Preparation of dye-loaded SiO2 nanoparticles

A room temperature method for the encapsulation of pyrene in SiO₂ nanoparticles is described. The relation between alkoxysilane surfactant chain length, reactant molar ratios and the uptake of dye, sample morphology, photophysical properties, and the ability of the silicate matrix to protect the encapsulated dye was examined. The synthesis can easily be adapted for the encapsulation of other hydrophobic and thermolabile substances, and used in the development of nanostructured optically active coatings, films and monoliths.     

Synthesis and application as polymer electrolyte of hyperbranched polyether made by cationic ring‐opening polymerization of 3‐{2‐[2‐(2‐hydroxyethoxy)ethoxy]ethoxymethyl}‐3′‐methyl‐oxetane

A novel cyclic ether monomer 3‐{2‐[2‐(2‐hydroxyethoxy)ethoxy]ethoxy‐methyl}‐3′‐methyloxetane (HEMO) was prepared from the reaction of 3‐hydroxymethyl‐3′‐methyloxetane tosylate with triethylene glycol. The corresponding hyperbranched polyether (PHEMO) was synthesized using BF₃·Et₂O as initiator through cationic ring‐opening polymerization. The evidence from ¹H and ¹³C NMR analyses revealed that the hyperbranched structure is constructed by the competition between two chain propagation mechanisms, i.e. active chain end and activated monomer mechanism. The terminal structure of PHEMO with a cyclic fragment was definitely detected by MALDI‐TOF measurement. A DSC test implied that the resulting polyether has excellent segment motion performance potentially beneficial for the ion transport of polymer electrolytes. Moreover, a TGA assay showed that this hyperbranched polymer possesses high thermostability as compared to its liquid counterpart. The ion conductivity was measured to reach 5.6 × 10^?5 S/cm at room temperature and 6.3 × 10^?4 S/cm at 80 °C after doped with LiTFSI at a ratio of Li:O = 0.05, presenting the promise to meet the practical requirement of lithium ion batteries for polymer electrolytes. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3650–3665, 2006     

Synthesis of poly(ethylene oxide) with pending 2,2,6,6‐tetramethylpiperidine‐1‐oxyl groups and its further initiation of the grafting polymerization of styrene

A new stratagem for the synthesis of amphiphilic graft copolymers of hydrophilic poly(ethylene oxide) as the main chain and hydrophobic polystyrene as the side chains is suggested. A poly(ethylene oxide) with pending 2,2,6,6‐tetramethylpiperidine‐1‐oxyls [poly(4‐glycidyloxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐co‐ethylene oxide)] was first prepared by the anionic ring‐opening copolymerization of ethylene oxide and 4‐glycidyloxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl, and then the graft copolymerization of styrene was completed with benzoyl peroxide as the initiator in the presence of poly(4‐glycidyloxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐co‐ethylene oxide). The polymerization of styrene was under control, and comblike, amphiphilic poly(ethylene oxide)‐g‐polystyrene was obtained. The copolymer and its intermediates were characterized with size exclusion chromatography, ¹H NMR, and electron spin resonance in detail. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3836–3842, 2006     

Guest sorption and desorption in the metal-organic framework [Co(INA)(2)] (INA=isonicotinate)--evidence of intermediate phases during desorption

The metal-organic framework [Co(INA)(2)]x0.5EtOH (INA = isonicotinate, NC(5)H(4)-4-CO(2)(-)), was synthesised under solvothermal conditions. Its X-ray crystal structure shows channels containing ethanol guests which are hydrogen-bonded to carboxylate oxygens of the framework. The pyridyl rings of the framework alternate between 'open' and 'closed' positions along the channels resulting in large variation in the channel cross-sectional area from ca. 1.4 by 2.3 A at the narrowest point to 4.9 by 5.3 A at the widest. Despite the very small windows, the ethanol guests (of van der Waals diameter ca. 4.2-6.1 A) may be reversibly desorbed and sorbed into the structure quantitatively, as shown by in situ variable-temperture IR spectroscopy and XRPD. The single-crystal structure of the desolvated form [Co(INA)(2)] shows that there is no change in the overall connectivity on desolvation, but the rotational positions of the pyridine rings are altered. This suggests that pyridyl rotation may occur to allow guests to pass in and out. When the synthesis was conducted in 1-propanol solvent [Co(INA)(2)]x0.5Pr(n)OHxH(2)O, was obtained, and a single-crystal X-ray structure revealed the same overall connectivity as in but with pyridine rings disordered over closed and open positions. There was no evidence of included guests from X-ray crystallography, suggesting that they are also highly disordered. Variable-temperature XRPD performed on bulk samples showed peaks which were unsymmetrical and exhibited shoulders, suggesting that for each pattern obtained the material actually consisted of several closely-related phases. The movements of the peaks during desolvation showed the presence of intermediate phases before the final desolvated product was formed. The peak positions of the intermediate phases matched more closely with the calculated pattern for than with or, suggesting that they may have disordered structures similar to. The results also suggest that the intermediate phase represents an initial increase in volume before a larger decrease in volume occurs to give the final desolvated material.     

Chemical constituents of Taraxacum formosanum

Three new compounds, taraxacine-A (1), taraxacine-B (2) and taraxafolin (3) together with twenty-five known compounds, which include two beta-carboline alkaloids, two indole alkaloids, two chlorophylls, two flavonoids, one coumarin, two triterpenoids, one monoterpenoid, one ionone, four steroids and eight benzenoids, were isolated and characterized from the fresh aerial parts of Taraxacum formosanum. Structures of new compounds were determined by spectral analysis.     

Application of co-eluting structural analog internal standards for expanded linear dynamic range in liquid chromatography/electrospray mass spectrometry

Non-linear standard calibration curves occur frequently in liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS), necessitating the use of non-linear regression curve fitting or a reduction in assay dynamic range. Non-linearity can be minimized by the use of stable isotope internal standards, if the cause of curve bending is ionization saturation. Unfortunately, stable isotope internal standards can be difficult or expensive to synthesize. Structural analog internal standards, if sufficiently close to analytes both in chemical structures and HPLC retention times, may mimic the effect of stable isotope internal standards. Tentative experimental evidence supporting this concept is presented in this paper.     

WATER-BLOWN POLYURETHANE RIGID FOAMS MODIFIED BY CHEMICAL PLASTICATION

1. INTRODUCTIONThese years, HCFC-141b may be the most used blowing agent for its useful properties. But, because of its high global warming effect leading to the destruction of the ozone layer, production of HCFC141b has been forbidden. However, there are…     

A Tail Measure With Variable Risk Tolerance: Application in Dynamic Portfolio Insurance Strategy

Methodology and Computing in Applied Probability - Risk measures for tail risk have an important application in the dynamic portfolio insurance strategies. We propose a new risk measure called...     

Exact solutions for Belousov-Zhabotinskii reaction-diffusion system

Abstract. We consider the following simplified model for the Belousou-Zhabotinskii(B-Z)reaction: