Gas permeability and stability of poly(1-trimethylsilyl-1-propyne-co-1-phenyl-1-propyne) membranes

A significant reduction in the gas permeability of the poly(1-trimethylsilyl-1-propyne) (PMSP) membrane was investigated in terms of the membrane thickness and the storage environment. The effects of physical aging were observed with thinner membranes and under vacuum conditions compared with storage in air. The decrease in the permeability coefficient was dependent on the decrease in the hole saturation constant of Langmuir adsorption (C'_H), which is related to the volume of the microvoids. Physical aging in the PMSP membrane affected not only the glassy domain but also the rubbery one. To stabilize the permeability of the PMSP membrane, a poly(1-trimethylsilyl-1-propyne-co-1-phenyl-1-propyne) [poly(TMSP-co-PP)] membrane was prepared. Poly(TMSP-co-PP) has the same unit of poly(1-phenyl-1-propyne), which membrane has stable permeability. The poly(TMSP-co-PP) with less than 20 mol % PP content was estimated to be a random copolymer based on theoretical gas permeation analysis. In the poly(TMSP-co-PP) membrane, the relation between the PP content and C'_H was similar to the relation between the PP content and the gas permeability. The stability of the permeability was dependent on the PP content. The poly(TMSP-co-PP) membrane containing 10 mol % PP had both high permeability and good stability under some of the aging conditions performed in this work. © 1995 John Wiley & Sons, Inc.     

A method for determining absolute configuratiom of β-amino acids by CD spectra of their DNP derivatives

Aromatic β-amino acids were converted to the Dnp derivatives, and aliphatic ones to Dnp-pMA derivatives. The sign of the Cotton effect near 400 nm reflected the configuration at the β-position without exception. Thus, the relation seems to afford a new reliable method for determining the absolute configuration of β-amino acids.     

Notable effect of an electron-withdrawing group at C3 on the selective formation of alkylidenecyclobutanes in the thermal denitrogenation of 4-spirocyclopropane-1-pyrazolines. Nonstatistical dynamics effects in the denitrogenation reactions

A detailed study of the thermal denitrogenation of 3-carbomethoxy-substituted 4-spirocyclopropane-1-pyrazolines 6 was conducted. Alkylidenecyclobutane derivatives 7 were selectively formed in a stereospecific manner. Unrestricted density functional calculations for a 1-pyrazoline 10a indicated that the concerted cleavage of two C-N bonds is the energetically favored process for the denitrogenation reaction to give the 2-spirocyclopropyl 1,3-diyl, followed by a conrotatory ring-closure process, which was calculated to be the energy minimum pathway, to afford a spiropentane derivative. The calculated energy minimum pathway is largely inconsistent with the experimental results observed for the denitrogenation of 6 and 10a. The contradiction between the experimental and standard computational results was solved by considering nonstatistical dynamics effects in the concerted denitrogenation reactions. Although the energy minimum pathway from the transition states of the concerted denitrogenation of the 3-carboalkoxy-substituted 1-pyrazolines involves generation of the corresponding 1,3-diradicals, many trajectory calculations using the Bohn-Oppenheimer molecular dynamics model from the transition state for the concerted denitrogenation led directly to the formation of alkylidenecyclobutanes at the UB3LYP/6-31G(d) level of theory.     

High-throughput solid-phase extraction of metal ions using an iminodiacetate chelating porous disk prepared by graft polymerization

A chelating porous sheet for use in solid-phase extraction was prepared by radiation-induced graft polymerization and subsequent chemical modifications. An epoxy-group-containing vinyl monomer was graft-polymerized onto a porous sheet made of polyethylene. The produced epoxy group of the graft chain was converted into an iminodiacetate group. The chelating porous sheet with a density of the iminodiacetate group of 2.1 mol/kg was cut into disks 13 mm in diameter to fit an empty cylindrical cartridge with a capacity of 6 mL. Breakthrough curves using the chelating-porous-disk-packed cartridge overlapped irrespective of the flow rate of the solution ranging up to 1500 mL/h because of negligible diffusional mass-transfer resistance of the copper ions to the iminodiacetate group of the graft chain.     

Boron‐Ketoiminate‐Based Polymers: Fine‐Tuning of the Emission Color and Expression of Strong Emission Both in the Solution and Film States

In this research, the synthesis of boron‐ketoiminate‐containing polymers is reported with large molecular weights ( = 20 000) and their optical properties are examined by UV–vis absorption and photoluminescence spectrometries. It is shown that the polymers exhibit strong emission both in the solution and solid states (Φ _PL,THF = 0.46–0.80, Φ _PL,film = 0.13–0.38). These optical properties can be explained by a donor–acceptor interaction between the boron ketoiminate and the electron‐donating comonomer such as fluorene or bithiophene. Furthermore, in the solid states, their emission colors can be successfully tuned from blue to orange by the substituents on the nitrogen atom with the difference of the steric hindrance (λ _PL,THF = 464–546 nm, λ _PL,film = 486–604 nm).

     

Real-time line projection for fast terahertz spectral computed tomography

We demonstrated fast terahertz spectral computed tomography by using real-time line projection of a terahertz beam. Two types of cross-sectional images of continuously rotating samples have been measured in only a few seconds. From temporal data, a peak-to-peak sinogram and cross sections have been reconstructed using a filtered backprojection algorithm. Using fast Fourier transform from temporal data, spectral cross sections of the sample have been obtained.     

Two-dimensional gratings-based phase-contrast imaging using a conventional x-ray tube

A Talbot-Lau interferometer using two-dimensional gratings and a conventional x-ray tube has been used to investigate a phase-contrast imaging technique that is sensitive to phase gradients in two orthogonal directions. Fourier analysis of Moiré fringe patterns was introduced to obtain differential phase images and scattering images from a single exposure. Two-dimensional structures of plastic phantoms and characteristic features of soft tissue were clearly obtained at 17.5 keV. The phase-stepping technique was also examined to investigate the spatial resolution of different phase retrieval methods. In the presented setup we found that the choice of phase retrieval method made little difference in image blur, and a large effective source size was found to give a high intensity in the image plane.