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181.
182.
Tracing the geographical origin of beefs being circulated in Korean markets based on stable isotopes
Yeon‐Sik Bong Woo‐Jin Shin A‐Reum Lee Young‐Soo Kim Kangjoo Kim Kwang‐Sik Lee 《Rapid communications in mass spectrometry : RCM》2010,24(1):155-159
We have examined the carbon, nitrogen and oxygen isotopic compositions of American, Mexican, Australian, New Zealand and Korean beefs, which are currently being circulated in Korean markets, to check whether stable isotope ratios can identify their country of origin. Each beef exhibited statistically distinct isotopic compositions, especially in oxygen and carbon, because of the different isotopic compositions of their water and cattle feeds. Nevertheless, their isotopic compositions still showed some overlap, especially among USA, Australian, and Korean beefs, which sometimes resulted in significant misidentification when a single isotope was considered. However, the discrimination was generally successful when both the carbon and the oxygen isotopes were used. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
183.
A Diels-Alder-based route to trans-fused angularly functionalized bicyclic structures has been developed. This transformation features the use of a tetrasubstituted dienophile in the cycloaddition step. 相似文献
184.
185.
We analyzed the thermal crystallization, glass‐transition behavior, and mechanical properties of melt‐extruded poly(trimethylene terephthalate) (PTT) films to investigate their physical aging and annealing effects. The physical aging and annealing of PTT films had an influence on the glass‐transition temperature, recrystallization behavior, and mechanical properties. When samples were aged at an ambient temperature, the crystallization temperature decreased largely within 5 h, the heat of crystallization increased, and the breaking stress and breaking elongation increased. The glass‐transition temperature of annealed samples, which was obtained from differential scanning calorimetry and dynamic mechanical measurements, increased with increasing annealing temperature below 80 °C but decreased above that temperature. In addition, the glass‐transition temperature and modulus of annealed samples were largely affected by the annealing time; in particular, they increased sharply within 1 h on annealing at 50 °C. Consequently, the change in the glass‐transition temperature on annealing was ascribed to the fact that the molecular constraint due to recrystallization and the mobility of rigid amorphous PTT chains competed with each other, being dependent on the annealing temperature. The mechanical properties of aged samples were closely related to their cold‐crystallization behavior. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1920–1927, 2001 相似文献
186.
By focusing on cold-crystallized poly(ether diphenyl ether metaketone) (PEKm), a more in-depth understanding of the nature
of the crystalline morphology has been gained, which may lead to thorough mechanisms for interpreting the observed thermal
behavior in PEKm. Apparently, cold-crystallized PEKm containing initially only a single P1 crystal can exhibit dual melting
peaks (300 and 320 °C), with the second high-melting peak corresponding to the P2 crystal that was subsequently formed via
P1 melting/repacking during the scan. However, dual morphism (preexisting P1 and P2 crystals) could be intentionally introduced
into PEKm if it was cold-crystallized at temperature schemes of decreasing order. The P1 and P2 crystals possess the same
unit cells (orthorhombic) and thus they differ only in the lamellae populations. The dual lamellar morphism in this PEKm sample
also exhibited similar dual melting peaks during scanning, which correspond to melting of the individual P1 and P2 in a sequential
order. This study has thus provided important clues in and shed new light on the interpretation of multiple melting with respect
to polymorphism in polymers. Relationships between the low-melting and high-melting lamellae in cold-crystallized polyketone
polymer have been thoroughly explored.
Received: 9 January 2001/Accepted: 3 February 2001 相似文献
187.
188.
Youngeup Jin Minjung Lee Sun Hee Kim Suhee Song Il Kim Han Young Woo Kwanghee Lee Hongsuk Suh 《Journal of polymer science. Part A, Polymer chemistry》2009,47(19):5068-5077
In this study, a novel conjugated polymer, poly(4,4‐bis(2‐ethylhexyl)‐4H‐cyclopenta[def]phenanthrene‐2,6‐vinylene) (PCPPV) has been synthesized and characterized. For the polymerization, Gilch's reaction was applied for the first time with the cyclopenta[def]phenanthrene system. The absorption and emission spectra of PCPPV are red‐shifted about 40–50 nm due to the vinylene units when compared with those of poly(2,6‐(4,4‐bis(2‐ethylhex‐yl)‐4H‐cyclopenta[def]phenanthrene)) (PCPP). The solid‐state fluorescence is significantly broadened, possibly due to π–π interactions introduced by the phenanthrene and vinylene moieties. In solution, as the concentration of polar solvent increased, the photoluminescence (PL) intensity decreased due to quenching and aggregation by the interchain interactions between the conjugated backbones. After annealing the film at 80 °C, the PL and electroluminescence (EL) emission spectra exhibited also the quenching and aggregation effects indicating the interchain interactions of PCPPV. The large number of aromatic rings in a unit and the increased planarity achieved through introduction of vinylene units are able to give interchain interactions stronger than fluorene or phenylene units. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5068–5077, 2009 相似文献
189.
Spherulite ring-band patterns and growth regimes in neat poly(?-caprolactone) (PCL) and its miscible blends were analyzed using polarized-light optical microscopy and differential scanning calorimetry (DSC). Spherulite growth in thin-film forms and transformation of spherulite patterns in different regimes were investigated by comparing neat PCL with its miscible blends. Three miscible diluents in PCL were probed: poly(p-vinyl phenol) (PVPh), poly(benzyl methacrylate) (PBzMA), and poly(phenyl methacrylate) (PPhMA), which represent strong H-bonding and weak polar interactions, respectively. Blending of PCL with miscible amorphous polymers changes the spherulite patterns significantly. The effect of different diluent polymers varies. Inclusion of different amorphous polymers in PCL leads to different extents of suppression in growth rates and induces different spherulitic patterns. The H-bonding interaction leads to that the PCL/PVPh blend shows dendritic crystals and no ring bands. Although PPhMA differs from PBZMA only by a methylene in the chemical structure of repeat unit, the coil-like textures of ring bands in the PCL/PPhMA blend are widely different from the zig-zag ring bands in the PCL/PBzMA blend. Regime plots show that the growth of neat PCL behaves quite differently from any of its blends with amorphous polymers (PVPh, PPhMA, or PBzMA). Regime plots for PCL/PBzMA blend also differ from those for the PCL/PPhMA blend, which correlates with the crystal patterns seen in these two blend systems. 相似文献
190.
A method to assemble (Z)-enyne esters via palladium-catalyzed cross coupling reactions of enol tosylates is reported. A base-mediated one-pot decarboxylative rearrangement of the enynes to enones is described. The scope of this process is examined. 相似文献