Electrical conductivity of poly(ethylene terephthalate)/expanded graphite nanocomposites prepared by in situ polymerization

Nanocomposites based on poly(ethylene terephthalate) (PET) and expanded graphite (EG) have been prepared by in situ polymerization. Morphology of the nanocomposites has been examined by electronic microscopy. The relationship between the preparation method, morphology, and electrical conductivity was studied. Electronic microscopy images reveal that the nanocomposites exhibit well dispersed graphene platelets. The incorporation of EG to the PET results in a sharp insulator‐to‐conductor transition with a percolation threshold (?_c) as low as 0.05 wt %. An electrical conductivity of 10^?3 S/cm was achieved for 0.4 wt % of EG. The low percolation threshold and relatively high electrical conductivity are attributed to the high aspect ratio, large surface area, and uniform dispersion of the EG sheets in PET matrix. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Synthesis of Novel Unsymmetrical and Symmetrical Diacetylenic Ketones

A convenient and efficient method for the preparation of unsymmetrical and symmetrical diacetylenic ketones bearing a carboxylate group.     

问题视角浅析

文中通过多视角分析解决数学问题,向学习者渗透了数学思想的辩证性和学习方法的灵活性,体现了"以人为本"现代理念下的数学教育.     

Preparation of PEO-b-PPO-b-PEO/α-cyclodextrin supramolecular hydrogels hybridized with exfoliated graphite nanoplates

Abstract

In this work, an effective method was developed to prepare novel PEO-b-PPO-b-PEO (EPE)/α-cyclodextrin (α-CD) supramolecular hydrogels containing exfoliated graphite nanoplates (xGNPs) by mixing an aqueous solution of α-CD with an aqueous dispersion of xGNPs at the presence of amphiphilic EPE copolymer. The EPE copolymer played three important roles in the preparation process: (1) as an exfoliating agent to break expanded graphites into xGNPs under ultrasonication, (2) as a dispersant to stabilize xGNPs in the aqueous solution, and （3）as a component to form the inclusion complexes with α-CD. The resultant xGNPs/EPE/α-CD hybridized hydrogels were characterized by scanning electron microscopy, wide-angle X-ray diffraction, differential scanning calorimetry, and Fourier transform infrared spectroscopy, which confirmed not only the formation of supramolecular hydrogel structure but also the homogenous dispersion of xGNPs in the hydrogel matrix. It was found that the existence of xGNPs can accelerate the speed of gel formation in comparison with that of the native EPE/α-CD hydrogel. Additionally, the water-retention ability and the release behavior of vancomycin hydrochloride for the xGNPs/EPE/α-CD hybridized hydrogels were investigated.     

Flammability and Thermal Oxidative Degradation Kinetics of Magnesium Hydroxide and Expandable Graphite Flame Retarded Polypropylene Composites

The flammability and the thermal oxidative degradation kinetics of expandable graphite (EG) with magnesium hydroxide (MH) in flame‐retardant polypropylene (PP) composites were studied by limiting oxygen index (LOI), UL‐94 test, and thermogravimetric analysis (TGA). The results show that EG is a good synergist for improving the flame retardancy of PP/MH composite and the effect is enhanced with decreasing EG particle size. The Kissinger method and Flynn‐Wall‐Ozawa method were used to determine the apparent activation energy (E) for degradation of PP and flame retarded PP composites. The data obtained from the TGA curve indicate that EG markedly increases the thermal degradation temperature of PP/MH composites and improves the thermal stability of the composites. The kinetic results show that the values of E for degradation of flame retarded PP composites is much higher than that of neat PP, especially PP/MH composites with suitable amount of EG, which indicates that the flame retardants used in this work have a great effect on the mechanisms of pyrolysis and combustion of PP.     

聚乙烯亚胺改性氧化石墨对水中Cr(Ⅵ)的吸附

通过对石墨氧化、酯化,将聚乙烯亚胺耦合接枝到氧化石墨表面,制备聚乙烯亚胺改性氧化石墨(PEI-GO).通过FTIR、XRD、TEM、RS和XPS等对合成材料进行表征,并研究了其对水中的Cr(Ⅵ)吸附和脱附性能.表征结果表明,聚乙烯亚胺成功嫁接到氧化石墨上,其氨基含量为4.36 mmol·g^-1.PEI-GO对水中Cr(Ⅵ)具有很好的吸附性能,吸附等温线符合Freundlich方程,吸附动力学可用拟二级动力学方程来描述.PEI-GO对水中Cr(Ⅵ)的吸附随pH的升高而降低.阴离子的存在降低吸附剂对Cr(Ⅵ)的吸附,不同阴离子的影响大小顺序为PO₄^3- >SO₄^2- >NO^3- >Cl^-.XPS结果表明,PEI-GO对Cr(Ⅵ)的去除是吸附-化学还原耦合作用的结果.经4次脱附再生循环,PEI-GO对Cr(VI)仍具有较高吸附量,表明该吸附剂再生性好,可循环使用.     

镍锌铁氧体/膨胀石墨/聚苯胺复合物的电磁损耗性能

用化学共沉淀法和原位乳液聚合法分别制备了镍锌铁氧体(Ni_xZn_1-xFe₂O₄)、Ni_0.7Zn_0.3Fe₂O₄/膨胀石墨(NZF/EG)二元复合物及其聚苯胺(PANI)包覆的三元复合物(NZF/EG/PANI)。用现代测试技术表征了样品的组成、结构、形貌和电磁性能。结果表明,NZF粒子较好地嵌入到EG的层间,PANI对NZF/EG的包覆效果良好;三元复合物的磁性能随磁性组分含量的减小而减弱,而电导率与EG和PANI的导电性及其相对含量相关联;复合物的电磁损耗性能优良,其中三元复合物优于二元复合物。含PANI 70wt%的NZF/EG/PANI三元复合物,制样厚度分别为1.5、2.0和2.5 mm时,其反射损耗峰值(有效带宽)分别为-19.99 dB(5.82 GHz),-20.33 dB (4.08 GHz)和-25.28 dB(3.67 GHz),具有优良的电磁波吸收效果。     

石墨炉原子吸收法测定PU材料中的铬

采用微波消解技术进行样品前处理,建立了石墨炉原子吸收法测定PU材料中铬含量的方法。在波长429.0 nm下,利用石墨炉程序升温测定,狭缝设为0.5 nm,塞曼效应作为背景校正。标准工作曲线线性良好,相关系数r=0.9986,方法检出限为0.051μg/L,测定结果的相对标准偏差为3.78%,加标回收率为92%～120%(n=6)。该方法简便、可行,适用于PU材料中铬的测定。     

微波消解–石墨炉原子吸收法测定化妆品中的铅

建立了微波消解–石墨炉原子吸收光谱法测定化妆品中铅的方法。探讨了样品前处理条件、基体改性剂的选择和优化、石墨炉升温条件等对测定结果的影响。在优化的试验条件下,铅的质量浓度在0~100 ng/mL范围内与吸光度具有良好的线性关系,线性相关系数r=0.9991,检出限为0.33 ng/mL。用该法对5种化妆品中的铅进行测定,加标回收率在95.0%~106.1%之间,测定结果的相对标准偏差不大于3.6%。该方法可应用于化妆品中痕量铅的分析。     

Synthesis of Privileged Scaffolds by Using Diversity‐Oriented Synthesis

An elegant reagent‐controlled strategy has been developed for the generation of a diverse range of biologically active scaffolds from a chiral bicyclic lactam. Reduction of the chiral lactam with LAH or alkylation with LHMDS to trigger different cyclization reactions have been shown to generate privileged scaffolds, such as pyrrolidines, indolines, and cyclotryptamines. Their amenability to substitution allows us to create various compound libraries by using these scaffolds. In silico studies were used to estimate the drug‐like properties of these compounds. Selected compounds were subjected to anticancer screening by using three different cell lines. In addition, all these compounds were subjected to antibacterial screening to gauge the spectrum of biological activity that was conferred by our DOS methodology. Gratifyingly, with no additional iterative cycles, our method directly generated anticancer compounds with potency at low nanomolar concentrations, as represented by spiroindoline 14 .