Studies on polymerization of vinyl acetate using ylide as an initiator and degradative transfer agent

The polymerization of vinyl acetate initiated by β-picolinium-p-chlorophenacylide was carried out at 30, 35, and 40°C, using the conventional dilatometric technique. The initiator and the monomer exponent values were 0.80 ± 0.15 and unity, respectively. The polymerization was inhibited in the presence of hydroquinone, but was favored by nonpolar solvent and polymerization temperature. The energy of activation was 90.3 kJ mol^?1. An average value of k/k_t for the present system was found to be 0.37 × 10^?2 L mol^?1 s^?1. The results are explained in terms of radical mode of polymerization with degradative initiator transfer; the principal mode of termination, however, was biomolecular.     

Spectroscopic studies of rhodamine 6G dispersed in polymethylcyanoacrylate

We report here electronic absorption, fluorescence and resonance Raman studies of rhodamine 6G laser dye dispersed in the polymethylcyanoacrylate matrix. In the electronic absorption and fluorescence spectra of dispersed rhodamine 6G, band maxima are red shifted compared to solution. Raman spectra show some new bands. These spectral changes arise due to matrix effect and interaction between rhodamine 6G and the host material involving amine group of rhodamine.     

Mössbauer study of natural wolframites

Natural Wolframite, (Fe _x Mn_1?x )WO₄ withx=0.95 to 0.41, obtained from seven different sites of two quartz-wolframites deposits of Degana and Sirohi in Rajasthan. India, have been studied by Mössbauer spectroscopy down to 20 K. X-ray diffraction studies with a monochromatic Cu radiation (λK_a-1.5405 Å), were carried out to determine the value ofx. The Mössbauer spectra of all seven samples were recored at 300, 200, 100, 50, 40, 30 and 20 K, and were least square fitted for different sites. The Mössbauer parameters are attributed to a high spin ferrous ion in a quite distorted octahedral symmetry, and only one sextet has been resolved below transition temperature.     

Sulfate determination in lagoon water (venice) by reversed-phase ion-interaction chromatography — a method validation

The validation of a new ion-interaction chromatographic method for sulfate determination is presented by the comparison with results obtained by ionchromatography. The two procedures were employed to quantify sulfate in model solutions and in samples of Venice lagoon water. The statistical t-test for multiple samples showed no significant difference between the two methods, at the 99% confidence level.     

Conjugate polymer-based membranes for gas separation applications: current status and future prospects

Conjugate polymers provide the possibility of exploiting both the chemical and physical attributes of the polymers for membrane-based gas separation. The presence of delocalized π electrons provides high chain stiffness with low packing density, thus making the membrane a rigid structure that favors facilitated transport. Historically, the polymeric membranes were constrained by the tradeoff relationship between gas permeability and gas selectivity. So, different methods were investigated to prepare the membranes that can overcome the limitation. In recent years, electroconductive polymeric membranes have gained attention with their enhanced transportation properties combining the separation behavior depending on both molecular size discrimination as well as the facilitated transport. They offer better selectivity toward polar gases such as CO₂ because of the increased solubility. This review is aimed to provide a literature survey on gas separation using conjugate polymers such as polyaniline, polypyrrole, and some derivatives of polythiophenes. It contains various methods used by different researchers to enhance the gas separation properties of the membranes with improved mechanical and thermal stability such as changing the morphology and membrane preparation methods. In addition, it provides the pros and cons of various factors affecting the conjugate polymer membrane performance. The major challenges and future work that can be done in improving the transportation properties through the membrane to achieve viable membranes are also discussed so that they can be used for commercial and practical applications in the future.     

Partition equilibria of phenols between water and anionic micelles : Correlation with the Octanol/Water System

The partition equilibria of a series of thirty substituted phenols bearing different chemical groups between aqueous solutions and sodium dodecylsulfate micelles was investigated by using micellar high-performance liquid chromatography and by studying the variation of the acidity constant. The contribution of each substituent to the free energy of transfer from water to micelles was estimated. The group contribution approach is shown to be valid for polysubstituted compounds under well defined conditions. A comparison with partition coefficients obtained in classical two-phase system (1-octanol/water), frequently used as biochemical model systems, is discussed     

Synthesis,Characterization, and Catalysis of Water-Soluble Trimeric and Monomeric Palladium Complexes of 8-Aminoquinolines

New water soluble neutral and cationic palladium complexes were synthesized using 8-aminoquinoline (8-AQ) and 2-methyl 8-aminoquinoline (2-Me 8-AQ) ligands and their catalytic properties were evaluated. The neutral trimeric complexes having a Pd₃N₃ core were found to form when Pd(OAc)₂ was reacted with 8-AQ or 2-Me 8-AQ irrespective of the stoichiometry between the 2 reagents. Controlled addition of triflic acid to the neutral trimeric complex resulted in the formation of a trimeric cationic palladium complex as well as a monomeric cationic complex. A cationic palladium complex having two units of 2-Me-8AQ ligand was also synthesized from the cationic monomeric complex. Crystal structures of the new palladium complexes are reported in this study. The water-soluble neutral palladium complex showed catalytic activity for the oxidation of benzyl alcohols to benzaldehydes, while the cationic palladium complexes were found to be efficient catalysts for the oxidation of styrenes to methyl ketones.     

Synthesis and solid-state spectroscopic investigation of some novel diorganotin(IV) complexes of tetraazamacrocyclic ligands

The tetradendate macrocyclic ligands, [H₂L-1 = 5,12-dioxa-7,14-dimethyl-1,4,8,11-tetraazacyclotetradeca-1,8-diene] and [H₂L-2 = 6,14-dioxa-8,16-dimethyl-1,5,9,13-tetraazacyclohexadeca-1,9-diene] have been prepared by the condensation reaction of 1,2-diaminoethane and 1,3-diaminopropane, respectively, with ethyl acetoacetate in methanol at room temperature. The diorganotin(IV) complexes of general formula [R₂Sn(L-1)/R₂Sn(L-2)] (R = Me, n-Bu and Ph) have been synthesized by template condensation reaction of 1,2-diaminoethane or 1,3-diaminopropane and ethyl acetoacetate with R₂SnCl₂ (R = Me or Ph) or n-Bu₂SnO in 2:2:1 molar ratio at ambient temperature (35 ± 2 °C) in methanol. The solid-state characterization of resulting complexes have been carried out by elemental analysis, IR, recently developed DART-mass, solid-state ¹³C NMR, ^119mSn Mössbauer spectroscopic studies. These studies suggest that in all of the studied complexes, the macrocyclic ligands act as tetradentate coordinating through four nitrogen atoms giving a skew-trapezoidal bipyramidal environment around tin center. Since, the studied diorganotin(IV) macrocyclic complexes are insoluble in common organic solvents, hence good crystals could not be grown for single crystal X-ray crystallographic studies. Thermal studies of all of the studied complexes have also been carried out in the temperature range 0-1000 °C using TG, DTG and DTA techniques. The end product of pyrolysis is SnO₂ confirmed by XRD analysis.     

Poly (3,4‐ethylenedioxythiophene) γ‐Fe2O3 polymer composite–super paramagnetic behavior and variable range hopping 1D conduction mechanism–synthesis and characterization

The present paper reports the preparation of poly (3,4‐ethylenedioxythiophene) (PEDOT) ferrimagnetic conducting polymer composite by incorporation of ferrite particles in the polymer matrix by emulsion polymerization. Synthesis of PEDOT–γ‐Fe₂O₃ composite was carried out by chemical oxidative polymerization of EDOT with ferrite particles in the presence of dodecylbenzenesulfonic acid (DBSA) that works as dopant as well as surfactant in aqueous medium. The resulting conducting composite possesses saturation magnetization (Ms) value of 20.56 emu/g with a conductivity of 0.4 Scm^?1, which was determined by VSM and four probe technique, respectively. B‐H curve reveals that ferrimagnetic particles of γ‐Fe₂O₃ show super‐paramagnetic behavior at room temperature which was also observed in PEDOT–γ‐Fe₂O₃ composite. The resulting conducting ferrimagnetic composite shows microwave absorption loss of 18.7–22.8 dB in the frequency range of 12.4–18 GHz. Thermogravimetric analysis of the composite revealed that the composite is thermally stable up to 230°C. The characterization of the PEDOT–γ‐Fe₂O₃ composite was carried out using XRD and FTIR spectroscopy. Copyright © 2007 John Wiley & Sons, Ltd.     

Excess volumes for binary liquid mixtures of methylethylketone with methylene chloride, 1,2-dichloroethane, trichloroethylene, tetrachloroethylene and cyclohexane at various temperatures

Dilatometric measurements of excess volumes V^E have been made for binary liquid mixtures of methylethylketone with methylene chloride (CH₂Cl₂), 1,2-dichloroethane (CH₂ClCH₂Cl) and tetrachloroethylene (CCl₂CCl₂) at 293.15 and 303.15 K, for mixtures of methylethylketone with trichloroethylene (CHClCCl₂) at 298.15 and 308.15 K, and for mixtures of methylethylketone with cyclohexane (c-C₆H₁₂) at 303.15 K. The values of V^E have been found to be highly positive for methylethylketone + c-C₆H₁₂, slightly positive for methylethylketone + CH₂Cl₂ and methylethylketone + CCl₂CCl₂, and slightly negative for methylethylketone + CHClCCl₂ and methylethylketone + CH₂ClCH₂Cl. The results indicate the existence of specific interactions of methylethylketone with CH₂Cl₂, CH₂ClCH₂Cl, CHClCCl₂ and CCl₂CCl₂.