Effect of plasticizing dopants on spectroscopic properties, supramolecular structure, and electrical transport in metallic polyaniline

Several 1,2-benzenedicarboxylic acid, 4-sulfo, 1,2-di(alkyl), or di(alkoxy) esters were synthesized and tested as plasticizing dopants which lead to solution processible (via counterion) polyaniline with improved mechanical properties and metallic-type conductivity. As evidenced by wide-angle X-ray diffraction and small-angle X-ray scattering studies, PANI doped with the above dopants shows in the solid state a layered type of structural organization with the chain-dopant-chain distance clearly correlated with the length of the alkyl substituent in the dopant. The addition of an external plasticizer of the type of dioctyl phthalate or tritolyl phosphate to PANI doped with the above diesters improves both the molecular ordering and the metallic behavior of the material. The largest range of metallic type of conductivity was found for di-butoxyethyl ester doped-PANI. Solution processibility of PANI can also be improved by the application of a new procedure called mixed-doping which involves Bronsted acid doping followed by Lewis acid one.