Aggregation behavior of organic‐soluble semi‐aromatic polyimides in N‐methylpyrrolidone systems

Aggregation behavior of the organic‐soluble semi‐aromatic polyimides, whose degrees of imidization range from 69 to 96%, obtained using 4,4′‐oxydianiline, 4,4′‐diamino‐3,3′dihydroxybiphenyl, and bicyclo[2.2.2]‐oct‐7‐ene‐2,3,5,6‐tetracarboxylic dianhydride (BCDA) in N‐methylpyrrolidone (NMP), NMP/cyclohexanone, and NMP/γ‐butyrolactone (BCDA‐based polyimides) were studied by static light scattering (SLS) and dynamic light scattering (DLS). The DLS analyses for the multirelaxation modes demonstrated the specific character unlike flexible polymers that the single BCDA‐based polyimide chains first associate with each other to form small clusters in the dilute region, and then expand to large aggregates by the entanglements between the small clusters with an increasing concentration into the semi‐dilute region. Given the semi‐aromatic structure of BCDA‐based polyimides weakening the charge transfer (CT) interaction between the diamine and the dianhydride unit, it is concluded that the unique aggregation behavior of BCDA‐based polyimides is dominated by the balance between the driving force for the “organic solubility” given by both the increase in bulkiness and the decrease in the CT interaction, and that for the “organic insolubility” derived from both the hydrogen‐bonded interaction of the phenolic hydroxyl groups and the π–π interaction of the phenyl rings. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Quadrupole field in hairpin-type cathode gun and mechanism of axial-astigmatism production

Mechanism of axial astigmatism production in the hairpin-type cathode gun was investigated by numerical calculation. The electrostatic potential in the gun was first decomposed into the axially symmetric and quadrupole components, and then the trajectory behavior was investigated by the generalized trajectory method. The axial astigmatism of the hairpin-type cathode gun was found to depend strongly on the Wehnelt voltage; it is small as long as the Wehnelt voltage is close to cutoff condition but starts to increase rapidly when the drive voltage exceeds a certain threshold. The reason for a negligible axial astigmatism at or close to the cutoff lies in the mutual dependence of the tip electric field intensity and the quadrupole field strength near the cathode. The tip quadrupole field strength is given by the product of the tip field intensity and the difference in the cathode curvature in the two orthogonal cross sections. A negligible axial astigmatism of the hairpin-type cathode gun in usual operations is due to a small quadrupole field close to the cutoff condition where the tip field is weak.     

Utilization of a Silicone Rubber Membrane for Passive Oxygen Supply in a Microbial Fuel Cell Treating Carbon and Nitrogen from Synthetic Coke-Oven Wastewater

Applied Biochemistry and Biotechnology - This study firstly introduced a silicone rubber membrane (SRM) into microbial fuel cell (MFC) for passive oxygen supply to simultaneously remove phenol and...     

Comprehensive Structural Analysis of the Bitter Components in Beer by the HPLC-Assisted Crystalline Sponge Method

Trans-iso-α-acid is one of the main contributors to the bitter taste of fresh beer and is known to transform into various derivatives during beer aging. However, structural characterization of the derivatives has been a challenging task because of the formation of too many components. Herein, we report that most of the transformation products of trans-iso-α-acid, isolated in this study in only small quantities by HPLC, can be structurally analyzed with the crystalline sponge method. Thirteen compounds, including eight that were previously unreported, have been successfully isolated and analyzed with complete assignment of their absolute configuration. This provides an improved understanding of the chemical transformations that occur during beer aging.     

Tetramethylammonium hydroxide (TMAH) thermochemolysis of 2-arylcoumaran lignin model compounds

Phenolic 2-arylcoumarans 1–6 were used to examine the behaviors of β-5 subunits in lignin during tetramethylammonium hydroxide (TMAH) thermochemolysis. Products were monitored by gas chromatography/mass spectrometry. The process predominantly provided dimeric products with the opened hydrofuran ring. Substituent changes at the γ-position of ring A and at the 5-position of ring B had a large effect on the product compositions. 2-Arylcoumarans 1 and 6 with the γ-CH₂OH substituent predominantly gave 2,3,3′,4′-tetramethoxystilbenes involving the elimination of the γ-CH₂OH substituent, while 2–5 with the γ-CH₃ substituent gave a mixture of 2,3,3′,4′-tetramethoxy-α-methylstilbenes and α-methoxy-α-(3′,4′-dimethoxyphenyl)-β-(2,3-dimethoxyphenyl)propanes. Substituent –CHCHCH₃ on ring B remained unaffected. Substituents –CHCHCH₂OH and –COOH on ring B produced the corresponding methyl ether and ester, respectively, by methylation. The –CHCHCHO substituent on ring B was converted to the –CHO substituent.     

Extensions of the D(?k2)-triples {k2, k2 ± 1, 4k2 ± 1}

Let n be a nonzero integer. A set of m distinct positive integers is called a D(n)-m-tuple if the product of any two of them increased by n is a perfect square. Let k be a positive integer. In this paper, we show that if {k ², k ² + 1, 4k ² + 1, d} is a D(−k ²)-quadruple, then d = 1, and that if {k ² − 1, k ², 4k ² − 1, d} is a D(k ²)-quadruple, then d = 8k ²(2k ² − 1).