Synthesis of SBS thermoplastic block copolymers in cyclohexane in the presence of diethylether used as a structure modifier

Diethylether (DEE) was used as a structure modifier during the synthesis of linear styrene-butadiene block copolymers of poly A-block-polyB-block-polyA type (SBS). The microstructures of synthesized polymers were analyzed, and the effect of DEE on polymerization kinetics was studied. Addition of DEE at 2 wt% concentration results in the highest styrene polymerization rate, while addition at 6 wt% concentration gives the highest butadiene polymerization rate. The vinyl content of the polybutadiene portion increases from 14 to 47% with an increase in the DEE concentration from 500 ppm to 10 wt% while thetrans- l,4 andcis-1,4 isomers decrease. For SBS polymer synthesized via a sequential method, the addition of DEE as a structure modifier minimizes the crossover deficiency which would otherwise result in a skewed molecular weight distribution with a higher polydispersity. For SBS polymers made via a coupling method, the coupling efficiency appears to be constant in a range of DEE concentration from 500 ppm to 1 wt% before declining with a further increase in DEE.     

Pressureless Sintering of Si3N4 Ceramic Using AlN and Rare-Earth Oxides

Using intermediate, liquid-forming compositions in the (Y,La)₂O₃-AlN system as additives, fully dense Si₃N₄ ceramics with high strength at high temperature have been obtained by pressureless sintering. The ceramics contain rod-shaped β-Si₃N₄ with M' or K' solid solutions as grain-boundary phases. The strength of these ceramics is 1150 MPa at 1200°C, and the room-temperature toughness is maintained at }7 MPa·m^1/2. Phase relations that are pertinent to the new additive compositions are delineated to rationalize their beneficial effects on sinterability and mechanical properties.     

Effects of neutral solvent addition on the body-centered cubic spheres of block copolymers

We employ self-consistent mean-field (SCMF) theory in studying the body-centered cubic (bcc) spheres of block copolymers in the presence of a neutral solvent. First we examine the accuracy of the dilution approximation then analyze the dependence of the bcc structural sizes with copolymer volume fraction ?, the interaction parameter χ_AB, and degree of copolymerization N. Our results reveal that both distribution of each component and the micro-structural length scales are greatly influenced by each parameter ?, χ_AB, and N. As expected, with decreasing ?, more solvent distributes non-uniformally in the segregated domains, therefore deviation from the dilution approximation increases. This also suggests that when the effective segregation parameter ?χ_ABN is fixed, a larger deviation is expected as χ_ABN increases (i.e. ? decreases). Although when both χ_ABN and ? are fixed, decreasing N (i.e. increasing χ_AB) enlarges the deviation from the dilution approximation. Furthermore, this solvent non-uniformity behavior is so significant that it even affects the dependence of the domain spacing L^* and the matrix length Λ^* with respect to (χ_AB)_effN=?χ_ABN near the ODT. When the systems are in molten state and/or in the concentrated regime, both L^* and Λ^* exhibit a sharp increase behavior as ODT is approached, due to many of the minority blocks being pulled from the spherical domains and swelling the matrix. With increasing solvent amount and/or χ_ABN, we observe that the increase of the degree for the minority blocks pulled from the spheres into the matrix near the ODT is not as significant as that in the melt. As such, the sharp increase behavior in L^* as well as Λ^* near the ODT smoothens and even disappears.     

工艺参数对陶瓷注射成型的影响与分析

本研究通过改变注射温度，注射压力，保压压力等几个主要参数，对形状，体积不同的注射成型体，试条，圆柱及子部件进行了一系列注射工艺实验。相应地对成型体的密度，弯曲强度及烧结体的密度和强度进行测量，并从陶瓷注射成型混合物的流动行为，热物理特性方面对注射这一复杂过程进行分析，探讨工艺参数对成型过程的内在影响，从而确定合理的注射工艺条件。     

Synthesis of Biodiesel from Soybean Oil using Heterogeneous KF/ZnO Catalyst

Biodiesel was produced by transesterification of soybean oil with methanol using ZnO loaded with KF as a solid base catalyst. It was found that the catalyst with 15 wt.% KF loading and calcined at 873 K showed the optimum activity. XRD, IR and Hammett indicator method were employed for the catalyst characterization. The results showed the activity of the catalysts was correlated with their basicity. The influence of various reaction variables on the conversion was also discussed.     

Facile preparation of amphiphilic oxyethylene-oxypropylene block copolymers by selective triazine coupling

A novel synthetic route for preparing high molecular weight poly(oxyalkylene) block copolymers has been developed by using 2,4,6-trichloro-1,3,5-triazine (cyanuric chloride, cc) as the coupling core. The coupling reaction involves the selective substitutions of oligo(oxyalkylene)-amines onto three chlorides of the triazine ring in a stepwise manner at 0, 25 and 130 °C. By judiciously selecting the starting amines and reaction conditions, one can tailor the copolymer structures with different block configurations (tri-block, multi-block, random and alternating block). The prepared copolymers can have a high molecular weight, up to 25,600 g/mol (GPC polydispersity=1.48), and also high thermal stability due to the presence of triazine functionalities. The copolymers with hydrophilic and hydrophobic oligo(oxyalkylene) blocks are of versatile properties in solubility (water soluble or water insoluble) and morphology (crystalline or amorphous). With a specific structure of alternating oligo(oxyethylene)/oligo(oxypropylene) blocks (2000 g/mol each block), the copolymer exhibits the property of self-association. It reduces the interfacial tension of toluene/water as low as 0.5 dyne/cm at the critical micelle concentration of 0.01 wt%.     

苏·乙酰对小菜蛾的生测及药效试验

乙酰甲胺磷与苏云金杆菌按一定比例混配有增效作用。按筛选的配方制成的20.6%苏·乙酰可湿性粉剂对小菜蛾的LC50为51.70 mg/ml,其80 g/667m2处理对小菜蛾药后3d的防效为92.23%,药后7 d的防效为90.34%,药后10 d的防效为81.16%,有较好的速效性及持效性。     

液晶聚酯的液晶行为与加工性能

液晶聚酯由于具有特异的液晶行为和高强高模性能而越来越受到人们的关注。本文对液晶聚酯的液晶态形成原因、液晶态类型与链结构的关系、液晶态热稳定性及其成型加工性能进行了讨论，指出了提高液晶态热稳定性的方法及液晶聚酯的发展趋势。     

A Novel Mixed-Valence Tetranuclear Iron-Oxygen Clusters in the Organically Templated Iron Phosphate [H3N(CH2)2NH3]2 Fe4O(PO4)4 ċH2O

A novel iron phosphate templated with ethylenediammonium cation, [H₃N(CH₂)₂NH₃]₂ Fe₄ O(PO₄)₄H₂O, has been synthesized hydrothermally and characterized by single-crystal X-ray diffraction, thermo-gravimetric analysis, magnetic susceptibility and Mossbauer spectroscopy. The compound crystallizes in the mono-clinic space group C2 with a= 30.3801(5),b= 10.1204(5),c= 10.0977(5) Å, = 107.712(1)°, V = 2957.5(4) ų and Z = 6. The structure contains 5 and 6-coordinated Fe atoms bridged by ₄-oxygen and PO₄ groups to form two types of mixed-valence Fe₄P₄ cubane-like clusters, which are connected via Fe- O- P bonds to give rise to intersecting channels that house the ethylenediammonium cations and water molecules. Room-temperature Mossbauer data confirm the presence of Fe^II and Fe^III.     

气体作自然对流时温度场测量中的全息层析技术

<正>1 引言 激光全息干涉技术是进行三维流场实验研究的重要手段之一.三维流场的全息层析,实际上就是在同时获得三维流场多方向干涉图的基础上,把三维流场分成一组平行的截面,根据多方位的干涉数据,由计算机分别对不同的截面重建三维流场的参量分布.由于这一方法