Ethylene polymerization by the chromium catalysts based on bidentate [O,PO] or [S,P] ligands

Novel chromium catalysts based on bidentate phenoxy‐phosphinoyl (HO‐2R₁‐4R₂‐6(Ph₂P?O)C₆H₂: R₁ = R₂ = H, 3a ; R₁ = tBu, R₂ = H, 3b ; R₁ = R₂ = tBu, 3c ; R₁ = R₂ = cumyl, 3d ; R₁ = anthracenyl, R₂ = H, 3e ) and thiophenol‐phosphine (HS‐2R₁‐4R₂‐6(Ph₂P)C₆H₂: R₁ = R₂ = H, 4a ; R₁ = SiMe₃, R₂ = H, 4b ) were prepared and characterized. Treatment with modified methyaluminoxane, these catalysts displayed moderate to high‐catalytic activities for ethylene polymerization. The activities of them were higher than those of the corresponding catalysts based on bidentate phenoxy‐phosphine ligands. Both the coordinated donors and the ortho‐substituent of the ligands played an important role in improving catalytic activity. The effects of reaction parameters, such as cocatalyst and Al/Cr molar ratio as well as reaction temperature, on ethylene polymerization behaviors were investigated in detail for two favorable catalytic systems, 3b /CrCl₃(thf)₃ and 4b /CrCl₃(thf)₃. Catalyst 4b /CrCl₃(thf)₃ displayed higher catalytic activity and better temperature tolerance for ethylene polymerization than 3b /CrCl₃(thf)₃. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 311–319, 2010     

Synthesis of amphiphilic linear‐hyperbranched graft‐copolymers via grafting based on linear polyethylene backbone

The synthesis of amphiphilic linear‐hyperbranched graft‐copolymers in a grafting‐from approach is reported. The linear polyethylene with terminated hydroxyls, prepared by copolymerization of ethylene and 10‐undecen‐1‐ol, was used as macroinitiator for ring‐opening multibranching polymerization of glycidol by a typical slow monomer addition approach. Successful attachment of the hyperbranched grafts to the linear polyethylene backbone was confirmed by ¹H/¹³C NMR, GPC, and TGA. The degree of polymerization and M_w/M_n of hyperbranched grafts were efficiently controlled by temperature, deprotonation ratio as well as the molar ratio of glycidol/hydroxyl (N_glycidol/N_OH). The complicated microstructures caused by unsymmetric glycidol structure were analyzed by DEPT and 2D HSQC spectra, the degree of branching of 0.63–0.66 were calculated, indicating the extent of branch is close to theoretical values. The thermal analysis of linear‐hyperbranched copolymers via TGA and DSC is also presented. To our knowledge, this is the first report of a linear‐hyperbranched graft‐copolymer with a crystalline and nonpolar linear‐polyethylene segment. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2146–2154     

The role of aromaticity on the building of nanohybrid materials functionalized with metalated (Au(III), Ag(III), Cu(III)) extended porphyrins and single‐walled carbon nanohorns: A theoretical study

An ab initio, systematic study on the aromaticity involving the group of metalated extended porphyrins, termed meso‐hexakis(pentafluorophenyl)‐substituted[26]hexaphyrin(1.1.1.1.1.1) (HP), was performed for the first time. The aromatic behavior of the system shifted to antiaromatic in the [28]HP analogue, due to the presence of hydrogen atoms that break the orbital symmetry. The absorption bands observed in the experiment were assigned to an intraligand charge transfer, where the intrametallic character is also important. The excited states reveal the absorption of visible light and the possibility of electronic transfer to different systems. We propose a system such as single‐walled carbon nanohorns (SWCNHs), due to their special electronic properties, and predict a novel nanohybrid material. The evidence of electronic communication between both species is presented in this work. The HP aromaticity and the spatial configuration of the interaction with SWCNHs are also related to the strength of electronic transfer among the systems, making the HP metalated antiaromatic species and their corresponding nanohybrids potential candidates to be used as building blocks in photovoltaic cell materials. © 2012 Wiley Periodicals, Inc.     

Hydrolysis, Condensation, and Tetragonal Phase Formation in Sol-Gel Zirconia Prepared with Electron-Irradiated Alkoxide Solutions

Sol-gel zirconia precursor, zirconium n-butoxide in ter-butanol, was irradiated with 1.3 MeV electrons to a dose of 330 KGy. Gelling was instantaneously produced when an aqueous solution of sulfuric, hydrochloric or acetic acid was added to the irradiated solution; no hydrolysis catalyst was required. Samples were characterized with X-ray powder diffraction, infrared spectroscopy, and electron paramagnetic resonance. The electron irradiation accelerated hydrolysis and condensation, which avoided the stabilization of the tetragonal phase via carboxyls, and decreased the capability of sulfate ions to stabilize it. These results suggest that the stabilization of the tetragonal phase of sol-gel zirconia via carboxyl and sulfate ions depends on their diffusion in the sol.     

Pressure effect on electronic,elastic and optical properties of Eu:CaF2 crystal: a first-principles study

The structure, electronic structure, elastic and optical properties of pure CaF₂ and Eu:CaF₂ are investigated by performing the generalized gradient approximation in the frame of density functional theory. The obtained lattice constant, band structure, elastic constants and imaginary part of dielectric function of pure CaF₂ agree well with the experimental and other theoretical results. These properties of Eu:CaF₂ are also calculated, and it follows that Eu doping leads to the crystal structure distorted, as well as the spin polarization of the system. Especially an impurity band is introduced in the bandgap, above the Fermi level, in the band structure of the Eu:CaF₂, narrowing the bandgap. In addition, it is observed that the optical peaks of Eu:CaF₂ shift towards the longer wavelength side, and the peak intensities drop compared with pure CaF₂. Furthermore, Eu doping induces a series of new peaks in the optical properties, which is probably caused by the transitions of the 4f electrons of the Eu atoms. It is worth mentioning that the effect of pressure on the optical properties of Eu:CaF₂ is also studied, we can hold that the optical peaks will have a blueshift.     

基于龙胆苦苷的二吲哚甲烷类拟单萜吲哚生物碱类似物合成及其抗肿瘤、逆转紫杉醇耐药活性研究

以环烯醚萜类化合物龙胆苦苷为合成模块,利用拟单萜吲哚生物碱的仿生合成途径和组合化学的研究思路,与色胺类衍生物(吲哚结构的活性单元片段)通过缩合反应,首次合成了23个二吲哚甲烷类拟单萜吲哚生物碱类似物。利用核磁共振波谱(NMR)和高分辨质谱(HRMS)等谱学手段对合成化合物的结构进行了表征,并初步评价了其抗肿瘤活性和逆转耐药活性。活性结果表明,化合物4i脱掉糖基保护基后的化合物5i对3种肿瘤细胞系(TE-1,CAL-62和FaDu)的抑制作用强于阳性对照盐酸阿霉素(Dox)。通过与紫杉醇的联合用药,发现部分化合物如4m、4n、4o、4r等能够有效降低人肺癌细胞紫杉醇耐药株A549/Taxol对紫杉醇的耐药性,具有良好的逆转耐药潜力。     

Length-Dependent Collective Vibrational Dynamics in Alpha-Helices

Functions of protein molecules in nature are closely associated with their well-defined three-dimensional structures and dynamics in body fluid. So far, many efforts have been made to reveal the relation of protein structure, dynamics, and function, but the structural origin of protein dynamics, especially for secondary structures as building blocks of conformation transition, is still ambiguous. Here we theoretically uncover the collective vibrations of elastic poly-alanine α-helices and find vibration patterns that are distinctively different over residue numbers ranging from 20 to 80. Contrary to the decreasing vibration magnitude from ends to the middle region for short helices, the vibration magnitude for long helices takes the minimum at approximately 1/5 of helix length from ends but reaches a peak at the center. Further analysis indicates that major vibrational modes of helical structures strongly depend on their lengths, where the twist mode dominates in the vibrations of short helices while the bend mode dominates the long ones analogous to an elastic Euler beam. The helix-coil transition pathway is also affected by the alternation of the first-order mode in helices with different lengths. The dynamic properties of the helical polypeptides are promising to be harnessed for de novo design of protein-based materials and artificial biomolecules in clinical treatments.     

Ultra-robust,self-healable and recyclable polyurethane elastomer via a combination of hydrogen bonds,dynamic chemistry,and microphase separation

Flexibility, robustness, transparency, and recyclability are critical to the application of self-healing polymer materials in the field of flexible electronics. However, integrating all the above properties remains a huge challenge to date. In this work, we put forward a facile strategy to prepare polyurethane (PU) elastomer with ultra-high strength and self-healing performance based on hydrogen bonds, disulfide dynamic chemistry, and microphase separation at the same time. Three different self-healing PUs were obtained by introducing disulfide bonds and different types of hydrogen bonds. A robust, transparent, and recyclable PU with amino-terminated chain extender (PUA) with fast and efficient self-healing performance was prepared. The mechanical and self-healing properties of the PUA were effectively balanced by the synergistic effect of reversible interaction of disulfide bonds and the formation of microphase separated structure. The results indicated that the PUA exhibited high transparency up to 90% and excellent mechanical property, e.g. the tensile strength and elongation at break can reach 37.10 MPa and 1080%, respectively. Meanwhile, it can achieve a high self-healing efficiency of 96.8% at 80 °C for 4 h and maintain 84% of the initial mechanical strength even after four times of recycling. Moreover, the colloid graphite/PUA flexible strain sensor was prepared by the combination of colloid graphite and PUA, which can accurately detect both large and tiny scale deformations.     

Small-angle neutron scattering study of the nano-sized features in an oxide dispersion-strengthened Fe12Cr alloy

Small-angle neutron scattering experiments, along with positron lifetime measurements and transmission electron microscopy observations, were performed on samples of an oxide dispersion-strengthened (ODS) Fe12Cr alloy and its non-ODS counterpart in order to characterize their nano-sized features. The nuclear and magnetic scattering data were analysed using the maximum entropy approach for obtaining the size distribution of the scattering centres in these materials. The positron annihilation results and the TEM information have made possible an interpretation of the volume distribution of the scattering centres having sizes below ~16 nm and their proper quantitative analyses. The smaller scattering centres in the ODS alloy exhibit distributions with modal values at ~6–7 and 12–14 nm. The peak at ~6–7 nm appears to be due to the overlapping of more than one type of scattering centres, while the one at ~12–14 nm can be exclusively attributed to the Y-rich centres. The quantitative analysis of the magnetic scattering data yields a volume fraction and number density of the Y-rich particles estimated in 0.70?±?0.03% and 0.77 × 10²² m^?3, respectively.