacetylene, (CH)z,2 has encouraged the search for other polymeric systems with greater chemical stability and plasticity.In 1968 Dall'Olio et al.3 reported a value of 8 W 1 cm-l for the conductivity of an oxy-pyrrole polymer. IVe have prepared shiny blue-black flexible films of polypyrrole* which, like (SN), and doped (CH)., show metallic properties. The room temperature conductivity of the present films, measured by four-probe technique is as high as 100 R-' cm-l. The films are stable in air and can be heated to 250 "C with little effect on their conducting properties. Thermal analysis confirms that the material is thermally inert below 250 "C after which the rate of weight loss increases and becomes very rapid above 600 "C. The films are prepared by the electrolytic oxidation of pyrrole in acetonitrile solution using a tetraethylammonium tetrafluoroborate electrolyte.4 Though the chemical composition of the films depends on the conditions of preparation, a typical composition is C4.0N,,.87H3.5(BF4) o.25 indicating that the pyrrole rings remain intact. This is consistent with polypyrrole being a polymer formed by linking the pyrrole units zria the cc carbon atoms as suggested previously.The pvrrole units carry a partial positive charge balanced by the BF4-ions somewhat akin to the AgBF, and AgClO, treated polyacetylene films reported by Clarke ef nZ.6 Raman and reflection i.r. spectra show bands characteristic of pyrroles7 confirming the presence of the pyrrole rings in the polymer. The films are less crystalline than pristine polyacetylene. Electron diffraction data show onlyo diffuse rings which correspond to a lattice spacing of 3.4 A , close to the value expected if the separation between the pyrrole chains were determined by the thickness of the pyrrole rings. Normally the chains of pyrrole rings are randomly oriented in the plane of the film. However, under certain circumstances the diffraction rings are arced as a result of the preferred orientation of the pyrrole chains. Scanning electron microscopy shows that the polypyrrole, in contrast to both (SN) . and (CH) does not consist of fibres but is a continuous film with a flotation density of 1.48 g ~m -~.The temperature dependence of the four-probe conductivity is weakly activated, decreasing from a value of 100 R-lcm-l a t room temperature to 30 t2-lcm-l on cooling to -193 "C. Thermop3wer measurements show t h a t the polymer is p-type which is consistent with the fact that it is partially oxidized. The room temperature value of the thermopower is 7pVdeg-l. This small value of the thermopower together with its linear temperature d...