Synthesis and Characterization of Hybrid Silica/Polyimides Obtained by Sol-Gel Processing

This work reports the synthesis and characterization of some hybrid silica/polyimides obtained by the sol-gel process. These hybrids present good thermostability with the degradation process starting above 470°C. The glass transition temperatures of the hybrids are slightly higher than that of the pure polyimide film, while dynamic contact angles are lower than that of the pure polyimide. The experiments show that increasing the silica content improves the thermal stability and decreases the dielectric constant of the hybrid polyimide films. Moreover, increasing the silica content leads to a higher rigidity of the hybrid polyimide films, as was proved by dynamic mechanical analysis, and to a slight decrease of the dynamic contact angles.     

Synthesis of 5-Cyanoindazole and 1-Methyl and 1-Aryl-5-Cyanoindazoles

5-Cyanoindazoles are conveniently prepared in two to three steps from commercially available 5-bromo-2-fluorobenzaldehyde.     

Synthesis, characterization and tumor cell growth inhibition of new trans platinum complexes with phosphane derivatives

We have reported the synthesis and characterization of two new trans platinum complexes in the phosphane series, where the phosphane ligand is triphenylphosphine [P(Ph)₃] and the group in the trans configuration is represented by chiral aliphatic amines, (racemic in complex 1 and S-NH₂CH₂CH(CH₃)CH₂CH₃ in complex 2). The anti-proliferative activity detected in tumor cells treated with the two new complexes is more pronounced when the aliphatic amine is racemic compared to the S-enantiomer. Moreover, for both compounds, the activity is fast after cell exposure and, unlike that of cisplatin, virtually independent of the duration of cell challenge.     

Dielectric behavior of some aromatic polyimide films

Aromatic polyimides were prepared by polycondensation reaction of two aromatic diamines, such as 4,4′-diaminodiphenylmethane (DDM) and 3,3′-dimethyl-4,4′-diaminodiphenylmethane (MDDM), with aromatic dianhydrides, such as 4,4′-isopropylidene-diphenoxy-bis(phthalic anhydride) (6HDA), benzophenonetetracarboxylic dianhydride (BTDA) and hexafluoroisopropylidene-bis (phthalic anhydride) (6FDA). These polymers are soluble in polar aprotic solvents and can be cast into thin films from such solutions. The polyimides show high thermal stability, with decomposition temperature being above 430 °C in air, and high glass transition temperature being in the range of 200–287 °C. The free standing films, having the thickness of tens of micrometers, exhibited good mechanical and electrical insulating properties. The dielectric constant, molecular mobility and AC conductivity of thin films prepared from these polymers were investigated in detailed. The study of their dielectric behavior evidenced low dielectric constant values, in the range of 2.88–3.48 at 1 Hz at room temperature, and three relaxation processes (γ,β₁ and β₂) were observed at sub-glass temperatures for polyimides based on 6HDA and 6FDA and only two (γ and β) relaxations were detected for polyimides based on BTDA. The cooperativity of the molecular motions associated with the relaxation processes was discussed.     

Synthesis,Characterization and Stability of Bismaleimides Containing Ester Groups in the Backbone

Abstract

A new series of bismaleimides containing ester groups in the backbone were synthesized from maleimido benzoic acid via its acid chloride with 4,4′-(hexa-fluoroisopropilidene)diphenol, 2,7-dihydroxynaphtalin, 1,3-dihydroxy-benzene and 4-hydroxyphenyl sulfone by simple condensation reaction. The monomers are characterized by IR, ¹H-NMR and elemental analysis. DSC studies of these bismaleimides indicated a curing exotherm in the temperature range 260–306°C with polymerization heat 92.9–139.6 J/g. Thermogravimetric analysis of the monomers showed high thermal stability for all bismaleimides.     

Multi-Level Robustness Evaluation Approach: From Robustness Criterion to Adapted Algorithm of Dong

This paper proposes an innovative concept for robustness evaluation guided by two crucial aims: indubitable identification of the factors that significantly affect the LC method and avoidance of unnecessary time and money wasting. The first phase of the proposed strategy includes robustness screening during the method optimization. Initial assumptions of the method robustness can be tracked as the rate of the response change while the factors deviate within the expected range. Therefore, partial and total robustness criteria are calculated. If the results obtained are not satisfactory, re-optimization of the method should be considered. Otherwise, extensive robustness testing defined by experimental design and multi-level factors estimation should be performed to confirm the method robustness. Firstly, the important factors are investigated by the standard graphical (normal probability plots) and statistical (algorithm of Dong and error estimation based on a priori declared negligible effects) procedures. Since these approaches have several drawbacks, they can result in the appearance of false negative or false positive results. Thus, the modification of the statistical tests is advised in order to make the final conclusions. Special attention was dedicated to the advantages of the adapted algorithm of Dong (so-called 75 % approach) in the absence of the effect sparsity. The new approach is presented on the optimization and robustness testing of LC method for determination of ramipril and its five impurities. It is proved that the proposed strategy can perform an overall robustness estimation and successfully reveal all important factors.     

Change of microstructure of polyimide thin films under the action of supercritical carbon dioxide and its influence on the transport properties

Thin films of four polyimides of various structures having ether, isopropylidene or hexafluoroisopropylidene groups in their repeating units, which had been synthesized in meta-cresol, were treated with supercritical carbon dioxide and their gas transport properties, were investigated. Transport parameters, (permeability and selectivity coefficients) measured before and after treatment with supercritical carbon dioxide, increased from 16 to 168 % and from 5 to 49 %, respectively.     

Some σ-double sequence spaces defined by Orlicz function

In this paper we introduce some new double sequence spaces using the notions of invariant mean and Orlicz function. We also examine some properties of the resulting sequence spaces.     

Adsorption of naphthalene onto sonicated talc from aqueous solutions

The adsorption behavior of naphthalene onto naturally hydrophobic talc from aqueous solution was investigated in this study. The natural talc was first pretreated by sonication to improve the surface characteristics and enhance the uptake capacity by increasing the specific surface area (SSA) of talc. The naphthalene uptake of talc was found as 276 mg g^?1 and increased to 359 mg g^?1 after the sonication. Adsorption studies also showed that the adsorption of naphthalene onto the sonicated talc was not affected by changes in pH suggesting that the main driving forces for naphthalene adsorption onto talc was hydrophobic bonding rather than electrostatic force. The pseudo-first and pseudo-second orders and intraparticle diffusion equation were used to evaluate the kinetic data and the constants were determined. Adsorption process of naphthalene onto talc followed the pseudo-second-order rate expression for different initial naphthalene concentrations. The Langmuir and Freundlich isotherm models were used to model the isotherm data for their applicability. The Freundlich isotherm best fitted for the adsorption of naphthalene onto talc.     

Δ-Strongly summable sequences spaces in 2-normed spaces defined by ideal convergence and an Orlicz function

In this paper, we study certain new difference sequence spaces using ideal convergence and an Orlicz function in 2-normed spaces and we give some relations related to these sequence spaces.