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1.
Comb copolymers consisting of polystyrene backbone and poly(tert-butyl (meth)acrylate) side chains were synthesized by combination of nitroxide (TEMPO)-mediated polymerization (NMP) and photoinduced grafting from macro-iniferters. First, poly(chloromethylstyrene), PCMS, with the degree of polymerization and two random poly(styrene-co-chloromethylstyrene) copolymers, P(S-co-CMS), with similar but different content (8 and 14 mol%) of CMS units, were synthesized by NMP. In the second step the CMS units both in the homopolymer and the copolymers were converted to N,N-diethyldithiocarbamyl groups (DC) yielding photosensitive multifunctional macro-iniferters. Finally, tert-butyl methacrylate tBuMA was grafted from the synthesized polymer backbones by iniferter technique under UV-irradiation yielding copolymers polystyrene-graft-poly(tert-butyl methacrylate) PS-g-P(tBuMA). Grafting initiated by the macro-iniferters containing ∼6-11 DC initiating sites per macromolecule proceeded by pseudo-living polymerization mechanism, i.e., the number-average molecular weight increased with conversion and the SEC traces were unimodal. In contrast, photo-polymerization initiated by highly functionalized polystyrene backbone was poorly controlled. Hydrolysis of loosely grafted copolymers PS-g-P(tBuMA) afforded amphiphilic copolymers polystyrene-graft-poly(methacrylic acid). Molecular parameters of the synthesized graft copolymers in dilute THF solutions were determined by scattering (DLS, SLS, SAXS) and viscometric measurements.  相似文献   

2.
A novel tin(II) phenylbis(phosphonate) compound has been synthesized hydrothermally and its structure has been determined by single crystal X-ray diffraction. The structure is monoclinic, space group P21/c (no. 14), a=4.8094(4), b=16.2871(13), ; β=106.292(6)°, , Z=2. The three-dimensional structure consists of 3-coordinated tin and 4-coordinated phosphorus double layers separated (pillared) by phenyl rings. These phenyl rings are placed 4.8 Å apart along the a-axis in the structure resulting in lower surface area (∼14 m2/g). The porosity has been increased by replacing phenyl groups by methyl groups (∼31 m2/g).  相似文献   

3.
4.
Crystal structure and phase transformations of calcium yttrium orthophosphate Ca3Y(PO4)3 were investigated by X-ray powder diffraction, selected-area electron diffraction, transmission electron microscopy and optical microscopy. The high-temperature phase is isostructural with eulytite, cubic (space group ) with a=0.983320(5) nm, V=0.950790(8) nm3, Z=4 and Dx=3.45 Mg m−3. The crystal structure was refined with a split-atom model, in which the oxygen atoms are distributed over two partially occupied sites. Below the stable temperature range of eulytite, the crystal underwent a martensitic transformation, which is accompanied by the formation of platelike surface reliefs. The inverted crystal is triclinic (space group P1) with a=1.5726(1) nm, b=0.84267(9) nm, c=0.81244(8) nm, α=109.739(4)°, β=90.119(5)°, γ=89.908(7)°, V=1.0134(1) nm3, Z=4 and Dx=3.24 Mg m−3. The crystal grains were composed of pseudo-merohedral twins. The adjacent twin domains were related by the pseudo-symmetry mirror planes parallel to with the composition surface . When the eulytite was cooled relatively slowly from the stable temperature range, the decomposition reaction of Ca3Y(PO4)3β-Ca3(PO4)2+YPO4 occurred.  相似文献   

5.
6.
High-resolution time-of-flight neutron powder diffraction was carried out to investigate the crystal structures of CeAlO3 over a wide temperature range between 4.2 and 1423 K. Confirming the recent result of X-ray powder diffraction, the room temperature structure is tetragonal with the space group I4/mcm (tilt system (a0a0c)). The tetragonal structure persists down to 4.2 K. However, above room temperature CeAlO3 undergoes three phase transitions: first to the orthorhombic Imma structure (tilt system (a0bb)) at, e.g., 373 K, then to the rhombohedral structure (tilt system (aaa)) at, e.g., 473 K, and finally, to the primitive cubic structure which exists above 1373 K. The sequence of phases, , which occurs in CeAlO3 is a rare one in oxide perovskites.  相似文献   

7.
8.
The title compounds were prepared from the elements in the stoichiometric ratio at 800 °C under exclusion of air. Tl6Si2Te6 crystallizes in the space group P1¯, isostructural with Tl6Ge2Te6, with , , , α=89.158(2)°, β=96.544(2)°, γ=100.685(2)°, (Z=2). Its structure is composed of dimeric [Si2Te6]6− units with a Si-Si single bond, while the Tl atoms are irregularly coordinated by five to six Te atoms. Numerous weakly bonding Tl-Tl contacts exist. Both title compounds are black semiconductors with small band gaps, calculated to be 0.9 eV for Tl6Si2Te6 and 0.5 eV for Tl6Ge2Te6. The Seebeck coefficients are +65 μV K−1 in case of Tl6Si2Te6 and +150 μV K−1 in case of Tl6Ge2Te6 at 300 K, and the electrical conductivities are 5.5 and 3 Ω−1 cm−1, respectively.  相似文献   

9.
The crystal structures of three new intermetallic ternary compounds in the LnNiSb3 (Ln=Pr, Nd and Sm) family have been characterized by single crystal X-ray diffraction. PrNiSb3, NdNiSb3 and SmNiSb3 all crystallize in an orthorhombic space group, Pbcm (No. 57), Z=12, with , , , and ; , , , and ; and , , , and , for Ln=Pr, Nd and Sm, respectively. These compounds consist of rare-earth atoms located above and below layers of nearly square, buckled Sb nets, along with layers of highly distorted edge- and face-sharing NiSb6 octahedra. Resistivity data indicate metallic behavior for all three compounds. Magnetization measurements show antiferromagnetic behavior with (PrNiSb3), 4.6 K (NdNiSb3), and 2.9 K (SmNiSb3). Effective moments of 3.62 μB, 3.90 μB and 0.80 μB are found for PrNiSb3, NdNiSb3 and SmNiSb3, respectively, and are consistent with Pr3+ (f 2), Nd3+ (f 3), and Sm3+ (f 4).  相似文献   

10.
Single crystals of the potassium uranyl iodate, K[UO2(IO3)3] (1), have been grown under mild hydrothermal conditions. The structure of 1 contains two-dimensional sheets extending in the [ab] plane that consist of approximately linear UO22+ cations bound by iodate anions to yield UO7 pentagonal bipyramids. There are three crystallographically unique iodate anions, two of which bridge between uranyl cations to create sheets, and one that is monodentate and protrudes in between the layers in cavities. K+ cations form long ionic contacts with oxygen atoms from the layers forming an eight-coordinate distorted dodecahedral geometry. These cations join the sheets together. Ion-exchange reactions have been carried out that indicate the selective uptake of Cs+ over Na+ or K+ by 1. Crystallographic data (193 K, MoKα, ): 1, orthorhombic, Pbca, a=11.495(1) Å, b=7.2293(7) Å, c=25.394(2) Å, Z=8, R(F)=1.95% for 146 parameters with 2619 reflections with I>2σ(I).  相似文献   

11.
High quality and large-sized Rb0.3MoO3 single crystals were synthesized by molten salt electrolysis method. X-ray diffraction (XRD) patterns and rocking curves, as well as the white beam Laue diffraction of X-ray images show the crystals grown by this method have high quality. The lattice constants evaluated from XRD patterns are a0=1.87 nm, b0=0.75 nm, c0=1.00 nm, β=118.83°. The in situ selected area electron diffraction (SAED) patterns along the , and zone axes at room temperature indicate that the Rb0.3MoO3 crystal possess perfect C-centered symmetry. Temperature dependence of the resistivity shows this compound undergoes a metal to semiconductor transition at 183 K.  相似文献   

12.
The crystal structures of the title compounds were solved using the single-crystal X-ray diffraction technique. At room temperature CsKSO4Te(OH)6 was found to crystallize in the monoclinic system with Pn space group and lattice parameters: ; ; ; β=106.53(2)°; ; Z=4 and . The structural refinement has led to a reliability factor of R1=0.0284 (wR2=0.064) for 7577 independent reflections. Rb1.25K0.75SO4Te(OH)6 material possesses a monoclinic structure with space group P21/a and cell parameters: ; ; ; β=106.860(10)°; ; Z=4 and . The residuals are R1=0.0297 and wR2=0.0776 for 3336 independent reflections. The main interest of these structures is the presence of two different and independent anionic groups (TeO66− and SO42−) in the same crystal.Complex impedance measurements (Z*=ZiZ) have been undertaken in the frequency and temperature ranges 20-106 Hz and 400-600 K, respectively. The dielectric relaxation is studied in the complex modulus formalism M*.  相似文献   

13.
The disordered structures and low temperature dielectric relaxation properties of Bi1.667Mg0.70Nb1.52O7 (BMN) and Bi1.67Ni0.75Nb1.50O7 (BNN) misplaced-displacive cubic pyrochlores found in the Bi2O3-MIIO-Nb2O5 (M=Mg, Ni) systems are reported. As for other recently reported Bi-pyrochlores, the metal ion vacancies are found to be confined to the pyrochlore A site. The B2O6 octahedral sub-structure is found to be fully occupied and well-ordered. Considerable displacive disorder, however, is found associated with the O′A2 tetrahedral sub-structure in both cases. The A-site ions were displaced from Wyckoff position 16d (, , ) to 96 h (, , ) while the O′ oxygen was shifted from position 8b (, , ) to Wyckoff position 32e (, , ). The refined displacement magnitudes off the 16d and 8b sites for the A and O′ sites were 0.408 Å/0.423 Å and 0.350 Å/0.369 Å for BMN/BNN, respectively.  相似文献   

14.
The first example of a unidimensional zirconium hydroxide fluoride was synthesized under mild solvothermal treatment and characterized by X-ray diffraction and thermal techniques. Monoprotonated ethylenediamine cations reside between the anionic chains. Crystal data for this material are as follows: [C2N2H9][Zr(OH)2F3], M=243.35, orthorhombic, space group Pca21, a=6.8016(13), b=6.1393(12), , , , Z=4, , μ(Mo-Kα)=1.777 mm−1, . The material transforms to an unknown layered material at ∼175 °C, a common occurrence for 1D structures where the chains are arranged in hydrogen-bonded layers and separated by interlayer organoammoniums. Collapse to the known condensed mineral phase Zr(FO)2.7 occurs at ca. 275 °C before finally transforming to the baddeleyite form of ZrO2 at ca. 460 °C.  相似文献   

15.
Homopolymerization of methyl acrylate (MA) and methyl methacrylate (MMA) by atom transfer radical polymerization (ATRP) were carried out at 90 °C using methyl-2-bromopropionate (MBP) as initiator, copper halide (CuX, X=Cl, Br) as catalyst, 2,2-bipyridine (bpy) or N,N,N,N,N-pentamethyldiethylenetriamine (PMDETA) as ligand in 1-butanol (less polar and containing OH) and acetonitrile (more polar) solvents. It was found that with CuCl/bpy catalyst ATRP of MA and MMA in 1-butanol proceeded faster than that in acetonitrile. The rate of ATRP of MA and MMA in acetonitrile and 1-butanol was comparable when CuCl/PMDETA used as catalyst system. The number-average molecular weights increased with conversion and polydispersities were low . The ATRP of MA and MMA with vinyl acetate telomer having trichloromethyl end group (PVAc-CCl3) were also used to synthesize new block copolymers. The structures and molecular weight of synthesized PVAc-b-PMA and PVAc-b-PMMA were characterized by 1H NMR, FTIR spectroscopy and gel permeation chromatography (GPC) and shown that the block copolymers were novel.  相似文献   

16.
New block copolymers with narrow molecular weight distribution based on (2,3-epithiopropylmethacrylate) (ETMA), methylmethacrylate (MMA) and n-butylmethacrylate (nBMA) have been successfully synthesized via reversible addition-fragmentation transfer (RAFT) polymerization. First, RAFT homopolymerization of ETMA and MMA was carried out using 2-(2-cyanopropyl) dithiobenzoate (CPDB) as the chain transfer agent (CTA) and 2,2-azobisisobutyronitrile (AIBN) as the initiator. PETMA-b-P(nBMA) copolymers were synthesized using PETMA homopolymers as the macro-chain transfer agent (MCTA), while PMMA-b-PETMA diblock copolymers were synthesized using PMMA as the MCTA. The evolution of the molecular weight and molecular weight distribution of the homo- and co-polymers were compatible with the RAFT polymerization features. Thin films from the block copolymers were prepared by spin coating a 1 wt% polymer solution from toluene, chloroform or THF. After the preparation, the films were annealed under 80% vapor pressure of chloroform for 1, 2 and 4 h and investigated with scanning electron microscopy (SEM). The most interesting results were found in the films prepared using PETMA-b-P(nBMA) copolymers (). The observed images suggested the formation of hybrid lamellar structures, ascribed to the combination of its higher molecular weight and solvents viscosity.  相似文献   

17.
The synthesis, single crystal structure determination, and Raman spectrum are reported for colorless transparent tribarium disodium tetracyanamide, Ba3Na2(CN2)4. The title compound crystallizes in the space group C2h5-P21/c (#14, , , , β=110.454(4)°, , Z=4, R/wR=0.0266/0.0543). Each sodium atom is surrounded by six nitrogen atoms in octahedral geometry. Sodium centered nitrogen octahedra are linked through face-sharing along the [100] direction to form one-dimensional (1D) chains. These chains are connected to each other through the carbon atoms of cyanamide and make a three-dimensional (3D) network with 1D channels along the [100] direction. Barium atoms and additional cyanamide anions reside in the channels. Each barium atom is irregularly coordinated with nitrogen and carbon from the cyanamide anions. The Raman spectrum shows symmetric vibrations of [NCN]2− corresponding to νsym (1241.5 cm−1) and 2δ (1356.4 cm−1).  相似文献   

18.
A new heterometallic iodide, PbI4Cu2(PPh3)4, was synthesized by reactions of PbI2, CuI and triphenylphosphine (PPh3) in DMF solution. The single-crystal X-ray diffraction analyses show that Pb(II) center adopts an unusual cis-divacant octahedral geometry. Crystal data: triclinic, space group , , , , α=106.623(4)°, β=103.478(6)°, γ=93.574(5)°, and Z=2. Density function theory (DFT) calculations and fragment orbital interaction analyses reveal the presence of a three-center four-electron (3c-4e) hypervalent bonding about lead; and the formation of the unusual cis-divacant [PbI4]2− octahedron is energetically favorable. The title yellow compound has an optical bandgap of 2.69 eV and shows remarkable red-infrared fluorescence emission at 732 nm with lifetime of 24 μs which is assigned as an iodine 5p-lead 6s to PPh3-lead 6p charge transfer (XM-LM-CT).  相似文献   

19.
The enthalpies of solution were determined for 1,1,3,3-tetramethylurea in ethanol, 1-propanol, 2-propanol, 1-butanol, and t-butanol (2-methyl-2-propanol). Measurements were made at 298.15 K and molalities m ≅ (0.007 to 0.036) mol · kg−1 with a precise isoperibol ampoule-type calorimeter. Standard enthalpies of solution and transfer from one alkanol to the other (including methanol) were calculated. The obvious relationship between the enthalpic and volumetric effects of solution of tetramethylurea in the n-alkanols (C1-C4) was discovered. The enthalpic effects of transfer caused by branching of the alkanol molecules, 1-propanol → 2-propanol, and 1-butanol → t-butanol, are opposite in sign and dominated by the configurational changes in the solvation environment of tetramethylurea.  相似文献   

20.
A novel non-centrosymmetric borate, BiCd3(AlO)3(BO3)4, has been prepared by solid state reaction methods below 750 °C. Single-crystal XRD analysis showed that it crystallizes in the hexagonal group P63 with a=10.3919(15) Å, c=5.7215(11) Å, Z=2. In its structure, AlO6 octahedra share edges to form 1D chains that are bridged by BO3 groups through sharing O atoms to form the 3D framework. The 3D framework affords two kinds of channels that are occupied by Bi3+/Cd2+ atoms only or by Bi3+/Cd2+ atoms together with BO3 groups. The IR spectrum further confirmed the presence of BO3 groups. Second-harmonic-generation measurements displayed a response of about 0.5×KDP (KH2PO4). UV-vis diffuse reflectance spectrum showed a band gap of about 3.19 eV. Solid-state fluorescence spectrum exhibited the maximum emission peak at around 390.6 nm. Band structure calculations indicated that it is an indirect semiconductor.  相似文献   

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