Study of the reactions of pyridinium poly(hydrogen fluoride) with some ternary oxides

The products of the reaction of pyridinium poly(hydrogen fluoride), PPHF, with KIO3, Na2SnO3, NaBiO3, K2CrO4, Na2MoO4 and Na2WO4 were KIO2F2; Na2SnF6; NaHF2, BiF3; K3CrF6, KHF2, (PyH)(3)CrF6; NaHF2, (PyH)(2)MoO2F4.2NaHF(2); and (PyH)(2)WO2F4.2NaHF(2), respectively, while KClO3, KBrO3 and KlO(4) react with complete decomposition to form KHF2 as the fluorinated product. This differential reactivity and mode of reaction has been discussed in terms of the oxidation state of the central atom, the nature and strength of the bonds and the complex behaviour of the formed intermediate or fluorinated products that undergo complexation or solvation with pyridine and/or hydrogen fluoride.

Dynamic Behavior of Poly(2-vinylpyridine) in Solution Studied by 13C Nuclear Magnetic Relaxation

Abstract: The dynamics of poly(2-vinylpyridine) in chloroform solution has been examined by C-13 spin-lattice relaxation time and NOE measurements as a function of temperature. The experiments were performed at 50.3 and 100.6 MHz. The backbone carbon relaxation data have been analyzed in terms of six motional models. Among these models, the models which consider conformational transitions and bond librations for the backbone were found to be more successful. Pyridyl ring motion has been modeled as a restricted rotation with the rotational amplitude varying with temperature. The activation energy parameters obtained from the relaxation data of the pyridyl ring carbon have been compared with the energy barrier for ring rotation estimated from conformational energy calculations using the AM1 semiempirical quantum chemical method. The results of the conformational energy calculations support the description of pyridyl ring motion as a restricted rotation.

Interfacial Regions Governing Internal Cavities of Dendrimers. Studies of Poly(alkyl aryl ether) Dendrimers Constituted with Linkers of Varying Alkyl Chain Length

This report deals with a study of the properties of internal cavities of dendritic macromolecules that are capable Of encapsulating and mediating photoreactions of guest molecules. The internal cavity structures of dendrimers are determined by the interfacial regions between the aqueous exterior and hydrocarbon like interior constituted by the linkers that connect symmetrically sited branch points constituting the dendrimer and head groups that cap the dendrimers. Phloroglucinol-based poly(alkyl aryl ether) dendrimers constituted with a homologous series of alkyl linkers were undertaken for the current study. Twelve dendrimers within first, second, and third generations, having ethyl, n-propyl, n-butyl, and n-pentyl groups as the linkers and hydroxyl groups at peripheries in each generation, were synthesized. Encapsulation of pyrene and coumarins by aqueous basic solutions of dendrimers were monitored-by UV-vis and fluorescence spectroscopies, which showed that a lower generation dendrimer with an optimal alkyl linker presented better encapsulation abilities than a higher generation dendrimer. Norrish type I photoreaction of dibenzyl ketone was carried out within the above: series of dendrimers to probe their abilities to hold guests and reactive inthermediate radical pairs within themselves. The extent of cage effect from the series of third generation dendrimers was observed to be higher with dendrimers having an n-pentyl group as the linker.

Oxidation of aqueous sulphur dioxide catalysed by poly-4-vinylpyridine-Cu(II) complex .2. Combined homogeneous and heterogeneous phase oxidation

Aqueous phase oxidation of sulphur dioxide at low concentrations catalysed by a PVP-Cu complex in the solid phase and dissolved Cu(II) in the liquid phase is studied in a rotating catalyst basket reactor (RCBR). The equilibrium adsorption of Cu(II) and S(VI) on PVP particles is found to be of the Langmuir-type. The diffusional effects of S(IV) species in PVP-Cu resin are found to be insignificant whereas that of product S(VI) are found to be significant. The intraparticle diffusivity of S(VI) is obtained from independent tracer experiments. In the oxidation reaction HSO3- is the reactive species. Both the S(IV) species in the solution, namely SO2(aq) and HSO3- get adsorbed onto the active PVP-Cu sites of the catalyst, but only HSO3- undergoes oxidation. A kinetic mechanism is proposed based on this feature which shows that SO2(aq) has a deactivating effect on the catalyst. A rate model is developed for the three-phase reaction system incorporating these factors along with the effect of concentration of H2SO4 on the solubility of SO2 in the dilute aqueous solutions of Cu(II). Transient oxidation experiments are conducted at different conditions of concentration of SO2 and O-2 in the gas phase and catalyst concentration, and the rate parameters are estimated from the data. The observed and calculated profiles are in very good agreement. This confirms the deactivating effect of nonreactive SO2(aq) on the heterogeneous catalysis.

Stabilization of thermal degradation of poly(methyl methacrylate) by polysulfide polymers

The thermal degradation of poly(methyl methacrylate) (PMMA) in the presence of polysulfide polymers, namely, poly( styrene disulfide) (PSD) and poly(styrene tetrasulfide) (PST) was studied using thermogravimetry (TG) and direct pyrolysis-mass spectrometric (DP-MS) analysis. Both PSD and PST were found to stabilizethe PMMA degradation, which was explained by both radical recombination and a chain-transfer mechanism. (C) 1997 John Wiley & Sons, Inc.

Structural characterization and chain dynamics of poly(alpha-methylstyrene peroxide) by NMR spectroscopy

Poly(alpha-methylstyrene peroxide) has been synthesized and characterized spectroscopically. The H-1 and C-13 NMR spectra are shown to reveal the stereochemical features and the endgroups in the peroxide chain. The preliminary studies on the chain dynamics of the polyperoxide chain has been done by measuring the spin-lattice relaxation times (T-1) of the main chain as well as the side chain carbons. It has been shown from the dependence of the spin-lattice relaxation times that the polyperoxide chain is more flexible compared to the corresponding hydrocarbon-backbone analog.

On the formation of poly(ethyleneoxide)-poly(vinylalcohol) blends

Poly(ethyleneoxide)-poly(vinylalcohol) blends were prepared and characterized using thermal, spectroscopic and structural methods, By all indications the blends appear to be microscopically inhomogeneous with no strong interpolymer bonding. The high degree of crystallinity in PEO regions induces a significant degree of ordering in neighbouring PVA regions, as evident from thermal properties. PVA obtained from solvent evaporation exhibits an irreversible endothermic transition which could be order-disorder type. Both IR and NMR spectroscopies also suggest the presence of subtle structural ordering influence of PEO on PVA. It is found to be possible to prepare self supporting films of the blends which consists of fine dispersion of PEO and PVA in each other. (C) 1999 Elsevier Science Ltd. All rights reserved.

Photophysics of PPV derivatives with varying conjugation lengths

Photoluminescence (PL), electroluminescence (EL) and photoconductivity (PC) of poly[(2,5-dimethoxy-p-phenylene) vinylene] (DMPPV) of varying conjugation length were studied. Thin film devices of the DMPPV with different conjugation lengths, as the active medium, were prepared. The PL emission spectra revealed the radiative decay of the singlet excitons with peak values corresponding to energies below the absorption onset. The PL. emission spectra of the copolymer films also revealed vibronic features, which get well resolved upon cooling to 80K, The devices exhibit light emitting diode (LED) behavior; the I-V curves and EL spectra are compared in these DMPPV samples having different conjugation lengths. The PC studies reveal subtle features, which can be attributed to the optically generated excitations in the system.

Surface chemical studies on the competitive adsorption of poly(acrylic acid) and poly(vinyl alcohol) onto alumina

The adsorption of poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) onto alumina has been studied as a function of pH, both individually and in the presence of each other. The adsorption density of PAA is found to decrease with an increase of pH while that of PVA shows the opposite trend. In a binary system containing PAA and PVA, the presence of PVA does not affect the adsorption of PAA onto alumina, but the addition of PAA diminishes the adsorption of PVA in the pH range investigated. The adsorption isotherm of PAA at acidic pH exhibits high-affinity Langmuirian behavior. The isotherms for PVA appear rounded and are of the low-affinity type, Once again the adsorption isotherms of PAA remain unaltered in the presence of PVA whereas those of PVA are significantly affected resulting in a lowering of the adsorption density consequent to PAA addition. A variation in the sequence of addition of PAA and PVA does not affect the adsorption behavior of either of the polymers, The electrokinetic behavior of alumina with PAA is hardly influenced by the addition of PVA, On the other hand, the electrophoretic mobility of alumina in the presence of PVA is significantly altered in the presence of PAA and closely resembles the trend observed with PAA alone. Desorption studies reveal that over 80% of PVA could be desorbed in the pH range 3-9 whereas in the case of PAA, the percent desorption increases from 20 to about 70% as the pH is increased from about 3 to 8. Solution conductivity tests confirm interaction of aluminum species and PAA in the bulk solution. FTIR spectroscopic data provide evidence in support of hydrogen bonding and chemical interaction in the case of the PAA-alumina system and hydrogen bonding with respect to the PVA-alumina interaction. (C) 1999 Academic Press.

Electrochemical co-deposition of bimetallic Pt-Ru nanoclusters dispersed on poly(3,4-ethylenedioxythiophene) and electrocatalytic behavior for methanol oxidation

Nanoclusters of bimetallic Pt-Ru are electrochemically deposited on conductive polymer, poly(3,4-ethylenedioxythiophene)(PEDOT), which is also electrochemically deposited on a carbon paper substrate. The bimetallic deposition is carried out in an acidic electrolyte consisting of chloroplatinic acid and ruthenium chloride at 0.0 V versus saturated calomel electrode (SCE) on PEDOT coated carbon paper. A thin layer PEDOT on a carbon paper substrate facilitates the formation of uniform, well-dispersed, nano clusters of Pt-Ru of mean diameter of 123 nm, which consist of nanosize particles. In the absence of PEDOT, the size of the clusters is about 251 nm, which are unevenly distributed on carbon paper substrate. Cyclic voltammetry studies suggest that peak currents of methanol oxidation are several times greater on PtRu-PEDOT electrode than on Pt-Ru electrode in the absence of PEDOT. (C) 2011 Elsevier B.V. All rights reserved.

Influence of HZSM-5 catalyst on the thermal degradation of poly(vinyl chloride) in solution

The kinetics of thermal degradation of poly(vinyl chloride) (PVC) in solution was investigated at various temperatures (210-250degreesC). The degradation rate coefficients were determined from the time evolution of the molecular weight distribution (MWD). The energy of activation, determined from the temperature dependence of the rate coefficient, was 26.6 kcal/mol. The degradation of PVC was also studied in the presence of a catalyst (HZSM-5 zeolite). The results indicated that increase of the degradation rate of PVC is first order with the HZSM-5 concentration up to 50 g/L and zero order at higher concentrations. The thermal degradation kinetics of PVC in the presence of 50 g/L of the catalyst was studied at various temperatures. The temperature dependency of the rate coefficient was used to calculate the activation energy (21.5 kcal/mol). This is consistent with the observation that the presence of a catalyst generally decreases the activation energy and promotes degradation. (C) 2002 John Wiley Sons, Inc.

Structural and dielectric studies on poly(l-lithocholic acid)

In this paper, we report the results pretaining to the study of the structural, microstructural and the dielectric properties of poly(I-lithocholic acid) (PL), and the composite of PL dispersed in PMMA. The density of the composites was measured using Archimedes principle. The microstructural properties of the composities were studied using XRD and SEM techniques, which give an idea about the dispersion of the polymer PL in the PMMA matrix. The dielectric constants er of the composites were measured with a HP 4194A Impedance/Gain-Phase Analyzer in the frequency range 100 Hz-40 MHz at room temperature. The dielectric constants of the composites at different frequencies were predicted using Clasius-Mossotti and Maxwell's models.

Synthesis of electrically conducting copolymers of aniline with o/m-amino benzoic acid by an inverse emulsion pathway

Copolymers of aniline and ortholmeta-amino benzoic acid were synthesized by chemical polymerization using an inverse emulsion pathway. The copolymers are soluble in organic solvents, and the solubility increases with the amino benzoic acid content in the feed. The reaction conditions were optimized with emphasis on high yield and relatively good conductivity (2.5 X 10(-1) S cm(-1)). The copolymers were characterized by a number of techniques including UV-vis, FT-IR, FT-Raman, EPR and NNM spectroscopy, thermal analysis, SEM and conductivity. The influence of the carboxylic acid group ring substituent on the copolymers is investigated. The spectral studies reveal that the amino benzoic acid groups restrict the conjugation along the polymer chain. The SEM micrographs of the copolymers reveal regions of amorphous and crystalline domain. Thermal studies indicate a marginally higher thermal stability for poly(aniline-co-m-amino benzoic acid) compared to poly(aniline-co-o-amino benzoic acid). (C) 2002 Elsevier Science Ltd. All rights reserved.

Synthesis of poly(alkyl aryl ether) dendrimers

Poly(alkyl aryl ether) dendrimers of up to four generations composed of a phloroglucinol core, branching components, and pentamethylene spacers are synthesized by a divergent growth methodology. A repetitive synthetic sequence of phenolic O-alkylation and O-benzyl deprotection reactions are adopted for the synthesis of these dendrimers. The peripheries of the dendrimers contain 6, 12, 24, and 48 phenolic hydroxyl groups, either in the protected or unprotected form, for the first, second, third, and fourth generations, respectively. Because of the presence of hydrophilic exterior and relatively hydrophobic interior regions, alkaline aqueous solutions of these dendrimers are able to solubilize an otherwise insoluble pyrene molecule and these supramolecular complexes precipitate upon neutralization of the aqueous solutions.

Thermal degradation studies of para-substituted poly(styrene peroxide)s

The thermal degradation of a series of para-substituted poly(styrene peroxide)s with electron-donating [CH3, C(CH3)(3)] and electron-attracting (Br) substitutents are investigated by thermogravimetric analysis (TGA). The results indicate that the Hammett relationship can describe quantitatively the trends in maximum rate of polymer decomposition (T-max) observed in TGA and thus thermostability of substituted poly(styrene peroxide)s depends only on the electronic nature of substituents and their ability to stabilize macroradicals formed during chain scission. The experimental results are also substantiated by thermochemical calculations. (C) 2002 Elsevier Science Ltd. All rights reserved.