Molecular weight distribution formed during free‐radical polymerization in the presence of polyfunctional chain transfer agents

Free‐radical polymerization of styrene was carried out in the presence of chain transfer agents (CTAs) with functionality, f = 1–4. The size exclusion chromatography (SEC) with an ultraviolet absorption detector (UV) was used to measure the molecular weight distribution (MWD). A Monte Carlo simulation method proposed earlier was used to investigate the experimental results. In this simulation method, one can observe the structure of each polymer molecule directly, and very detailed information can be obtained in a straightforward manner, including the elution curve of SEC. It was found that up to the functionality f = 3, the equal reactivity model that assumes the reactivity of all functional groups in a CTA is equal agrees reasonably well with the experimental results. However, with f = 4, the reactivity of the fourth functional group seems to decrease and the substitution effects may need to be accounted for to fine control the formed branched structure. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1267–1275, 1999     

Direct measurement of acid-base interaction energy at solid interfaces

We have studied acid-base interactions at solid-liquid and solid-solid interfaces using interface-sensitive sum frequency generation (SFG) spectroscopy. The shift of the sapphire hydroxyl peak in contact with several polar and nonpolar liquids and polymers was used to determine the interaction energy. The trend in the interaction energies cannot be explained by measuring only water contact angles. Molecular rearrangements at the sapphire interface, to maximize the interaction of the acid-base groups, play a dominant role, and these effects are not accounted for in the current theoretical models. These results provide important insights into understanding adhesion, friction, and wetting on solid interfaces.     

Experimental study on mixing enhancement in two dimensional supersonic flow

 Studies on mixing enhancement with two dimensional (2D) lobed nozzle have been conducted in a dual stream supersonic flow facility. The distributions of momentum flux, stagnation pressure and stagnation temperature across a plane at different axial distances from the nozzle exit were considered as a measure of mixing. The results indicated an enormous enhancement in mixing when 2D lobed nozzle was employed in comparison with conventional plain 2D nozzle. The enhanced mixing performance could be attributed to the large scale axial vortices observed in the flow-field of subsonic lobed nozzles by earlier investigators. Received: 27 December 1996 / Accepted: 21 August 1997     

Synthesis,characterization, DFT calculations and antimicrobial activity of Cd(II) complexes with the condensation product of 2-quinolinecarboxaldehyde and Girard’s T reagent

The chloro (1) and isocyanato (2) Cd(II) complexes with the condensation product of 2-quinolinecarboxaldehyde and trimethylammonium acetohydrazide chloride (Girard’s T reagent) (HLCl) have been synthesized and characterized by elemental analysis, IR, and NMR spectroscopy. The crystal structure of chloro Cd(II) complex (1) was determined. In 1 and 2, coordination surrounding of Cd(II) consists of deprotonated hydrazone ligand coordinated through NNO-donor atoms and two monodentates at the rest of the coordination places. Quantum chemical calculations of the molecular structures and the relative stabilities of linkage isomers of the Cd(II) complex showed that the isomer with N–Cd–N coordination of OCN^? is the most stable. The investigated Cd(II) complexes showed lower activity than standard antimicrobial drugs.     

From Micro to Macro: A Relativistic Treatment of the Chiral Energy Shifts Caused by Static Electromagnetic Effects on Free Electrons

Free electron systems are ubiquitous in nature and have demonstrated intriguing effects in their collective interactions with weak electric and magnetic fields, especially in aqueous environments. Starting from the Dirac Hamiltonian, a fully relativistic expression is derived for the electron energy shift in the presence of a spatiotemporally constant, weak electromagnetic field. The expectation value of this energy shift is then computed explicitly using the Fourier transforms of the fermionic fields. To first order in the electromagnetic fields, the average relativistic energy shift is found to be completely independent of the electron spin-polarization coefficients. This effect is also considerably larger than that predicted in quantum mechanics by the analogous Zeeman shift. Finally, in the non-relativistic limit, it is shown how to discriminate between achiral and completely polarized states, which leads to a concluding discussion of possible mesoscopic and macroscopic manifestations of electron spin states across many orders of magnitude in the physical world, with stark implications for biological and other complex systems.     

凸柱面透镜列阵线聚焦系统

主要描述了柱面透镜列阵聚焦系统的原理及结构,分析了凹柱面透镜列阵线聚焦系统中非球面透镜损坏的原因,介绍了凸柱面透镜列阵线聚焦系统的设计原则、性能及在中日合作Ｘ射线激光实验中的使用情况     

Performance comparison of self-focusing with 1053- and 351-nm laser pulses

Hole boring characteristics of laser beams are studied using two different laser wavelengths in preformed plasmas with overdense regions. We have shown that a whole beam self-focusing is created in plasma with a considerable density scale length using a 1 microm wavelength laser. The whole beam self-focusing of this type could be used for guiding the ultrahigh intense laser pulse to a highly compressed core for studying the feasibility of a fast ignitor. There is a clear difference in the hole-boring characteristics between two laser wavelengths at 1053 and 351 nm, both in the experiment and the simulation. Using the third-harmonic laser, a whole beam self-focusing is never created. The 351-nm laser beam broke up into filaments resulting in plasma jets observed in our interferogram.     

Living carbocationic polymerization of p-halostyrenes. III. Syntheses and characterization of novel thermoplastic elastomers of isobutylene and p-chlorostyrene

Novel linear and three-arm star radial thermoplastic elastomers (TPE) comprising rubbery polyisobutylene (PIB) center blocks connected to glassy poly(p-chlorostyrene) (PpClSt) outer blocks have been synthesized by sequential monomer addition. For triblock polymer synthesis isobutylene (IB) was added continuously to a bifunctional initiating system (dicumylmethyl ether/TiCl₄) dissolved in CH₃Cl/methylcyclohexane solvent mixture at –80°C. After the living PIB sequence has reached the desired molecular weight p-chlorostyrene (pClSt) was added to produce the PpClSt end blocks. The synthesis conditions for the TPEs were developed with the help of model experiments using the 2-chloro-2,4,4-trimethylpentane (TMPCl)/TiCl₄ initiating system and subsequent PIB-PpClSt diblock syntheses. The triblock and radiol block polymers after solvent extraction exhibited excellent TPE characteristics. Copolymer compositions were determined by ¹H-NMR and UV spectroscopy and further characterization was carried out by GPC, DSC, DMTA, and selective solvent extraction techniques. The TPEs exhibit two T_g's characteristic of glassy PpClSt (129°C) and rubbery PIB (?70°C) segments. Cast TPE films were clear and gave tensile strengths of 1.2-21 MPa with elongations of 460–1500%. Transmission electron microscopy (TEM) of a triblock polymer containing ca. 38 wt % PpClSt suggests cylindrical PpClSt domains of 40–70 nm length and 25–35 nm diam embedded in a PIB matrix.     

Kinetics of initial thermal decomposition and detonation parameters-studies on RDX:TNT system

The initial low temperature thermal decomposition of various compositions in the binary system—1,3,5 trinitro-1,3,5 triazacyclohexane (RDX) and 2,4,6 trinitro toluene (TNT) has been studied using thermogravimetry, high temperature infrared spectroscopy and photomicroscopy. A linear correlation has been observed between the activation energies for the initial stage of thermal decomposition and velocity of detonation in this system.

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Zusammenfassung Mittels Thermogravimetrie, Hochtemperatur-IR-Spektroskopie und Fotomikroskopie wurde die einleitende thermische Zersetzung bei niedriger Temperatur von verschiedenen Gemischen des binären Systems von 1,3,5-Trinitro-1,3,5-triazazykIohexan (RDX) und 2,4,6 Trinitrotoluol (TNT) untersucht. Zwischen der Aktivierungsenergie des Anfangsschrittes der thermischen Zersetzung und der Detonationsgeschwindigkeit in diesem System konnte einer lineare Korrelation nachgewiesen werden.

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, 1,3,5--1,3,5 2,4,6- . .