Synthesis and Characterization of Thermally Curable Benzoxazine‐Functionalized Polystyrene Macromonomers

Summary: Thermally curable benzoxazine ring‐containing polystyrene macromonomers were synthesized and characterized. 1,4‐Dibromo‐2,5‐bis(bromomethyl)benzene and 1,4‐dibromo‐2‐(bromomethyl)benzene were used as initiators in the atom transfer radical polymerization of styrene. The resulting polymers were used in combination with 3‐aminophenylboronic acid hemisulfate, for a Suzuki coupling. The obtained polymers, with amino groups in the middle or end of the chains, were reacted with formaldehyde and phenol to yield benzoxazine ring‐containing macromonomers. In addition to the glass transition temperature of the polystyrene segment observed at ca. 105 °C, differential scanning calorimetry thermograms exhibit an exotherm at ca. 276 °C corresponding to the oxazine thermal polymerization. Both macromonomers undergo thermal curing with the formation of thermosets having polystyrene segments.

Structure of the benzoxazine‐functionalized polystyrene.     

Diamminebis(2,4,6‐tribromophenolato‐O)copper(II)

The title compound, [Cu(C₆H₂Br₃O)₂(NH₃)₂], a monomeric centrosymmetric Cu^II complex, crystallizes in the monoclinic system. The CuO₂N₂ coordination sphere is trans planar, [Cu—O 1.943 (5) Å and Cu—N 1.977 (6) Å], with the fifth and sixth coordination sites occupied by Br atoms from the phenoxide ions [Cu—Br 3.129 (1) Å], resulting in an elongated distorted octahedral structure for the CuO₂N₂Br₂ coordination. Each of the NH₃ groups forms two hydrogen bonds with the Br and O atoms of the CuO₂N₂Br₂ moiety of a neighbouring mol­ecule. This arrangement constitutes a one‐dimensional chain along the x axis of the unit cell.     

High Performance Liquid Chromatography for the Determination of Metoclopramide in Pharmaceutical Preparations Using Pre‐column Derivatization with Fluorescamine

A simple, rapid and sensitive high performance liquid chromatography (HPLC) method was developed for the determination of metoclopramide in pharmaceutical preparation. The method is based on the derivatization of metoclopramide with fluorescamine. The separation was achieved on a C₁₈ column using methanol‐water (70:30, V/V) mobile phase. Fluorescence detector was used at the excitation and emission of 403 and 485 nm, respectively. The method was validated for linearity, limit of detection, limit of quantification, precision, accuracy, recovery, robustness and system suitability. The assay was linear over the concentration range of 100–2000 ng/mL. The mean recovery was 100.37%. The proposed method was successfully applied to the assay of metoclopramide in tablet preparation. The preparation was also analyzed with an official method and statistical comparison by t‐ and F‐tests revealed that there was no significant difference between the results of the two methods with respect to mean values and standard deviations at the 95% confidence level.     

Stabilization of a viscoelastic Timoshenko beam

A viscoelastic Timoshenko beam is investigated. We prove an exponential decay of solutions for a large class of kernels with weaker conditions than the existing ones in the literature. This will allow the use of other types of viscoelastic material for Timoshenko type beams than the usually used ones.     

Optical response of Lorentzian nanospheres in the quasistatic limit

Significance of the Lorentzian dispersion relationship in controlling the optical response of the nanospheres surrounded by a homogeneous non-absorbing dielectric medium is examined. Nanospheres with size much smaller than the wavelength of the incident light are considered as prototype systems that can cover the generic optical response of Lorentzian nanoparticles. Absorption cross-section of the Lorentzian nanospheres is treated in the quasistatic approximation of classical electrodynamics and the resulting optical resonance is evaluated in terms of its dependencies on the parameters of the system. It has been illustrated that the underlying dispersion governs both the amount and the direction of the shift experienced by the optical resonance of nanospheres. Contrary to Drude nanospheres (well-known red shifters), Lorentzian nanospheres are shown to be blue shifters of the optical resonance. The amount of blue shift is dominated by the increase in the oscillator strength of the nanosphere material. Embedding media with higher dielectric constant and/or materials with larger high frequency dielectric constant lead to a suppression of the amount of blue shift induced by the oscillator strength. Further quantification of the blue shift characteristics against the red shift characteristics of Drude nanospheres is provided. The results can be instrumental for manipulating the optical response of plexcitonic nanophotonic devices.     

Analytical solutions of a class of inverse coefficient problems

This paper is devoted to some class of inverse coefficient problems. By using a well-known transformation, the inverse problem is transformed to a new problem without the unknown time dependent coefficient. Therefore, the new inverse problem can be solved easily. To show the efficiency of the present method, some examples are presented.     

Photophysical properties of PPP and PPV derivatives bearing polystyrene or polycaprolactone as side groups

This contribution reports on detailed photophysical investigations of poly(p-phenylene) PPP and poly(p-phenylene-vinylene) (PPV) derivatives laterally decorated with polystyrene (PPV-PSt) or poly(ε-caprolactone) (PPP-PCL, PPP-altPCL, PPV-PCL and PPV-PCL-Br). The polymers emit blue and exhibit very high relative and absolute photoluminescence quantum yield, Φ_f, in dilute solution, thin film (spin-coated and inkjet-printed) and bulk state. This is ascribed to the presence of the lateral macromolecules, which suppress the strong π-π interactions and consequently excimers formation. Lower Φ_f value was obtained for the bromine containing polymer and its corresponding model compound dibromodistyrylbenzene Br₂-DSB, which was ascribed to heavy atom effect enabling intersystem crossing from S₁ to T₁. However, studies at 77 K did not reveal phosphorescence, in contrast an enhancement of the fluorescence intensity with respect to room temperature measurement was observed.     

A rapid and highly sensitive spectrofluorimetric method for the determination of venlafaxine by charge transfer complexation reaction with <Emphasis Type="Italic">p</Emphasis>-bromanil and <Emphasis Type="Italic">p</Emphasis>-chloranil

Simple, rapid and highly sensitive spectrofluorimetric methods were developed for the determination of venlafaxine in pure and pharmaceutical preparations. The proposed methods were based on the reaction of venlafaxine as n-electron donor with π-acceptors namely, p-bromanil and p-chloranil. The method for the determination of venlafaxine over a concentration range of 5–100 and 5–150 ng/mL, for p-bromanil and p-chloranil methods, respectively. The intra- and inter-day precisions were satisfactory, the relative standard deviations did not exceed 1.69%. The proposed method was successfully applied to the determination of venlafaxine in its pharmaceutical preparations with good accuracy; the mean recovery percentages were 99.80%. The results were compared favorably with those of the reference method.     

Pyridine-2,5-dicarboxylic acid complexes of nickel(II) with 2,2′-bipyridine and 1,10-phenanthroline coligands; syntheses,crystal structures,spectroscopic and thermal studies

Two pyridine-2,5-dicarboxylic acid (pydcH₂) complexes of nickel(II) with 2,2′-bipyridine and 1,10-phenanthroline were synthesized and characterized by elemental, spectroscopic, thermal analysis, magnetic measurements and single crystal X-ray diffraction techniques. Both [Ni(pydc)(bipy)₂]·7H₂O and [Ni(pydc)(phen)₂]·6.5H₂O crystallize in the monoclinic system and P2₁/c space group. The Ni(II) ions are coordinated by two bidentate bipy or phen ligands and one pydc dianion in a distorted octahedral geometry. The pydc ligand is coordinated through the pyridine nitrogen atom and oxygen atom of carboxyl group as a bidentate ligand. Both carboxylate groups of pydc are deprotonated but only the 2-carboxylate is coordinated to the metal. Thermal decompositions of the complexes have been studied over the range 30–600 °C on heating in a static air atmosphere.