排序方式: 共有74条查询结果,搜索用时 15 毫秒
1.
Nam Joo Lee Dongseok Kim Kwangho Yoo Yeji Yu Byeong-Su Kim Jeung Gon Kim 《Journal of polymer science. Part A, Polymer chemistry》2020,58(22):3237-3244
A simple and divergent synthetic strategy of bottlebrush polymers (BBPs) is presented, consisting of postpolymerization modification of a macromonomer and grafting-through polymerization. Beginning with a single macromonomer, its direct modification could build a library of macromonomers with an identical chain length, thus guaranteeing the precision in the synthesis of BBPs. In this study, a newly designed norbornenyl-terminated poly(methyl acrylate) (NB-PMA) is proposed as a chemically robust template. Ti-mediated transesterification of NB-PMA successfully produces structurally diverse polyacrylates while maintaining the terminal norbornenyl group intact. All macromonomers obtained from transesterification possess a good grafting-through ring-opening metathesis polymerization reactivity, furnishing homo, random, and block BBPs in a controllable manner. Moreover, atomic force microscopy analysis supports the controlled side-chain length distribution in the resulting BBPs. 相似文献
2.
A research was conducted on a new mixing device referred as a “vent slot mixer”, using experimental and computational methods.
The experiment was conducted in a laboratory-scale supersonic wind-tunnel of Mach number 2. Inflow air was under atmospheric
air condition, and hydrogen gas was used as fuel. In addition, the computational simulation approach was performed to support
the experimental result. The vent slot mixer can directly entrain the main airflow into the recirculation region, inducing
complex flow structures in the recirculation region. This also leads to gradual development of the shear layer to reduce the
total pressure loss mainly induced by a recompression shock. Contrary to typical shear layers of step mixer, for the vent
slot mixer, two-dimensional large-scale structures and weak shocks were clearly identified around the shear layer through
experimental and computational methods. When the fuel was injected from one circular injector in the recirculation region,
the high fuel concentration of the vent slot mixer was evenly distributed along the spanwise direction, but with the step
mixer the fuel was highly concentrated along the region downstream of the injector. Therefore, the vent slot mixer is effective
to uniformly spread the fuel toward the spanwise direction in the recirculation region. As the fuel injection rate increased,
the shear layer downstream of the vent slot mixer grew uniformly along the spanwise direction; consequently, shock structures
such as a recompression shock and weak shocks on the shear layer were significantly mitigated at J = 3.2. 相似文献
3.
Li L Dai X Liu Y Clevenger JO Field RW Jeung GH Geum N Lyyra AM 《Journal of Molecular Spectroscopy》2001,205(1):139-145
The predissociation of the 1(3)Sigma(-)(g) v >/= 10 levels of (7)Li(2) has been observed by pulsed and continuous-wave perturbation-facilitated optical-optical double-resonance spectroscopy (PFOODR). Our ab initio calculation shows that the inner wall of the 1(3)Sigma(-)(g) potential intersects the 1(3)Pi(g) repulsive potential at internuclear distance R = 2.00 ?. The predissociation is due to a DeltaS = 0, DeltaLambda = +/-1 rotational-electronic interaction with the repulsive 1(3)Pi(g) state. Copyright 2001 Academic Press. 相似文献
4.
[reaction: see text] We report the catalytic asymmetric allylation of ketones under highly concentrated reaction conditions with a catalyst generated from titanium tetraisopropoxide and BINOL (1:2 ratio) in the presence of isopropanol. This catalyst promotes the addition of tetraallylstannane to a variety of ketones to produce tertiary homoallylic alcohols in excellent yield (80-99%) with high enantioselectivities (79-95%). The resulting homoallylic alcohols can also be epoxidized in situ using tert-butyl hydroperoxide (TBHP) to afford cyclic epoxy alcohols in high yield (84-87%). 相似文献
5.
Komaragiri V McCarter B Bililign S Hagebaum-Reignier D Ledentu V Jeung GH 《The Journal of chemical physics》2005,123(2):24303
Quenching mechanisms of the Li3p and Li4p states in collision with the nitrogen molecule are studied by laser-induced fluorescence spectroscopy and by a quantum chemical calculation. The Li3p state is observed to be efficiently quenched to the Li3s state detected as intense 3s-->2p emission. The Li4p state is efficiently quenched to the Li4s and Li3d states detected as 4s-2p and 3d-2p emissions, respectively. The potential-energy surfaces for the Li(2s-4p)N2 states show a large number of conical intersections and avoided crossings resulting from the couplings between the ionic [Li+(N2)-] and covalent configurations. There are a large number of stable excited states, and we give here the spectroscopic constants for the lowest two stable isomers correlating to Li2p+N2. 相似文献
6.
Kim SY Augustine S Eo YJ Bae BS Woo SI Kang JK 《The journal of physical chemistry. B》2005,109(19):9397-9403
We use a first-principles calculation and small-angle neutron scattering (SANS) to investigate the mechanism and the nanosize products of the sol-gel reaction with diphenylsilanediol (DPD) and 3-methacryloxypropyltrimethoxysilane (MEMO) precursors in synthesizing a hybrid waveguide material. It is predicted that switching between a DPD hydroxyl and a MEMO methoxy with a reaction rate of 6.8 x 10(-6) s(-1) at 300 K is the fastest process for the first reaction step, thus generating diphenylmethoxysilanol (DPM) and 3-methacryloxypropyldimethoxysilanol (MEDO) as products. However, we determine that this reaction pathway could be modified by the presence of the H2O released from a catalyst such as Ba(OH)2.H2O. Next, switching between the DPM hydroxyl and the MEDO methoxy is followed to generate diphenyldimethoxysilane (DPDM) and 3-methacryloxypropylmethoxysilanediol (MEMDO). However, condensation between a MEMDO hydroxyl and a DPDM methoxy is found to be most favorable for the third reaction step, which generates the DPDM-MEMDO dimer and CH3OH molecule as products. In a similar fashion, a DPDM methoxy of the DPDM-MEMDO dimer can condense with a MEMDO hydroxyl of the second DPDM-MEMDO dimer to increase the chain, but its reaction rate of 2.8 x 10(-11) s(-1) is predicted to be about 5 times smaller than that between a DPDM methoxy and a MEMDO hydroxyl. This implies that the reaction rate for the larger nanostructures becomes smaller. Additionally, our SANS measurements determine that the final products from our sol-gel reaction are on the nanometer scale, at sizes from 1.76 to 2.36 nm. 相似文献
7.
[reaction: see text] Using L-proline as catalyst in the asymmetric aldol reaction and a series of benzamides and naphthamides, we have accomplished a dynamic kinetic resolution that simultaneously establishes the stereochemistry of the atropisomeric amide's chiral axis and a stereogenic center. The enantioselectivities ranged from 82% to 95% and the diastereoselectivities from 2.1:1 to 7.0:1. 相似文献
8.
Chae-Hyoung Kim In-Seuck Jeung Byungil Choi Toshinori Kouchi Kenichi Takita Goro Masuya 《Proceedings of the Combustion Institute》2011,33(2):2375-2382
Non-reacting and reacting experiments on the ignition by a plasma jet (PJ) torch were performed to understand the correlation between fuel injection location and combustion characteristics in unheated Mach 2 airflow. Fuel was injected through three sonic injectors in the recirculation region behind a backward-facing step: a parallel injector at 2 mm from the bottom wall and two normal injectors at 2 and 9 mm from the step wall. In order to mitigate the combustion pressure interaction with nozzle, an isolator was installed between the nozzle and combustor. The combustion performance of normal injection was little affected by the difference of fuel injection locations. Moreover, normally injected fuel was escaped not to be held in the recirculation region despite of low fuel injection rates. This led to lower combustion performance relative to the parallel injection which provided fuel not to leave the recirculation region. In this case, the role of the recirculation region was to fully hold fuel, and the PJ torch provided hot gases as a heat source and acted as a flame-holder to ignite fuel–air mixtures. In a low temperature inflow condition, combustible regions were constrained around the bottom wall where embedded with the PJ torch. When thermal choking occurred in the combustor, it induced shock train both in the combustor and isolator. Under this unstable condition, the combustion performance of the normal injection was lower than that of the parallel injection. This is because the normal injection led most fuel into low temperature incoming air-stream. 相似文献
9.
Hyoung Jin Lee Yeong Ryeon Kim Sei-Hwan Kim In-Secuk Jeung 《Proceedings of the Combustion Institute》2011,33(2):2351-2358
Hydrogen is expected to be used as a clean energy carrier. However, when high-pressure hydrogen is suddenly released into the air through tubes, self-ignition can occur by a diffusion ignition mechanism. In this paper, the phenomena of self-ignition and flame propagation during the sudden release of high-pressure hydrogen were investigated experimentally. Experimental results show that self-ignition can occur when bursting pressure is sufficiently high in spite of the shortness of the tube. For example, self-ignition was observed at a bursting pressure as high as 23.5 MPa with 50 mm long tube. When self-ignition successfully occurs, a hydrogen jet flame is produced by the ignition. The flame is then stabilized at the tube outlet. From photodiode signals and flame images, the propagation of a flame inside the tube is confirmed and the flame is detected near the rupture disk as the bursting pressure increases. When the tube length is not long enough to produce self-ignition, a hydrogen flame is observed in the only boundary layer at the end of tube and it quenches after the flame exits the tube. Consequently, the formation of a complete flame across the tube is important to initiate self-ignition, which sustains a diffusion flame after jetting out of the tube into the air. Also, in order to establish a complete flame across the tube, it is necessary to have sufficient length such that the mixing region is generated by multi-dimensional shock–shock interactions. 相似文献
10.
Jeung Gon Kim 《Journal of polymer science. Part A, Polymer chemistry》2017,55(15):2554-2560
Post‐polymerization modification is an important synthetic method to produce macromolecules with various chemical and physical properties. With this technique, functional groups of polymer molecules within the same structural scaffold can be varied, and thus, accurate research on structure‐property relationships is possible. To add practicality, the direct post‐polymerization of commodity polymers has been pursued, but only limited success has been realized. In this report, a study on various transesterification methods for the synthesis of functional polyacrylates beginning with a poly(methyl acrylate) (PMA), one common acrylate polymer, is presented. The Zn‐based catalytic system, a combination of Zn4(OCOCF3)6O and 4‐dimethylaminopyridine with instant methanol removal, exhibited the highest reactivity among many catalysts and conditions. Assorted alcohols were reacted with PMA to produce the corresponding polyacrylates. This method was successfully extended to post‐polymerization modification of a PMA‐containing block copolymer, PS‐b‐PMA and synthesis of acrylate copolymers with functional group density control. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2554–2560 相似文献