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81.
Erkki Aitola Arto Puranen Harri Setl Sami Lipponen Markku Leskel Timo Repo 《Journal of polymer science. Part A, Polymer chemistry》2006,44(22):6569-6574
Vinylcyclohexane (VCH) was copolymerized with ethene and propene using methylaluminoxane‐activated metallocene catalysts. The catalyst precursor for the ethene copolymerization was rac‐ethylenebis(indenyl)ZrCl2 ( 1 ). Propene copolymerizations were further studied with Cs‐symmetric isopropylidene(cyclopentadienyl)(fluorenyl)ZrCl2 ( 2 ), C1‐symmetric ethylene(1‐indenyl‐2‐phenyl‐2‐fluorenyl)ZrCl2 ( 3 ), and “meso”‐dimethylsilyl[3‐benzylindenyl)(2‐methylbenz[e]indenyl)]ZrCl2 ( 4 ). Catalyst 1 produced a random ethene–VCH copolymer with very high activity and moderate VCH incorporation. The highest comonomer content in the copolymer was 3.5 mol %. Catalysts 1 and 4 produced poly(propene‐co‐vinylcyclohexane) with moderate to good activities [up to 4900 and 15,400 kg of polymer/(mol of catalyst × h) for 1 and 4 , respectively] under similar reaction conditions but with fairly low comonomer contents (up to 1.0 and 2.0% for 1 and 4 , respectively). Catalysts 2 and 3 , both bearing a fluorenyl moiety, gave propene–VCH copolymers with only negligible amounts of the comonomer. The homopolymerization of VCH was performed with 1 as a reference, and low‐molar‐mass isotactic polyvinylcyclohexane with a low activity was obtained. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6569–6574, 2006 相似文献
82.
Markku Niemenmaa 《Monatshefte für Mathematik》1986,101(3):183-191
We say that a near-ring (N,+,·) has an almost trivial multiplication (ATM) if the product of two elements belongs to the intersection of the additive cyclic groups generated by these two elements. We show that every finite near-ring with ATM can be decomposed to a direct sum where the summands are either near-rings defined on cyclic groups or near-rings whose minimal ideals are zero near-rings. Finally, we show how to construct these summands on cyclic groups. 相似文献
83.
Maçôas EM Khriachtchev L Pettersson M Fausto R Räsänen M 《The journal of physical chemistry. A》2005,109(16):3617-3625
The conformational system of propionic acid (CH3CH2COOH) is studied in solid argon. It is predicted by the ab initio calculations that this molecule has four stable conformers. These four structures are denoted Tt, Tg+/-, Ct, and Cg+/-, and they differ by the arrangement around the C-O and Calpha-C bonds. The ground-state Tt conformer is the only form present at 8 K after deposition of an argon matrix containing propionic acid. For the CH3CH2COOH and CH3CH2COOD isotopologues, narrow-band excitation of the first hydroxyl stretching overtone of the conformational ground state promotes the Calpha-C and C-O internal rotations producing the Tg+/- and Ct conformers, respectively. A subsequent vibrational excitation of the produced Tg+/- form induces its conversion to the Cg+/- conformer by rotation around the C-O bond. In the dark, all of the produced conformers decay to the conformational ground state at different rates. The decay kinetics and its temperature dependence allow the identification of the conformers by IR absorption spectroscopy, which is supported by ab initio calculations of their vibrational spectra. For the CH3CH2COOD isotopologue, the excitation of molecules isolated in different matrix sites results in site-dependent photoisomerization rates for the Calpha-C and C-O internal rotations, which also confirm the identification of the photoproducts. 相似文献
84.
The HArF molecule can occupy in solid Ar thermally unstable and stable configurations, and their microscopic structure is not understood at the moment. We present additional experimental results on the formation of two HArF configurations and analyze them with emphasis on possible reactions of the unstable configuration with matrix vacancies to form the stable configuration. We conclude that the existing computational scenarios do not describe fully the present experimental data. In order to explain qualitatively the experimental results, two tentative models are discussed. The first model is based on local mobility of matrix vacancies produced during photolysis and the second model considers isomerization of the HArF at Arn supermolecule. More importantly, the present results constitute the experimental basis for future theoretical studies. 相似文献
85.
Colacio E Lloret F Kivekäs R Ruiz J Suárez-Varela J Sundberg MR 《Chemical communications (Cambridge, England)》2002,(6):592-593
A 2D grid-shaped cyanide-bridged Co(II)-Au(I) bimetallic coordination polymer, [Co(DMF)2(Au(CN)2)2], has been prepared from the [Au(CN)2]- building block; sheets associate pair-wise by aurophilic interactions and the compound exhibits zeolite-like properties. 相似文献
86.
Complexes [Mg(thd)2(A)] (Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione; A = ethylenediamine, en (2); N,N'-dimethylethylenediamine, dmeda (3); N,N'-diethylethylenediamine, deeda (4); N,N,N',N'-tetramethylethylenediamine, tmeda (5); diethylenetriamine, dien (6); triethylenetetra-amine, trien (7); 1,2-ethanediol (8)) and [Mg(thd)2(EtOH)]2(1,3-propanediol) (9) were prepared and characterized by NMR spectroscopy, mass spectrometry, and thermal analysis. Crystal structures of compounds 2, 5, and 7 are presented. In all structures, Mg exhibits distorted six-coordination, with four shorter distances between Mg and keto-oxygens and two longer distances between Mg and nitrogen atoms (2, 5, 7). The structure of 2 consists of two monomeric complexes which form an asymmetric unit. The structure of 7 is similar to 2, but the trien molecule has coordinated through one terminal and one vicinal N atom to Mg. All complexes containing amines evaporated almost completely, but the complex 8, which contained 1,2-ethanediol, was thermally unstable and decomposed when heated. At temperatures below the dissociation temperature, all adducts of diamines appeared to evaporate intact. 相似文献
87.
We propose an optical system to implement rewritable transparent broad-band color filters. The filter consists of a linear variable filter and a liquid crystal spatial light modulator in which an expected filter function is written. A time-integrated intensity image was taken while the filter was passing the lens aperture of a CCD camera. The averaged norm error between the implemented and the expected filter functions was about 5.4#x0025;. The system was applied to spectral estimation in a two-dimensional color image. 相似文献
88.
Paula Aulaskari Markku Ahlgrn Pirjo Vainiotalo Esko Pohjala 《Journal of heterocyclic chemistry》2000,37(1):87-93
New high yield preparation methods were developed for the pharmaceutically interesting compounds, 1‐benzyl‐, 1‐methyl‐, and 1H‐5‐[(2‐oxo‐2‐phenyl)ethyl]imidazoles 1a‐c , respectively. The title compounds were synthesized by four different methods using various starting materials. Two of the methods involved transformation reactions of the key intermediates, 1‐substituted‐5‐[(2‐nitro‐2‐phenyl)ethenyl]imidazoles 2a‐c and 1‐substituted‐5‐[(2‐nitro‐2‐phenyl)ethyl]imidazoles 3a‐c , while the other two utilized the oxidation of 1‐substituted‐5‐[(2‐hydroxy‐2‐phenyl)ethyl]imidazoles 4a‐c , with chromic oxide, and the umpolung reaction of benzaldehyde followed by a condensation reaction of the umpolung intermediate with imidazolecarboxaldehydes 6a‐c. 相似文献
89.
Adnan S. Abu‐Surrah Martti Klinga Timo Repo Markku Leskel Tony Debaerdemaeker Bernhard Rieger 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(2):e44-e45
The title compound was formed upon slow evaporation of a solution of the solvated dicationic complex bis(acetonitrile)bis[1,2‐bis(diphenyl‐phosphino)ethane]palladium(II) bis(tetrafluoroborate) in deuterated chloroform. The dinucleur palladium complex forms triclinic crystals and there is an inversion center between the Pd atoms. Compared to the corresponding monomeric compound, the Cl—Pd—Cl angles decrease upon briding from 94.19 (7) to 86.96 (4)°. 相似文献
90.
Stable operation of a cw optical parametric oscillator near the signal-idler degeneracy 总被引:1,自引:0,他引:1
The frequency stability of a cw optical parametric oscillator (cw OPO) near the signal-idler degeneracy has been studied. The strong tendency of a near-degenerate OPO to mode hop has been suppressed by using a bulk Bragg grating as a spectral filter in the OPO cavity. An experimental demonstration of stable parametric oscillation in a single longitudinal mode of the OPO cavity is reported, together with the capability of tuning the signal-idler difference frequency from 1 to 4 THz. The OPO has potential use in cw terahertz generation. 相似文献