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Abstract

A conductive polypyrrole (PPy) film was successfully synthesized in a homogeneous supercritical carbon dioxide (scCO2)/acetonitrile (AN) system. The occurrence of a homogeneous supercritical state was confirmed by observations of the phase behavior of the system through a high-pressure cell with a viewing window. The concentration of a supporting electrolyte, tetrabutylammonium hexafluorophosphate (TBAPF6), significantly changed the phase behavior of the scCO2/AN system. The polymerization rate of the film in that system decreased with further addition of CO2. This result suggested that the low viscosity of scCO2 did not play an important role in improving the growth rate of the PPy film. The low polymerization rate might have been due to the electron-transfer resistance arising from the low dielectric constant of scCO2/AN mixture. The roughness of the film prepared in the homogeneous scCO2/AN system was ¹/10 that synthesized in AN itself as a solvent. The slow growth of film and the high diffusion rate of the monomer seemed to account for the smooth flat film formation.

A novel carbon−sulfur (C2S) analogue of polyacene has been synthesized and characterized. The polymer is composed of a nondegenerate trans−cisoid polyacetylene backbone in which all hydrogen atoms are replaced with sulfur atoms to form thiophene rings that are fused into a linear cross-conjugated ladder-type structure. The newly developed synthetic route of the ladder-type polymer is based on an intramolecular condensation of a prepolymer consisting of 3-(alkane-1-sulfinyl)thiophen-2,5-diyl units in triflic acid. The geometric and band electronic structure of the ladder-type polymer were calculated and analyzed at the PM5 level of theory. The fused ring structure imposes strong quinonoid-type character to the originally benzenoid polyene backbone, which destabilizes the HOMO and stabilizes the LUMO and thus reduces the band gap. The shift of absorption and emission maxima to longer wavelengths responding to lower π−π* transition energies than those of polythiophene and the smaller gap between electrochemical p- and n-doping potentials are consistent with the reduction of the band gap. The microstructure of the isolated oligomers in their neutral, singly oixidzed, and doubly oxidized states were computed for short and intermediate chain length. Various energetic and structural aspects of the convergence behavior from the properties of small cations or dications to those of an isolated polaronic or bipolaronic defects on a sufficiently long chain were monitored and are discussed. The geometric structures of the p-doped ladder-type polymer in the form of either polaron or bipolaron were calculated by adopting suitable boundary conditions to represent charged unit cells. The geometry relaxation process for the charged ladder-type backbone induces the appearance of a stronger quinonoidic character than that in the case of polythiophene, which suggests that the fused rings more easily adopt quinonoid forms than thiophene rings. Calculated energetic aspects of the doping behavior and the paramagnetic resonance spectra of p-doped polymers revealed that the ladder-type polymer possesses polaron as the prevailing charged species, in contrast to many other π-conjugated polymers where bipolaron is the lowest-energy charge storage configuration.

The synthetic routes to ladder polymers that consist of benzenetetrayl subunits with oxo and methylsulfonio linkages are described. As the key intermediate, poly(phenylene oxide)s having pendant methylsulfenyl groups are prepared by copper-catalyzed oxidative polymerization of the corresponding phenols with O2. The oxidation of the polymer with an equimolar amount of H2O2 in the presence of acetic acid effects the high-yielding conversion of methylsulfenyl to methylsulfinyl groups without the formation of the undesired methylsulfonyl groups. The superacidified condensation of the resulting polymer (Swern reaction of aryl sulfoxides) under dilution conditions induces the polymer-analogous intramolecular electrophilic ring-closing reaction of the hydroxymethylphenylsulfonium cation onto the adjacent benzene ring to yield the required ladder polymer, which has proved to be a semiconductor with an intrinsic electric conductivity of 2 × 10^-5 S/cm. A comparison of the spectroscopic properties of the ladder polymer with those of the model compounds such as 5-methylphenoxathiinium triflate and phenoxathiin discloses π-electron delocalization over the methylsulfonio linkages, demonstrating the efficacy of the ladderization for p−π/d−π interactions in arylsulfonium moieties. This synthetic approach permits the thio and alkylsulfonio ladder linkages for a variety of phenyl ethers to form in high yields.

The polymerization of 2,3,5,6-tetraphenylhydroquinone (or 2,2‘,3,3‘,5,5‘-hexaphenyl-4,4‘-dihydroxybiphenyl) with α,ω-tetrahydroperfluoroalkanediol and decafluorobiphenyl was carried out to synthesize a series of copolymers III (Mw = 49 100−80 900). The copolymers III are composed of arylene ether (10−30 mol %) and fluorinated alkane (90−70 mol %) moieties. The reaction of III with chlorosulfonic acid gave sulfonated polymers IV, which are soluble in polar organic solvents and form flexible and transparent films by casting from solution. The polymers IV have glass transition temperatures of 109−155 °C and decomposition temperatures of ca. 300 °C. The hydrated polymers show protonic conductivity (3.4 × 10^-3 S cm^-1), which does not decrease at temperatures up to 170 °C.

Methyl phenyl sulfoxide was found to undergo self-polycondensation in triflic acid in the presence of diphenylamine to produce poly(methylsulfonio-1,4-phenylene triflate). Diphenylamine formed a charge-transfer (CT) complex with the hydroxy methyl phenyl sulfonium cation produced by the protonation of the sulfoxide, facilitating the electrophilic substitution reaction of the sulfonium cation onto the carbon atom of the terminal phenyl ring. The obtained polymer is a highly crystalline material whose structure was determined by X-ray analysis using the typical geometric parameters of the sulfoniophenylene dimer and trimer model compounds. The orthorhombic unit cell of the polymer (a = 10.875 Å, b = 10.449 Å, and c = 18.629 Å) contains eight monomeric units. The space group is Pbcn (#60). Two molecular chains along the c axis pass through the unit cell, one through the corner and the other through the center. The crystal structure of the polymer not only revealed a structural relevance to those of oxy- and thiophenylene polymers but also provided support for CT complex formation between the polymer and diphenylamine.

The facilitated transport of oxygen in a liquid membrane containing [meso-α,α,α,α-tetrakis(o-pivalamidophenyl)porphyrinatocobalt(II)]−laurylimidazole (CoP) as an oxygen carrier leads to high permeability and permselectivity of oxygen against nitrogen. The oxygen permeation was properly analyzed by a dual-mode model and using the oxygen-binding constants spectroscopically determined, to give permeation parameters of the membrane such as the diffusion coefficient (DCoP) of the CoP mobile carrier and the physical diffusion coefficient of oxygen. DCoP was in accordance with that electrochemically determined. The facilitated permeation was represented by the product of the CoP concentration and DCoP in the membrane solution. DCoP decreased with solution viscosity and increased with the measured temperature. High oxygen permeability (10^-7 cm³(STP) cm cm^-2 s^-1 cmHg^-1) was observed, e.g. for the membrane of the 31 wt % CoP methylanisole solution at 10 °C, where the facilitation factor and the oxygen/nitrogen permselectivity were over 20 and 40, respectively.

A novel design of anticancer drug delivery system, based on an electrostatic binding of negatively charged liposomes and cationic metalloporphyrins under physiological conditions, is reported. A lack of cytotoxicity of the iron(III) porphyrin-loaded liposomes and an efficient generation of a toxic hydroxyl radical (OH^•) from a superoxide anion radical (O2^-•) through the iron(III)-catalyzed dismutation and the Fenton-like reaction allow for a targeted necrosis of tumor cells where the concentration of O2^-• is locally increased as a result of the reduced activity of superoxide dismutase and catalase in these cells. Keywords: Anticancer drug delivery system; liposome; cationic metalloporphyrins; superoxide anion radical; hydroxyl radical

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