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...

An apparatus is described for making transport measurements, especially thermopower, on single crystals of highly conducting organic solids. It is designed specifically for small fragile anisotropic samples such as TCNQ salts. The temperature range is 400−1.2 k. A slow ac technique is used so that stray thermal emfs are eliminated and measurements can be taken with a small (0.5 K) temperature gradient for good temperature resolution in regions where the transport properties are changing quickly.

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