The Experts below are selected from a list of 195 Experts worldwide ranked by ideXlab platform
Ben Zhong Tang - One of the best experts on this subject based on the ideXlab platform.
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mesogen jacketed liquid crystalline Polyacetylene containing triphenylene discogen synthesis and phase structure
Polymer Chemistry, 2013Co-Authors: Zhenqiang Yu, Keqing Zhao, Shuang Yang, Bing Shi Li, Erqiang Chen, Ben Zhong TangAbstract:Triphenylene-containing acetylenes with one or three methylene units as spacers and the corresponding mesogen-jacketed liquid crystalline Polyacetylenes (MJLCPAs) were designed and synthesized, the mesomorphic properties and phase behaviors of the monomers and novel side-chain liquid crystalline polymers were investigated. The monomers [HCC(CH2)mC18H6(OC6H13)5; m = 1, 3] are prepared by consecutive etherization, coupling, and etherization reactions, and the chemical structures were confirmed by mass spectroscopy and 1H/13C-NMR. The phase behaviors of the monomers were investigated by differential scanning calorimetry (DSC), polarized light microscopy (PLM), and wide-angle X-ray diffraction (WAXD). The results show that both of the monomers form a hexagonal columnar liquid crystal phase at room temperature. The monomers are polymerized using [Rh(nbd)Cl]2 as catalyst and producing soluble polymers in the yields of 55% and 52%, respectively. The chemical structures and phase behaviors of the two polymers are characterized and evaluated by IR, NMR, TGA, DSC, and WAXD analyses. Both of the two polymers show enhanced thermal and chemical stability with thermal decomposition temperatures up to higher than 340 °C due to the protection of the “jacketed effect” of the side-chain triphenylenes wrapped around the rigid Polyacetylene main-chain. The polymers adopt a columnar shaped structure and self-organized into hexagonally packed columnar phase. The relative electron density maps of the columnar structure are also reconstructed.
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Synthesis of Functional Disubstituted Polyacetylenes Bearing Highly Polar Functionalities via Activated Ester Strategy
ACS Macro Letters, 2011Co-Authors: Xiao A Zhang, Qiuli Zhao, Li Tong-bao, Hui Zhao, Ben Zhong TangAbstract:We demonstrate a facile synthetic route to functional disubstituted Polyacetylenes bearing highly polar groups based on polymer reactions. A pentafluorophenyl (PFP) ester-containing diphenylacetylene was designed and polymerized to obtain PFP activated ester-functionalized disubstituted Polyacetylene (P1). P1 was used as a parent polymer to further react separately with diverse amines, giving rise to a series of functional disubstituted Polyacetylenes with a chiral moiety and hydroxyl and carboxyl groups in high yields under mild condition. Spectral characterization data indicated that the polymers’ structures were well consistent with the expected results. The helicity and emission property of polymers were also studied.
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Liquid‐crystalline and light‐emitting Polyacetylenes
Journal of Polymer Science Part A, 2003Co-Authors: Ben Zhong TangAbstract:Rigid polymer backbones have often been considered to be detrimental to the packing of mesogenic pendants, and Polyacetylenes have generally been regarded as unpromising materials for light-emitting applications. Our group, however, has succeeded in creating a series of liquid-crystalline Polyacetylenes with rigid backbones and a variety of light-emitting Polyacetylenes with luminescent chromophores. Here we demonstrate that the rigid Polyacetylene skeleton can play a constructive role in guiding the alignments of mesogenic pendants and prove that Polyacetylenes can be highly emissive with photoluminescence quantum yields of up to 98% and electroluminescence performances comparable or superior to those of the best blue-light-emitting polymers. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2607–2629, 2003
Y. W. Park - One of the best experts on this subject based on the ideXlab platform.
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energetics and electronic structure of a Polyacetylene chain contained in a carbon nanotube
Physical Review B, 2003Co-Authors: G C Mcintosh, David Tomanek, Y. W. ParkAbstract:Using density-functional theory, we calculate the energy and electronic structure of a Polyacetylene chain interacting with various carbon nanotubes. We find that Polyacetylene chains are weakly attracted exohedrally or endohedrally to nanotubes. The equilibrium separation between the chain and the wall is close to 3.3 A, suggesting an energetic preference for Polyacetylene to be enclosed in nanotubes wider than the (5,5) tube. The chains are expected to be spontaneously pulled into open nanotubes by forces amounting to a fraction of a nanonewton. Electronic structure calculations reveal the occurrence of a peak at the Fermi level in the electronic density of states, caused by the weak interaction between Polyacetylene and the carbon nanotube, which may facilitate the onset of superconductivity in this system.
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Microwave conductivity of alkali-metal-doped Polyacetylene
International Conference on Science and Technology of Synthetic Metals, 1994Co-Authors: E.s. Choi, E.b. Park, J.y. Park, Y. W. ParkAbstract:Summary form only given. We report the temperature dependence of microwave conductivity in alkali-metal doped Polyacetylene. The measurements have been performed at 4.5 GHz using the cavity perturbation method. The high density- Polyacetylene films are synthesized following the modified Shirakawa method. Doping of Polyacetylene with alkali metals has been accomplished by vapor phase method. The results are compared with the dc conductivity measured by the four-probe or Montgomery method and their analysis are under study.
Ashish Rawson - One of the best experts on this subject based on the ideXlab platform.
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Stability of falcarinol type Polyacetylenes during processing of Apiaceae vegetables
Trends in Food Science and Technology, 2013Co-Authors: Ashish Rawson, Nigel P. Brunton, Padraig Mcloughlin, Brijesh K. Tiwari, Maria G. TuohyAbstract:Carrots are known as an excellent source of pro-vitamin A and other phytochemicals such as phenolics, and is one of the most consumed vegetable around the world. These phytochemicals are believed to help protect against various chronic diseases such as cardiovascular disease and cancer. The presence of Polyacetylenes (PAs) has been known in carrots for many years however it is in recent times that researchers have found evidence for health promoting properties of PAs. In particular falcarinol type PAs have been under continuous study due to their range of bioactivities which could provide health benefits. In common with other vegetables a high proportion of Apiaceae vegetables are processed prior to consumption. The renewed interest in the biological relevance of falcarinol type Polyacetylenes has lead to many investigations into the effect of processing on their levels. The primary objective of the present review is to summarise and critically evaluate the effects of food processing technologies on Polyacetylene levels of different Apiaceae vegetables with a view to coming to a consensus as to the best practices to optimise their retention in processed products.
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effect of ultrasound and blanching pretreatments on Polyacetylene and carotenoid content of hot air and freeze dried carrot discs
Ultrasonics Sonochemistry, 2011Co-Authors: Ashish Rawson, Maria G. Tuohy, Brijesh K. Tiwari, Colm P Odonnell, Nigel P. BruntonAbstract:The effect of ultrasound and blanching pretreatments on Polyacetylene (falcarinol, falcarindiol and falcarindiol-3-acetate) and carotenoid compounds of hot air and freeze dried carrot discs was investigated. Ultrasound pretreatment followed by hot air drying (UPHD) at the highest amplitude and treatment time investigated resulted in higher retention of Polyacetylenes and carotenoids in dried carrot discs than blanching followed by hot air drying. Freeze dried samples had a higher retention of Polyacetylene and carotenoid compounds compared to hot air dried samples. Color parameters were strongly correlated with carotenoids (p < 0.05). This study shows that ultrasound pretreatment is a potential alternative to conventional blanching treatment in the drying of carrots.
Maria G L Brandao - One of the best experts on this subject based on the ideXlab platform.
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new evidences of antimalarial activity of bidens pilosa roots extract correlated with Polyacetylene and flavonoids
Journal of Ethnopharmacology, 2004Co-Authors: F Q Oliveira, Valter Ferreira De Andradeneto, Antoniana U Krettli, Maria G L BrandaoAbstract:Abstract Bidens pilosa is among the several plants used in Brazil to treat malaria. It was demonstrated that crude extracts from roots prepared with 80% ethanol by percolation are active in vitro against Plasmodium falciparum and the activity is correlated with the presence of Polyacetylene and flavonoids. This extract was submitted to column chromatography with ether and ether methanol (1:1) and two fractions, enriched in Polyacetylene and flavonoids, respectively, were obtained. The extract and the fractions were assessed by HPLC/DAD analysis and antimalarial tests in vivo. Ethanol extract showed by HPLC the presence of several peaks for Polyacetylene and flavonoids, compounds corresponding to quercetin-3,3′-dimethoxy-7-0-rhamnoglucopyranose and the acetylene 1-phenyl-1,3-diyn-5-en-7-ol-acetate, previously identified in this extract. The peaks for flavonoids were absent in ether fraction and those ones for Polyacetylene in ether:methanol. In in vivo tests, ethanol extract caused 36% of reduction of parasitaemia at fifth day, and 29% at seventh day. Ether:methanol fraction caused 38% of reduction at fifth day but was inactive at day 7. The survival of the animals treated with 80% ethanol extract was higher than in the fractions. The results showed that the in vivo activity of ethanol extract depends on the presence of Polyacetylene and flavonoids.
Kazuo Akagi - One of the best experts on this subject based on the ideXlab platform.
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helical carbon and graphitic films prepared from iodine doped helical Polyacetylene film using morphology retaining carbonization
Journal of the American Chemical Society, 2008Co-Authors: Mutsumasa Kyotani, Satoshi Matsushita, Takuro Nagai, Yoshio Matsui, Masaki Shimomura, Akira Kaito, Kazuo AkagiAbstract:In this communication, we report a novel preparation of the helical carbon nanofibril-fabricated thin film from the iodine-doped filmy helical Polyacetylene through a carbonization process. Carbonization of the helical Polyacetylene films by way of iodine doping is found to afford carbon and graphitic films completely preserving morphologies and even helical nanofibril structures.
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synthesis of helical Polyacetylene in chiral nematic liquid crystals using crown ether type binaphthyl derivatives as chiral dopants
Journal of the American Chemical Society, 2005Co-Authors: Kazuo Akagi, Taizou Mori, G Piao, Mutsumasa KyotaniAbstract:A series of crown ether type binaphthyl derivatives (CEBDs) were synthesized and used as chiral dopants to induce chiral nematic (N*) liquid crystals (LCs). The twisting powers of the CEBDs for phenylcyclohexane (PCH)-derived nematic LCs were evaluated. It was found that the twisting powers of the CEBDs increased with decreasing ring size of the crown ether. Helical Polyacetylenes were synthesized in the N*-LCs induced by the CEBDs. The relationship between the morphology of the helical Polyacetylene and the helical structure of the N*-LC was investigated. The result showed that the interdistance between the fibril bundles of the helical Polyacetylene was equal to a half-helical pitch of the N*-LC and the screw direction of the Polyacetylene fibrils was opposite to that of the N*-LC.
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The Soliton State of Heavily Doped Polyacetylene
Molecular Crystals and Liquid Crystals, 1993Co-Authors: C.o. Yoon, Kazuo Akagi, You-gyoung Park, Hideki ShirakawaAbstract:Abstract We propose that the heavily doped Polyacetylene is formed by the soliton-antisoliton pair condensation which is a mixed state of the delocalized charge carriers and the virtually bound states. With this proposal, the metallic conductivity and the temperature independent magnetic susceptibility as well as the infrared active vibrational modes (IRAV) observed in the heavily doped Polyacetylene can be understood simultaneously. Furthermore, the persistence of the C˭C and C—C vibrational modes appeared in Raman spectra for the heavily doped Polyacetylene can also be understood with this soliton-antisoliton condensed state model. The highest conductivity estimated from this phenomenological model is [sgrave] RT ˭ 35,000 S/cm, consistent with the observed (and confirmed) maximum conductivity of the heavily doped Polyacetylene.
