Effect of low‐temperature physical aging on the dynamic transitions of atactic polystyrene in the glassy state

The local and cooperative dynamics of atactic PS (a‐PS) were studied by broadband dielectric relaxation spectroscopy (BDRS) and attenuated total reflectance Fourier transform infrared spectroscopy (ATR‐FTIR). The a‐PS has been subjected to thermal rejuvenation and subsequent quenching, short‐term aging (6 weeks), and long‐term aging (1 year) at ambient conditions. Where for the rejuvenated sample only an α‐ and a γ‐relaxation is observed, short‐term aging results in an additional β*‐relaxation that merges with the α‐relaxation at longer aging times. The γ‐relaxation is increasing in intensity and activation energy during aging. The α‐process shows no spectral changes and shift in the relaxation time upon aging. This may be attributed to a possible erasure of history of the material during the temperature‐sweep mode measurement. Fourier transform infrared spectroscopy (FTIR) results suggest that the energetically favorable trans‐trans (tt) conformers are increased in population with aging. © 2019 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019 , 57, 1394–1401     

二维红外相关光谱研究缠结对冷冻升华无规聚苯乙烯分子运动的影响

用冷冻升华法制备了浓度为1×10^－4 和2×10^－5 g/mL的单链无规聚苯乙烯(a-PS). 利用FTIR测试方法, 测定a-PS在等温处理时红外吸收峰的时间依赖性与温度依赖性, 研究样品中链缠结和链结构单元的堆积等因素对红外吸收峰的影响, 进而探讨链缠结对a-PS分子运动的影响. 同时, 也通过二维相关分析来研究a-PS等温实验过程中, 链缠结的变化情况以及官能团之间的变化顺序, 推断在a-PS等温时, 与链结构单元的堆积相联系的苯环振动首先发生, 其次才是与链缠结相关联的CH₂振动发生变化, 并由此确定缠结对冷冻升华a-PS分子运动的影响.     

Differential pulse voltammetric determination of arsenic(III,V) and antimony (III,V) in glasses

Summary Analytical methods based on differential pulse voltammetry (DPV) have been described for the determination of total As, As(III), As(V), total Sb and Sb(III) as trace to minor constituents in complex glasses. For total As, the sample is decomposed with HF-H₂SO₄-KMnO₄. The As(V) is chemically reduced to As (III) by hypophosphite and a DPV scan is carried out at the dropping mercury electrode from –0.2 to –0.7 Vvs. SCE (E _p –0.41V). As(V) is determined by decomposing the sample in HF-H₂SO₄ and volatilizing the As(III) as AsF₃. The chemical reduction of As(V) and the DPV scan are then applied. If the glass can be decomposed with cold HF, the As(III) present in the glass can be determined by applying the DPV scan after cold sample-dissolution. For Sb(III), the sample is decomposed with HF-H₂SO₄, diluted, and adjusted to 1M in HCl. A DPV scan is conducted from –0.03 to –0.5 V (E _p –0.15 V). Sb(V) is not reduced in the 1M HCl supporting electrolyte. Total Sb is determined by using an aliquot of the sample solution adjusted to 6M in HCl. The DPV sweep is carried out from –0.5 to –0.1 V [E _p for Sb(V) and Sb(III) is –0.30 V]. The methods have been applied to a wide range of glass compositions and the results compared with values obtained by spectrophotometry and coulometric titration.

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Bestimmung von Arsen(III, V) und Antimon(III, V) in Gläsern mit Hilfe der Differential-Puls-Voltammetrie

Zusammenfassung Analytische Methoden auf der Grundlage der Differential-Puls-Voltammetrie (DPV) für die Bestimmung des gesamten Arsens, As(III), As(V), des gesamten Antimons und Sb(III) als Spuren in komplexen Gläsern wurden beschrieben. Zwecks Bestimmung des Gesamt-As wird die Probe mit Flußsäure +Schwefelsäure + Permanganat aufgeschlossen. As(V) wird mit Hypophosphit reduziert und die DPV wird an einer Quecksilber-Tropfelektrode zwischen –0,2 und –0,7V gegen eine ges. Kalomelelektrode (E _p =–0,41V) durchgeführt. Zur Bestimmung von As(V) wird die Probe mit HF-H₂SO₄ unter Verflüchtigung des As(III) als AsF₃ aufgeschlossen. Dann erfolgt die Reduktion des As(V) und die DPV. Wenn sich das Glas mit kalter HF lösen läßt, wird anwesendes As(III) mittels DPV in dieser Lösung bestimmt. Zur Bestimmung des Sb(III) wird die Probe mit HF-H₂SO₄ zersetzt, verdünnt und bis zur 1-Molarität mit HCl versetzt. Dann wird mit DPV zwischen –0,03 und –0,5V gemessen (E _p =–0,15V). Sb(V) wird in 1M salzsaurer Lösung nicht reduziert. Das Gesamt-Sb wird in einem Aliquot der Probelösung bestimmt, das dazu mit HCl bis zur 6fachen Molarität versetzt wird. Der DPV-Bereich wird von –0,5 bis –0,1 V ausgenützt (E _p f:ur Sb(V) und Sb(III) ist –0,30 V). Das Verfahren wurde für Gläser verschiedenster Zusammensetzung angewendet. Die Ergebnisse wurden mit den Resultaten der Spektrophotometrie und der coulometrischen Titration verglichen.

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Presented at the 8th International Microchemical Symposium, Graz, August 25–30, 1980.     

Phase transitions and relaxation processes in ethylene-vinyl acetate copolymers probed by fluorescence spectroscopy

The steady-state fluorescence of pyrene and anthracene are used to investigate the relaxation processes of several random ethylene-co-vinyl acetate copolymers, EVA, with defined comonomer compositions (EVA-9, EVA-18, EVA-25, EVA-33 and EVA-40). The temperature of the relaxation processes are compared with those of low-density polyethylene (LDPE) and poly(vinyl acetate) (PVAc). The polymer relaxation processes are assigned to T_g=300-310 K (glass transition temperature of the PVAc); T_α=270-300 K (relaxation processes of the ethylene units present in LDPE and EVA); T_g=220-250 K (glass transition of the LDPE and of the EVA); T_γ or T_β=160-190 K (relaxation processes of interfacial defects of methylenic chains of LDPE and rotation of the acetate group of the PVAc and the EVA); and T_γ=90-130 K (relaxation processes of small sequences of methylene units of LDPE and end groups of PVAc). An Arrhenius-type function was employed as an attempt to represent the experimental data of fluorescence intensity versus temperature above the γ-relaxation temperature. As obtained with other techniques, there is not a simple relationship between the polymer relaxation processes and the vinyl acetate content that can be explained by the morphology in these copolymers.     

3‐Deoxy‐β‐d‐ribo‐hexopyranose (3‐deoxy‐β‐d‐glucopyranose)

The β‐pyranose form, (III), of 3‐deoxy‐d ‐ribo‐hexose (3‐deoxy‐d ‐glucose), C₆H₁₂O₅, crystallizes from water at 298 K in a slightly distorted ⁴C₁ chair conformation. Structural analyses of (III), β‐d ‐glucopyranose, (IV), and 2‐deoxy‐β‐d ‐arabino‐hexopyranose (2‐deoxy‐β‐d ‐glucopyranose), (V), show significantly different C—O bond torsions involving the anomeric carbon, with the H—C—O—H torsion angle approaching an eclipsed conformation in (III) (−10.9°) compared with 32.8 and 32.5° in (IV) and (V), respectively. Ring carbon deoxygenation significantly affects the endo‐ and exocyclic C—C and C—O bond lengths throughout the pyranose ring, with longer bonds generally observed in the monodeoxygenated species (III) and (V) compared with (IV). These structural changes are attributed to differences in exocyclic C—O bond conformations and/or hydrogen‐bonding patterns superimposed on the direct (intrinsic) effect of monodeoxygenation. The exocyclic hydroxymethyl conformation in (III) (gt) differs from that observed in (IV) and (V) (gg).     

Molecular and crystal structure of 5-phenyl, 5-m-nitrophenyl,and 5-spirocyclopentane derivatives of 3-amino-2,4,4-tricyanobicyclo [4,4,0] deca-2,10-diene

To examine the ability of 3-amino-2,4,4-tricyanobicyclo[4,4,0]deca-2,10-dienes (I) to form dimeric associates, we have investigated molecular and crystal structure of three derivatives of (I): 5-phenyl (II), 5-m-nitrophenyl (III), and 5-spirocyclopentano (IV). Hydrogen bonding via the aminonitrile fragment leads to formation of centrosymmetric dimeric associates in compounds (II, III) and a chain structure in (IV). Crystal data for (II): space group P2₁/c, a=8.726(3), b=15.879(5), c=15.597(5) Å, α=γ=90, β=105.13(2)⁰, V=2086.2 ų, Z=4, R=0.093; for (III): space group C2/c, a=24.725(8), b=9.004(5), c=24.391(8) Å, α=γ=90, β=125.36(2)⁰, V=4428.2ų, Z=8, R=0.080; for (IV): space group C2/c, a=24.443(8), b=10.240(5), c=16.645(6) Å, α=γ=90, β=108.89(2)⁰, V=3941.8 ų, Z=8, R=0.089.     

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.     

Liquid-liquid extraction and separation studies of uranium(vi)

Summary Separation of uranium(VI) from iron(III), molybdenum(VI), vanadium (V), bismuth(III), zirconium(IV) and thorium(IV) is achieved by liquid-liquid extraction with 4-methyl-3-pentene-2-one (mesityl oxide; MeO) from sodium salicylate media (0.1M, pH 6.0). The extracted species is UO₂(HO·C₆H₄COO)₂·2MeO. A procedure for separating 50g of uranium from mg amounts of the other metals is described.

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Flüssig-flüssig-Extraktion und Trennung von Uran(VI)

Zusammenfassung Die Trennung des U(VI) von Fe(III), Mo(VI), V(V), Bi(III), Zr(IV) und Th(IV) läßt sich durch Flüssig-flüssig-Extraktion mit 4-Methyl-3-penten-2-on] (Mesityloxid, MeO) aus 0,1M Natriumsalicylat bei pH 6,0 durchführen. Die extrahierte Verbindung ist UO₂(HO·C₆H₄COO)2·2MeO. Ein Verfahren zur Abtrennung von 50g Uran von Milligrammengen der anderen Metalle wurde beschrieben.

     

Polymorphic crystal forms and morphology of syndiotactic polystyrene in miscible states

X-ray diffraction and optical microscopy characterization were performed to evaluate the phenomenon of alteration of polymorphism of syndiotactic polystyrene (s-PS) in the presence of other blending miscible polymers: poly(2,6-dimethyl-p-phenylene oxide) (PPO) or atactic polystyrene (a-PS). Both α and β crystal forms were observed in the neat s-PS sample, but only β-form crystal was found in miscible blends of s-PS with a-PS or PPO. The order and neighboring chain segments of neat s-PS are different from those of s-PS/PPO or s-PS/a-PS blends; thus, it is plausible that the greater randomness in the melt state of s-PS/a-PS or s-PS/PPO blends might be unfavorable for formation of α-form crystals from melts. The final spherulitic morphology the s-PS/a-PS or s-PS/PPO blends suggests that the amorphous-state miscibility of does not change much the spherulitic structure of s-PS. The radial growth rate is, in general, depressed with the presence of blending miscible polymers in s-PS of equal T_g or PPO of higher T_g. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 2725–2735, 1998     

Biphasic oxidation of diaquadichloro(1,10-phenanthroline)chromium(III) by N-bromosuccinimide and the formation of chromium(IV) and chromium(V)

The kinetics of oxidation of diaquadichloro(1,10-phenanthroline)chromium(III) complex, [Cr^III(phen)(H₂O)₂Cl₂]⁺, by N-bromosuccinimide (NBS) is biphasic. The first faster step involves the oxidation of Cr(III) to Cr(IV). The second slower step is due to the oxidation of Cr(IV) to Cr(V). The reaction product is isolated and characterized by electron spin resonance (ESR), IR, and elemental analysis. The chromium(V) product is consistent with the formula [Cr^V(phen)Cl₂(O)]Br. The rate constants k_f and k_s, for the faster and the slower steps respectively, were obtained using an Origin 9.0 software program. Values of both k_f and k_s, varied linearly with [NBS] at constant reaction conditions. The effect of pH on the reaction rate is investigated over the pH (4.11–6.01) range at 25.0°C. The rate constants k_f and k_s increased with increasing pH. This is consistent with hydroxo forms of the chromium species being more reactive than the aqua forms. Chromium(III) complexes, more often than not, are inert. The oxidation of the Cr(III) complex to Cr(IV), most likely, proceeds by an outer sphere mechanism. Since chromium(IV) is labile the mechanism of its oxidation to chromium(V) is not certain.     

Electron transfer. 109. The reaction of dimeric molybdenum(V) with carboxylato-bound chromium(V). A third mechanistic variation

The bridged dimer of molybdenum(V), Mo₂O₄²⁺ (aq) is oxidized to Mo(VI) by carboxylato-bound chromium(V). Reaction of bis(chelated) Cr(V) with excess (Mo^V)₂ yields a chelated Cr(III) complex, but this conversion proceeds through a pink Cr(IV) intermediate, indicating that the oxidation of (Mo^V)₂ entails a series of le^? steps, passing through a reactive transient, the mixed valence complex, Mo^VMo^VI. When experiments are carried out in buffers of the ligating acid, 2-ethyl-2-hydroxybutanoic acid, two stages of ligation of (Mo^V)₂ by the ligand anion, characterized by rate constants near 10⁴ and 0.14 M^?1 s^?1 (19°C; pH 3.0; μ = 0.6 M) must be considered. In quick mixing experiments, the first, but not the second, of these proceeds before the redox reaction gets under way, and autocatalytic redox profiles are observed. If the slower ligation is allowed to reach completion before Cr(V) is added, reduction to Cr(IV) is greatly accelerated and conforms to the superposition of two processes, whereas the reduction of Cr(IV) to Cr(III) is slow and exhibits a rate independent of [Cr^IV]. A proposed sequence applicable to the latter conditions includes reductions of Cr(V) at two ligation levels, slow unimolecular conversion of (Mo^V)₂ to an activated form, and rapid reduction of the latter with Cr(IV). Here Cr(IV) has assumed the role of a scavenger for the reactive form of (Mo^V)₂.     

Inorganic speciation of As(III, V), Se(IV, VI) and Sb(III, V) in natural water with GF-AAS using solid phase extraction technology

The paper presents a procedure for the multi-element inorganic speciation of As(III, V), Se(IV, VI) and Sb(III, V) in natural water with GF-AAS using solid phase extraction technology. Total As(III, V), Se(IV, VI) and Sb(III, V) were determined according to the following procedure: titanium dioxide (TiO₂) was used to adsorb inorganic species of As, Se and Sb in sample solution; after filtration, the solid phase was prepared to be slurry for determination. For As(III), Se(IV) and Sb(III), their inorganic species were coprecipitated with Pb-PDC, dissolved in dilute nitric acid, and then determined. The concentrations of As(V), Se(VI) and Sb(V) can be calculated by the difference of the concentrations obtained by the above determinations. For the determination of As(III), Se(IV) and Sb(III), palladium was chosen as a modifier and pyrolysis temperature was 800 °C. Optimum conditions for the coprecipitation were listed for 100 ml of sample solution: pH 3.0, 15 min of stirring time, 40.0 μg l⁻¹ Pb(NO₃)₂ and 150.0 μg l⁻¹ APDC. The proposed method was applied to the determination of trace amounts of As(III, V), Se(IV, VI) and Sb(III, V) in river water and seawater.     

A model for dynamic relaxations in amorphous polymers. I. Conceptual framework,formal implementation of simplest version,and application to poly(ester carbonates)

A new model for the dynamic relaxations occurring below the glass transition temperature in amorphous polymers is introduced. This model combines ideas from theoretical solidstate physics, thermodynamics, and statistical mechanics. Formal analogies are made between the dynamic relaxations and phase transitions. The concepts of percolation theory are briefly discussed. The molecular level motions which might be giving rise to each dynamic relaxation are incorporated within this framework. The simplest version of the model is then formally implemented within the context of bisphenol-A polycarbonate (BPAPC) and its poly (ester carbonates) (PEC). The following results are calculated: (1) Characteristic temperatures (T_c) for BPAPC, similar to γ₁, and γ₂ relaxation temperatures observed by dynamic mechanical spectroscopy (DMS) at commonly used measurement frequencies. (2) T_c for the β₂ relaxation in tetrabromo-BPAPC much higher than the T_c in BPAPC. (3) A slow and monotonic increase in both the intensity and the T_cof the γ₂ relaxation with an increasing fraction of terephthalate comonomer in PEC copolymers. It is hoped that this model, which is admittedly tentative at this time, will be useful as a working hypothesis. The next paper of this series will provide extensions and generalizations of the model, and its application to the poly (alkyl methacrylates).     

Biphasic Oxidation of cis‐Diaquabis(1,10‐phenanthroline)chromium(III) by N‐Bromosuccinimide and the Formation of Chromium(IV) and Chromium(V)

The oxidation of cis‐diaquabis(1,10‐phenanthroline)chromium(III) [cis‐Cr^III(phen)₂(H₂O)₂]³⁺ by ‐bromosuccinimide (NBS) to yield cis‐dioxobis(1,10‐phenanthroline)chromium(V) has been studied spectrophotometrically in the pH 1.57–3.56 and 5.68–6.68 ranges at 25.0°C. The reaction displayed biphasic kinetics at pH < 4.0 and a simple first order at the pH > 5.0. In the low pH range, the reaction proceeds by two successive steps; the first faster step corresponds to the oxidation of Cr(III) to Cr(IV), and the second slower one corresponds to the oxidation of Cr(IV) to Cr(V), the final product of the reaction. The formation of both Cr(IV) and Cr(V) has been detected by electron spin resonance (ESR). The ESR clearly showed the formation and decay of Cr(IV) as well as the formation of Cr(V). Each oxidation process exhibited a first‐order dependence on the initial [Cr(III)]. The pseudo–first‐order rate constants k₃₄ and k₄₅, for the faster and slower steps, respectively, were obtained by a computer program using Origin7.0. Both rate constants showed first‐order dependence on [NBS] and increased with increasing pH.     

Interaction of Aluminium (III) with the f-Family Ions Np(VI), Pu(VI), Np(V), Np(IV), Pu(IV), Nd(III), and Am(III) in the Course of Simultaneous Hydrolysis

The interaction of Np(VI), Pu(VI), Np(V), Np(IV), Pu(IV), Nd(III), and Am(III) with Al(III) in solutions at pH 0–4 was studied by the spectrophotometric method. It was shown that, in the range of pH 3–4, the hydrolyzed forms of neptunyl and plutonyl react with the hydrolyzed forms of aluminium. In the case of Pu(VI), the mixed hydroxoaqua complexes (H₂O)₃PuO₂(-OH)₂Al(OH)(H₂O)₃ ²⁺ or (H₂O)₄PuO₂OAl(OH)(H₂O)₄ ²⁺ are formed at the first stage of hydrolysis. Np(VI) also forms similar hydroxoaqua complexes with Al(III). The formation of the mixed hydroxoaqua complexes was also observed when Np(IV) or Pu(IV) was simultaneously hydrolyzed with Al(III) at pH 1.5–2.5. The Np(IV) complex with Al(III) has, most likely, the formula (H₂O) _n (OH)Np(-OH)₂Al(OH)(H₂O)₃ ³⁺. At pH from 2 to 4.1 (when aluminium hydroxide precipitates), the Np(V) or Nd(III) ions exist in solutions with or without Al(III) in similar forms. When pH is increased to 5–5.5, these ions are almost not captured by the aluminium hydroxide precipitate.     

The novel triazine cored tripodal and trinuclear Schiff base‐oxime metal complexes: Their magnetic properties and thermal decompositions

2,4,6‐tris(4‐hydroxybenzimino)‐1,3,5‐triazine [ 1 , 2 ] ( III ) have been synthesized by the reaction of 1 equiv melamine and three equiv 4‐hydroxybenzaldehyde, and characterized by means of elemental analysis, ¹H‐NMR (nuclear magnetic resonance spectroscopy), Fourier transform infrared (FTIR) spectrscopy, liquid chromatography‐mass spectroscopy (LC‐MS). L ( IV ) has been synthesized by the reaction of one equiv ( III ) and three equiv 4‐(thiophenoxy)phenyloxylohydroxymoyl chloride ( II ) , and characterized by means of the same methods. Then, four novel trinuclear Fe(III) and Cr(III) complexes involving tetradentate Schiff bases N,N′‐bis(salicylidene)ethylenediamine‐(salenH₂) or bis(salicylidene)‐o‐phenylenediamine‐(salophen H₂) with L (IV) have been synthesized and characterized by means of elemental analysis, FTIR spectrscopy, LC‐MS, thermal analyses. The metal ratios of the prepared complexes have been determined using AAS. The aim of the present study is synthesis of novel tridirectional‐trinuclear systems and to present their effects on magnetic behavior of [salenFe(III)], [salophenFe(III)], [salenCr(III)], and [salophenCr(III)] capped complexes. The complexes have also been characterized as low‐spin distorted octahedral Fe(III) and Cr(III) bridged by keton‐oxime group. J. Heterocyclic Chem., (2011).     

Evaluation of a rapid technique for measuring actinide oxidation states in a ground water simulant

A system using an ion chromatograph coupled to a flow-cell scintillation detector for rapidly measuring the oxidation states of actinides at low concentrations (<10–6M) in aqueous solutions was evaluated. The key components of the system are a cation–anion separation column (Dionex, CS5) and a flow cell detector with scintillating cerium activated glass beads. The typical procedure was to introduce a 0.5 ml aliquot of sample spiked with actinides in the +III to +VI oxidation states into a 5 ml sample loop followed by 4 ml of synthetic groundwater simulant. Separation was achieved at a flow rate of 1 ml/min using an isocratic elution with oxalic, diglycolic, and nitric acids followed by distilled water. Tests were first conducted to determine elution times and recoveries for an acidic solution (pH 2) and a ground water simulant (pH 8) containing Am(III), Pu(IV), Th(IV), Pu(V), and U(VI). Then, an analysis was performed using a mixture of Pu(IV), Pu(V), and Pu(VI) in the ground water simulant and compared to results using the DBM extraction technique. Approximate elution times were the same for both the acidic solution and the ground water simulant. These were as follows: Pu(V) at 10 min, Am(III) at 15 min, Pu(IV) at 25 min, Th (IV) at 28 min and U(VI) at 36 min. Recoveries for the acidic solution were quantitative for U(VI) and Th(IV) and exceeded 80% for Am(III). Recoveries for the ground water simulant were quantitative for U(VI), but they were generally not quantitative for Th(IV), Pu(IV), and Am(III). For Th(IV) and Pu(IV), less than quantitative recoveries were attributed to the formation of neutral hydroxides and colloids; for Am(III) they were attributed to insoluble carbonates and/or hydroxycarbonates. When applied to the measurement of plutonium in the ground water simulant, the technique provided showed good agreement with the dibenzoylmethane (DBM) extraction technique, but it could not distinguish between Pu(V) and Pu(VI). This was likely due to the reduction of Pu(VI) to Pu(V) in the sample by the oxalic acid eluent. However, in spite of this limitation, the technique can be used to distinguish between Pu(IV) and Pu(V) in aqueous environmental samples within a pH range of 4 to 8 and an E _H range of -0.2 to 0.6 V, the predominance region for Pu(III), (IV), and (V). In addition, this technique can be used to corroborate oxidation state analysis from the dibenzoylmethane (DBM) extraction method for environmental samples.     

Effects of thermal history,crystallinity, and solvent on the transitions and relaxations in poly(bisphenol-A carbonate)

The following system of nomenclature for the transitions and relaxations in polycarbonate has been proposed: α = T_g = 150, β = 70, γ = ?100, and δ = ?220°C (frequency range of 10–50 Hz). The three component peaks of the γ relaxation are denoted by γ₁, γ₂, and γ₃ relaxations correspond to phenylene, coupled phenylene-carbonate, and carbonate motions, respectively. Dynamic mechanical analysis of poly(bisphenol-A carbonate) using the DuPont 981–990 DMA system shows that the magnitude of the β relaxation depends upon the thermal history of the polycarbonate; annealing greatly reduces the intensity of the β relaxation. A relaxation map constructed for the β relaxation gives an activation energy of 46 kcal/mol. Exposure of polycarbonate to methylene chloride vapor for various times shows that after an induction period of about 5 min the intensity of the γ₃ relaxation at ?78°C decreases whereas the intensity of the γ₁ relaxation of ?30°C is unaffected and the ratio E″(γ₁)/E″(γ₃) increases linearly with the square root of time. This has been ascribed to the interaction of methylene chloride on the carbonate group in polycarbonate. Thermal crystallization of polycarbonate does not affect the positions of the γ relaxation and the glass transition peaks, but merely reduces their intensity. The glass transition peak intensity falls off sharply in comparison to the γ relaxation intensity. Both the γ₃ and γ₁ peaks in polycarbonate have been observed simultaneously for the first time by dynamic mechanical analysis. Impact strength measurements show that methylene chloride treatment of polycarbonate results in a change in mode of failure from ductile to brittle with a resultant 40-fold reduction in impact energy for fracture. Thermally crystallized polycarbonate exhibits brittle fracture with very low force and energy at break.     

EQCM Study of Iridium Anodic Oxidation in H2SO4 and KOH Solutions

In the present study anodic oxidation of iridium layer formed thermally on a gold‐sputtered quartz crystal electrode has been investigated by electrochemical quartz crystal microgravimetry (EQCM) in the solutions of 0.5 M H₂SO₄ and 0.1 M KOH. The emphasis here has been put on the microgravimetric behavior of iridium as a metal, because a few previous EQCM studies reported in literature have been devoted to iridium oxide films (IROFs). The objective pursued here has been to elucidate the nature of the main voltammetric peaks, which occur at different ranges of potential in the solutions investigated. It has been found that anodic oxidation of iridium electrode in 0.5 M H₂SO₄ and 0.1 M KOH solutions is accompanied by irregular fluctuations of the electrode mass at 0.4 V<E<0.8 V followed by regular increase in mass at 0.8 V<E<1.2 V. The cathodic process initially, at 1.2 V>E>0.9 V, proceeds without any or with slight increase in electrode mass, whereas at E<0.8 V a regular decrease in mass is observed. It has been found that mass to charge ratio characterizing the processes of interest is 2 to 3 g F^?1in acidic medium, whereas in the case of alkaline one it is 4 to 6 g F^?1. The main pair of peaks seen in the voltammograms of Ir electrode in alkaline medium at E<0.8 V is attributable to redox transition Ir(0)→Ir(III), whereas those observed in the case of acidic medium at E>0.8 V should be related to the redox process Ir(0)→Ir(IV) going via intermediate stage of Ir(III) formation. As a consequence of these redox transitions, the gel‐like surface layer consisting of Ir(III) or Ir(IV) hydrous oxides forms on the electrode surface.     

Regeneration of the Oxidation Catalysts Based on the Aqueous Solutions of Non‐Keggin Mo‐V‐P Heteropoly Acids by Molecular Oxygen

Kinetic peculiarities of regeneration of the aqueous solutions of non‐Keggin‐type Mo‐V‐P heteropoly acids H_aP_zMo_yV_x′O_b (HPA‐x′) and their acidic salts by O₂ are studied. The HPA‐x′ solutions have heightened thermal stability that permits to consider them as highly efficient catalysts for different oxidation processes. In the HPA‐x′ and their salts solutions, these peculiarities prove to be similar. The studied reaction is of the first order with respect to O₂ and V(IV), if [V(IV)] is higher than 0.8 M. As [V(IV)] decreases during the reaction, its order with respect to V(IV) increases to the third. The apparent activation energy of the reaction at temperatures 150–170°С is 37.5 kJ mol^?1. The obtained kinetic equation was used to calculate a new effective air reactor for the regeneration of the homogeneous HPA‐x′ catalyst in a pilot process of methylethylketone synthesis.