HPLC and MALDI-TOF MS analysis of highly branched polystyrene: resolution enhancement by branching

Temperature gradient interaction chromatography (TGIC) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) were applied for the characterization of highly branched polystyrenes (PS) prepared by linking living polystyryl anions using 4-chlorodimethylsilylstyrene. Reversed-phase (RP)-TGIC showed an unexpectedly high resolution according to the number of branches despite significant overlap of the molecular weight as confirmed by MALDI-TOF MS. The enhancement of the resolution is ascribed to the contribution of the nonpolar groups in the branched PS: the dimethylsilyl groups in the branching unit as well as the sec-butyl initiator groups. As the number of branches increases, the number of nonpolar groups increases, which in turn increases the RP-TGIC retention synergistically with increasing molecular weight. In contrast, a poorer resolution was found in normal-phase-TGIC, in which the nonpolar groups reduce the retention. The resolution in RP-TGIC appears superior to that of liquid chromatography at the chromatographic critical condition (LCCC) of PS. It is seemingly due to the synergistic contribution of the incremental PS molecular weight to the functionality in the branched PS in RP-TGIC while only the functionality contributes to the separation in LCCC. This type of resolution enhancement could be utilized efficiently for the analysis of highly branched polymers such as dendrimers or hyperbranched polymers.     

Estimation of the variance for a controlled branching process

In this paper we obtain estimators for the variance of the offspring distribution of a controlled branching process and we derive, for these estimators, some moments and asymptotic properties as consistency and limiting distribution. Research supported by the Ministerio de Ciencia y Tecnología and the FEDER through the Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica, grant BFM2003-06074.     

具有支化结构溴化丁基橡胶的合成及表征

研究了将锂端基苯乙烯-异戊二烯共聚物溶液与溴化丁基橡胶胶液反应合成具有支化结构的溴化丁基橡胶的方法,以期提高丁基橡胶的某些性能,拓宽丁基橡胶的应用领域.采用三台联用(LS VIS RI)、DSC、氧弹燃烧等方法对合成产物进行表征,并将产物硫化测定其硬度、拉伸应力、比重等性能,与非支化溴化丁基橡胶之性能进行对比.     

高支化碱溶性聚酯的合成及光成像研究

通过1，2，4-苯三甲酸酐和环氧氯丙烷合成高支化碱溶性聚酯，再用丙烯酸与多官能团环氧树脂反应产物对高支化聚酯改性得到高支化碱溶性感光聚合物；研究了这类聚合物的碱溶性、感光性和光成像特性。探索了光致抗蚀剂的配方组成和成像因素。结果表明，以接枝引入15%改性多官能团环氧树酯配制的光致抗蚀剂综合性能最好，分辨率3um以内（白光）。     

Synthesis and structural characterization of single-crystalline branched nanowire heterostructures

We report the synthesis of three-dimensional single-crystalline branched nanowire heterostructures, where the backbones and branches are assembled with ZnS and CdS, respectively. Growth of branch and backbones with control over the compositions was enabled via sequential seeding of gold nanocluster catalysts. Elemental mapping data confirmed that branched nanowire heterostructures were synthesized with the intended chemical modulation, CdS branches on ZnS backbones. Transmission electron microscopy studies showed that the growth of heterostructure branches occurs epitaxially from the backbone while maintaining single-crystalline structure. This unique class of heterostructures holds great potential in assembling electronics and photonics in three dimensions.     

Assessment of low probability events of dynamical systems by controlled Monte Carlo simulation

Various procedures to extend the applicability and to increase the efficiency of Monte Carlo simulation (MCS) for the analysis of complex dynamical systems are discussed. In particular, the capabilities of the methods denoted Russian Roulette and Splitting (RR&S) and Double and Clump (D&C) are reviewed with regard to their capabilities to analyze such systems. In this context, the difficulties in identifying the ‘important' regions for simulation are detailed. It is shown that these difficulties may be circumvented by a newly introduced ‘distance controlled' MCS. This procedure, which allows the prediction of very low probability events and the analysis of systems of higher dimension, is applicable not only to mechanical systems and structures but also to complex dynamical systems encountered, for example, in economics, physics, etc. The procedure is shown to be particularly suited to cases where exact analytical methods and direct Monte Carlo simulation are infeasible, hence, being well suited for practical application.     

Synthesis of TiC by controlled ball milling of titanium and carbon

Titanium and carbon powder mixtures with compositions of Ti_100−x C _x (x = 50, 40, 30) were milled under a helium atmosphere using a magneto ball mill. Controlled ball milling was performed in a higher energy impact mode and a lower energy shearing mode. For Ti₅₀C₅₀ and Ti₆₀C₄₀ powder mixtures milled in impact mode, TiC was formed via a mechanically-induced self-propagating reaction (MSR). When milling Ti₇₀C₃₀ in impact mode, the reaction to form TiC proceeded gradually as milling progressed; indicating that, for milling conditions that lead to the formation of TiC via MSR, a minimum carbon content is required to sustain the self-propagating reaction to form TiC. Milling in shearing mode resulted in the gradual formation of TiC during milling. This study found that increasing the carbon content of the starting powder mixture slowed the milling process. Replacing the activated carbon starting powder with high purity graphite was found to have little effect on the ignition time; indicating that the slowing of the milling process is not due to graphite acting as a lubricant during milling. Rather, this slowing of the milling process is most likely due to an increased carbon content resulting in an increase in the volume of the powder mixture. This would have a similar effect during milling to decreasing the ball:powder weight ratio (BPR), which is known to slow the milling process.     

Nonparametric estimation of the offspring distribution and the mean for a controlled branching process

In this paper, under a nonparametric context, some estimators for the mean and the offspring distribution of a controlled branching process are provided. Their conditional and unconditional moments and their asymptotic properties (consistency, normality) are investigated. Finally, as an illustration, a simulated example is presented. Research supported by the Plan Nacional de Investigación Científica, Desarrollo e Innovación Tecnológica, grant BFM2000-0356 and the Consejería de Educación, Ciencia y Tecnología de la Junta de Extremaduray y el Fondo Social Europeo, grant IPR00A056.     

新型高度支化聚氨酯-酰亚胺的合成与表征

以季戊四醇(PAT)、甲苯-2,4-二异氰酸酯(TDI)、异佛尔酮二异氰酸酯(IPDI)以及均苯四甲酸二酐(PM-DA)通过两步法制得了两种新型具有高度支化结构的聚氨酯-酰亚胺(PUITPP和PUIIPP)。研究发现:PUITPP在40℃时预聚反应的时间为40min,酰亚胺化反应在120℃反应2h后完成。高度支化PUITPP和PUIIPP均为晶相分明的半结晶态,分子链间距(d)分别为0.3896nm和0.4089nm。这两种嵌段共聚物分别在228.5℃和215.8℃附近出现两个玻璃化转变,它们在N2中呈现出两个失重台阶,对应的热分解温度(Td)分别在230℃和630℃,玻璃化温度则分别为220℃和325℃。另外它们能溶于少数几种强极性非质子有机溶剂,且对无机稀酸具有一定的抗腐蚀性。     

Synthesis of multiple collinear helical modes generated by a phase-only element

Phase-only elements are generally more desirable than complex-amplitude-modulated elements not only because of the higher diffraction efficiency but the readier implementation and fabrication. A novel iterative algorithm is proposed for generating multiple helical modes by a single phase-only element. A superposition of four helical modes is demonstrated experimentally by using a spatial light modulator.     

A branched material based on biomimetic design: Synthesis and electrochemical properties

Based on the biomimetic route the metal material with tree-like fractal structure was prepared, which showed a rough surface observed by scanning electron microscopy. According to the electrochemical experiments, the formed material exhibited the strong catalytic capability as an electrode in hydrogen evolution reaction, comparing with other conventional structure materials under comparable scales. We suggested this promotion of property arose from the contribution of the great surface area and the excellent connectivity offered from the fractal structure.     

Synthesis of MgAl2O4 spinel: seeding effects on formation temperature

Four different methods of MgAl₂O₄ spinel synthesis in the presence and absence of seeds were studied. The four methods used for MgAl₂O₄ synthesis were (a) one sol (boehmite) and one solution [Mg(NO₃)₂]; (b) two sols (boehmite and magnesia); (c) two nitrates (Al and Mg nitrates) and two alkoxides (Al isopropoxide and Mg ethoxide). The use of a nitrate route led to the formation of spinel at the lowest temperature without the influence of seeding. Seeding with spinel crystallites of all the powders except the one-sol and one-solution diphasic gels apparently resulted in a lower formation temperature of MgAl₂O₄ spinel, and this lowering of crystallization temperature can be explained by the nucleation and epitaxial growth mechanism.     

Synthesis of multiple tasks of a planar six-bar mechanism by wavelet series

This paper introduces a method for the synthesis of the multiple tasks of a planar six-bar mechanism by wavelet series. Based on the theory of wavelet series, a mathematical model for assessing the output of multiple tasks of planar linkage mechanisms was generated. The multiple tasks that combine a function generation and a rigid body guidance will be presented throughout this paper. For function generation, a numerical atlas database, including 31,775 groups of basic dimensional types of a planar slider-crank mechanism was created based on the relationships of the wavelet feature parameters. For rigid body guidance synthesis, an output feature parameters database of a planar four-bar motion generation, including 178,810 groups of the basic dimensional types was created by analysing the relationships of the wavelet coefficients between the rigid body rotation angle and the coupler rotation angle of its corresponding basic dimensional types. The actual sizes and installation position parameters of the planar six-bar mechanism were calculated using the fuzzy identification method and theoretical formulas. Finally, an application is presented to illustrate the validity and practicality of the proposed theory.     

碳纳米管管径的可控性研究

为了合理有效控制碳纳米管(CNTs)的管径,比较研究了化学气相沉积(CVD)-模板法与CVD-中毒法.通过透射电镜(TEM)观察碳纳米管形貌及其管径尺寸,分析了不同条件下,碳纳米管的形貌差异,讨论了制备阳极氧化铝(AAO)膜的氧化电压对碳纳米管的管径、管的有序度的影响和碳酸钠毒物对碳纳米管的管径、管形、产率的影响,并且分析了两种制备方法的生长机理.结果表明,在CVD-模板法中,在一定范围内,电压升高可以使AAO膜孔增大,从而控制碳纳米管的外径;在CVD-中毒法中,微量的碳酸钠粉末能增大碳纳米管的内径.     

Formation of chiral branched nanowires by the Eshelby Twist

Manipulating the morphology of inorganic nanostructures, such as their chirality and branching structure, has been actively pursued as a means of controlling their electrical, optical and mechanical properties. Notable examples of chiral inorganic nanostructures include carbon nanotubes, gold multishell nanowires, mesoporous nanowires and helical nanowires. Branched nanostructures have also been studied and been shown to have interesting properties for energy harvesting and nanoelectronics. Combining both chiral and branching motifs into nanostructures might provide new materials properties. Here we show a chiral branched PbSe nanowire structure, which is formed by a vapour-liquid-solid branching from a central nanowire with an axial screw dislocation. The chirality is caused by the elastic strain of the axial screw dislocation, which produces a corresponding Eshelby Twist in the nanowires. In addition to opening up new opportunities for tailoring the properties of nanomaterials, these chiral branched nanowires also provide a direct visualization of the Eshelby Twist.     

聚甲基丙烯酰吗啉枝化壳聚糖梳型聚合物的pH敏感性及其对辅酶A的控制释放

利用马来酸酐单酰化壳聚糖(CS-Ma)与甲基丙烯酰吗啉(MAMP)共聚, 合成了一种新型梳型聚合物-聚甲基丙烯酰吗啉枝化壳聚糖[P(CS-Ma-MAMP)],并用FTIR、H1-NMR对其结构进行表征, 聚合物的分子量用凝胶渗透色谱(GPC)测定.用UV研究了其对辅酶A(Co A)的控制释放,结果表明在24℃、pH=6.8时,随着聚合物水溶液浓度的增大,对辅酶A的控制量就增多;pH在3.7～9之间变化时,可以通过调节聚合物水溶液的pH实现对辅酶A的控制释放,并初步探讨了其控制释放的机理.