Removal of thorium from aqueous solution by adsorption using PAMAM dendron-functionalized styrene divinyl benzene

Third generation poly(amido)amine (PAMAM) dendron was grown on the surface of styrene divinylbenzene (SDB) by divergent polymerization method. This new chelating resin (PAMAMG3-SDB) has been investigated in liquid–solid extraction of thorium. The effects of analytical parameters such as pH, contact time, concentration of thorium, resin dose and temperature on adsorption were investigated. Kinetic and isotherm studies of the adsorption were also carried out to understand the nature of adsorption of thorium on the chelating resin. Kinetic data followed a pseudo-second-order model and equilibrium data were best fitted with Langmuir model. The maximum adsorption capacity of thorium ions was determined to be 36.2 mg g^?1 at 298 K. Thermodynamic parameters such as standard enthalpy, entropy, and free energy of adsorption of thorium on PAMAMG₃-SDB were calculated as ?10.498 kJ mol^?1, 0.0493 kJ mol^?1 K^?1 and ?25.208 kJ mol^?1 respectively at 298 K from temperature dependent equilibrium data.     

Synthesis and characterization of a novel polytriazole resin with low‐temperature curing character

A novel low‐temperature curing polytriazole resin was prepared from a triazide and a tetraalkyne and characterized. The resin can be cured at 70°C. The glass transition temperature T_g and thermal decomposition temperature T_d5 of the cured resin with the molar ratio of azide to alkyne group [A]/[B] = 1.0:1.0 reached 324 and 355°C, respectively. The study on the curing kinetics of the resin shows that the apparent activation energy of the curing reaction is 93 kJ mol^?1. The flexural strength of the cured resin reached 137.6 MPa at room temperature and 102.6 MPa at 185°C. Copyright © 2007 John Wiley & Sons, Ltd.     

A Highly Oxidizing and Isolable Oxoruthenium(V) Complex [RuV(N4O)(O)]2+: Electronic Structure,Redox Properties,and Oxidation Reactions Investigated by DFT Calculations

The electronic structure and redox properties of the highly oxidizing, isolable Ru^V?O complex [Ru^V(N₄O)(O)]²⁺, its oxidation reactions with saturated alkanes (cyclohexane and methane) and inorganic substrates (hydrochloric acid and water), and its intermolecular coupling reaction have been examined by DFT calculations. The oxidation reactions with cyclohexane and methane proceed through hydrogen atom transfer in a transition state with a calculated free energy barrier of 10.8 and 23.8 kcal mol^?1, respectively. The overall free energy activation barrier (ΔG^≠=25.5 kcal mol^?1) of oxidation of hydrochloric acid can be decomposed into two parts: the formation of [Ru^III(N₄O)(HOCl)]²⁺ (ΔG=15.0 kcal mol^?1) and the substitution of HOCl by a water molecule (ΔG^≠=10.5 kcal mol^?1). For water oxidation, nucleophilic attack on Ru^V?O by water, leading to O? O bond formation, has a free energy barrier of 24.0 kcal mol^?1, the major component of which comes from the cleavage of the H? OH bond of water. Intermolecular self‐coupling of two molecules of [Ru^V(N₄O)(O)]²⁺ leads to the [(N₄O)Ru^IV? O₂? Ru^III(N₄O)]⁴⁺ complex with a calculated free energy barrier of 12.0 kcal mol^?1.     

Controlled radical polymerization of styrene mediated by the C‐phenyl‐N‐tert‐butylnitrone/AIBN pair: Kinetics and electron spin resonance analysis

Kinetics of the free radical polymerization of styrene at 110 °C has been investigated in the presence of C‐phenyl‐N‐tert‐butylnitrone (PBN) and 2,2′‐azobis(isobutyronitrile) (AIBN) after prereaction in toluene at 85 °C. The effect of the prereaction time and the PBN/AIBN molar ratio on the in situ formation of nitroxides and alkoxyamines (at 85 °C), and ultimately on the control of the styrene polymerization at 110 °C, has been investigated. As a rule, the styrene radical polymerization is controlled, and the mechanism is one of the classical nitroxide‐mediated polymerization. Only one type of nitroxide (low‐molecular‐mass nitroxide) is formed whatever the prereaction conditions at 85 °C, and the equilibrium constant (K) between active and dormant species is 8.7 × 10^?10 mol L^?1 at 110 °C. At this temperature, the dissociation rate constant (k_d) is 3.7 × 10^?3 s^?1, the recombination rate constant (k_c) is 4.3 × 10⁶ L mol^?1 s^?1, whereas the activation energy (E_a,diss.), for the dissociation of the alkoxyamine at the chain‐end is ～125 kJ mol^?1. Importantly, the propagation rate at 110 °C, which does not change significantly with the prereaction time and the PBN/AIBN molar ratio at 85 °C, is higher than that for the thermal polymerization at 110 °C. This propagation rate directly depends on the equilibrium constant K and on the alkoxyamine and nitroxide concentrations, as well. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1219–1235, 2007     

Synthesis, cure kinetics, and thermal properties of a novel boron–silicon hybrid polymer

A novel boron–silicon hybrid polymer (PASB) was synthesized from polycondensation between phenylboron dichloride and dichloromethylsilane with Grignard reagent. The structure of PASB was characterized using fourier transform infrared spectra, ¹H-NMR, ¹³C-NMR, and gel permeation chromatography. The curing behavior of PASB was investigated by means of non-isothermal differential scanning calorimetry and the kinetic parameters were determined by the Kissinger’s and Ozawa’s methods, respectively. The results showed that both the methods for calculating the activation energy value gave fairly close results of 104.4 and 107.7 kJ mol^?1, respectively. A reasonable curing cycle for the resin system was also established, which suggested that it was reasonable to choose a curing temperature between T _i0 (452.0 K) and T _f0 (554.0 K). These results can provide theoretical guidance reference for determining the curing of the resin system. The thermal stability of cured PASB resin was studied by means of thermogravimetric analysis under nitrogen atmosphere and the temperature of 5 % mass loss (Td₅) was 610.1 °C, the residue at 1,000 °C was 87.8 %, which showed that the cured PASB resin exhibited excellent thermal properties and made it potentially useful as high performance matrix resin and precursor for ceramics.     

Tough epoxy resins cured with aminimides

Aminimide compounds ( 1–4 ) thermally generating isocyanates and tertiary amines were found to be excellent curing agents for epoxy resin. Tensile behavior, glass transition temperature, and degree of curing for the combination of EPIKOTE 828 prepolymer with a series of curing agents ( 1–4 ) are reported. The resins exhibit a large elongation at breakage and a high fracture energy per unit volume. The epoxy resins (EP-AI) cured with 3 or 4 containing no hydroxyl group showed larger ultimate elongations (up to 15%) and higher fracture energies (ca. 8 J/cm³) than the resins (EP–AI_OH) cured with 1 or 2 . The curing reaction depends on the structure of aminimide (presence of hydroxyl group and generation of mono- or bisisocyanates). The origin of toughness and dependence of physical properties on the curing condition and the structure of aminimides were discussed. It was concluded that relatively slow curing at elevated temperature controlled by thermal decomposition of aminimides was a reason for the toughness.     

Spectral and kinetic evidence for attack at coordinated phenanthroline in the reaction between aliphatic amines and transition metal complexes of 5-nitro-1,10-phenanthroline

Various transition metal complexes of 5-nitro-1,10-phenanthroline react with aliphatic amines in dipolar aprotic solvents to give deeply coloured species. The spectral changes, which can be reversed upon addition of acid or of the appropriate protonated amine, do not depend either on the nature of the metal and the ancillary ligands or on the geometry of the complexes; this has been taken as evidence that the colour forming process is due to a specific interaction of aliphatic amines with coordinated phenanthroline. While the rate of reaction of [Pt(5-NO₂phen)Cl₂] and [Pd(5-NO₂phen)Cl₂] with Br^?, which is known to displace Cl^? in the substrates, depends strongly on the nature of the central atom, the second order rate constant at 25°C being 3.2 × 10^?4 dm³mol^?1s^?1 and 1.35 dm³mol^?1s^?1 for the platinum and the palladium derivative respectively, the rate of reaction with n-propylamine has a comparable value for both substrates. This is further evidence that amines attack the coordinated phenanthroline, rather than the central atom. On the basis of the spectral features and the reaction stoicheiometry, the adducts of metal complexes of 5-NO₂phen and aliphatic amines are presumably Meisenheimer-like complexes.     

Synthesis of aromatic amine curing agent containing non-coplanar rigid moieties and its curing kinetics with epoxy resin

A kind of aromatic diamine, 4′, 4″-(2, 2-diphenylethene-1, 1-diyl)dibiphenyl-4-amine (TPEDA), was successfully synthesized via Suzuki coupling reaction. The TPEDA containing nonplanar rigid moieties can be used as epoxy resins curing agent to improve the complex properties of cured composites. The curing kinetics during thermal processing of E51/TPEDA system was investigated by nonisothermal differential scanning calorimeter. The average activation energy (E _α), pre-exponential factor (lnA), and reaction order (n) calculated from the Kissinger, the Ozawa, the Friedman and the Flynn–Wall–Ozawa methods were 55.8 kJ mol^?1, 9.4 s^?1 and 1.1, respectively. By the aid of estimated kinetic parameters, the predicted heat generation vs temperature curves fit well with the experimental data, which supported the validity of the estimated parameters and the applicability of the analysis method used in this work. By the introduction of nonplanar rigid moieties, the cured epoxy resins with TPEDA exhibited a higher glass transition temperature (T _g = 258 °C), good thermal stability (≈395 °C at 10 % mass-loss), and high char yield (36.6 % at 700 °C under nitrogen) compared with conventional curing agents.     

Effect of functionalized multiwall carbon nanotubes on the curing kinetics and reaction mechanism of bismaleimide–triazine

Functionalized multiwall carbon nanotubes (f-MWCNTs) with varying functionalization degrees were prepared by chemical methods. The effect of f-MWCNTs on the cure kinetics of bismaleimide–triazine (BT) resin was studied through nonisothermal differential scanning calorimetry (DSC) methods. The reaction activation energy (E _α ) was determined by Flynn–Wall–Ozawa method. The results show that f-MWCNTs have more acceleration ability than pristine MWCNTs, due to more groups on the surface of f-MWCNTs than that of pristine MWCNTs. The activation energy was decreased from a value of 91.3 kJ mol^?1 for the neat BT resin to 74.2 kJ mol^?1 at the small mass loading (1.0 %) of f7-MWCNTs. The effect of f-MWCNTs on the reaction mechanism has been investigated. It shows that the f-MWCNTs accelerate the cure reaction of BT resin by providing the Lewis acids (H⁺) to make the “Diels–Alder” reaction and “ENE” reaction of BT resins more efficient. These findings offer useful insights into the cure technology of thermosetting resin filled with f-MWCNTs, without negative effect on the cure reaction.     

Rate constants for reactions of SO4˙− radicals in acetonitrile

Rate constants have been measured for the reactions of the sulfate radical, SO₄^˙?, with alkanes, alkenes, alcohols, ethers, and amines in 95% acetonitrile solution. The rate constants were in the range of 10⁶ L mol^?1 s^?1 for the abstraction reactions and 10⁷?10⁹ L mol^?1 s^?1 for the addition and electron transfer reactions. These values are 20 to 80 times lower than those measured in aqueous solutions. Furthermore, the rate constants for the reactions of SO₄^˙? with the primary alcohols increase with the number of carbon atoms and then level off, in contrast to the behavior observed in aqueous solution, where the rate constant increases more sharply for the larger alcohols. © 1993 John Wiley & Sons, Inc.     

Rheological properties of wheat gliadins in aqueous propanol

Rheological properties of wheat gliadins in 50%(V/V) aqueous propanol were carried out as a function of gliadin concentration c and temperature.The solutions at 20 g L 1 to 200 g L 1 behave as Newtonian fluids with an flow activation energy of 23.5 27.3 kJ mol 1.Intrinsic viscosity [η] and Huggins constant k H are determined according to Huggins plot at c ≤ 120 g L 1.The results reveal that gliadins are not spherical shaped and the molecular size tends to increase with temperature due to improved solvation.     

Curing kinetics of arylamine-based polyfunctional benzoxazine resins by dynamic differential scanning calorimetry

In this study, the curing kinetics of polyfunctional benzoxazine resins based on arylamine, i.e. aniline and 3,5-xylidine, designated as BA-a and BA-35x, respectively, were investigated. Non-isothermal differential scanning calorimetry (DSC) at different heating rates is used to determine the kinetic parameters and the kinetic models of the curing processes of the arylamine-based polyfunctional benzoxazine resins were proposed. Kissinger, Ozawa, Friedman, and Flynn-Wall-Ozawa methods were utilized to determine the kinetic parameters of the curing reaction. BA-a resin shows only one dominant autocatalytic curing process with the average activation energy of 81-85 kJ mol⁻¹, whereas BA-35x exhibits two dominant curing processes signified by the clear split of the curing exotherms. The average activation energies of low-temperature curing (reaction (1)) and high-temperature curing (reaction (2)) were found to be 81-87 and 111-113 kJ mol⁻¹, respectively. The reaction (1) is found to be autocatalytic in nature, while the reaction (2) exhibits nth-order curing kinetics. In addition, the predicted curves from our kinetic models fit well with the non-isothermal DSC thermogram.     

Thermal degradation and flame retardancy of epoxy resins containing intumescent flame retardant

Pentaerythritol diphosphonate melamine-urea-formaldehyde resin salt, a novel cheap macromolecular intumescent flame retardants (IFR), was synthesized, and its structure was a caged bicyclic macromolecule containing phosphorus characterized by IR. Epoxy resins (EP) were modified with IFR to get the flame retardant EP, whose flammability and burning behavior were characterized by UL 94 and limiting oxygen index (LOI). 25 mass% of IFR were doped into EP to get 27.2 of LOI and UL 94 V-0. The thermal properties of epoxy resins containing IFR were investigated with thermogravimetry (TG) and differential thermogravimetry (DTG). Activation energy for the decomposition of samples was obtained using Kissinger equation. The resultant data show that for EP containing IFR, compared with EP, IFR decreased mass loss, thermal stability and R _max, increased the char yield. The activation energy for the decomposition of EP is 230.4 kJ mol⁻¹ while it becomes 193.8 kJ mol⁻¹ for EP containing IFR, decreased by 36.6 kJ mol⁻¹, which shows that IFR can catalyze decomposition and carbonization of EP.     

Résonance Magnétique Nucléaire en phase nématique. Exploration de la barrière d'empêchement à la libre rotation pour le fluorure d'acroyle et l'acroléine

The NMR spectrum of acrolein and acroyl fluoride (CH₂?CH? COX with X?H and F) oriented in a nematic phase has been measured and information about conformational equilibrium s-cis ? s-trans has been obtained. The barrier to internal rotation of the COX group has been studied with various hypotheses. Good agreement between experimental and calculated spectra has been obtained using the potential equation V(?) = Σ_nV_n(1 – cos n?)/2, with V₁ = ?200 cal mol^?1, V₂ = 1500 cal mol^?1 and V₃ = 400 cal mol^?1 for the fluorine compound, and V₁ = 1200 cal mol^?1, V₂ = 3000 cal mol^?1 and V₃ = 2000 cal mol^?1 for acrolein; this last compound is found to be mostly in the s-trans conformation.     

Pressure effects on cation migration in 2,5‐di‐tert‐butyl‐1,4‐benzoquinone radical anion

Pressure effects on the two‐site jumping of sodium and potassium cations in a 2,5‐di‐tert‐butyl‐1,4‐benzoquinone ion pair have been studied using a high‐pressure EPR technique. The rate constants of the intramolecular and intermolecular migrations for Na⁺ and K⁺ were determined from an EPR spectral simulation. The migration rates were found to be accelerated by increasing the external pressure. Using the pressure dependence of the migration rates, we estimated the activation volumes of the intramolecular (ΔV₁^?) and intermolecular (ΔV₂^?) processes for the Na⁺ and K⁺ migrations: ΔV₁^? = ?5.3 cm³ mol^?1 and ΔV₂^? = ?29 cm³ mol^?1 for Na⁺, and ΔV₁^? = ?8.3 cm³ mol^?1 and ΔV₂^? = ?0.85 cm³ mol^?1 for K⁺. Based on the results, the mechanisms for the two‐site jumping of Na⁺ and K⁺ are discussed in terms of volume. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 397–401, 2001     

ULTRASONIC RELAXATION KINETICS OF PLANAR:OCTAHEDRAL EQUILIBRIA OF A NICKEL MACROCYCLIC COMPLEX

Abstract

The equilibrium between the diamagnetic, planar nickel(II) macrocyclic complex known as NiCR²⁺(CR is 2,12-dimethyl-3,7,11,17-tetraazabicyclo[11.3.1]heptadeca-1(17),2, 11,13,15pentaene) and its paramagnetic, six-coordinate dimethanol adduct has been examined in methanol solution as the tetrafluoroborate salt. From the temperature dependence of the electronic absorption spectrum, thermodynamic parameters of ΔH°₄₆ = ?4.35 kcal mol^?1 and ΔS°₄₆ = ?8.72 cal deg^?1 mol^?1 were determined. From the excess ultrasonic absorption a relaxation frequency of 15 MHz was observed from which rate constants of k₄₆ of 8.6 × 10⁷ s^?1 and k₆₄ of 7.9 × 10⁶ s^?1 were calculated. The rate constant k₄₆ is nearly the same as the rate constant for solvent exchange which had previously been determined by NMR. This implies that the solvent exchange is effected by the octahedral-planar equilibrium and that a two-step mechanism with a five-coordinate intermediate can be eliminated.     

Temperature and shear dependencies of rheology of poly(acrylonitrile‐co‐itaconic acid) dope in DMF

Poly(acrylonitrile‐co‐itaconic acid) (poly(AN‐co‐IA)) precursor required for carbon fiber production is made into a dope and spun into fibers using a suitable spinning technique. The viscosity of the resin dope is decided by the polymer concentration, polymer molecular weight, temperature, and shear force. The shear rheology of concentrated poly(AN‐co‐IA) polymer solutions in N,N‐dimethylformamide (DMF), in the range of 1 × 10⁵–1 × 10⁶ g mol^?1, has been investigated in the shear rate (γ′) range of 1 × 10¹–5 × 10⁴ min^?1. The zero shear viscosity (η₀) has been evaluated at different temperatures. The temperature dependence of zero shear viscosity conformed to the Arrhenius–Frenkel–Eyring model. The free energy of activation of viscous flow (ΔG_V) values were in the range 5–32 kJ mol^?1 and this value increased with increase in polymer concentration and molecular weight. A master equation for the ΔG_V value of the polymer solution of any and concentration (c) is suggested. The power law fitted well for the shear dependency of viscosity of these polymer solutions. The pseudoplasticity index (n) diminished with increase in polymer concentration and molecular weight. An empirical relation between viscosity (η) and was found to exist at constant shear rate, concentration and temperature. For each , the equation relating n, c, and T was established. Copyright © 2008 John Wiley & Sons, Ltd.     

Free-radical chain oxidation of 1,4-dioxane and styrene in the presence of fullerene C60

The antiradical activity of fullerene C₆₀ was studied for the oxidation of 1,4-dioxane and styrene initiated by azobisisobutyronitrile and benzoyl peroxide as model reactions. The effective rate constants of the reaction of peroxyl radicals with fullerene C₆₀ (k ₇) and the stoichiometric inhibition factor (f _eff) were determined in air ( $P_{O_2 }$ = 0.21 atm) and oxygen ( $P_{O_2 }$ = 1.0 atm). The rate of the liquid-phase oxidation of 1,4-dioxane does not depend on $P_{O_2 }$ , and the effective rate constant of inhibition is k ₇ = (2.4 ± 0.2) × 10⁴ L mol^?1 s^?1. Chain termination in the oxidation of styrene occurs when C₆₀ reacts with both the peroxyl radicals (k ₇ = (1.2 ± 0.1) × 10³ L mol^?1 s^?1) and alkyl (k ₈ = 1.07 × 10⁷ L mol^?1 s^?1) radicals.     

Kinetics and Mechanism of the Decarbonylation of Benzoylformyl Palladium(II) Complex

The benzoylformyl Pd(II) complex, Pd(PPh₃)₂(Cl)(COCOPh), thermally decomposes to the corresponding benzoyl complex by the loss of CO. The predominant route of decarbonylation is led by a reversible dissociation of a phosphine ligand. The disappearance of the benzoylformyl complex in solutions follows first order kinetics not only in the existence of excess PPh₃ but also in the absence of added PPh₃. Through the treatments of both preequilibrium and the steady state approximations to the kinetic data, the rate constants of the intramolecular acyl migration, k₁ and k₂; as well as the equilibrium constant and the individual rate constants of the reversible phosphine dissociation step, K, k_d and k_d, were determined in CHCl₃. The activation parameters for k_d, being ^ΔH^? = 25.4 Kcal Mol^?1, ^ΔS^? = 15.9 eu, ^ΔG^? = 20.7 Kcal Mol^?1;and for k_?d, being ^ΔH^? = 13.0 Kcal Mol^?1, ^ΔS^? = ?7.9 eu, ^ΔG^? = 15.4 Kcal Mol^?1, were evaluated.     

Synthesis, structure analysis and thermodynamics of [Ni(H2O)4(TO)2](NO3)2·2H2O (TO = 1,2,4-triazole-5-one)

A novel complex [Ni(H₂O)₄(TO)₂](NO₃)₂·2H₂O (TO = 1,2,4-triazole-5-one) was synthesized and structurally characterized by X-ray crystal diffraction analysis. The decomposition reaction kinetic of the complex was studied using TG-DTG. A multiple heating rate method was utilized to determine the apparent activation energy (E _a) and pre-exponential constant (A) of the former two decomposition stages, and the values are 109.2 kJ mol^?1, 10^13.80 s^?1; 108.0 kJ mol^?1, 10^23.23 s^?1, respectively. The critical temperature of thermal explosion, the entropy of activation (ΔS ^≠), enthalpy of activation (ΔH ^≠) and the free energy of activation (ΔG ^≠) of the initial two decomposition stages of the complex were also calculated. The standard enthalpy of formation of the new complex was determined as being ?1464.55 ± 1.70 kJ mol^?1 by a rotating-bomb calorimeter.