Absorption cross-sections of the C-h overtone of volatile organic compounds: 2 methyl-1,3-butadiene (isoprene), 1,3-butadiene, and 2,3-dimethyl-1,3-butadiene

Many molecules or transient radicals have well-documented absorption cross-sections in the ultraviolet (UV) region, but their absorption cross-sections in the near-infrared (NIR) region are much less often known and are difficult to measure. We propose a method to determine the unknown NIR absorption cross-sections using the known absorption cross-sections in the UV region, in which single-path UV absorption spectroscopy and NIR continuous wave cavity ringdown spectroscopy (cw-CRDS) are employed in a cross-arm reaction chamber for simultaneous measurements. Without knowing the actual sample partial pressures (or concentrations), the NIR absorption cross-sections can be accurately determined through the two sets of measurements. The method is demonstrated by measuring the NIR absorption cross-section of the first overtone of the asymmetric C-H stretch of 2-methyl-1,3-butadiene (isoprene) (3.24 (+/-0.16) x 10(-22) cm(2) molecule(-1)) at 1651.52 nm using the known value of the absorption cross-section at 220 nm. The diode laser wavelength was calibrated by atmospheric cavity ringdown spectra of CH(4), CO(2), and H(2)O. By comparison with sample pressure measurements, this method can also be used as a pressure calibration means for the reaction chamber, and this has been demonstrated with two additional measurements of the absorption cross-sections of 1,3-butadiene and 2,3-dimethyl-1,3-butadiene (2.50 (+/- 0.08) x 10(-22) and 2.82 (+/-0.16) x 10(-22) cm(2) molecule(-1), respectively) at 1651.52 nm. The applicability of the method to determining absorption cross-sections using the simultaneous measurements of cw-CRDS and single-path absorption spectroscopy is discussed.     

1,1,4,4-四苯基-1,3-丁二烯衍生物的合成

以苯乙酮和溴代苯为原料,通过格氏反应先制得1,1-二苯基乙醇(1),收率为91.3%;(1)经脱水和氯甲基化得到1,1-二苯基-3-氯丙烯(2),收率为92.9%;(2)再与二苯甲酮衍生物经格氏反应制得了1,1,4,4-四苯基-1,3-丁二烯衍生物(3a)和(3b),收率高于54.0%,并对各步合成的工艺条件进行了研究.HPLC测得(3a)和(3b)质量分数均高于99.0%.通过紫外光谱、红外光谱、质谱、1H NMR和元素分析对产物的组成和结构进行了鉴定.     

Evaluation of 1,3-butadiene dimerization and secondary reactions in the presence and absence of oxygen

Thermal stability evaluation of exothermic chemical reactions is of great importance to the safer design and operation of chemical processes. Dominant reaction stoichiometries and their thermochemistry parameters are key elements in the evaluation process. Identification of significant reaction pathways under possible process conditions will lead to an understanding of the overall thermodynamic and kinetic behavior. The kinetics of 1,3-butadiene (BD) is an excellent example of conjugated dienes that undergo addition reactions. At elevated temperatures, 1,3-butadiene monomers can dimerize exothermally, and as temperature increases, secondary exothermic reactions will take place. The very high temperature and pressure rates that these reactions can attain may lead to a reaction runaway or even a thermal explosion. BD is a vapor at ambient conditions, usually stored as a pressurized liquid, and is a carcinogen, so the experimental evaluation is potentially difficult and hazardous. In this paper, the thermal stability of BD is evaluated. Dimerization and other secondary reactions are investigated by experimental thermal analysis using an automatic pressure adiabatic calorimeter (APTAC), by theoretical computational quantum chemistry methods, and empirical thermodynamic-energy correlations. A theoretical approach is conducted to predict some of the BD reaction behavior. Results are compared to other literature data obtained using different experimental methods.     

聚丁二烯段1,2结构含量对SBS表面相分离形貌的影响

本文以三嵌段共聚物聚(苯乙烯-丁二烯-苯乙烯)(SBS)为研究对象,原子力显微镜(AFM)为研究手段,对PB段1,2结构的含量对SBS表面微相分离形貌的影响进行了研究,研究结果表明,无论采用甲苯还是环己烷为成膜溶剂,PS呈都圆柱状分散在连续的橡胶相中,但是随着聚丁二烯段1,2结构含量由28%增加到33%,其结构排列的有序性会发生相应下降.此外,本文还对制膜所选择的溶剂种类对嵌段共聚物形貌的影响进行了讨论.     

1,1-二(对-二乙氨基苯基)-4-(α-萘基)-4-苯基-1,3-丁二烯的合成及其光电性能研究

以α-溴代萘和苯乙酮为主要原料合成了1-(α-萘基)-1-苯基-3-氯丙烯,该化合物与4,4'-双(二乙氨基)二苯甲酮经Grignard反应,脱水后得到目标产物1,1-二(对-二乙氨基苯基)-4-(α-萘基)-4-苯基-1,3-丁二烯(CT),产品纯度98.86%,收率36.4%.通过质谱与核磁共振对产物的结构进行了表征,并对其进行X-射线单晶衍射分析,确定了分子构型.以Y-TiOPc为电荷产生材料,CT为空穴传输材料制备的功能分离型光导体光导性能参数为:V0=-850V,VR=-20V,Rd=17.5V,E1/2=0.60lx·s,表明CT具有优良的空穴传输特性.     

Fluorohydrogenated amorphous carbon (a-C:H, F) films prepared by the r.f. plasma decomposition of 1,3-butadiene and carbon tetrafluoride

Amorphous fluorohydrogenated carbon films (a-C:H, F) were prepared by the r.f. glow discharge decomposition of a hydrocarbon (C₄H₆) diluted with a fluorocarbon (CF₄). An increase in the CF₄ content of the deposition gas mixture was accompanied by a corresponding increase in the fluorine content and a decrease in the hydrogen content of the films. The IR spectra indicate fluorine incorporation in the film primarily via the monofluoride mode. No absorption owing to CF₂ and CF₃ could be detected. The film density and optical bandgap stayed fairly constant until about 40–50% dilution with CF₄. Further dilution of the hydrocarbon with CF₄ resulted in a large drop in the deposition rate, film density, optical bandgap, oxygen plasma etch resistance and thermal stability. These film properties differ from those of a-C:H, F films obtained by the r.f. plasma decomposition of substituted benzenes (Sah et al., Appl. Phys. Lett., 46 (1992) 739).     

The electrical properties of polymer nanocomposites with carbon nanotube fillers

The electrical properties of polymer nanocomposites containing a small amount of carbon nanotube (CNT) are remarkably superior to those of conventional electronic composites. Based on three-dimensional (3D) statistical percolation and 3D resistor network modeling, the electrical properties of CNT nanocomposites, at and after percolation, were successfully predicted in this work. The numerical analysis was also extended to investigate the effects of the aspect ratio, the electrical conductivity, the aggregation and the shape of CNTs on the electrical properties of the nanocomposites. A simple empirical model was also established based on present numerical simulations to predict the electrical conductivity in several electronic composites with various fillers. This investigation further highlighted the importance of theoretical and numerical analyses in the exploration of basic physical phenomena, such as percolation and conductivity in novel nanocomposites.     

The theory of polymer dynamics

Recent years have brought exciting theoretical advances to understanding the behavior of macromolecular systems under nonequilibrium conditions. Developments in diffusion-controlled reactions of polymers are bringing molecular insights to reactive blending technologies, and improved theories relating to associating polymers should aid in the design of thickening agents and coatings. Recent progress in molecular theories of flow and deformation may facilitate the design of branched polymers with tailored rheological properties and improved adhesives.     

The micromechanics of polymer fracture

Formation of incipient submicroscopic cracks in polymers under load have been studied by small-angle X-ray scattering. The main regularities of crack formation under different loading conditions have been analyzed. The connection between the submicrocrack concentration and the deformation of a stressed polymer has been shown. The main parameters of crack formation defining the strength properties of a polymer, i.e., the size of initial submicrocracks transverse to the axis of loading, which is determined by the structural heterogeneity of a material, and the concentration of submicrocracks before rupture, have been established. The analysis of the quantitative correlation between these parameters allows one to formulate the main statements regarding the micromechanics of polymer fracture. From comparing the volume and surface parameters of crack formation of a stressed polymer, the dominating role of the surface in the process of fracture has been demonstrated.     

The observation of polymer reptation

Direct visualization of reptating macromolecules has been achieved. The concept of reptation, which until recently had only been directly confirmed by computer simulations, is now supported by two separate experiments. In one, a few fluorescencelabeled actin filaments were directly observed in an unlabeled semi-dilute entangled network. The Figure shows snapshots of a filament moving in the network.      

聚合物的热膨胀

热膨胀既是聚合物的基本属性,同时也与聚合物结构与性能密切相关。本文在提出聚合物热膨胀产生机制的基础上,介绍了测量聚合物热膨胀的方法,讨论了热膨胀在聚合物基础研究中的应用,着重评述了热膨胀在PTC材料为代表的聚合物基复合材料设计中的重要价值。     

Chemical reactivity of aluminium with boron carbide

The chemical reactivity of boron carbide (B₄C) with metallic aluminium (Al) was studied at temperatures ranging from 900 to 1273 K (627–1000 °C). Al–B₄C powder mixtures were cold pressed, heated for 1–450 h under 10⁵ Pa of purified argon and characterized by X-ray diffraction (XRD) optical metallography (OM), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Whatever the temperature in the investigated range, B₄C has been observed to react with solid or liquid Al. As long as the temperature is lower than 933 K (660 °C), i.e. as long as Al is in the solid state, interaction proceeds very slowly, giving rise to the formation of ternary carbide (Al₃BC) and to diboride (AlB₂). At temperatures higher or equal to 933 K, Al is in the liquid state and the reaction rate increases sharply. Up to 1141 ± 4 K (868 ± 4 °C), the reaction products are Al₃BC and AlB₂: at temperatures higher than 1141 K, Al₃ BC is still formed while Al₃B₄₈C₂ (β-AlB₁₂) replaces AlB₂. In the three cases, interaction proceeds via the same mechanism including, successively, an incubation period, saturation of aluminium in B and C, nucleation and growth by dissolution–precipitation of Al₃BC and a C-poor boride and, finally, the passivation of B₄C by Al₃BC. These results are discussed in terms of solid–liquid phase equilibria in the Al–B–C ternary system, with reference to the binary invariant transformation: α-AlB₁₂ + L ⇔ AlB₂, which has been found to occur at 1165 ± 5 K (892 ± 5 °C). This revised version was published online in November 2006 with corrections to the Cover Date.     

The reactivity of sodium borohydride with various species as characterized by adiabatic calorimetry

The reactivity of sodium borohydride in the presence of other species has been examined by adiabatic calorimetry. In combination with water, sodium borohydride exhibits an exotherm at room temperature accompanied by generation of gas (presumed to be hydrogen). Addition of potassium hydroxide to a sodium borohydride-water mixture is found to stabilize the solution and require a higher temperature for reaction to occur. However, if iron oxide is also included, reaction takes place near room temperature. Very rapid reaction was found when a metal chloride was brought in contact with a solution containing sodium borohydride, water, and potassium hydroxide. When sodium borohydride was added to an oxygenated hydrocarbon, reaction at room temperature also took place, but to a more limited extent. Peak temperatures above 200 degrees C and maximum pressures in excess of 2000 psia were observed in most cases. Kinetics extracted from the calorimetry data are presented for some of the sodium borohydride combinations.     

The hydration of Portland and aluminous cements with added polymer dispersions

We have studied the hydration of ordinary Portland cement and Secar 71 aluminous cement with added polyvinyl alcohol, polyvinyl acetate, acrylic, poly (vinylidene chloride-acrylic), poly (styrene-acrylic) polymers and poly (styrene-butadiene) rubber latex. We have used the techniques of conduction and differential scanning calorimetry, infrared spectroscopy and X-ray diffraction in our studies.The nature of the interactions between the polymers and the two cements is significantly different. For Portland cement all polymers were found to retard the hydration rate to some extent, with the acrylics producing the maximum affect, whereas in the case of Secar 71, polymer additions had minimal effects on the hydration of or heat evolution from the cement. Our results suggest that many polymers interact with Portland cements in a chemical way although for aluminous cements the observations are less clear except in the case of polyvinyl alcohol-acetate.     

The concept of one polymer composites modelled with high density polyethylene

One polymer composite materials have been prepared using a difference in melting points between the components. This depends on the fact that aligned and extended chains provide thermodynamically more stable crystals, which thus will have higher melting points than conventionally crystallized melts. The growth of transcrystalline regions in the melt matrix at the interface plus an observed partial melting between fibre and matrix are indications of a strong and intimate interfacial bond with a gradient in morphologies for the system studied, high-density polyethylene. The pull-out test is a simple and adequate method for evaluating the interfacial shear strength of one polymer composites. The value for the high-density polyethylene composite falls between the strengths for glass-reinforced polyester and epoxy resins. However, the interfacial strength in the polyethylene composites is due mainly to the unique epitaxial bonding rather than the radial forces from compressive shrinkage. The low critical aspect ratio for the filaments in these polyethylene composites suggests possible advantageous uses as short fibrereinforced materials where the interfacial strength is a controlling factor.On leave from Universidad Nacional Del Sur, Planta Piloto de Ingenieria Quimica, Bahia Blanca, Argentina.     

NanoHPLC-nanoESI(+)-MS/MS quantitation of bis-N7-guanine DNA-DNA cross-links in tissues of B6C3F1 mice exposed to subppm levels of 1,3-butadiene

1,3-Butadiene (BD) is an important industrial chemical and a common environmental pollutant present in urban air. BD is classified as a human carcinogen based on epidemiological evidence for an increased incidence of leukemia in workers occupationally exposed to BD and its potent carcinogenicity in laboratory mice. A diepoxide metabolite of BD, 1,2,3,4-diepoxybutane (DEB), is considered the ultimate carcinogenic species of BD due to its ability to form genotoxic DNA-DNA cross-links. We have previously employed capillary HPLC-ESI(+)-MS/MS (liquid chromatography-electrospray ionization tandem mass spectrometry) methods to quantify DEB-induced DNA-DNA conjugates, e.g. 1,4-bis-(guan-7-yl)-2,3-butanediol (bis-N7G-BD), 1-(guan-7-yl)-4-(aden-1-yl)-2,3-butanediol (N7G-N1A-BD), and 1,N(6)-(1-hydroxymethyl-2-hydroxypropan-1,3-diyl)-2'-deoxyadenosine (1,N(6)-HMHP-dA), in tissues of laboratory mice exposed to 6.25-625 ppm BD (Goggin et al. Cancer Res. 2009, 69(6), 2479-2486). However, typical BD human exposure levels are 0.01 to 3.2 ppb in urban air and 1-2.0 ppm in an occupational setting, requiring greater detection sensitivity for these critical lesions. In the present study, a nanoHPLC-nanoESI(+)-MS/MS method was developed for ultrasensitive, accurate, and precise quantitation of bis-N7G-BD in tissues of laboratory mice treated with low ppm and subppm concentrations of BD. The LOD value of the new method is 0.5 fmol/100 μg DNA, and the LOQ is 1.0 fmol/100 μg DNA, making it possible to quantify bis-N7G-BD adducts present at concentrations of 3 per 10(9) nucleotides. Bis-N7G-BD adduct amounts in liver tissues of mice exposed to 0.5, 1.0, and 1.5 ppm BD for 2 weeks were 5.7 ± 3.3, 9.2 ± 1.5, and 18.6 ± 6.9 adducts per 10(9) nucleotides, respectively, suggesting that bis-N7G-BD adduct formation is more efficient under low exposure conditions. To our knowledge, this is the first quantitative analysis of DEB specific DNA adducts following low ppm and subppm exposure to BD.     

1,3-二氧五环对锂电极的钝化作用

首次利用1,3-二氧五环(DOL)对金属锂电极进行预处理,以使该电极钝化,提高其界面稳定性.电化学阻抗谱(EIS)分析表明,当金属锂电极长时间浸泡在电解液中时,经过DOL预处理的锂电极与未经处理的锂电极相比,具有更低、更稳定界面阻抗.同时,扫描电子显微镜(SEM)观察也证明,在长时间浸泡后,经过预处理的锂电极表面要比未经处理的锂电极表面,更加平整,并有更少的锂枝晶出现.显然,DOL预处理对锂电极具有很好的钝化作用.进而,由于预处理在锂电极表面生成稳定的界面膜所具有的钝化作用,经过该处理的锂电极在连续的充放电循环中,显示出更高的循环效率.