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991.
Dr. Takayuki Arai Keumhee Jang Dr. Yasuhito Koyama Dr. Shigeo Asai Prof. Toshikazu Takata 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(19):5917-5923
A supramolecular cross‐linked cross‐linker, capable of introducing rotaxane cross‐links to vinyl polymers, has been developed for the rational synthesis of polyrotaxane networks. The experimental results reveal that the combination of an oligocyclodextrin (OCD) and a terminal bulky group‐tethering macromonomer (TBM) forms a polymer‐network structure having polymerizable moieties through supramolecular cross‐linking. Radical polymerization of a variety of typical vinyl monomers in the presence of the vinylic supramolecular cross‐linker (VSC) afforded the corresponding vinyl polymers cross‐linked through the rotaxane cross‐links (RCP) as transparent stable films in high yields under both photoinitiated and thermal polymerization conditions. A poly(N,N‐dimethylacrylamide)‐based hydrogel synthesized by using VSC, RCPDMAAm, displayed a unique mechanical property. The small‐angle X‐ray scattering (SAXS) results, indicating patterns characteristic of a polyrotaxane network, clearly suggested the presence and role of the rotaxane cross‐links. The confirmation of the introduction of rotaxane‐cross‐links into vinyl polymers strongly reveals the significant usefulness of VSC. 相似文献
992.
Fanke Meng Hwanjong Jang Prof. Amir H. Hoveyda 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(9):3204-3214
An exceptionally site‐ and E‐selective catalytic method for preparation of Si‐containing alkenes through protosilylation of terminal alkynes is presented. Furthermore, the vinylsilanes obtained are used as substrates to generate vicinal or geminal borosilanes by another catalytic process; such products are derived from enantioselective protoborations of the Si‐substituted alkenes. All transformations are catalyzed by N‐heterocyclic carbene (NHC) copper complexes. Specifically, a commercially available imidazolinium salt, cheap CuCl (1.0 mol %) and Me2PhSi–B(pin), readily and inexpensively prepared in one vessel, are used to convert terminal alkynes to (E)‐β‐vinylsilanes efficiently (79–98 % yield) and in >98 % E and >98 % β‐selectivity. Vinylsilanes are converted to borosilanes with 5.0 mol % of a chiral NHC–Cu complex in 33–94 % yield and up to 98.5:1.5 enantiomeric ratio (e.r.). Alkyl‐substituted substrates afford vicinal borosilanes exclusively; aryl‐ and heteroaryl‐substituted alkenes deliver the geminal isomers preferentially. Different classes of chiral NHCs give rise to high enantioselectivities in the two sets of transformations: C1‐symmetric monodentate Cu complexes are most suitable for reactions of alkyl‐containing vinylsilanes and bidentate sulfonate‐bridged variants furnish the highest e.r. for substrates with an aryl substituent. Working models that account for the observed trends in selectivity are provided. Utility is demonstrated through application towards a formal enantioselective total synthesis of naturally occurring antibacterial agent bruguierol A. 相似文献
993.
Mee Rahn Kim Soo Yeon Heo Du-Jeon Jang 《Journal of colloid and interface science》2009,339(1):217-221
The hexagonally arranged close-packed concave nanotexture of the master surface of nanoporous alumina has been imprinted several times on aluminum films and gold films by thermal evaporation and on polystyrene films by spin coating. The degradation of the nanotextures with replica pattern transfer has been monitored by measuring the topology and the wettability of duplicated films. The trough-to-crest height of the topography decreases while the wettability of the nanotexture increases significantly as replication goes on. Air fractions calculated with measured water contact angles decrease substantially with replication although they also depend strongly on the materials and the shapes of duplicating nanotextures. 相似文献
994.
M.-E. Lee Y.-C. Yeh Y.-H. Chung C.-L. Wu C.-S. Yang W.-C. Chou C.-T. Kuo D.-J. Jang 《Physica E: Low-dimensional Systems and Nanostructures》2005,26(1-4):422
The carrier capture and relaxation of type II ZnTe/ZnSe quantum dots have been investigated with ultrafast time-resolved photoluminescence upconversion. The carrier capture times were 7 and 38 ps for the Volmer–Weber mode and Stranski–Krastanow mode, respectively. We found that the carrier relaxation of QDs exhibits faster decay under the Volmer–Weber growth mode than under the Stranski–Krastanow growth mode. We attribute the difference of carrier relaxation to the wetting layer formed in the Stranski–Krastanow growth mode. 相似文献
995.
Seung Hwan Joo Jong Hak Kim Sang Wook Kang Jyongsik Jang Yong Soo Kang 《Journal of Polymer Science.Polymer Physics》2007,45(16):2263-2269
When poly(N‐vinyl pyrrolidone‐co‐vinyl acetate) (PVP‐co‐PVAc) containing amide and ester groups were complexed with silver salts to form silver polymer electrolyte membranes, their separation performance of propylene/propane mixtures showed the high selectivity of propylene over propane of 55 and the high mixed gas permeance of 12 GPU (1 GPU = 1.0 × 10?6 cm3(STP) cm?2 s?1 cmHg?1). The separation performance strongly depends on the composition of the copolymer: the higher concentration of PVP in the copolymer, the better separation performance was achieved. These results suggest that the amide group is more effective in facilitated propylene transport than the ester group, primarily due to the stronger interaction of the silver ions with the amide than the ester oxygens, as demonstrated by FT‐IR and FT‐Raman spectroscopies. In‐situ FT‐IR spectra upon propylene sorption also demonstrate that the interaction strength of the silver ions with the ligands is arranged: amide > C?C > ester. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2263–2269, 2007 相似文献
996.
邻硝基苯基荧光酮-吐温80吸光光度法测定钢铁中微量钼 总被引:4,自引:1,他引:3
研究了Mo(Ⅵ)-(o-NPF)-Tween 80的尤度分析条件,在0.1m01·L-1硫酸介质中,配合物组成为Mo(Ⅵ)(o-NPF)=12,λmax=528nm,ε表现=1. 4×105,0~20μg/25m1符合比耳定律。体系允许较大量氟离子存在,可消除一定量Ti(Ⅵ)、Nb(Ⅴ)、zr(Ⅳ)、Sn(Ⅳ)、Sb(Ⅱ)等离予的严重干扰影响。可直接测定钢铁中微量钼,操作简便,结果满意。 相似文献
997.
Der‐Jang Liaw Ching‐Cheng Huang Chun‐Wei Fu 《Journal of polymer science. Part A, Polymer chemistry》2006,44(15):4428-4434
A novel organosoluble polynorbornene bearing a polar, pendant, ester‐bridged epoxy group [poly(oxiran‐2‐ylmethyl 2‐methylbicyclo[2.2.1]hept‐5‐ene‐2‐carboxylate) (polyOMMC)] was prepared via the living ring‐opening metathesis polymerization (ROMP) of active norbornenes with a Ru catalyst. PolyOMMC exhibited excellent solubility in a variety of solvents. The number‐average molecular weight of polyOMMC linearly increased with the [M]/[I] ratio (where [M] is the monomer concentration and [I] is the initiator concentration), and a narrow polydispersity of 1.09–1.19 was observed; this was considered a living polymerization. When ROMP of oxiran‐2‐ylmethyl 2‐methylbicyclo[2.2.1]hept‐5‐ene‐2‐carboxylate with [M]/[I] = 350 was carried out at 30 °C in CH2Cl2, the number‐average molecular weight (7.01 × 104; polydispersity index = 1.07) was close to the calculated molecular weight (7.28 × 104), and a diblock copolymer was observed after the addition of another monomer ([M]/[I] = 350) with an increase in the number‐average molecular weight (1.60 × 105; polydispersity index = 1.11), which was close to the calculated molecular weight (1.61 × 105). The modified polynorbornenes retained good solubility in methylene chloride, tetrahydrofuran, dimethyl sulfoxide, dimethylformamide, N,N‐dimethylacetamide, and N‐methyl‐2‐pyrrdione. High‐performance polynorbornenes with active epoxy groups could be designed with great potential for applications in photoresists, UV curing, and elastomers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4428–4434, 2006 相似文献
998.
Ga‐Young Lee Han‐Na Jang Ju‐Yeon Lee 《Journal of polymer science. Part A, Polymer chemistry》2008,46(9):3078-3087
2,4‐Bis‐(3,4‐dicarboxyphenylcarboxyethoxy)‐1‐(2,2‐dicyanovinyl)benzene dianhydride (4) was prepared and reacted with 4,4′‐oxydianiline, 4,4′‐diaminobenzanilide and 4,4′‐(hexafluoroisopropylidene)dianiline to yield novel Y‐type polyimides 5‐7 containing 2,4‐dioxybenzylidenemalononitrile groups as nonlinear optical (NLO) chromophores, which constitute parts of the polymer backbone. The resulting polyimides 5‐7 are soluble in polar solvents such as dimethylsulfoxide and N,N‐dimethylformamide. Polymers 5‐7 showed a thermal stability up to 330 °C in thermogravimetric analysis thermograms with Tg values obtained from differential scanning calorimetry thermograms in the range 179–194 °C. The second harmonic generation (SHG) coefficients (d33) of poled polymer films at the 1064 nm fundamental wavelength were around 5.56 × 10?9 esu. The dipole alignment exhibited exceptionally high thermal stability even at 20 °C higher than the glass‐transition temperature there was no SHG decay below 215 °C because of the partial main‐chain character of polymer structure, which is acceptable for NLO device applications. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3078–3087, 2008 相似文献
999.
Byong Sun Chun Jae Youn Hwang Jang Roh Rhee Taewan Kim Shin Saito Satoru Yoshimura Masakiyo Tsunoda Migaku Takahashi Young Keun Kim 《Journal of magnetism and magnetic materials》2006
Magnetic tunnel junctions (MTJs) comprising amorphous Co70.5Fe4.5Si15B10, possessing low saturation magnetization of 560 emu/cm3, as a free layer have been investigated. The switching behaviours were confirmed for the micrometer-sized elements experimentally, using the scanning magneto-optical Kerr effect (scanning MOKE). A micromagnetic modelling study was also carried out for the submicrometer-sized elements. By using either a CoFeSiB single or a synthetic antiferromagnetic free-layer structure, the magnetization switching field became much lower than conventionally used CoFe free layered MTJs. 相似文献
1000.
Hyun-Jun Ha Sun-Shin Jung Zan-Zhi Huang Dong-Ho Jang Gun-Sik Park Jin-Gyu Song Gong-Man Park Hyee-Jea Kang 《International Journal of Infrared and Millimeter Waves》1999,20(12):2099-2106
Ku-band (14-14.5 GHz) folded waveguide TWT operated at the beam voltage and current of 6 kV and 0.1 A, respectively, has been studied experimentally. The RF circuit is designed by using a linear theory [1] and its predicted gain for a single stage is 20 dB. The cold test of the assembled RF circuit shows a good agreement with the theoretical prediction [2]. 相似文献