Synthesis and Structure/property Relationships of Ring-Sulfonated Polyaniline.

The main objectives of the present investigation were: (1) to synthesize self protonic doped conducting polyaniline by various methods, and find the best synthetic route; (2) to examine whether the solubility of polyaniline would be changed after parent polyaniline had been sulfonated; (3) to determine the thermal doping stability of the conducting forms and thermal stability of the insulating forms of parent and sulfonated polyaniline; (4) to use electronic spectra as a probe to elucidate the changes of the geometry and conformation of sulfonated polyaniline; (5) to develop a hypothesis to rationalize the charge transport properties of sulfonated polyaniline; (6) to compare electrochemical properties of parent polyaniline and sulfonated polyaniline. The most significant results and conclusions are as following: (1) Fuming sulfuric acid as a sulfonation agent gives the best sulfonation level and conductivity for the polymer. (2) The solubility of polyaniline is improved greatly by the presence of the -SO_sp {3}{-} groups, specifically, sulfonated polyaniline dissolves in basic aqueous solutions. (3) The conductivity of the polymer is independent of pH for pH less than 7; the sodium salt of sulfonated polyaniline, an insulator, can be converted into a conducting form by treating it with aqueous HCl. (4) The covalently bonded sulfonic groups on the polyaniline chain increase the doping stability for the conducting form and the stability of the backbone for the insulating form at high temperatures. (5) Sulfonation of the phenyl rings on the polyaniline backbone increases the torsional angle between adjacent rings to relieve the steric strain. (6) The transport studies slow that the charge is more localized in sulfonated polyaniline than in the polyaniline system. (7) The first redox process in cyclic voltammetry is dependent on pH for pH less than 7 due to the active protons on the polymer backbone.