A novel type of Si-containing poly(urethane-imide)s: synthesis, characterization and electrical properties

A novel type of a Si-containing poly(urethane-imide) (PUI) was prepared by two different methods. In the first method, Si-containing polyurethane (PU) prepolymer having isocyanate end groups was prepared by the reaction of diphenylsilanediol (DSiD) and toluene diisocyanate (TDI). Subsequently the PU prepolymer was reacted with pyromellitic dianhydride (PMDA) or benzophenonetetracarboxylic dianhydride (BTDA) in N-methyl pyrolidone (NMP) to form Si-containing modified polyimide directly. In the second method, PU prepolymer was reacted with diaminodiphenylether (DDE) or diaminodiphenylsulfone (DDS) in order to prepare an amine telechelic PU prepolymer. Finally, the PU prepolymer having diamine end groups was reacted with PMDA or BTDA to form a Si-containing modified polyimide. Cast films prepared by second method were thermally treated at 160 °C to give a series of clear, transparent PUI films. Thermogravimetric analysis indicated that the thermal degradation of PUI starts at 265 °C which is higher than degradation temperature of conventional PU, confirming that the introduction of imide groups improved the thermal stability of PU.To characterize the modified polyimides and their films, TGA, FTIR, SEM and inherent viscosity analyses were carried out. The dielectrical properties were investigated by the frequency-capacitance method. Dielectric constant, dielectric breakdown strength, moisture uptake and solubility properties of the films were also investigated.     

Synthesis and Comparison of Extraction Properties of p‐tert‐Butylcalix[n]arene Nitrile Derivatives for Selected Metals and Dichromate Anions

The article describes the syntheses and extraction properties of two p‐tert‐butylcalix[6]arene nitrile derivatives (3 and 4). The trinitrile derivative 3 has been synthesized from 5,11,17,23,29,35‐hexa‐tert‐butyl‐37,38,39,40,41,42‐hexahydroxycalix[6]arene 1. The compound 1 was directly converted to its hexanitrile derivative 4. In these syntheses, it was thought to explore the role of nitrile sites in the extraction of various metal cations and HCr₂O₇ ^?/Cr₂O₇ ^2? anions. The liquid‐liquid extraction properties of 3 and 4 towards selected alkali/transition metal cations and HCr₂O₇ ^?/Cr₂O₇ ^2? anions are reported. It has been observed that receptor 3 does not extract alkali/transition metal cations effectively, but shows affinity towards HCr₂O₇ ^?/Cr₂O₇ ^2? anions at low pH. The compound 4 is an effective form for transferring Ni²⁺ selectively, while it shows poor transferring ability for HCr₂O₇ ^?/Cr₂O₇ ^2? anions from an aqueous into a dichloromethane layer. It was observed that the cavity size of the calix[n]arenes and the cooperativity of the functionalities play important roles in two phase extraction systems.     

Preparation and characterization of sulfonated polyimide ionomers via post‐sulfonation method for fuel cell applications

This paper describes our work on the synthesis of a series of sulfonated homo‐/co‐polyimides (SPI) which were obtained by post‐sulfonation method over three steps. In the first step, 4,4′‐oxydianiline (ODA) and 4,4′‐diaminodiphenylsulfone (DDS) dissolved in N‐methyl pyrrolidone (NMP) were reacted with benzophenonetetracarboxylic dianhydride (BTDA) in order to yield poly(amic acid) (PAA). Secondly, precipitated PAA was sulfonated via concentrated sulfuric acid (95–98%) at room temperature to give post‐sulfonated PAA (PSPAA). Finally, PSPAA was converted into post‐sulfonated PI (PSPI) by the thermal imidization method. PSPIs with ion exchange capacity (IEC) ranging from 0.20 to 0.67 meq/g were prepared. The thermal properties of the PSPIs were evaluated and high desulfonation temperature was found in the range of 190–350°C, suggesting the high stability of sulfonic acid groups. In water, PSPI‐5 membrane displayed similar proton conductivity to Nafion®117, whereas this membrane showed poor conductivity in dry state. All PSPIs displayed good solubility in common polar aprotic solvents such as NMP and dimethylacetamide (DMAc). Furthermore, the effects of post‐sulfonation reaction on chemical structure, thermal oxidative behavior, and physical properties of the PSPI membranes such as membrane quality/stability and water uptake were discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

Investigation of Metal Ion Removal Selectivity Properties of the Modified Polyacrylamide Hydrogels Prepared by Transamidation and Hofmann Reactions

Modified crosslinked polyacrylamides having different functional groups prepared by transamidation reaction in aqueous and non‐aqueous medium and by Hofmann reaction were used as chelating agents for removal of Cu(II), Cd(II) and Pb(II) ions from aqueous solutions at different pH values. Under non‐competitive conditions, polymers adsorbed different amounts of metal ions, depending on their functional groups and swelling abilities. The metal ion adsorption capacities of polymers changed between 0.11–1.71 mmol/g polymer. Under competitive conditions, while the polymers having mainly secondary amine groups were highly selective for Cu(II) ions (99.4%), those having mainly secondary amide and carboxylate groups have shown high selectivity towards Pb(II) ions (99.5%). The selectivity towards Cu(II) ion decreased and Pb(II) ion selectivity increased by the decrease of the pH of the solutions. The high initial adsorption rate (<10 min) suggests that the adsorption occurs mainly on the polymer surface. A regeneration procedure by treatment with dilute HCl solution showed that the modified polymers could be used several times without loss of their adsorption capacities.     

A New Chemometric Strategy in Electrochemical Method Optimization for the Quantification of Cefdinir in Tablets,Effervescent Tablets and Suspension Samples

A new voltammetric method, based on the use of single‐use pencil graphite electrode, was developed for the quantitative determination of cefdinir by square wave voltammetry. Chemometric optimization strategy was used to select the suitable values for three experimental parameters (pH of the supporting electrolyte, frequency and square wave amplitude) by applying a 3³ full factorial design model. The optimal voltammetric conditions were found to be pH 5.0 for supporting electrolyte (Britton‐Robinson buffer), 43 mV for square wave amplitude and 108 Hz for frequency. Square wave voltammograms of calibration, validation and unknown samples were recorded between 0.0–1400 mV under the optimized voltammetric conditions. Linear regression equation was computed in the linear working range of 0.5–20 μg/mL by using the relationship between the concentration and peak current at 600 mV. The optimized voltammetric method was validated by assessing the analysis results of validation samples. Then the proposed method was applied for the quantitative determination of cefdinir in three different pharmaceutical preparations, namely film‐coated tablets, effervescent tablets and powder for oral suspension. It was concluded that the proposed voltammetric method was suitable for the quantitative analysis of commercial pharmaceutical preparations containing cefdinir.     

Admissible equivalence transformations for linearization of nonlinear wave type equations

In the present paper, we consider a general family of two‐dimensional wave equations, which represents a great variety of linear and nonlinear equations within the framework of the transformations of equivalence groups. We have investigated the existence problem of point transformations that lead mappings between linear and nonlinear members of particular families and determined the structure of the nonlinear terms of linearizable equations. We have also given examples about some equivalence transformations between linear and nonlinear equations and obtained exact solutions of nonlinear equations via the linear ones.     

Characterization of paraben substituted cyclotriphosphazenes,and a DNA interaction study with a real-time electrochemical profiling based biosensor

Microchimica Acta - This paper describes an amperometric method for studying DNA-drug candidate interactions. It uses an automatted electrochemical biosensor (MiSens®) based on real-time...     

The impact of futures trading on volatility of the underlying asset in the Turkish stock market

This paper examines the impact of the introduction of stock index futures on the volatility of the Istanbul Stock Exchange (ISE), using asymmetric GARCH model, for the period July 2002-October 2007. The results from EGARCH model indicate that the introduction of futures trading reduced the conditional volatility of ISE-30 index. Results further indicate that there is a long-run relationship between spot and future prices. The results also suggest that the direction of both long- and short-run causality is from spot prices to future prices. These findings are consistent with those theories stating that futures markets enhance the efficiency of the corresponding spot markets.     

Implementation and Evaluation of Age-Aware Downlink Scheduling Policies in Push-Based and Pull-Based Communication

As communication systems evolve to better cater to the needs of machine-type applications such as remote monitoring and networked control, advanced perspectives are required for the design of link layer protocols. The age of information (AoI) metric has firmly taken its place in the literature as a metric and tool to measure and control the data freshness demands of various applications. AoI measures the timeliness of transferred information from the point of view of the destination. In this study, we experimentally investigate AoI of multiple packet flows on a wireless multi-user link consisting of a transmitter (base station) and several receivers, implemented using software-defined radios (SDRs). We examine the performance of various scheduling policies under push-based and pull-based communication scenarios. For the push-based communication scenario, we implement age-aware scheduling policies from the literature and compare their performance with those of conventional scheduling methods. Then, we investigate the query age of information (QAoI) metric, an adaptation of the AoI concept for pull-based scenarios. We modify the former age-aware policies to propose variants that have a QAoI minimization objective. We share experimental results obtained in a simulation environment as well as on the SDR testbed.     

Removal of Phenol by Using Montmorillonite,Clinoptilolite and Hydrotalcite

This work is to study the removal of phenol from aqueous solutions by adsorption using three different adsorbents, clinoptilolite, montmorillonite, and hydrotalcite (HT). Except for montmorillonite, the other adsorbents were treated. Clinoptilolite was modified using cetyltrimethylammonium bromide (CTAB) and hydrotalcite was calcined by heating to 550C. Adsorption isotherms of phenol on all of the mentioned adsorbents was determined by using the batch equilibration technique and indicated that, the adsorption behavior could be modelled by using the Modified Freundlich equation. The differences observed in the isotherms were explained by the variations in adsorbent-adsorbate interactions under the effects of the different surface structures of adsorbents and the pH dependent ionization behavior of phenol. Calcined hydrotalcite (HTC) was found to be the best among the studied adsorbents since it can adsorb 52% of phenol from a solution containing initially 1 g/L phenol for the 1/100 adsorbent solution ratio while the others can adsorb only 8% of phenol for the same concentration and adsorbent solution ratio.