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Transport in Porous Media - The RANS modelling of turbulence across fluid-porous interface regions within ribbed channels has been investigated by applying double (both volume and Reynolds)... 相似文献
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Ashley M. Nelson Sean T. Hemp Jessica Chau Timothy E. Long 《Journal of polymer science. Part A, Polymer chemistry》2015,53(24):2829-2837
The incorporation of acrylic functionality into caffeine enables the preparation of a vast array of novel thermoplastics and thermosets. A two‐step derivatization provided a novel caffeine‐containing methacrylate monomer capable of free radical polymerization. Copolymers of 2‐ethylhexyl methacrylate and caffeine methacrylate (CMA) allowed for a systematic study of the effect of covalently bound caffeine on polymer properties. 1H NMR and UV‐vis spectroscopy confirmed caffeine incorporation at 5 and 13 mol %, and SEC revealed the formation of high molecular weight (co)polymers (>40,000 g/mol). CMA incorporation resulted in a multistep degradation profile with initial mass loss closely correlating to caffeine content. Differential scanning calorimetry, rheological, and thermomechanical analysis demonstrated that relatively low levels of CMA increased the glass transition temperature, resulting in higher moduli and elucidating the benefits of incorporating caffeine into polymers. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2829–2837 相似文献
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Shadap Lathewdeipor Tyagi Jaya Lakshmi Poluri Krishna Mohan Novikov Sergei Lo Chun-Wan Timothy Mozharivskyj Yurij Kollipara Mohan Rao 《Transition Metal Chemistry》2021,46(3):231-240
Transition Metal Chemistry - Metal complexes 1–9 have been synthesized by reacting the benzothiazole–pyrazole derivative ligands (L1, L2 and L3) with the metal precursors of ruthenium... 相似文献
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Dr. Sevan D. Houston Dr. Hui Xing Prof. Paul V. Bernhardt Timothy J. Vanden Berg Dr. John Tsanaktsidis Dr. G. Paul Savage Prof. Craig M. Williams 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(11):2735-2739
The scope and limitations of Eaton's rhodium(I)-catalyzed valence isomerization of cubane to cyclooctatetraene (COT) were investigated in the context of functional group tolerability, multiple substitution modes and the ability of cubane-alcohols to undergo one-pot tandem Ley–Griffith Wittig reactions in the absence of a transition metal catalyst. 相似文献
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Timothy R. Totsch Victoria L. Stanford Oleksander Klep Mary K. Burdette Benjamin Grant Stephen H. Foulger Gary M. Gray 《Journal of polymer science. Part A, Polymer chemistry》2020,58(13):1825-1842
Linear polyphosphonates with the generic formula –[P(Ph)(X)OR′O]n– (X = S or Se) have been synthesized by polycondensations of P(Ph)(NEt2)2 and a diol (HOR′OH = 1,4-cyclohexanedimethanol, 1,4-benzenedimethanol, tetraethylene glycol, or 1,12-dodecanediol) followed by reaction with a chalcogen. Random copolymers have been synthesized by polycondensations of P(Ph)(NEt2)2 and mixture of two of the diols in a 2:1:1 mol ratio followed by reaction with a chalcogen. Block copolymers with the generic formula –[P(Ph)(X)OR′O](x + 2) –[P(Ph)(X)OR′O](x + 3)– (X = S or Se) have been synthesized by the polycondensations of Et2N[P(Ph)(X)OR′O](x + 2)P(Ph)NEt2 oligomers with HOR′O[P(Ph)(X)OR′O](x + 3)H oligomers followed by reaction with a chalcogen. The Et2N[P(Ph)(X)OR′O](x + 2)P(Ph)NEt2 oligomers are prepared by the reaction of an excess of P(Ph)(NEt2)2 with a diol while the HOR′O[P(Ph)(X)OR′O](x + 3)H oligomers are prepared by the reaction of P(Ph)(NEt2)2 with an excess of the diol. In each case the excess, x is the same and determines the average block sizes. All of the polymers were characterized using 1H, 13C{1H}, and 31P{1H} NMR spectroscopy, TGA, DSC, and SEC. 31P{1H} NMR spectroscopy demonstrates that the random and block copolymers have the expected arrangements of monomers and, in the case of block copolymers, verifies the block sizes. All polymers are thermally stable up to ~300°C, and the arrangements of monomers in the copolymers (block vs. random) affect their degradation temperatures and Tg profiles. The polymers have weight average MWs of up to 3.8 × 104 Da. 相似文献
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Dr. David Scheerer Prof. Dr. Heng Chi Dr. Dan McElheny Prof. Dr. Timothy A. Keiderling Prof. Dr. Karin Hauser 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(16):3524-3534
Site-specific isotopic labeling of molecules is a widely used approach in IR spectroscopy to resolve local contributions to vibrational modes. The induced frequency shift of the corresponding IR band depends on the substituted masses, as well as on hydrogen bonding and vibrational coupling. The impact of these different factors was analyzed with a designed three-stranded β-sheet peptide and by use of selected 13C isotope substitutions at multiple positions in the peptide backbone. Single-strand labels give rise to isotopically shifted bands at different frequencies, depending on the specific sites; this demonstrates sensitivity to the local environment. Cross-strand double- and triple-labeled peptides exhibited two resolved bands that could be uniquely assigned to specific residues, the equilibrium IR spectra of which indicated only weak local-mode coupling. Temperature-jump IR laser spectroscopy was applied to monitor structural dynamics and revealed an impressive enhancement of the isotope sensitivity to both local positions and coupling between them, relative to that of equilibrium FTIR spectroscopy. Site-specific relaxation rates were altered upon the introduction of additional cross-strand isotopes. Likewise, the rates for the global β-sheet dynamics were affected in a manner dependent on the distinct relaxation behavior of the labeled oscillator. This study reveals that isotope labels provide not only local structural probes, but rather sense the dynamic complexity of the molecular environment. 相似文献
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Isaiah R. Speight Dr. Igor Huskić Dr. Mihails Arhangelskis Dr. Hatem M. Titi Dr. Robin S. Stein Prof. Timothy P. Hanusa Prof. Tomislav Friščić 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(8):1811-1818
The “disappearing polymorph” phenomenon is well established in organic solids, and has had a profound effect in pharmaceutical materials science. The first example of this effect in metal-containing systems in general, and in coordination-network solids in particular, is here reported. Specifically, attempts to mechanochemically synthesize a known interpenetrated diamondoid (dia) mercury(II) imidazolate metal–organic framework (MOF) yielded a novel, more stable polymorph based on square-grid (sql) layers. Simultaneously, the dia-form was found to be highly elusive, observed only as a short-lived intermediate in monitoring solvent-free synthesis and not at all from solution. The destabilization of a dense dia-framework relative to a lower dimensionality one is in contrast to the behavior of other imidazolate MOFs, with periodic density functional theory (DFT) calculations showing that it arises from weak interactions, including structure-stabilizing agostic C−H⋅⋅⋅Hg contacts. While providing a new link between MOFs and crystal engineering of organic solids, these findings highlight a possible role for agostic interactions in directing topology and stability of MOF polymorphs. 相似文献