Statistical fluorinated copolymers from heterogeneous atom transfer radical copolymerization of styrene and 2,2,2‐trifluoroethyl methacrylate with similar reactivity ratios

Fluorinated copolymers with statistical structure of azeotropic or gradient composition were prepared from heterogeneous atom transfer radical copolymerizations of styrene (S) and 2,2,2‐trifluoroethyl methacrylate (T). The polymerization kinetic studies show that while the propagation rate constant of S increased with a decreasing S content in the comonomer feed ratio, the propagation rate of T decreased with decreases of the S content in the comonomer feed ratio. The polymerization rate and controllability of the heterogeneous ATRP of S and T were regulated by the solubility of Cu(II)/ligand in the reaction mixture, based on a mechanistic analysis and solubility tests of the Cu(II)/ligand system in the reaction media. The reactivity ratios of S and T were 0.22 and 0.35, as evaluated from kinetic analysis of monomer conversions higher than 35%. These statistical polymers self‐assembled in T to form giant vesicles GVs) with broad diameter distribution in the range of 1–10 μm. Unlike the methods normally used to prepare gradient copolymers by spontaneous controlling with feeding model or batch polymerization of comonomers with obvious differences in the reactivity ratio, in this contribution, we report a novel synthetic strategy for preparing gradient copolymers can also be prepared from both monomers with very similar reactivity ratio. © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Steric hindrance effect on thermo‐responsive behaviors of well‐defined water‐soluble semi‐rigid polymers

Three series of water‐soluble semi‐rigid thermo‐responsive polymers with well‐defined molecular weights based on mesogen‐jacketed liquid crystal polymers, poly[bis(N‐(2‐hydroxypropyl) pyrrolidone) 2‐vinylterephthalate] [P(2‐HPPVTA)], poly[bis(N‐(1‐methyl‐2‐hydroxyethyl) pyrrolidone) 2‐vinylterephthalate] [P(1‐M‐2‐HEPVTA)] and poly[bis(N‐hydroxypropyl pyrrolidone) 2‐vinylterephthalate] (PHPPVTA) have been synthesized via reversible addition‐fragmentation chain transfer polymerization. The steric hindrance effects on liquid crystalline property and thermo‐responsive behaviors of semi‐rigid water‐soluble polymers (P(2‐HPPVTA), P(1‐M‐2‐HEPVTA), and PHPPVTA) were carefully investigated. From molecular structure, the steric hindrance of P(1‐M‐2‐HEPVTA) is stronger than that of P(2‐HPPVTA). Polarized light microscope and one‐dimensional wide‐angle X‐ray diffraction revealed that both the P(2‐HPPVTA) and P(1‐M‐2‐HEPVTA) display a columnar nematic phase, indicating that the steric hindrance effect do not affect liquid crystalline behavior of the polymers. The dynamic light scattering results demonstrated that P(1‐M‐2‐HEPVTA) exhibited lower cloud point compared with that of P(2‐HPPVTA) at the same mass concentration and the same molecular weight. The more significant molecular weight and concentration dependence on cloud point have been observed in P(2‐HPPVTA) solution than in P(1‐M‐2‐HEPVTA) solution. We also discovered that the cloud points of both P(2‐HPPVTA) and P(1‐M‐2‐HEPVTA) solution are lower in D₂O than in H₂O. It is noted that the cloud point of PM‐2 is 9.9 °C lower in D₂O than in H₂O, much less pronounced than the cloud point difference of PH‐2. The differences of thermo‐responsive behaviors between P(2‐HPPVTA) and P(1‐M‐2‐HEPVTA) were resulted from the steric hindrance effect existed in their side groups. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013 , 51, 3429–3438     

A PDE approach to risk measures of derivatives

This paper proposes a partial differential equation (PDE) approach to calculate coherent risk measures for portfolios of derivatives under the Black-Scholes economy. It enables us to define the risk measures in a dynamic way and to deal with American options in a relatively effective way. Our risk measure is based on the representation form of coherent risk measures. Through the use of some earlier results the PDE satisfied by the risk measures are derived. The PDE resembles the standard Black-Scholes type PDE which can be solved using standard techniques from the mathematical finance literature. Indeed, these results reveal that the PDE approach can provide practitioners with a more applicable and flexible way to implement coherent risk measures for derivatives in the context of the Black-Scholes model.     

DISSIPATION AND DISPERSION APPROXIMATION TO HYDRODYNAMICAL EQUATIONS AND ASYMPTOTIC LIMIT

The compressible Euler equations with dissipation and/or dispersion correction are widely used in the area of applied sciences, for instance, plasma physics, charge transport in semiconductor devices, astrophysics, geophysics, etc. We consider the compressible Euler equation with density-dependent （degenerate） viscosities and capillarity, and investigate the global existence of weak solutions and asvmototic limit.     

Metal-Mediated Controllable Creation of Secondary, Tertiary, and Quaternary Carbon Centers: A Powerful Strategy for the Synthesis of Iron, Cobalt, and Copper Complexes with in Situ Generated Substituted 1-Pyridineimidazo[1,5-a]pyridine Ligands

An efficient strategy for the synthesis of a wide variety of coordination complexes has been developed. The synthetic protocol involves a solvothermal in situ metal-ligand reaction of picolinaldehyde, ammonium acetate, and transition-metal ions, leading to the generation of 12 coordination complexes supported by a novel class of substituted 1-pyridineimidazo[1,5-a]pyridine ligands (L1-L5). The ligands L1-L5 were afforded by metal-mediated controllable conversion of the aldehyde group of picolialdehyde into a ketone and secondary, tertiary, and quaternary carbon centers, respectively. Complexes of various nuclearities were obtained: from mono-, di-, and tetranuclear to 1D chain polymers. The structures of the in situ formed complexes could be controlled rationally via the choice of appropriate starting materials and tuning of the ratio of the starting materials. The plausible mechanisms for the formation of the ligands L1-L5 were proposed.     

On the decomposition of the absolute ruin probability in a perturbed compound Poisson surplus process with debit interest

We consider a compound Poisson surplus process perturbed by diffusion with debit interest. When the surplus is below zero or the company is on deficit, the company is allowed to borrow money at a debit interest rate to continue its business as long as its debt is at a reasonable level. When the surplus of a company is below a certain critical level, the company is no longer profitable, we say that absolute ruin occurs at this situation. In this risk model, absolute ruin may be caused by a claim or by oscillation. Thus, the absolute ruin probability in the model is decomposed as the sum of two absolute ruin probabilities, where one is the probability that absolute ruin is caused by a claim and the other is the probability that absolute ruin is caused by oscillation. In this paper, we first give the integro-differential equations satisfied by the absolute ruin probabilities and then derive the defective renewal equations for the absolute ruin probabilities. Using these defective renewal equations, we derive the asymptotical forms of the absolute ruin probabilities when the distributions of claim sizes are heavy-tailed and light-tailed. Finally, we derive explicit expressions for the absolute ruin probabilities when claim sizes are exponentially distributed.     

Optimization of extraction of evodiamine and rutaecarpine from fruit of Evodia rutaecarpa using modified supercritical CO(2)

Evodiamine and rutaecarpine have been intensively studied due to their pharmacological actions and clinical applications. In this report, supercritical fluid was used to extract evodiamine and rutaecarpine from the unripe fruit of Evodia rutaecarpa. Response surface methodology using Box-Behnken experimental design was utilized to optimize parameters for supercritical carbon dioxide extraction with methanol as co-solvent. The effect of various values of dynamic extraction time (30-90min), temperature (50-70°C) and pressure (200-400bar) on extraction yields of the two compounds was evaluated. Determinations of the extracts were performed by high-performance liquid chromatography. The experimental data obtained were fitted to second-order polynomial equations and analyzed by analysis of variance. The highest yields predicted were 1.217mg/g for evodiamine and 0.969mg/g for rutaecarpine at the optimal values (time 78min, temperature 62°C, pressure 280bar and co-solvent flow rate 0.4mL/min), based on the selected range of experimental conditions.     

Metal-enhanced fluorescence of carbon nanotubes

The photoluminescence (PL) quantum yield of single-walled carbon nanotubes (SWNTs) is relatively low, with various quenching effects by metallic species reported in the literature. Here, we report the first case of metal enhanced fluorescence (MEF) of surfactant-coated carbon nanotubes on nanostructured gold substrates. The photoluminescence quantum yield of SWNTs is observed to be enhanced more than 10-fold. The dependence of fluorescence enhancement on metal-nanotube distance and on the surface plasmon resonance (SPR) of the gold substrate for various SWNT chiralities is measured to reveal the mechanism of enhancement. Surfactant-coated SWNTs in direct contact with metal exhibit strong MEF without quenching, suggesting a small quenching distance for SWNTs on the order of the van der Waals distance, beyond which the intrinsically fast nonradiative decay rate in nanotubes is little enhanced by metal. The metal enhanced fluorescence of SWNTs is attributed to radiative lifetime shortening through resonance coupling of SWNT emission to the reradiating dipolar plasmonic modes in the metal.     

Improved dehydrogenation properties of Ca(BH4)2-LiNH2 combined system

Ca(BH(4))(2)-LiNH(2) combined system is shown to release hydrogen at much lower temperature compared to the pure Ca(BH(4))(2). The improved dehydrogenation in this system can be ascribed to a combination reaction between [BH(4)] and [NH(2)] based on the reaction mechanism of positive H and negative H.