Investigation of Polymerization and Cyclization of Dimethyldiethoxysilane by 29Si NMR and FTIR

Dimethyldiethoxysilane (DMDES) appears to be a very promising modifier to introduce functional groups to a silicate network. The polymerization and cyclization of DMDES under acid-catalyzed conditions (DMDES : Ethanol : water : HCl = 1:4:4:3.68 × 10^–4 in molar ratio) were investigated by high resolution liquid ²⁹Si nuclear magnetic resonance (NMR) and Fourier transform infrared spectrometry (FTIR). Time-dependent NMR and FTIR data illustrate that monomers of (CH₃)₂Si(OC₂H₅)₂, (CH₃)₂Si(OC₂H₅)(OH), and (CH₃)₂Si(OH)₂ reach meta-equilibrium in less than 4 minutes. 3-membered rings ((CH₃)₂SiO)₃ appear about half an hour later and 4-membered rings ((CH₃)₂SiO)₄ an hour later, which continue to be formed over 24 hours. The relative concentrations of monomers, linear structures and cyclic structures suggest a modified model for the kinetics of cyclization, where 4-membered rings are formed by dimer-dimer interactions, as opposed to monomer-trimer interactions previously proposed.     

CROSSLINKING AND COMPATIBILIZATION IN BLENDS OF POLYSTYRENE AND POLYETHYLENE

This paper investigated the influences of butadiene rubber (BR) and dicumylperoxide (DCP) on thermal and rheological behaviour, morphology and mechanical proper-ties of PS/LLDPE/SBS blend. Addition of DCP alone was found to decrease the mechanicalproperties of PS/LLDPE/SBS blend due to the decomposition of PS. When BR was addedtogether with DCP, it is found that the co-crosslinking of BR, SBS and PE takes place,and the decomposition of PS is reduced simultaneously because of the consumption of thefree radicals in the crosslinking process. Synergism was thus realised which resulted in theimprovement of the ductility of blend.     

毛细管电泳-激光诱导荧光法测定缺氧缺血新生大鼠脑组织中氨基酸

建立了新生儿缺氧缺血性脑病(H IE)发生时脑组织中兴奋性氨基酸(EAA)含量的高效毛细管电泳-激光诱导荧光检测(CE-LIF)的新方法。方法的最佳条件为:40 mmol/L硼砂溶液,分离电压20 kV,压力进样5 s,λem=488 nm、λex=560 nm。随机分为假手术组、新生儿缺氧缺血性脑病(H IE)组,小剂量地塞米松(DXM)组和大剂量DXM组的新生大鼠脑组织中EAA的含量测定,结果表明:假手术组EAA含量较低,H IE组EAA含量显著升高,大、小剂量DXM预处理后,EAA含量较H IE组有不同程度的降低。     

Catalytic performance and structural characterization of ferric oxide and its composite oxides supported gold catalysts for low-temperature CO oxidation

The preparation and catalytic activity of ferric oxide and its composite oxides supported gold catalysts for low-temperature CO oxidation were investigated detailedly, and characterized extensively by XRD, XPS, TPR, EC and XAFS techniques. It was found that containing highly dispersed Au of partially oxidized state, these nano-structured oxides supported Au/Fe2O3 and Au/NiFe2O4 catalysts had higher low-temperature activities. The possible catalytic active center is the gold of partially oxidized state (Auζ+).     

毛细管电泳-限制性片段长度多态性分析检测胃癌H-ras基因点突变

建立一种毛细管电泳快速高效检测限制性内切酶酶切产物的方法, 使其更好地用于基因诊断. 以甲基纤维素(Methyl cellulose, MC)为筛分介质, 用pUC19 DNA/Msp I (Hpa II) Marker标准DNA片段为实验对象, 通过考察筛分介质的浓度、pH值、毛细管的温度和运行电压优化出分离小于600 bp的双链DNA片段的最适条件, 并将此方法应用于临床59例胃癌患者肿瘤组织H-ras基因12位密码子点突变情况的检测. MC是一种良好的筛分介质, 运用其进行毛细管电泳对于遗传性疾病的诊断将更加快速、准确、简便、灵敏.     

通过柱切换技术与高效液相色谱联用的限进性柱对盐酸贝那普利的在线富集性能

以自制的限进性填料柱为预处理富集柱,Luna C₁₈柱为分析柱,通过柱切换技术将限进性填料柱与高效液相色谱联用(RAM-HPLC),研究了盐酸贝那普利的在线富集效果。考察了进样体积与峰面积、系统总压力的关系,以及常规进样与大体积进样的差别。当进样体积在100 μL以内时,峰面积随进样体积的增加而增加;当进样体积大于80 μL时,系统总压力变化明显。考虑对整个系统的保护,选择80 μL作为最大进样体积。同一浓度的样品进样20 μL与进样80 μL所得峰面积之间的线性关系良好。RAM柱对盐酸贝那普利具有良好的富集作用,能够有效提高HPLC的灵敏度,而且具有简单、经济的特点。     

Polymorphism of nylon‐6 in multiwalled carbon nanotubes/nylon‐6 composites

The effects of pristine and amino‐functionalized multiwalled carbon nanotubes (MWNTs) on the crystallization behaviors of nylon‐6 were investigated by differential scanning calorimetry and X‐ray diffraction. The results indicate the presence of polymorphism in nylon‐6 and its composites, which is dependent on the MWNTs concentration and the cooling rate. More MWNTs and slow cooling from the melt favors the formation of α crystalline form. With the increase in cooling rates, the crystallinity of neat nylon‐6 decreases, and that of the composites decreases initially but increases afterward. Moreover, the degree of crystallinity of the composites is higher than neat nylon‐6 under high cooling rates, counter to what is observed under low cooling rates. The heterogeneous nucleation induced by MWNTs and the restricted mobility of polymer chains are considered as the main factors. Furthermore, addition of MWNTs increases the crystallization rate of α crystalline form but amino‐functionalization of MWNTs weakens this effect. The influence of thermal treatment on the crystalline structure of MWNTs/nylon‐6 composites is also discussed. A γ–α phase transition takes place at lower temperature for MWNTs/nylon‐6 composites than for nylon‐6. The annealing peaks of the composites annealed at 160 °C are higher than that of neat nylon‐6, and the highest annealing peak is obtained for amino‐functionalized MWNTs/nylon‐6 composites. This phenomenon is closely related to the different nucleation and recrystallization behaviors produced by various MWNTs in confined space. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1499–1512, 2006     

The effects of irradiation cross-linking on the thermal degradation and flame-retardant properties of the HDPE/EVA/magnesium hydroxide composites

High-density polyethylene/ethylene vinyl-acetate copolymer/magnesium hydroxide composites were crosslinked via high-energy electron beam irradiation in the presence of triallylisocyanurate. The structure of the cross-linking network was determined with the help of rheological measurements through advanced rheological extended systems (ARES). The thermal and flame-retardant properties of the irradiated composites were investigated by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and cone calorimetry. Results showed that the cross-linking network structure could enhance the thermal stability of composites, and did favor to smoke suppression. However, the peak heat release rate (PHRR) increased and the time to PHRR shortened, inferring that the composites after irradiation cross-linking were easier to combust. The char microstructure after cone calorimetry test was observed and used to give explanation of the above results.     

反射相移对光学玻璃电流传感器抗电磁干扰能力的影响

在光学玻璃电流传感器中，如果光线反射转向时在光的ｐ，ｓ分量之间引入反射相移，则会对该传感器的抗电磁干扰能力产生不良影响，本文对这种情况进行了理论上的分析，并给出了数值模拟和实验的结果。     

Faraday mirror-typed optical current transformers and its theoretical analysis

A Faraday mirror-typed optical current transformer (OCT) design with turn-back optical paths is proposed to overcome the harmful effects of the linear birefringence inside bulk glass current sensing head, which can double the sensitivity and improve the state of polarization of the system output. The theoretical analysis of the working principle, the simulation of the polarization state of the output light beam and the comparison between it and the OCT with polarization preserving total reflection (PPTR) layers are presented. The results show that this design has a good suppressing effect on the degeneration of the polarization state of the output light, which has certain reference significance on the performance improvement of the present bulk glass OCT, and the development of practical OCTs.