AFM study of morphological development during the melt-crystallization of poly(ethylene oxide)

The atomic force microscope (AFM) has been used to investigate morphological development during the crystallization of poly(ethylene oxide) (PEO) from the melt. PEOs with molecular weights of 1 × 10⁵ and 7 × 10⁶ were used. Height and amplitude images were recorded, using the tapping mode. For both polymers, the mode of spherulite development varied with the velocity of the growth front. For slow growth velocities, the growth of the crystallites was linear, with growth initially occurring by single lamellae, later developing into growth arms by screw dislocation spawning of crystallites. At intermediate growth velocities, stacks of lamellae develop rapidly. The splaying apart of adjacent crystals and growth arms is abundant. The operation of growth spirals was observed directly in this growth velocity range. The crystals formed by the giant screw dislocations diverge immediately from the original growth direction, providing a source of interlamellar splaying. At low and intermediate velocities, the front propagates by the advance of primary growth arms, with the regions between the arms filled in by arms growing behind the primary front. At the highest velocity observed here, the formation of lamellar bundles and immediate splaying results in recognizable spherulites developing at the earliest stages of crystallization. The change from linear growth to splaying and nonlinear growth are qualitatively explained in terms of driving force, elastic resistance and the presence of compositional and/or elastic fields in the melt. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2311–2325, 1998     

用长气体靶研究22Na+α共振散射

在日本东京大学CRIB 次级束装置上,用长气体靶开展了22Na+ α共振散射的厚靶实验研究。针对长气体靶实验中的两体运动学重构问题,提出了一套包括构建空间复杂几何关系、计算能量损失以及反应运动学的逐事件分析方法;对22Na+α共振散射的实验数据进行了重构分析,得到了E_c.m. = 4.2 ~ 5.4 MeV 区间22Na( α,α ) 的激发函数,从实验的激发函数中观测到了复合核26Al 5 个较为明显的共振峰。鉴于26Al 共振态的衰变模式比较复杂,本工作发现的26Al新共振态的能级性质有待进一步的理论分析。The 22Na+α resonant scattering is studied via a conventional thick target inverse kinematic method with an extended gas target. A data analysis method is proposed for the two-body reaction kinematic reconstruction, in which the spatial geometry, the reaction kinematics and the energy losses are considered. The experimental data of 22Na+ αresonant scattering have been thus reconstructed, and the excitation function is obtained in the energy interval of Ec.m. =4.2~5.4 MeV. Five resonant states in 26Al are observed in the experimental excitation function. Since several decay modes coexist for the observed 26Al resonant states, multi-channel theoretical analysis is thus needed to reveal their structure and decay features.     

On the molecular mechanism of the crystal transformation (tetragonal-hexagonal) in polybutene-1

The phase transformation from the tetragonal to the hexagonal crystal modification in highly oriented lamellae of poly-butene-1 has been followed by transmission electron microscopy (TEM). It is found that the reaction-controlling step is the nucleation process. No lattice orientation relationship (besides the [001]-direction, which is parallel in both crystal modifications) exists between non-transformed and transformed crystals. The nucleation is strongly enhanced by thermal or external stresses. Crystal growth, nucleated by external stresses, was observed at temperatures as low as — 150°C. The molecular mechanisms of the transformation are discussed.     

Optimisation of a key cross-coupling reaction towards the synthesis of a promising antileishmanial compound

During the course of a research program aimed at identifying novel antileishmanial compounds, a multi-gram synthesis of N-(trans-4-((4-methoxy-3-((R)-3-methylmorpholino)-1H-pyrazolo[3,4-d]pyrimidin-6-yl)amino)cyclohexyl)-2-methylpropane-1-sulfonamide ((R)-1) was required. This letter describes optimisation of the reaction conditions and protecting group strategy for a key Buchwald-Hartwig coupling, delivering the required quantities of (R)-1, as well as further compounds in the series.     

Selective Cleavage of β-Keto and Vinylogous β-Keto Esters by 3-Quinuclidinol

As a result of a continuing study utilizing nitrogenous bases^2–6, we now wish to report that the base 3-quinuclidinol (13) is useful for the cleavage of β-keto and vinylogous β-keto esters.     

Total Synthesis of (6R,10R,13R,14R,16R,17R,19S,20R,21R,24S, 25S,28S,30S,32R,33R,34R,36S,37S,39R)‐Azaspiracid‐3 Reveals Non‐Identity with the Natural Product

A convergent and stereoselective total synthesis of the previously assigned structure of azaspiracid‐3 has been achieved by a late‐stage Nozaki–Hiyama–Kishi coupling to form the C21?C22 bond with the C20 configuration unambiguously established from l ‐(+)‐tartaric acid. Postcoupling steps involved oxidation to an ynone, modified Stryker reduction of the alkyne, global deprotection, and oxidation of the resulting C1 primary alcohol to the carboxylic acid. The synthetic product matched naturally occurring azaspiracid‐3 by mass spectrometry, but differed both chromatographically and spectroscopically.     

Terahertz Transmission Spectroscopy of Nonpolar Materials and Relationship with Composition and Properties

Terahertz time-domain spectroscopy is used to study properties of non-polar materials. Terahertz absorption spectra and refractive indices are measured in a number of glasses, lubricating oils, and types of paper. The results are correlated with material properties.