| Since the discovery in 1977 that doping polyacetylene with iodine increased its conductivity many orders of magnitude, conducting polymers have generated much scientific interest. Polyaniline is a very important material in the class of conducting polymers due to its ease of synthesis, environmental stability, and rich redox and acid/base chemistry. However, polyaniline is far from being well understood. The primary deficiency is the lack of knowledge concerning the relationship between structure and properties. Until recently, processing has been limited to casting the emeraldine base form of the polymer from low concentration N-methyl-2-pyrrolidinone (NMP) solutions, and possibly drawing.; This work addressed the general need for quantitative relationships between processing, structure, and properties of polyaniline. New processing methods were developed for producing both emeraldine base and leucoemeraldine base fibers, with processing parameters related to the fiber microstructure. The influence chemical structure (oxidation state) exerted on the linear viscoelastic properties of concentrated polyaniline solutions was characterized and an electrochemical method was developed for determination of oxidation state in fabricated articles. An endothermic transition at about 385°C was discovered in leucoemeraldine base and assigned to melting of crystallites. The oxidation state was found to significantly influence both the morphological development and electrical properties of spin coatings, as evidenced by differential scanning calorimetry and the temperature dependence of conductivity and thermoelectric power. Orientation effects were characterized with both near infrared prism coupling and polarized infrared spectroscopy. Finally, a time-dependent Hartree-Fock method was employed at the AM1 semiempirical level to predict the frequency dependent polarizability tensors of four polymers (isotactic polypropylene, poly(ethylene terephthalate), pyromellitic dianhydride-oxydianiline (PMDA-ODA) polyimide, and the emeraldine base form of polyaniline). Comparison of the theoretical predictions with experimental intrinsic birefringence allowed evaluation of the theoretical predictions of polarizability anisotropy.; The conclusions drawn here strongly demonstrate that the crucial link necessary to understanding the relationship between processing and properties of polyaniline is the structure. Whether the structural characteristic is void microstructure in as-spun fibers, oxidation state in solutions, crystallinity in spin coatings, or molecular orientation in films, it is structure that determines properties (both mechanical and electrical) in polyaniline. |
