Further studies of M3(μ3-O)(μ-X)3(μ-O2CCH3)3L3 (M=Mo,W) type clusters with nine core electrons

Four new compounds having nine cluster electrons and cores of the types Mo₃OCl₃, Mo₃OBr₃, and W₃OCl₃ are reported. Compound (1) prepared by reduction of [Bu₄N][Mo₃OCl₆(OAc)₃] in THF with metallic zinc, was shown by X-ray crystallography to be Mo₃OCl₄(OAc)₃ (THF)₂ (1). It forms crystals in space groupP2₁ with unit cell dimensionsa=9.472(2) Å,b=13.546(4) Å,c=9.652(2) Å, =101.70(2)°,V=1201(1) Å₃,Z=2. The [Mo₃(₃-O)(-Cl)₃]⁴⁺ core is surrounded by three -O₂CCH₃ anions, one Cl^–, and two THF and has Mo-Mo distances of 2.620(1) Å, 2.613(1) Å, and 2.530(1) Å, with the shortest bond between the two Mo atoms to which the THF molecules are coordinated. Compounds [Bu₄N]₂ [Mo₃OBr₆(O₂CCH₃)₃] · Me₂CO, (2) and [Mo₃OBr₃(O₂CCH₃)₃(PMe₃)₃]₃ · BF₄, (3) are the first two nine-electron Mo₃ species with a [Mo₃(₃-O) Br₃]⁴⁺ core. Both were obtained by zinc reduction of [Mo₃OBr₆(O₂CCH₃)₃]^– in the presence of (NBu₄) Br (2) or PMe₃ and NaBF₄ (3), and each was characterized crystallographically. Compound (2) crystallized in space group Cc with unit cell dimensionsa=25.037(5) Å,b=12.827(2) Å,c=21.484(4) Å, =122.96(1)⁰,V=5790(3) ų,Z=4. While the anion has no crystallographically required symmetry, its virtual symmetry is C_3v . The Mo-Mo distances are 2.619(2) Å, 2.610(3) Å, 2.644(2) Å, with a mean value of 2.624[14] Å. Compound (3) crystallized in space groupP2₁/c with unit cell dimensionsa=10.846(2) Å,b=25.033(5) Å,c=12.641(5) Å, =94.74(2)⁰,V=3420(2) ų,Z=4. The cation occupies a general position but has virtual C_3v symmetry, with Mo-Mo distances of 2.601(2) Å, 2.610(2) Å, 2.627(2) Å, with a mean value of 2.613[14] Å. Thus the anionic and cationic Mo₃ clusters in (2) and (3), respectively, have average Mo-Mo distances that are equal within experimental error. Compound (4), [NEt₄]₂ [W₃OCl₆(O₂CCH₃)₃] is the first 9-electron compound of this type containing tungsten. It was prepared by reduction of [Et₄N][W₃OCl₆(OAc)₃] in benzene with Na/Hg. It crystallized in space groupP2₁2₁2₁ with unit cell dimensionsa=11.076(2) Å,b=14.345(2) Å,c=21.026(3) Å,V=3574(1) ų,Z=4. The anion resides on a general position but has virtual C_3v symmetry, with W-W distances of 2.577(1) Å, 2.612(1) Å, 2.584(1) Å and a mean value of 2.591[15] Å.     

IMPACT PROPERTIES OF METALLOCENE - CATALYZED ETHYLENE-α-OLEFIN COPOLYMERS

The impact properties of two selected metallocene-catalyzed ethylene-butene copolymers and one conventionalcopolymer were evaluated using Izod impact test. It is found that the metallocene-catalyzed copolymer shows superior impactproperties. This result was explained on the basis of the more homogeneous inter-molecular composition distribution andnarrower molecular weight distribution, which leads to more homogeneous morphology with fewer defects. Stepwisecrystallization improves the impact properties, especially in the crack propagation process, to a large extent. This is due to thedecrease of entanglements by stepwise crystallization, which is advantageous for the chain slip and shear. The polymer withheterogeneous intra-molecular composition distribution exhibits a more evident improvement of impact properties understepwise crystallization.     

STUDY ON STYRENE-BUTADIENE BLOCK COPOLYMER FOR THE MODIFICATI0N OF TIRE TREAD

This paper mainly deals with the design and synthesis of a novel styrene-butadieneblock copolymer. When this copolymer is used in the tread portion of tyres, it can improvewet skid resistance and reduce rolling resistance without sacrificing its general physical-mechanical properties. The visco-elastic curve of tire tread using the novel copolymer asits rubber portion was showed. Reactivity ratios for two monomers in the polymerizingsystem were calculated. The diagrams of differelitial, integral and finite difference calculithroughout the whole molecular chain were presented. The influence of the micro- andmacro-structure of the copolymer chain on wet skid resistance and rolling resistance wasdiscussed     

尼龙1010／尼龙6共聚物的表观相图研究

采用显微熔点法和ＤＳＣ测定了尼龙１０１０／尼龙６共聚物的表观相图；分析了投料比与链节结构单元含量的关系。最低熔点时尼龙１０１０／尼龙６的理论重量投料比为６０／４０，摩尔比为３３．３／６６．７，实验结果与此相近。     

Preparation and properties of composites made from rice straw and poly(vinyl chloride) (PVC)

Rice straw was employed for the preparation of lignocellulosic‐poly(vinyl chloride) (PVC) composites. The effect of pretreatment of rice straw, concentration of PVC, pressure as well as pressing temperature on the mechanical properties and water absorption was studied. Also, the effect of lignin as coupling agent on the mechanical properties and water absorption of composite was studied. Composites of rice straw comprising both PVC and a coupling agent offer superior properties compared to those made from only rice straw and PVC. The extent of improvement in the mechanical properties and dimensional stability of composites depended not only on the pretreatment of rice straw, concentration of PVC and lignin but also on pressure and pressing temperature. Copyright © 2004 John Wiley & Sons, Ltd.     

Simultaneous determination of trace uranium(VI) and zinc(II) by adsorptive cathodic stripping voltammetry with aluminon ligand

Uranium(VI) complexed with aluminon (3-[bis(3-carboxy-4-hydroxy-phenyl)methylene]-6-oxo-1,4-cyclohexadiene-1-carboxylic acid triammonium salt) was determined by adsorptive cathodic stripping voltammetry (ACSV) using a hanging mercury drop electrode. Trace uranium(VI) and zinc(II) can be simultaneously determined in a single scan in the presence of aluminon and urea. Optimal conditions were found to be: accumulation time; 180–200 s, accumulation potential; 50 mV versus Ag/AgCl, scan rate; 40 mV s⁻¹, supporting electrolyte; 0.1 M sodium acetate buffer at pH 6.5–7.0, and concentration of aluminon; 1×10⁻⁶ M. The linear range of uranium(VI) and zinc(II) were observed over the concentration range 2–33 and 30–120 ng ml⁻¹, respectively. The detection limit (S/N=3) are 0.2 ng ml⁻¹ (uranium) and 30 ng ml⁻¹ (zinc). A good reproducibility shows RSDs of 2.5–4.0% (n=10). The procedure offers high selectivity, with the presence of urea masking some metal ions.     

EVA-g-VC的结构和动态粘弹性

本文研究了聚乙烯-醋酸乙烯酯(EVA,VAc:14％)与氯乙烯(VC)接枝共聚物(EVA-g-VC)的相结构和分子结构。接枝物EVA-g-VC由游离EVA、均聚PVC和EVA-VC接枝高分子三者组成,EVA呈连续相,PVC呈分散微粒。EVA-g-VC中EVA的含量越高,PVC粒子体积越小。实验结果表明,接枝物中“凝胶”的EVA玻璃化温度,随投料比(VC/EVA)的减小而升高;另外随VC/EVA减小,凝胶中PVC的含量和PVC的分子量也减小。这些结果说明,VC/EVA较小时得到的接枝物中,EVA上VC接枝点的数目较多,而PVC接枝链的长度较短。EVA-VC是不相容两相——EVA和PVC的“粘着剂”,其作用表现在:VC/EVA越小,接枝物中EVA和PVC的玻璃化温度越靠近。     

Nitroxide mediated living radical polymerization of styrene onto poly (vinyl chloride)

Nitroxide‐mediated ‘living’ free radical polymerisation (LREP) was employed for the first time to prepare graft copolymer by having arylated poly (vinyl chloride) (PVC‐Ph) as a backbone and polystyrene (PS) as branches. The graft copolymerization of styrene was initiated by arylated PVC carrying 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) groups as a macroinitiator. Thus, the arylated PVC was prepared in the mild conditions and these reaction conditions could overcome the problem of gelation and crosslinking in polymers. Then, 1‐hydroxy TEMPO was synthesized by the reduction of TEMPO with sodium ascorbate. This functional nitroxyl compound was coupled with brominated arylated PVC (PVC‐Ph‐Br). The resulting macro‐initiator (PVC‐Ph‐TEMPO) for ‘living’ free radical polymerization was then heated in the presence of styrene to form graft copolymer. DSC, GPC, ¹HNMR, and FT‐IR spectroscopy were employed to investigate the structure of the polymers. Copyright © 2007 John Wiley & Sons, Ltd.     

Volatile constituents of flowers and leaves of Anthemis hyalina

The chemical composition of the essential oils of the flowers and leaves of Anthemis hyalina were analyzed by GC and GC-MS for the first time. The oils were found to contain seventy-two components. cis-Chrysanthenyl acetate (14.9% and 17.8%), camphor (11.6% and 1.7%), terpinen-4-ol (8.3% and 1.2%), germacrene-D (5.1% and 2.1%), β-caryophyllene (4.1% and 5.4%), myrcene (3.6% and 16.9%), bicyclogermacrene (3.5% and 0.9%), α-pinene (2.3% and 4.1%), cis-β-ocimene (2.1% and 4.3%) and isospathulenol (0.4% and 4.3%) were found to be the major constituents of the oils of flowers and leaves respectively. Published in Khimiya Prirodnykh Soedinenii, No. 5, pp. 428–429, September–October, 2006.     

Application of the essential work of fracture concept to nanostructured polymer materials

The first part of the paper deals with a critical discussion of the methodical basis of essential work of fracture (EWF) concept with respect to the specimen geometry (especially the notch depth) and application to polymers. In the second part, an in situ testing device, which combines a tensile testing machine with an optical strain-field measuring system, has successfully demonstrated possibility of characterization of fracture behaviour of polystyrene-polybutadiene block copolymers and block copolymer/homopolymer blends as examples of nanostructured polymer materials. It has been shown that knowledge of the time evolution of the strain field close to the crack tips leads to a simple verification of the basic precondition for the applicability of the EWF concept, the precondition “plastic zone coalescence-before-stable crack propagation”.