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81.
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Propylene was polymerized with the catalyst system (C2H5)2A1C1/ VCk/ anisole at -78°C using various conditions. The resulting polymers were successively extracted by diethyl ether, hexane, and heptane, leaving the residue. The polymers of the four series were characterized by intrinsic viscosity, gel permeation chromatography, 13C nuclear magnetic resonance, infrared spectroscopy, x-ray diffraction, and by differential scanning calorimetry. The combined evidence from the various methods indicates that this catalyst system leads to stereoblock polymers which can be fractionated according to stereochemical composition and sequence length. 相似文献
83.
The standard deviation [sgrave] is known to be an absolute measure of Gaussian (G) distributions, because it (or multiples of it) always determines a constant fraction of the material. However, this is not true for distribution functions other than Gaussian. The weight fractions corresponding to weight standard deviations (±[sgrave]w) of Schulz-Flory distributions depend on the polymolecularity index xw/xn, approaching a limiting value of W(xw ± [sgrave]w) = 86.5 for xw/xn →∞. The use of weight standard deviations is meaningless for generalized logarithmic normal (LN) distributions if xw/xn 52. The weight fractions W(Xn ± [sgrave]n) around the number-average degree of polymerization of G and LN distributions first go through a maximum before decreasing with increasing xw/xn. The weight fractions W(xn ± [sgrave]n) decrease steadily with higher xw/xn. 相似文献
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Elias Nursyafiqah Wahab Roswanira Abdul Jye Lau Woei Mahat Naji Arafat Chandren Sheela Jamalis Joazaizulfazli 《Cellulose (London, England)》2021,28(9):5669-5691
Cellulose - A greener processing route to replace the current environmentally-unfriendly esterification technique to produce biofuels such as pentyl valerate (PeVa) was explored. This study... 相似文献
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Dr. Vladimir Stepanenko Dr. Xue‐Qing Li Jana Gershberg Prof. Dr. Frank Würthner 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(13):4176-4183
The self‐assembly behavior of an achiral perylene bisimide (PBI) organogelator that bears two 3,4,5‐tridodecyloxybenzoylaminoethyl substituents at the imide positions has been investigated in chiral solvents (R)‐ and (S)‐limonene in great detail by circular dichroism (CD) spectroscopy and atomic force microscopy (AFM). CD spectroscopic studies on dilute solutions revealed a preferential population of one‐handed helical assemblies in chiral solvent with an enantiomeric excess close to 100 %, whereas AFM images of more than 100 nanofibers of the organogel obtained from more concentrated solutions were found to consist of both handed helices with an enantiomeric excess of only 20 %. This discrepancy is attributed to the fast gelation process at high dye concentration that evidently proceeds through non‐equilibrated nuclei in a kinetic rather than thermodynamic self‐assembly process. Under these conditions the chiral induction from the homochiral solvent may not be adequate in effectively populating only one‐handed helices. 相似文献
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Magaly A. M. Lyra José L. Soares-Sobrinho Regina C. B. Q. Figueiredo Jana M. Sandes ádley A. N. Lima R?mulo P. Tenório Danilo A. F. Fontes Fabiana L. A. Santos Larissa A. Rolim Pedro J. Rolim-Neto 《Journal of inclusion phenomena and macrocyclic chemistry》2012,73(1-4):397-404
The current chemotherapy for Chagas disease is still based on benznidazole, which has low solubility, but complexation with cyclodextrins provides a way of increasing the solubility. The objective of this work was to characterize the inclusion complexes formed between benznidazole (BNZ) and randomly 2-methyled-β-cyclodextrin (RM-β-CD) in aqueous solution and study cytotoxicity and trypanocidal. BNZ:RM-β-CD solution complex systems were prepared and characterized using the phase solubility diagram, nuclear magnetic resonance and a photostability assays, also to investigate the in vitro trypanocidal activity with epimastigote forms of Trypanossoma cruzi and the study of cytotoxicity against mammal cells. The phase-solubility diagram displayed an A L-type feature, providing evidence of the formation of soluble inclusion complexes. The continuous variation method showed the existence of a complex with 1:1 stoichiometry. Toxicity assays demonstrated that inclusion complexes were able to reduce the toxic effects caused by benznidazole alone and that this did not interfere with the trypanocidal activity of the benznidazole. The use of inclusion complexes benznidazole:cyclodextrin is thus a promising alternative for the development of a safe and stable liquid formulation and a new option for the treatment of Chagas disease. 相似文献