Benzoylation of polyphenylene oxide: Characterization and gas permeability investigations

Benzoylation of polyphenylene oxide (PPO) was carried out with aromatic acid chlorides bearing specific groups at para-position (H, methyl, Br, Cl and nitro), which differ in their polarity and bulk. The reaction conditions were optimized individually to get the high degree of substitution. These materials were characterized for thermal as well as other physical properties that are known to affect the gas permeation. In a series investigated, the nitrobenzoyl substitution on PPO resulted in the highest increase in glass transition temperature and the lowest thermal stability. An estimation of the packing density parameters—fractional free volume by density measurement and the d-spacing by X-ray diffraction analysis showed an increase in the packing density. The gas permeability was found to decrease in all the cases of benzoylation. The helium and oxygen based selectivities were increased, while CO₂ based selectivities were decreased. The unusual trend observed in the gas permeation properties is explained on the basis of nature of substituent and the degree of substitution.     

Relationship between transport properties and phase transformations in mixed-conducting oxides

To elucidate the relationship between transport properties and phase transformations in mixed-conducting oxides, Sr_0.9Ca_0.1Co_0.89Fe_0.11O_3−δ (SCCFO) and SrCoO_3−δ (SCO) were chosen as the model materials and have been investigated in detail. Oxygen permeation measurements verified that both oxides are well permeable to oxygen at elevated temperatures, e.g., at 900 °C during a cooling procedure, oxygen permeation rates as large as 1.5 and 2.0 mL/min/cm² could be obtained with disk-shaped SCCFO and SCO membranes of thickness 1.5 mm, respectively. But when cooled to critical temperatures, the oxygen permeability of these kinds of oxides diminished sharply, which could be recovered by increasing the temperature again to certain values. Abrupt changes on electrical conductivity were also observed for both oxides around the same region of temperature as that of oxygen permeability. As indicated by high-temperature X-ray diffraction and thermal analysis, the SCCFO and SCO systems undergo phase transformation between a low-temperature orthorhombic brownmillerite structure (B) or a hexagonal 2H-type structure (H) and a high-temperature cubic perovskite structure (C), respectively. The present results suggest the observed abrupt changes in transport properties versus temperature are attributed to such phase transformation, which may be directly associated with the order-disorder transition of oxygen vacancies. Moreover, compared to the B/C transformation that mainly involves an order-disorder transition on the oxygen sublattice, the H/C one necessarily also involves the cooperative long-range reorganization on the cation sublattice. Therefore it occurs at a higher temperature and absorbs more heat quantity than those of B/C transformation.     

Polymerization of Si-containing acetylenes. XIV. Polymerization of diphenylacetylenes with bulky silyl groups and polymer properties

Polymerization and polymer properties of diphenylacetylenes with bulky silyl groups (SiMe₂–i-Pr, SiMe₂–t-Bu, SiMe₂Ph, SiEt₃) at para or meta position were studied under comparison with those of the SiMe₃ derivatives. The present monomers polymerized in good yields with TaCl₅-cocatalysts to form high molecular-weight polymers (M _w > 4 × 10⁵). The polymer yields of para-substituted monomers were similar to that of the SiMe₃ derivative, while those of meta substituted monomers were lower than that of m-SiMe₃ derivative. Most of the polymers were totally soluble in common solvents such as toluene and CHCl₃, although the polymers with p-SiMe₂–t-Bu and p-SiMe₂Ph groups were partly insoluble in all solvents. These polymers resembled SiMe₃-containing homologues in the UV-visible absorption and thermal stability. The oxygen permeability coefficients of these polymers were in the range of 10^?9?10^?8 cm³ (STP) cm/(cm²·s cm Hg)—lower than those of the corresponding SiMe₃-containing polymers. © 1993 John Wiley & Sons, Inc.     

聚二乙氧基磷腈的制备及其膜对气体的透过性能

研究了聚二乙氧基磷腈(PEOP)的制备方法,对合成有机磷腈高聚物的Allcock法进行了改进;表征并研究了PEOP膜对O-2、N_2、H_2、CO_2、CH_4等气体的透过性能。结果表明:在严格的实验条件下,可得到线型结构的PEOP,产率高于Allcock法,达50％左右,所得PEOP为无色透明弹性体,具有良好的成膜性,其膜具有较高的气体透过系数和分离系数,是一类有潜在应用前景的新型膜分离材料。     

Determination of lactulose and mannitol in urine by HRGC

Alteration of intestinal permeability towards compounds like sugars is an indication of abnormalities observed in some diseases. Measurement of the dual sugar absorption of lactulose and mannitol is a non-invasive test of intestinal permeability. The use of this test is however limited by difficulties in the analysis of sugars in urine at low concentrations. In this study we have developed an analytical procedure for quantitative assay of the lactulose–mannitol pair in urine by high resolution gas chromatography. The minimum detectable amounts are 7.5 pg for lactulose and 4.4 pg for mannitol. The calibration curves are linear in the range of 100–6400 mg L^?1. Recoveries are within the range 86–102 % for mannitol and 84–105 % for lactulose.     

Relaxation of a viscoelastic gel bar: II. Silica gel

Silica gel is shown to be elastic in the presence of dry alcohol, but viscoelastic (VE) in aqueous media; the rate of VE relaxation increases with the concentration of water. At 25 vol% water in ethanol, the rate of viscoelastic relaxation decreases with pH, approaching zero (i.e., elastic behavior) at pH 1.5. Elastic behavior is also seen in methanol, but VE relaxation is rapid upon addition of 1% triethylamine. It is concluded that VE relaxation results from attack by the liquid on siloxane bonds in the gel network. The kinetics of relaxation are well described by the theory presented in Part I.     

The Varigrad and similar apparatus in gradient liquid chromatography: A systematic computational approach. Part 1: Theoretical development

Different methods for producing a pre-assigned gradient in liquid chromatography are presented. A systematic approach to the calculations involved is given. The derived equations are mostly Poisson and Poisson summation distributions which are tabulated in the literature. The incremental method of gradient elution developed by Scott has been modified. In the modified apparatus two mixing chambers are used instead of one. This leads to an appreciable decrease in the number of reservoirs needed for the same precision in fitting a desired gradient. The application of the derived equations, together with other Varigrad modifications, will be given in Part 2 of this paper (to be published shortly in this Journal).     

Polymerization of [o-(trimethylgermyl)phenyl] acetylene and polymer characterization

[o-(Trimethylgermyl)phenyl]acetylene was polymerized in the presence of WCl₆, W(CO)₆-hv, etc., to give polymers whose weight-average molecular weights reached ca. 7.0 X 10⁵ at the highest. When the MoOCl₄-n-Bu₄Sn-EtOH (1 : 1 : 1) catalyst was used, the polydispersity ratio of the polymer obtained was 1.08, and the number-average molecular weight increased in direct proportion to monomer conversion; these indicate that this polymerization is a living polymerization. The polymer had the structure ? [CH?C(C₆H₄-o-GeMe₃)]_n ? and was a dark purple solid (λ_max = 551 nm, ε_max = 6100 M^-1 cm^-1 in THF) soluble in organic solvents such as toluene and chloroform. The onset temperature of weight loss of the polymer in TGA in air was ca. 230°C, and the glass transition temperature was above 180°C. The Po₂ of the present polymer is 105 barrers—larger than the value of natural rubber and fairly close to that of poly(dimethylsiloxane). © 1993 John Wiley & Sons, Inc.     

Local-orbital-based correlated ab initio band structure calculations in insulating solids: LiF

 A local-orbital-based ab initio approach to calculate correlation effects on quasi-particle energies in insulating solids is presented. The use of localized Wannier-type Hartree–Fock orbitals allows correlation effects to be efficiently assessed. First a Green's function approach based on exact diagonalization is introduced and this is combined with an incremental scheme, while subsequently different levels of perturbative approximations are derived from the general procedure. With these methods the band structure of LiF is calculated and good agreement with experiment is found. By comparing the different approximations proposed, including the exact diagonalization procedure, their relative quality is established. Received: 25 June 2001 / Accepted: 31 August 2001 / Published online: 19 December 2001     

Poly(3,4-ethylenedioxythiophene)-modified nafion membrane for direct methanol fuel cells

Membranes Nafion 117 are modified with poly(3,4-ethylenedioxythiophene) (PEDT) by chemical polymerization of EDT with H₂O₂ or FeCl₃ as the oxidants in a two-compartment cell. Depending on the oxidant and polymerization conditions, PEDT is deposited either as a thin film on the membrane surface or inside the Nafion membrane depending on whether FeCl₃ or H₂O₂ is used as the oxidant. The decrease in the ionic conductivity and methanol permeability is studied as a function of the polymerization time. A linear dependence is found with H₂O₂ and a t ^−1/2 dependence, with FeCl₃. The contributions of PEDT and Nafion to the overall conductivity of the composite membranes are separated by impedance measurements. The modified membranes (FeCl₃) are also tested in direct methanol fuel cells (DMFC). The methanol permeation through the membranes is measured by operating the fuel cell in an electrolysis mode. The influence of the modified membranes on the DMFC current-voltage characteristics is studied with 2 M CH₃OH and O₂ at 1.2 bar_abs and 80°C. Membrane electrode assemblies (MEAs) are prepared by hot pressing the modified membrane between two commercial gas diffusion electrodes with 1 mg cm⁻² of Pt loading. A decrease of the methanol permeation of 25% is observed at MEA with the modified membrane (1 h polymerization time), compared with that of MEA with a Nafion membrane. However, the overall DMFC performance decreases in the same relation: a maximal power density of 36 W cm⁻² is measured at MEA with a PEDT-modified membrane compared with 45 W cm⁻² for MEA with a Nafion membrane. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 11, pp. 1330–1339. Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22, 2005, Moscow. The text was submitted by the authors in English.