Pyrrole polyacetylene electrodes

An interesting composite material has been prepared by the electropolymerization of pyrrole on polyacetylene electrodes (45). Because oxidized polypyrrole is far more stable in air than polyacetylene, the resulting composite has the stability of polypyrrole. With different synthetic conditions, either a thin layer of polypyrrole was deposited over individual fibrils of the polyacetylene film or a dense polypyrrole film coated the entire film. When the dense polypyrrole film covered the entire polyacetylene film, the interior... 

The electrochemical polymerization method was used to prepare layers of conductive polymers on electrodes pre-coated with another conductive polymer or using films of a conductive polymer as electrode. This was the method used to prepare a composite of poly acetylene and polypyrrole [150,151] A sandwichlike composite with layers of polypyrrole adhered to polyacetylene was obtained using undoped polyacetylene electrodes. The use of doped polyacetylene induced pyrrole polymerization in the bulk of the film. A strong improvement in the stability of polyacetylene was observed exposure to ambient temperature of 30 days or to water for 20 minutes did not reduce the conductivity of both materials. 

The electrochemical polymerization of pyrrole or thiophene readily lends itself to formation of composites. Polypyrrole-acetylene laminates have been made by using polyacetylene as an electrode 295). The polypyrrole forms as a 5 pm skin on the polyacetylene. If the polyacetylene is first doped, the polypyrrole completely permeates the film. In both cases the conductivity of the composite reached 30-40 S cm-1 and was much less sensitive than that of pure polyacetylene to exposure to moist air or water, so that the polypyrrole protects the polyacetylene even in the case where it permeates the film. In this latter case, treatment with ammonia caused the conductivity to drop by 30 x whereas for the sandwich films the conductivity dropped by 4600 x through the film but only 17 x in the surface layers. 

Poly thiophene, PTP, and polypyrrole, PPR, blends with PS and PC were prepared by Wang et al. [1990] by thiophene or pyrrole electrochemical polymerization using electrodes coated with PS or PC hlms. The thiophene or pyrrole diffuses into the fihn and polymerizes in-situ in the film. Threshold conductivity occurs at 18 wt% for both conducting polymers in PS. Lower levels exist for PTP (12 wt%) and PPR (7 wt%) in PC. Miscibility of PPR/PC is attributed to the lower threshold limit as phase separated blends would be expected to have higher values. Previous studies with polyacetylene/PS blends reported threshold conductivity at 16 wt% polyacetylene [Aldissi and Bishop, 1985]. 

As reported by Krische and Ahlgren [213], the electrochemical polymerization of pyrrole on a polyacetylene anode produces a composite of polyacetylene and polypyrrole. Polypyrrole appears to form on the outer surface of polyacetylene at 1.0 V (versus SCE) when an electrode with neutral polyacetylene grown on it is immersed in an electrolyte of 0.1 M tetrabutylammonium tetrafluoroborate and 0.1 M pyrrole dissolved in acetonitrile. When doped polyacetylene was used, the pyrrole seemed to form on the polyacetylene fibrils, leaving a porous material similar to the original polyacetylene. In either case, the copolymers have conductivities approaching 40 S cm" and demonstrate increased stability in the presence of air and moisture compared to pristine poly acetylene. 

In this review, we discuss the electrode/electrochemical properties and technological applications of -conjugated polymers. It is organized by material and the matmals are grouped in two classes, the polyaromatic polymer films such as the polymer derivatives of aniline, pyrrole, and thiophene, and the linear polyenes such as polyacetylene, polythiazyl. The report does not intend to review the preparation procedures or the physical properties of these materials since they have been summarized elsewhere It is also limited to work published in the scientific literature without attempting to include the numerous patents which have appeared in the last few years. 

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