Electronic Conduction in Polymers. I. The Chemical Structure of Polypyrrole

Abstract

The pyrolysis of tetraiodopyrrole in an inert atmosphere at temperatures from 120-700° yields black, infusible, amorphous polymers insoluble in solvents. Depending on the pyrolysis temperature, iodine may be present in the polymers as iodine of substitution and as chemisorbed molecular iodine, which is very tenaciously held. As a first approximation, the structure may be regarded as a three-dimensional network of pyrrole rings cross-linked in a nonplanar fashion by direct carbon to carbon linkages. The secondary nitrogen atoms form a hydroquine type system which may be oxidized by iodine or molecular oxygen under alkaline conditions. The extent of oxidation depends on the hydroxyl ion concentration. The nonplanarity of the oxidized quinonoid system renders it unstable but stability is enhanced, as in the triphenylmethane dyestuffs, by the formation of a carbinol. Despite their nonplanarity polypyrroles are relatively good conductors of electricity. The resistivity ranges from 1-200 ohm cm depending on the temperature of pyrolysis.