Kazuyuki Chiba

Electrochemical preparation of a ladder polymer containing phenazine rings

Abstract The electrochemical and spectroscopic identification of the structure of the electroactive polymer poly(o-phenylenediamine), (PPD), which is prepared on electrode surfaces as a thin coating film by electropolymerization of o-phenylenediamine in an acidic aqueous solution, was carried out, as well as comparison with the results obtained for the chemically prepared polymer similar to the PPD, o-phenylenediamine and some related compounds. As a result, it is demonstrated that the structure of the PPD is essentially different from those of the electroactive polymers prepared by electropolymerization of aniline and its derivatives and that the PPD is a ladder polymer with phenazine rings.

Electrode kinetics of electroactive electropolymerized polymers deposited on graphite electrode surfaces

A kinetic examination of the charge-transport processes (i.e. (i) heterogeneous electron-transfer process of electrode/film interfaces and (ii) homogeneous charge-transport process within films) at electroactive electropolymerized film-coated electrodes was conducted by normal pulse voltammetry. The films employed were of poly(o-phenylenediamine), Poly(N-methylaniline) and poly(N-ethylaniline), which were prepared on electrodes as coating films by electrooxidative polymerization of the corresponding monomers in an acidic solution. It was found that process (i) obeys the conventional Butler-Volmer equation and that process (ii) can be treated as a Fickian diffusion process. In addition, the kinetic parameters characterizing processes (i) and (ii) (i.e. the standard rate constant (k°) and transfer coefficient (α) for process (i), and the apparent diffusion coefficient (Dapp for process (ii)) were estimated: Dapp = ca (1–4)×10−8 cm2 s−1 s−1, k° = ca. (4–6)×10−4 cm s−1, αa (for anodic process) = 0.83–0.86 and αc (for cathodic process)=0.13–0.23. The are compared with the data reported previously for other electroactive polymer films.

Electrochemical studies of fused-pyrrole systems

Abstract An electrochemical study of fused pyrroles, i.e. , 1,4-dihydropyrrolo-[3,2-b]pyrrole (PP), 3,6-di-t-butyl-1,4-dihydropyrrolo[3,2-b]pyrrole (BPP) and dimethyl 1,4-dihydro-3,6-di-t-butyl-pyrrolo[3,2-b]pyrrole-1,4-dicarboxylate (BMPP), was carried out. PP could be polymerized electrochemically on InSn oxide conducting glass (ITO), basal-plane pyrolytic graphite, Pt or Au electrodes, while BPP and BMPP could not be electropolymerized. The polymeric film (PPP) prepared from PP was electroactive in both acetonitrile and aqueous solutions. The morphology of PPP films was found to depend on the supporting electrolytes used. The conductivity of the film was 5 × 10 −5 S cm −1 just after its preparation and decreased gradually when exposed to air. The film thickness (φ) was linearly related to the amount ( Q ) of charge passed in the polymerization, with Q in the range 5 to 150 mC cm −2 (slope of the φ versus Q plot: 4 μm C −1 cm 2 ). The PPP film was found to undergo degradation via electrochemical oxidation at the electrode and chemical oxidation by oxygen in air. Furthermore, the physical and electrochemical properties are compared with those of polypyrroles, polymers of other fused heterocycles, etc.

Interfacial crystallization and electronic properties of platinum double salts

Insoluble platinum double salts were crystallized by a novel method involving a solid-liquid interface. The platinum complexes included Magnus Green Salt, MGS ([Pt(NH)3)4]2+ [PtCl4]2−) and PBC ([Pt(bpy)2]2+[Pt(CN)4]2−). The crystallization and molecular ordering of MGS and PBC on a Nafion membrane were achieved by controlling the diffusion of the cation and anion components to the solid-liquid interface. The electrical conductivity of the MGS film on Nafion was greatly augmented by oxidizing the polynuclear complex. A device consisting of the PBC film on Nafion, methyl viologen, and triethanolamine displayed photoelectrochromism.

Polymerization of Transition Metal Complexes in Solid Polymer Electrolyte Membranes

Abstract Prussian blue (PB), which is a mixed-valent polynuclear metal complex, was formed in the presence of the solid polymer electrolyte membrane Nafion (Nf). According to the stepwise dipping method, in which either Fe2+ or Fe(CN)6 3− of the component ions of PB was first incorporated into the matrix membrane and then the membrane was immersed into a solution containing the other component ion, a thin layer of PB was deposited on the surface of Nf or inside Nf depending upon the sequence of incorporation of the component ions. A dissipative structure of periodic PB layer deposit inside Nf was found to be formed under a specific condition of the stepwise method. PB was also formed inside Nf as a broader line by the countercurrent diffusion method in which both component ions were incorporated into Nf from opposite surfaces. The position of PB in Nf varied with the concentration ratio of Fe2+ to Fe(CN)6 3− in this case.

Electropolymerization of N,N′-dimethyl-1,4-dihydropyrrolo[3,2-b]pyrrole: a new heteroaromatic polymer

The electro-oxidative polymerization of N,N′-dimethyl-1,4-dihydropyrrolo[3,2-b]pyrrole (DMPP) in acetonitrile solution led to the formation of a polymeric film on the electrode surfaces. This poly-DMPP film underwent reversible oxidation and reduction processes in both acetonitrile and aqueous solution. The formal redox potential (E°′) was ca. 0.10 V vs. a sodium chloride/saturated calomel electrode in 0.1M-NaClO4 in acetonitrile solution. The electrical conductivity was 1.1 × 10–5 S cm–1 at 298 K. Further physical, electrochemical, electrical, and spectroscopic characterization of poly-DMPP was carried out, and the results were compared with those obtained previously for poly-(1,4-dihydropyrrolo[3,2-b]pyrrole) film.