Tadashi Shimura

Self-assembled monolayers of carboxylate ions on passivated iron for preventing passive film breakdown

Self-assembled monolayers (SAMs) of carboxylate ions Cn−1H2n−1CO2− (CnA−) with the carbon number, n=12–18 and 16-hydroxyhexadecanoate ion HO(CH2)15CO2− (HOC16A−) were prepared on an iron electrode previously passivated in a borate buffer at pH 8.49 by treatment in aqueous solutions of their sodium salts for many hours. Breakdown of the passive film on the electrode coated with the SAM was examined by anodic polarization measurement in the borate buffer containing 0.1 M of Cl−. The pitting potentials of the passivated electrodes coated with the SAMs of CnA− and HOC16A− shifted toward a more positive potential than that of the uncoated electrode, indicating prevention of passive film breakdown by blocking diffusion of Cl− through the SAM to defects of the passive film. No breakdown was observed over the potential range of the passive region by coverage of the passive film with the SAM in some cases. The SAMs on the passive film were characterized by contact angle measurements and X-ray photoelectron and Fourier transform infrared reflection spectroscopies.

Prevention of passive film breakdown on iron in a borate buffer solution containing chloride ion by coverage with a self-assembled monolayer of hexadecanoate ion

Abstract Breakdown of a passive film on iron in a borate buffer solution (pH 8.49) containing 0.1 M of Cl − was suppressed by coverage of the passive film surface with a self-assembled monolayer (SAM) of hexadecanoate ion C 15 H 31 CO 2 − (C 16 A − ). The pitting potential of an iron electrode previously passivated in the borate buffer at 0.50 V/SCE increased by treatment in an aqueous solution of sodium hexadecanoate for many hours, indicating protection of the passive film from breakdown caused by an attack on defects of the film with Cl − . No breakdown occurred over the potential range of the passive region by coverage with the SAM of C 16 A − in some cases. Structures of the passive film and the monolayer were characterized by X-ray photoelectron and Fourier transform infrared reflection spectroscopies and contact angle measurement with a drop of water.

Synthesis of organometallic conducting polymers using soluble poly(n-alkylphenylene)s as ligands

Abstract Homogeneous reaction of soluble poly(n-hexylphenylene) (PHP) with a molybdenum carbonyl complex, (py) 3 Mo(CO) 3 , afforded an organometallic π-conjugated polymer at ambient temperature. The product was soluble in common organic solvents such as chloroform or THF and its infrared and UV-visible absorption spectra and electrochemical properties indicated a formation of ( η 6 -arene)Mo(CO) 3 -type complex polymer, PHP-Mo(CO) 3 . The ratio of Mo(CO) 3 units to benzene rings in PHP-Mo(CO) 3 was estimated at 1 5 from the ratio of v(CO) and v(CC) peak absorbances in the infrared spectrum and by the colorimetric analysis of Mo content. Reaction of poly(n-butylphenylene) (PBP) with chromium hexacarbonyl also afforded a organometallic polymer containing Cr(CO) 3 moieties, PBP-Cr(CO) 3 . Conductivity of PHP-Mo(CO) 3 and PBP-Cr(CO) 3 was higher than that of free PHP and PBP, respectively, in the neutral state, although the activation energy for the conductivity is not seriously changed by the complex formation.

Thermal polymerizations of alkali 4-(2-bromoethyl)benzoates in bulk

Thermal polymerizations of alkali 4-(2-bromoethyl)benzoates (2-BEBAs) were investigated. The polymerization of the lithium salt at 220°C for 2 h under reduced pressure in bulk, followed by esterification, produced poly(methyl 4-vinylbenzoate), having a number-average molecular weight (Mn) of 9500 in a 54% yield. Thus, elimination of hydrogen bromide to form a double bond occurred, followed by vinyl polymerization. In contrast, polymerization of the potassium salt at 200°C for 2 h afforded poly(oxycarbonyl-1,4-phenylene-ethylene) (polyester 1), having an inherent viscosity of 0.19 dL g−1 in a 95% yield: i.e., polycondensation proceeded to afford the polyester. Reaction of the sodium salt at 220°C for 2 h produced polyester 1 having Mn of 4000 in a 28% yield as well as 4-vinylbenzoic acid in a 9% yield. In the reaction of the sodium salt, both polycondensation and double bond formation occurred. Thus, these polymerizations depended on the counter cations of 2-BEBAs.

Electrochemical synthesis and redox properties of a polyruthenocene electrode film

Abstract A thin and uniform polyruthenocene film was prepared by electroreduction of [Ru( η 5 -C 5 H 5 )( η 5 -C 5 H 4 CCl =CHCHO)] in acetonitrile and its electrochemical properties were investigated by cyclic voltammetry. This film undergoes a moderately reversible oxidation, the mechanism of which is explainable as an ECE reaction with a slow chemical step. The kinetics of the chemical step are first-order to the ruthenocene concentration and depend on both solvent and electrolyte anion. The kinetic constant is higher at larger donor number of solvent, lower viscosity of solvent and/or higher coordinating ability of electrolyte anion, implying the competitive coordination of both solvent and electrolyte anion.