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L. A. Gower D. J. Lyman 《Journal of polymer science. Part A, Polymer chemistry》1995,33(13):2257-2266
Copolyether-urethane-ureas based on methylene bis(4-phenylisocyanate), polypropylene glycol (or polytetramethylene glycol), and ethylene diamine showed improvement in packing order within the already present phases when subject to both thermal annealing and slow solvent evaporation techniques using glass as the casting substrate. However, formation of these copolymer films directly onto IR salt crystals led to major disturbances in the copolymer morphology due to the dissolving of inorganic salt into the polymer casting solution. These disturbances appear to be caused by a salt-urea segment interaction. The urea amide I band (1635 cm?1) appears to be a sensitive indicator of such changes in these copolymers. © 1995 John Wiley & Sons, Inc. 相似文献
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Alkali-metal magnetometers compete with SQUID detectors as the most sensitive magnetic field sensors. Their sensitivity is limited by relaxation due to spin-exchange collisions. We demonstrate a K magnetometer in which spin-exchange relaxation is completely eliminated by operating at high K density and low magnetic field. Direct measurements of the signal-to-noise ratio give a magnetometer sensitivity of 10 fT Hz(-1/2), limited by magnetic noise produced by Johnson currents in the magnetic shields. We extend a previous theoretical analysis of spin exchange in low magnetic fields to arbitrary spin polarizations and estimate the shot-noise limit of the magnetometer to be 2x10(-18) T Hz(-1/2). 相似文献
57.
S. V. Conjeevaram R. S. Benson D. J. Lyman 《Journal of polymer science. Part A, Polymer chemistry》1985,23(2):429-444
Trimethylene oxide was polymerized to polyoxytrimethylene glycol by two synthetic routes. High molecular weight polytrimethylene oxide was synthesized using a coordination catalyst system consisting of triethylaluminum, acetylacetone, and water, then ozonized and reduced with lithium aluminum hydride in anhydrous ether to form hydroxyl end-capped polyoxytrimethylene glycol. In the second route, the polyoxytrimethylene glycols were synthesized directly by the cationic polymerization of trimethylene oxide with boron trifluoride/ethyl ether as catalyst and 1,4 butanediol as co-initiator. (AB)n block copolyether–urethane–ureas based on these polyoxytrimethylene glycols were synthesized and characterized by differential scanning calorimetry, and dynamic mechanical and stress–strain measurements. 相似文献
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D. W. Koetsier A. Bantjes J. Feijen D. J. Lyman 《Journal of polymer science. Part A, Polymer chemistry》1978,16(2):511-521
Anionic polymerization has been used as a technique for the synthesis of five-block copolymers of polystyrene (PS), polyisoprene (PI), and poly(ethylene oxide) (PEO). Two types of such polymers, PEO-PI-PS-PI-PEO and PEO-PS-PI-PS-PEO with varying PEO block length, have been prepared, using potassium naphthalene as the initiator and tetrahydrofuran as the solvent. The polymers were purified by extraction with ethyl acetate, diethyl ether, and water. After the addition of each monomer, a sample from the living polymer solution was taken and analyzed by spectroscopy (infared (IR) and proton magnetic resonance (PMR)), osmometry, and gel-permeation chromatography (GPC) to obtain information about composition, molecular weight and molecular weight distribution of the intermediate polymers. The five-block copolymers have also been characterized by the same techniques and by elemental analysis. 相似文献
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James Elver Johnson Mohammad Arfan Richard Hodzi Lyman R. Caswell Susan Rasmussen 《Photochemistry and photobiology》1990,51(2):139-144
Abstract— Photolysis at 254 nm of alkyl benzohydroxamates [C, H, CONHOR: R = CH3 H2 CH3 CH(CH3 )2 , CH2 C6 H5 CH(CH3 )C2 H5 CH(CH3 )- n -C6 H13 ] in acetonitrile or hydrocarbon solvents gives benzamide. These reactions can be sensitized by benzophenone (at ca. 350 nm) and are quenched by cis-piperylene. Racemization occurred when 2-octyl (+)-benzohydroxamate was irradiated in cyclohexane. These results are consistent with a mechanism involving a triplet biradical. Photolysis of phenyl benzohydroxamate [C6 H5 CONHOC6 H5 ] and benzyl N -methylbenzohydroxamate [C6 H5 CON-(CH3 )OCH2 Q6 H5 ] cannot be quenched with ris-piperylene and appear to be singlet reactions. 相似文献
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Claire McGraw Kirsten Swonger Koretz Daniel Oseid Edward Lyman Anne Skaja Robinson 《Molecules (Basel, Switzerland)》2022,27(11)
Background: Membrane cholesterol dysregulation has been shown to alter the activity of the adenosine A2A receptor (A2AR), a G protein-coupled receptor, thereby implicating cholesterol levels in diseases such as Alzheimer’s and Parkinson’s. A limited number of A2AR crystal structures show the receptor interacting with cholesterol, as such molecular simulations are often used to predict cholesterol interaction sites. Methods: Here, we use experimental methods to determine whether a specific interaction between amino acid side chains in the cholesterol consensus motif (CCM) of full length, wild-type human A2AR, and cholesterol modulates activity of the receptor by testing the effects of mutational changes on functional consequences, including ligand binding, G protein coupling, and downstream activation of cyclic AMP. Results and conclusions: Our data, taken with previously published studies, support a model of receptor state-dependent binding between cholesterol and the CCM, whereby cholesterol facilitates both G protein coupling and downstream signaling of A2AR. 相似文献