Highly electroconductive polypyrrole composites

Abstract

Following up our pioneering works on polypyrrole (PP) [1, 2], one of the few synthetic metals having a fairly good stability in air, we have tried to overcome some of the limits of its synthesis and handling. It was known that PP may be synthesized by oxidative polymerization with chemicals, giving black substances having a high molecular weight and insulating properties [3, 4]; on the contrary the electrochemical oxidation produces highly conducting materials (up to 1 to 5 x 102Scm ~) [2], but it is limited by the shape and nature of the electrode; PP films prepared in this way are brittle and generally show poor mechanical properties; the preparation of PP plastics composites, always by anodic oxidation, is at the moment being actively investigated [5, 6] and appears to be the best way to combined mechanical and electrical characteristics of both partners; however, it is somewhat intriguing and does not solve the problem of obtaining large specimens. We thought that many of the previous problems might be solved by finding a general method of producing highly conducting PP by oxidative polymerization by chemicals, directly on a suitable matrix, thus attaining most requirements mentioned above with few disadvantages. In the course of our study on the chemical polymerization of pyrrole to highly conducting PP [7], we have found that by supporting the monomer on a porous substrate before contacting it with an oxidant solution, it was possible to improve the volumic conductivity of the polymer formed. In terms of conductivity per gram of electroactive material, an improvement by a factor of up to 3 or 4 was found. Good conductivities, very close to those from electrochemical oxidation, were obtained by a careful testing of experimental conditions. The most suitable supporting material to date seems to be an ordinary filter paper (for instance Whatman no. 91 filter paper), but also wood, clothes, glass fibres, polystyrene and silica gel granules may give interesting results as far as both mechanical properties and the conductivity of the composite materials are concerned. Among various oxidants tested we found that ferric salts show the best performance. Thus many paper strips (50 mm × 5 ram) were charged with pyrrole and