Thermal degradation and flame retardancy of flexible polyvinyl chloride containing solid superacid

The objective of the present article was to study the thermal degradation behavior and flame retardancy of flexible polyvinyl chloride (PVC) composites containing TiO₂/SO ^2?₄ solid superacid because of its strong catalytic ability for esterification and dehydration. The TiO₂/SO ^2?₄ solid superacid was synthesized by using precipitation immersion method, and its structure was investigated by X-ray diffraction. As expected, the value of limiting oxygen index for PVC/Sb₂O₃/(TiO₂/SO ^2?₄ ) composite was 32.5% and the char yield of PVC/Sb₂O₃/(TiO₂/SO ^2?₄ ) composite was significantly improved compared to neat PVC in thermogravimetry tests. In addition, the peak heat release rate and smoke production rate of PVC/Sb₂O₃/(TiO₂/SO ^2?₄ ) decreased by 14% and 42%, respectively, compared with neat PVC. Moreover, the results of cone calorimetry tests and electron micrograph of char residue showed that the char yield of TiO₂/SO ^2?₄ was enhanced, resulting in a strong char layer structure with outstanding fire retardance cone. In conclusion, the results of this work showed that the addition of solid superacid promoted the decomposition and dehydration of PVC, which formed a compact and continuous char layer on the surface of the material. Hence, the study provides a new perspective for producing composites with excellent flame retardancy and smoke suppression properties of PVC.

     

Determination of enantiomeric excess by capillary electrophoresis

Capillary electrophoresis (CE) is becoming an established method for the determination of chiral trace impurities. This paper provides an overview of the state of the art of CE for such determinations. Detection limits of 0.1% impurity is widely accepted as a minimum requirement for chiral trace impurity determinations. This can be relatively easily achieved with CE. However, determination of lower concentrations requires careful optimization of the separation system. Four factors that are of particular significance for trace enantiomeric determinations: resolution, limit of detection, linear range and type of detection, are discussed. Further, the advantages and disadvantages of derivatization in this context are treated as well as the separation approach, ie., direct chiral separation or separation after the formation of diastereomers. It is concluded that the limit of impurity detection can be about 0.05% when UV detection is employed. Using laser-induced fluorescence detection, a quantitative determination at the 0.005% level is often possible.     

A theoretical study of electronic excited states of photosynthetic reaction center in Rhodopseudomonas viridis

The electronic singlet vertical excited states of photosynthetic reaction center (PSRC) in Rhodopseudomonas (Rps.) viridis were investigated by ZINDO and INDO/S methods. The effects of the interactions of pigment-pigment and pigment-protein on the electronic excitations were examined. The calculation results showed that the interactions of pigment-pigment and pigment-protein play an important role in reasonably assigning the experimental absorption and circular dichroism (CD) spectra of PSRC in Rps. virids. By comparing the theoretically computed excited states with the experimental absorption and CD spectra, satisfactory assignments of the experimental spectroscopic peaks were achieved.     

新型含氟聚芳醚酮的合成与表征

聚芳醚酮具有很高的热稳定性和优良的电性能及机械性能 ,已经被广泛应用于宇航、电子及核能等高技术领域 [1] .氟元素的引入可以降低材料介电常数、折光指数和吸水率 ,提高热稳定性、溶解性和阻燃性 ,增加材料透明度 ,使这类聚合物在光电子、光学和微电子等应用领域的研究倍受关注 [2～ 4 ] .本文在合成含三氟甲基苯侧基的聚芳醚酮 [5] 的基础上 ,设计并合成了新型的含氟量更高的单体和聚合物 ,并对其性能进行了初步研究 .1　实验部分1 .1　试剂与仪器　 [3,5 -二 (三氟甲基 ) ]苯代对苯醌 (自制 ) ;锌粉 ,A.R.级 ,天津化学试剂一厂产品 ;…     

2,6-O-二戊基-3-O-三氟乙酰β-环糊精和聚硅氧烷混合手性石英毛细管柱分离对映体

本文合成了部分烷基化三氟乙酰化的β-环糊精手性固定相(DP-TFA-β-CD),并把它与普通聚硅氧烷OV-7混合制备出了柱效高、热稳定性好的手性石英毛细管柱。与直接涂DP-TFA-β-CD相比,混合固定相能在较短分析时间内对卤代烃、醇、酯、γ-内酯、胺等对映体有更好的拆分。     

有序自组装聚合物纳米结构

采用水辅助方法(water-assisted fabrication method),分别以4-十二烷基苯磺酸掺杂的聚苯胺(PANI-DBSA)和聚2-甲氧基-5-(2′-乙烯基-己氧基)苯乙炔(MEH-PPV)两种功能高聚物为成膜材料,冷凝水滴为模板,利用水滴在聚合物溶液表面的自组装,制备出了两种纳米层次以上的蜂窝状有序多孔聚合物薄膜.通过原子力显微镜和共聚焦荧光显微镜对其形貌、电学性质和荧光图像进行了表征.     

Dimethylformamide as a carbon monoxide source in fast palladium-catalyzed aminocarbonylations of aryl bromides

Dimethylformamide (DMF) acts as an efficient source of carbon monoxide and dimethylamine in the palladium-catalyzed aminocarbonylation (Heck carbonylation) of p-tolyl bromide to provide the dimethylamide. Addition of amines to the reaction mixture in excess delivers the corresponding aryl amides in good yields. The amines employed, benzylamine, morpholine, and aniline, all constitute good reaction partners. The reaction proceeds smoothly with bromobenzene and more electron-rich aryl bromides, but electron-deficient aryl bromides fail to undergo aminocarbonylation. The reactions are conducted at 180-190 degrees C for 15-20 min with microwave heating in a reaction mixture containing imidazole and potassium tert-butoxide: the latter is required to promote decomposition of the DMF solvent at a suitable rate. The beneficial effects of controlled microwave irradiation as an energy source for the rapid heating of the carbonylation reaction mixture are demonstrated. The carbonylation procedure reported herein, which relies on the in situ generation of carbon monoxide, serves as a convenient alternative to other carbonylation methods and is particularly applicable to small-scale reactions where short reaction times are desired and the direct use of carbon monoxide gas is impractical.     

THE ADSORPTION OF OXYGEN OVER ThO_2-BaF_2 CATALYST

IntroductionInthcsclcctivcoxidationofalkanes.suchas'theoxidativccouplingofmcthanc(0CM)andthcoxidativcdch}'drogenationofcthanc(0DE)t0prcparccth}'lene.bothoxidcionsofthelatticeandtheox}'genspeciesovercataIystsuffocepla}'animportantrole.Althoughcxtcnsivcinvcstigationshavcbeengivcntothecharactcrizationofox}'gcnspccicsandthcreactionofox}'gcnspecicsx`ithalkanes,itisstilldifficulttosayt`hichoncsofox}'gcnspcciesarcthcactivcspecicsinthcactivation0falkancs.bccauscthenaturcofcatal}'stsandthecxperimcntc…     

Illustration of a simple and versatile scheme for reversing enantiomeric elution order and facilitating enantiomeric impurity determination in capillary electrophoresis

Determination of enantiomeric purity is most often done under overload conditions, which leads to deformed peaks. In general, the best resolutions are obtained when the small peak appears before the large peak in the electropherogram. To be able to determine the R(+)-impurity in the S(-)-form as well as the S(-)-impurity in the R(+)-form the elution orders have to be reversed. The present paper describes reversal of enantiomeric elution order for the basic analyte propranolol and the acidic analyte ibuprofen. For propranolol, a charged heptakis-(6-sulfo)-beta-cyclodextrin (CD) is used in the background electrolyte. For ibuprofen, a mix of the charged heptakis-(6-sulfo)-beta-CD and the uncharged heptakis-(2,3,6-tri-O-methyl)-beta-CD is used in the background electrolyte. The use of a coated capillary and reversal of the polarity shift the elution order, buffer composition is unchanged in both cases. The enantiomers of propranolol and ibuprofen are well separated on both the coated and uncoated capillaries. Detection limits of enantiomer impurities are investigated using spiked samples of both propranolol and ibuprofen.     

MoO3、NiO、ZnO在小表面金红石上的分散行为

Dispersion of MoO3, NiO, ZnO on rutile TiO2 with low specific surface area was studied with Mercury Porosimeter, SEM, XPS and Ammonia Extraction method. The dispersion thresholds of MoO3, NiO, ZnO on three rutile TiO2 carriers were obtained with XPS, and com-pared with those on anatase TiO2 with high specific surf are area. Ammonia Extraction method was used to identify the surface oxide species interarting with support surface in different strength and it was found that the proportions of oxides that can not be extracted by ammonia extraction are different for MoO3, NiO and ZnO which are supported on rutile TiO2.