The role of chain and dopant engineering in the preparation of processible conducting polymers with desired properties

We discuss spectroscopic, structural and processing peculiarities of polyaniline (PANI) doped with two types of protonating agents, namely diesters of 4-phthalosulfonic acid (abbreviated as DEPSA) and diesters of sulfosuccinic acid (abbreviated as DESSA). In our approach PANI doped with DEPSA or DESSA is considered as a comb-shaped macromolecular system in which dopant anions arc regarded as side groups attached to the main chain via ionic bonds. This type of supramolecular architecture facilitates the self-organization of doped macromolecules into layered or in some cases lamellar structures. Plasticizing ester groups, present in the dopant anions, lower the glass transition temperature, T-g which in all cases is below room temperature. This low T-g induces several features which previously were not reported for doped PANI. First, the polymer can be stretched at room temperature up to three times its original length. Second. it exhibits low temperature termochromism which is manifested by an abrupt transformation of the UV-vis-NIR spectrum characteristic of delocalized charge carriers into a spectrum typical of localized charge carriers. An interesting correlation can be found between the temperature of the onset of this low temperature thermochromism, the temperature of the metal to insulator transition determined from the sigma = f(T) relationship and the temperature of the freezing of the dopant molecular motion derived from the analysis of the temperature dependence of elastic neutron scattering intensity. The coincidence of these three temperatures underlines a key role of the dopant motion in the transport properties of low T-g, plasticized PANT.