EMULSION POLYMERIZATION PROCESS FOR ORGANICALLY SOLUBLE AND ELECTRICALLY CONDUCTING POLYANILINE

An emulsion process has been developed for the direct synthesis of the emeraldine salt of polyaniline (PANI) that is soluble in organic solv ents. The process entails formation of emulsion particles with a mean hydrodynamic diameter of 150 nm and consisting of a water-soluble orga nic solvent (e.g., 2-butoxyethanol), a water-insoluble organic acid (e .g., dinonylnaphthalenesulfonic acid, aniline, and water. Aniline is p rotonated by the organic acid to form a salt which partitions into the organic phase. As oxidant (ammonium peroxydisulfate) is added to the reaction mixture, PANI intermediates are formed in the organic phase. As the reaction proceeds, the emulsion flocculates, forming a two-phas e system. The reaction features an induction period followed by an exo thermic polymerization, at which time soluble PANI forms in the organi c phase. The reaction progress is conveniently monitored by temperatur e, pH, and open circuit potential. When dinonylnaphthalenesulfonic aci d (DNNSA) is employed as the organic acid, the resulting product is hi ghly soluble in organic solvents such as xylene and toluene (not a dis persion), has high molecular weight (M-w > 22 000), and forms moderate ly conductive (10(-5) S/cm) films. We have also found that the conduct ivity of PANI-DNNSA films may be enhanced (up to 5 orders of magnitude ) by treating the films with surfactants-such as benzyltriethylammoniu m chloride (BTEAC) or low-molecular-weight alcohols and ketones such a s methanol and acetone. Electron microscopy shows that the conductivit y enhancement phenomenon observed upon treatment with surfactants is d ue to self-assembly of PANI-DNNSA molecules into an interconnected net work morphology. In the case of alcohol or ketone treatment the film c onductivity is enhanced due to extraction of excess dopant, densificat ion of the polymer, and a concomitant increase in crystallinity.