Synthesis and Physical Properties of Highly Sulfonated Polyaniline

摘要

Sulfonated polyaniline (EB-SPAN) is a self-doped conducting polymer. It has ahigh water solubility and a novel pH-dependent DC conductivity that is of interest for fundamental science and also for applications in such areas as rechargeable battery and pH control technologies. We report here the extensive characterization and details of synthesis of a new form of sulfonated polyaniline (LEB-SPAN) which shows novel or significantly improved chemical and physical properties. LEB-SPAN has a much high sulfur to nitrogen ratio (S/N) of N approx. 0.75, 50% larger than that previously reported for EB-SPAN, S/N approx. 0.50. This change in composition leads to significant alteration of the properties including an order of magnitude increase in the room temperature DC conductivity to approx. 1 S./cm, nearly double the solubility in water, and a completely different pH-dependence of the oxidation potential (E1/2). For LEB-SPAN the DC conductivity is unaffected by pH over the range 0 < or = pH < or = 14, strikingly different from the behavior of both parent polyaniline and EB-SPAN which become insulating for pH > or = 3 and pH > or = 7.5; respectively. Temperature-dependent DC conductivity and EPR measurements for LEB-SPAN reveal a lower activation energy for the conductivity and a higher density of states at the Fermi energy as compared with EB-SPAN. The dramatic differences in the pH-dependence of the DC conductivity, cyclic voltammetry (CV), FTIR, and UV-Vis results for LEB-SPAN and EB-SPAN are shown to be a consequence of the much higher S/N ratio in LEB-SPAN. jg p3.