Cold crystallization and thermal shrinkage of uniaxially drawn poly(ethylene 2,6-naphthalate) by solid-state coextrusion

Solid-state coextrusion has been used to prepare uniaxially drawn films from isotropic poly(ethylene 2,6-naphthalate) (PEN) of a minimum degree of crystallinity (ca. 5%) both below and above its glass transition temperature T_g. The onset of cold crystallization (T_c) of the drawn films has been studied as a function of the extrusion temperature (ET) and the draw ratio (EDR). It has been shown that T_c decreases markedly on draw, as much as 95°C, and, at constant draw ratio T_c goes through a minimum in the T_g region. For undrawn PEN, annealing below 153°C has no significant effect on T_c. To evaluate the crystallization rate constant (k) and the activation energy (E_a) of the drawn specimens, a nonisothermal DSC procedure has been used. With increasing EDR, k increases markedly and E_a goes down over threefold compared with the undrawn polymer. At high ET, strain-induced crystallization has also been shown to play an important role in lowering E_a for cold crystallization. Thermal shrinkage above T_m indicates a high elastic recovery, underlining the efficiency of deformation, ca. 93%, achieved by solid-state coextrusion.     

外偶极电场作用下H_2O,D_2O和T_2O的可逆分解电压

采用密度泛函B3P86方法和6-311++G(3df,3pf)基组,计算了在-0.05～0.05a.u.外偶极电场作用下,H2O,D2O,T2O,H2,D2,T2,O2的电子能量、核运动能量和熵值,在此基础上通过计算H2O(g)→H2(g)+O2(g)、D2O(g)→D2(g)+O2(g)、T2O(g)→T2(g)+O2(g)的焓变ΔH、熵变ΔS、Gibbs函数变化ΔG,最后得到了H2O,D2O,T2O的可逆分解电压Er.计算结果表明,外偶极电场存在时,H2O,D2O,T2O的Gibbs自由能变ΔG和可逆分解电压Er都有明显的变化,当外偶极电场正方向增加时,其Gibbs自由能变ΔG和可逆分解电压Er均趋于线性增加;当外偶极电场负方向增加时,其Gibbs自由能变ΔG和可逆分解电压Er均趋于线性减小;在相同外偶极电场作用下,Gibbs自由能变ΔG和可逆分解电压Er随H2O,D2O,T2O依次增加.     

The aggregation of nonionic surfactants in the presence of poly(methacrylic acid)

The solution properties of homogeneous hexaethylene and octaethylene glycol mono(n-dodecyl) ethers, C₁₂E₆ and C₁₂E₈, respectively, and octaethylene glycol mono(n-decyl) ether, C₁₀E₈, with poly(methacrylic acid) (PMA) were investigated by dye solubilization, surface tension, fluorescence, viscosity, and pH measurements. The data were discussed regarding non-cooperative and cooperative binding of surfactant to polymer. Whereas in the interaction with poly(acrylic acid) (PAA), the critical aggregation concentrations (cac or T ₁) of these surfactants were lower than the respective critical micelle concentration (cmc), in that with the more hydrophobic PMA, T ₁’s of C₁₂E₆ and C₁₂E₈ were higher than the respective cmc, but that of C₁₀E₈ was lower than its cmc. These may be ascribed to the hydrophobic microdomains (HMD) of the PMA coil in water, probably in its inside. It is considered that some surfactants are bound first to the HMD non-cooperatively and then they are abruptly bound cooperatively at T ₁. This raises T ₁ higher than cmc when the cmc is low, and the amount bound by the HMD is relatively large and vice versa. T ₁ of C₁₂E₆ or C₁₂E₈ is the former case, and that of C₁₀E₈ is the latter. Thus, different from PAA, T ₁ for PMA + nonionic surfactant system consists of the amount of non-cooperative binding and the cac of the cooperative binding in equilibrium. Therefore, this T ₁ has a different meaning from that for PAA and should be called apparent T ₁. As the binding to the HMD is dependent on PMA concentration and cac is not, which is like in the PAA system, separation of apparent T ₁ from the HMD binding was achieved by extrapolating T ₁’s to zero PMA concentration (denoted intrinsic T ₁). This value for C₁₂E₈ was found to be lower than the respective cmc and also lower than the respective T ₁ for PAA. With increase in surfactant concentration, the pH of PMA solution rose and demonstrated a peak. This pH rise and fall may be induced by loosening of the HMD coil due to binding increase and by rearrangement of PMA + surfactant complex in high surfactant concentrations region. By raising the initial pH, the HMD were loosened; consequently, T ₁ rose a little, and at higher pH, no surfactant binding took place.     

Polarit?t bin?rer L?sungsmittelgemische: Bestimmung von ET(30)-Werten und Korrelation mit kinetischen L?sungsmittel-Effekten

Zusammenfassung Zur empirischen Beschreibung der Polarität binärer Lösungsmittelgemische wurden mit einem solvatochromen Betain-Farbstoff E_T-Werte für folgende Systeme bestimmt: Methanol/Butanol-2, Methanol/2-Methylbutanol-2, Methanol/Pyridin, Methanol/Acetonitril, Methanol/Toluol und Ethanol/ 2,2,2-Trifluorethanol. In allen Systemen treten mehr oder weniger starke Abweichungen vom idealen Mischungsverhalten auf, was im einzelnen diskutiert wird. In den genannten Lösungsmittelgemischen wurde parallel die Kinetik der Ligandensubstitution an einem neutralen Kupfer(II)-bis-chelatkomplex vermessen. Die E_T-Werte korrelieren mit den lnkWerten (k = Geschwindigkeitskonstante für den durch das Solvens induzierten Ligandenaustausch). Dies weist darauf hin, daß die Bildung des Übergangszustandes durch H-Brücken erleichtert wird.

---

Polarity of binary solvent mixtures: Determination of E_T(30)-values and correlation with kinetic solvent effects

Summary The polarity of binary solvent mixtures is empirically described by E_T-values as determined with a solvatochromic betaine dye. The following mixtures were studied: methanol/butanol-2, methanol/2-methylbutanol-2, methanol/pyridine, methanol/acetonitrile, methanol/toluene and ethanol/2,2,2-trifluoroethanol. All mixtures behave as more or less non-ideal systems which is discussed in detail. Parallel to the determination of E_T-values the kinetics of ligand substitution in a neutral copper(II)-bis-chelate complex were studied in the same set of solvent mixtures. The E_T-values correlate with the corresponding lnk-values (k = rate constant for solvent induced ligand substitution). This would mean that the formation of the transition state is facilitated by hydrogen bonding.

Für finanzielle Unterstützung bedanken wir uns bei der Deutschen Forschungsgemeinschaft und dem Verband der Chemischen Industrie e.V. Der verwendete Salicylaldehyd wurde uns von der Firma Bayer AG, Leverkusen, zur Verfügung gestellt.     

Hydrogen Peroxide Biosensor Based on the Electrochemistry of the Myoglobin‐TATP Composite Film

Abstract

Direct electrochemistry of the myoglobin‐triacetone triperoxide (Mb‐TATP) composite on carbon paste (CP) electrode is reported. This electrode gives a well‐defined and quasi‐reversible cyclic voltammogram for the Mb Fe^III/Fe^II redox coupled with the formal potential (E?′) of ?0.302 V (vs. Ag/AgCl) in pH 6.92 phosphate buffer. Electronic and vibrational spectroscopies show that the Mb in the composite retains a structure similar to its native form. The enzymatic reactivity to the reduction of H₂O₂ has been studied for the Mb‐TATP film. The analytical performances have been obtained with the linear range of 78.32–1135.64 µM, the detection limit of 55 µM (S/N=3), and the apparent Michaelis‐Menten constant (K _m) of 662.8 µM. This H₂O₂ biosensor based on the electrocatalysis of the immobilized Mb presents a higher stability within two weeks.     

Unusual Effects of Pure Nonionic and Mixed Nonionic–Cationic Micelles on the Rate of Alkaline Hydrolysis of N-Hydroxyphthalimide

Pseudo-first-order rate constants, k_obs, for the alkaline hydrolysis of N-hydroxyphthalimide, 1, at 0.02 M NaOH and 30°C remain essentially independent of the total concentration of C₁₂E₂₃, [C₁₂E₂₃]_T, at ≤0.005 M C₁₂E₂₃. The increase in [C₁₂ E₂₃]_T from 0.005 to 0.015 M causes a nonlinear decrease in k_obs. The rate of hydrolysis becomes either too slow or the change in absorbance values becomes significantly small to allow a reliable observed data fit to a first-order kinetic equation at ≥0.020 M C₁₂E₂₃ in the absence and presence of total concentration of cetyltrimethylammonium bromide, [CTABr]_T ranging from 0.003 to 0.020 M. The values of fraction of nonionized 1, F_SH, obtained at reaction time t = 0 and 0.02 M NaOH, remain ～0 at ≤0.010 M C₁₂E₂₃ while they increase from 0.39 to 0.89 with the increase of [C₁₂E₂₃]_T from 0.015 to 0.10 M. The values of k_obs show a nonlinear decrease of ～5-fold with the increase of [C₁₂E₂₃]_T from 0.0 to 0.010 M in the presence of 0.02 M NaOH and [CTABr]_T range of 0.003 to 0.020 M. The values of F_SH remain ≤～0.10 at ≤0.015 M C₁₂E₂₃ while they vary between 0.40 and 0.90 within a [C₁₂E₂₃]_T range 0.02 to 0.05 M in the presence of 0.02 M NaOH and [CTABr]_T ranging from 0.003 to 0.020 M. The values of F_SH represent the fraction of nonionized 1 trapped almost irreversibly by pure C₁₂E₂₃, and mixed C₁₂E₂₃–CTABr micelles.     

Kinetic Analysis of Thermal Decomposition of Ca(OH)2 Formed During Hydration of Commercial Portland Cement by DSC

In this paper, evaluation of kinetic parameters (the activation energy – E,the pre-exponential factor – A and the reaction order – n) with simultaneous determination of the possible reaction mechanism of thermal decomposition of calcium hydroxide (portlandite), Ca(OH)₂ formed during hydration of commercial Portland-slag cement, by means of differential scanning calorimetry (DSC) in non-isothermal conditions with a single heating–rate plot has been studied and discussed. The kinetic parameters and a mechanism function were calculated by fitting the experimental data to the integral, differential and rate equation methods. To determine the most probable mechanism, 30 forms of the solid-state mechanism functions, f(α_c) have been tried. Having used the procedure developed and the appropriate program support, it has been established that the non-isothermal thermal decomposition of calcium hydroxide in the acceleratory period (0.004<α_c<0.554) can be described by the rate equation: d α_c/dT=A/βexp(−E/RT)f(α_c), which is based on the concept of the mechanism reaction:f(α_c)=2(α_c)^1/2. The mechanism functions as well as the values of the kinetic parameters are in good agreement with those given in literature. This revised version was published online in August 2006 with corrections to the Cover Date.     

Development of master curves for discriminating the mechanism of solid state reactions from experimental data obtained by using the cyclic and controlled rate thermal analysis

The cyclic and Controlled Rate Thermal Analysis method (CRTA) has been used. The two rates automatically selected in the cyclic curve are small enough to allow the two states of the sample to be compared have nearly the same reacted fraction. Thus, the activation energy can be calculated without previous knowledge of the actual reaction mechanism. Provided that the activation energy,E, is known, a procedure has been developed for determining the kinetic law obeyed by the reaction by means of master curves that represent the values of the reacted fraction, α, as a function of?E/R(1/T-1/T _0.5),T _0.5 being the temperature at which α=0.5. This procedure has been tested by studying the thermal decomposition reaction of BaCO₃.     

GC-MS Analysis of Contaminants in Breathing Oxygen

Abstract

Oxygen used for flight crews and for extra-hospital therapies is kept in vacuum containers and maintained as liquid phase (LOX) until use; by using this procedure, the weight of the breathing apparatus is reduced, thus extending breathing oxygen availability and improving safety by using atmosphere pressure sampler.

On the other hand, because of its low boiling point (?183°C), during storage and distribution, LOX shows continuous evaporation with a constant increase in pollutant concentration obtained in the LOX production.

Therefore, LOX is subjected to a strict quality control to evaluate the contamination levels from production until its use.

In this study, an analytical procedure has been optimised to measure the main LOX contaminants (freon, chlorinated solvents, light hydrocarbons, CO₂, CO, and N₂O) based on a single technique (GC-MS) and two chromatographic columns (Poraplot Q/HT and HP-Plot molecular sieve 5 A). The proposed method is an improvement in terms of time as well cost of analysis and selectivity with respect to the present methods based on three chromatographic techniques (GC-ECD, GC-FID, GC-HID) and four different columns.     

Raman spectroscopy of arsenolite: crystalline cubic As4O6

The complete Raman spectrum of arsenolite, cubic crystalline As₄O₆, is reported for the first time. The previously unseen E_g mode has been found at 443 cm⁻¹. Further, there is additional support for the assignment of the 415 cm⁻¹ mode as T_2g.     

Chemical Tailoring Assisted non-TADF to TADF Switching in Carbazole-Benzophenone Emitter – An In-silico Investigation

Organic light-emitting diodes (OLEDs) have become one of the most popular lighting technologies since they offer several advantages over conventional devices. In carbazole-benzophenone (CzBP) OLED devices, the polymeric form of the compound is previously reported to be Thermally Activated Delayed Fluorescence (TADF)-active (ΔE_ST ≈0.12 eV), while the monomer ( CzBP ) (ΔE_ST≈0.39 eV) does not. The present study examines the effect of chemical tailoring on the optical and photophysical properties of CzBP using DFT and TDDFT methods. The introduction of a single −NO₂ group or di-substitution (−NO₂, −COOH or −CN) in the selected LUMO region of the reference CzBP monomer significantly reduces ΔE_ST≈0.01 eV, projecting these systems as potential TADF-active emitters. Furthermore, the chemical modification of CzBP -LUMO alters the two-step TADF mechanism (T₁→T₂→S₁) in CzBP (E_S₁>E_T2>E_T₁) to the Direct Singlet Harvesting (T₁→S₁) mechanism (E_T2>E_S₁>E_T₁), which has recently been identified in the fourth-generation OLED materials.     

Thermal analysis study on the simultaneous grain refinement and modification of 380.3 aluminum alloy

In this research, effect of integrated Al–10Sr–1Ti–2B master alloy has been studied on the microstructure and solidification characteristics of 380.3 aluminum alloy. Thermal Analysis has been used as a technique to study the cooling curves and first derivative curves during solidification of the alloy. Effect of integrated grain refiner and modifier on solidification parameters such as α-Al dendrite growth temperature (T _G,α), α-Al dendrite recalescence undercooling (?T _R,α), aluminum–silicon eutectic growth temperature (T _G,E), and eutectic recalescence undercooling (?T _R,E) has been determined. By increasing master alloy content, T _G,α and ?T _R,E have been increased, but, ?T _R,E has been decreased, and T _G,E increases first and then decreases. Aluminum–silicon eutectic depression temperature ( $ \Updelta T_{\text{G,E}}^{{{\text{Al}} - {\text{Si}}}} $ ) can be used as a parameter to control the modification of eutectic silicon. The results of this research indicate that the optimum level of Al–10Sr–1Ti–2B master alloy for the simultaneous grain refinement and modification of 380.3 alloy is about 0.5 mass%.     

Stable α-heteroatom-free dialkylcarbenes: a DFT study

The stability of the singlet dicyclopropylcarbene (ΔE _S–T = 15.3 kcal/mol, 1) is increased not only by cyclization to 2,5-dicyclopropylcyclopentanylidene (ΔE _S–T = 20.3 kcal/mol, 2), but even more so by unsaturation to 2,5-dicyclopropylcyclopentenylidene (ΔE _S–T = 22.5 kcal/mol, 3). In a further attempt to pave the way toward synthesis of new stable dialkylcarbenes, we introduced different substituents on the α-cyclopropyls of 3, where the stability was increased over twice of 1 (ΔE _S–T = 37.8 kcal/mol) for 2,5-bis(2,3-dihydroxycyclopropyl)-3,4-dinitrocyclopentenylidene, 3_{\textOH-\textNO 2} {\mathbf{3}}_{{{\text{OH}}{-}{\text{NO}}_{ 2}}} .     

Facile Construction of the 7,8‐Olefin Linkage in Vitamin D3: A Practical Synthesis Benefiting the Vitamin D3 Analog Study

Abstract

A facile procedure for construction of the 7,8‐olefin linkage in vitamin D₃ is described. Treatment of a mixture of A‐ring phosphine oxide and CD‐ring ketone in THF with lithium hexamethyldisilazide (LHMDS) at ?20°C followed by gradual heating to 50°C gives the key intermediate of vitamin D₃ analogs in excellent yield. This simplified procedure makes possible small‐scale synthesis benefiting the vitamin D₃ analog study.     

Synthesis of diblock copolymers with cellulose derivatives. 3. Cellulose derivatives carrying a single pyrene group at the reducing-end and fluorescent studies of their self-assembly systems in aqueous NaOH solutions

Novel cellobiose and cellulose (DP _n =ca. 30) derivatives, N-(1-pyrenebutyloyl)-4-O-(β-d-glucopyranosyl)-β-d-glucopyranosylamine (6), N-(15-(1-pyrenebutyloylamino)-pentadecanoyl)-4-O-(β-d-glucopyranosyl)-β-d-glucopyranosylamine (7), N-(1-pyrenebutyloyl)-β-cellulosylamine (13), N-(15-(1-pyrenebutyloylamino)-pentadecanoyl)-β-cellulosylamine (14) carrying a pyrene group as a single fluorescent probe at the reducing end, were prepared in order to investigate their self-assembly systems in solutions. The relative intensity of the excimer emission at ca. 480 nm due to dimerized pyrenes (intensity I _E) to the monomer emission at ca. 380 nm due to isolated pyrene (intensity I _M), i.e., I _E/I _M, was monitored in various solutions. In water/dimethyl sulfoxide (DMSO) mixed solvent (0–98%, v/v), the ratio I _E/I _M remained low (0.04) for compound 6 over the range of water concentrations, indicating that pyrenes at C-1 position of compound 6 were diffused. On the other hand, the ratio I _E/I _M increased (0.04–4.96) for compound 7 with the increase in water concentration, indicating that pyrenes at C-1 position were associated. In aqueous NaOH solutions (4.4–17.5%, w/w), compound 14 showed a large increase in the ratio I _E/I _M (0.84–8.14) with the increase in NaOH concentration, compared to compound 13 (0.06–0.41). It was found that the association of hydrophobic groups at the reducing-end of cellulose could be controlled by the hydrophilic–hydrophobic balance of compounds and the solvent polarity.     

KOH/t-Butanol, eine wertvolle Alternative bei der Ma?analyse sehr schwacher S?uren

Zusammenfassung Ein neues Verfahren zur Bestimmung von Wasser in organischen Lösungsmitteln (auch in Spuren) wird beschrieben. Die Solvatochromie des Pyridiniumphenolbetains E _T30, die über eine einfach auszuführende UV-Absorptionsmessung bestimmt wird, ermöglicht zusammen mit einer zwei-Parameter-Gleichung eine exakte Wasserbestimmung in organischen Lösungsmitteln als Schnelltest und stellt damit eine Alternative zur Karl-Fischer-Titration dar.

---

A new, uncomplicated procedure for the determination of small concentrations of water in organic solvents

Summary A new procedure for the determination of water (even in trace amounts) in organic solvents is described. The solvatochromism of the pyridiniumphenol betaine, E _T30, determined by a simple UV-absorption measurement, together with a two-parameter equation, permits an exact determination. The procedure is rapid and is, therefore, an alternative to the Karl-Fischer titration.

Herrn Prof. Dr. C. Rüchardt wird für die Unterstützung gedankt.     

超分子凝胶性质与溶剂参数关系的研究进展

为了能有效地开发功能性凝胶, 人们对超分子凝胶机理做了大量研究. 但目前的研究还局限于凝胶因子结构和外界环境等影响因素, 而有关溶剂对超分子凝胶体系的影响规律还不十分清楚. 本文将结合最新研究进展详细地讨论凝胶性质(如凝胶-溶胶转变温度(T_gel)、临界凝胶浓度(CGC)、凝胶流变学性质等)与溶剂参数(如ε、E_T(30)、χ、δ、δ_d、δ_p、δ_h等)的关系, 揭示溶剂影响凝胶性质的规律; 在此基础上, 进一步介绍了超分子凝胶行为预测模型: 一维模型、Teas图模型和Hansen空间模型, 并讨论了各模型的优缺点, 以期为新型超分子凝胶体系的设计提供参考.     

The effect of CH<Subscript>3</Subscript>, F and NO<Subscript>2</Subscript> substituents on the individual hydrogen bond energies in the adenine–thymine and guanine–cytosine base pairs

The substituent effects on the geometrical parameters and the individual hydrogen bond (HB) energies of base pairs such as X–adenine–thymine (X–A–T), X–thymine–adenine (X–T–A), X–guanine–cytosine (X–G–C), and X–cytosine–guanine (X–C–G) have been studied by the quantum mechanical calculations at the B3LYP and MP2 levels with the 6–311++G(d,p) basis set. The electron withdrawing (EW) substituents (F and NO₂) increase the total binding energy (ΔE) of X–G–C derivatives and the electron donating (ED) substituent (CH₃) decreases it when they are introduced in the 8 and 9 positions of G. The effects of substituents are reversed when they are located in the 1, 5, and 6 positions of C, with exception of CH₃ in the 1 position and F in the 5 position, which in both cases the ΔE value decreases negligibly small. With minor exceptions (X=8–CH₃, 8–F, and 9–NO₂), both ED and EW substituents increase slightly the ΔE values of X–A–T derivatives. The individual HB energies (∆E _HBs) have been estimated using electron densities that calculated at the hydrogen bond critical points (HBCPs) by the atoms in molecules (AIM) method. Most of changes of individual HBs are in consistent with the ED/EW nature of substituents and the role of atoms entered H-bonding. The remarkable change is observed for NO₂ substituted derivative in each case.     

Hydrothermal Synthesis of Regular Octahedron Fe3O4 Microcrystals

Regular octahedron Fe₃O₄ microcrystals have been synthesized by a hydrothermal process on a large scale directly Fe substrates for the first time. X-ray diffraction (XRD) and scanning electron microscopy (SEM) have been used to investigate the novel fractal microcrystals. The results show that the regular octahedron Fe₃O₄ microcrystals can be obtained using this simple method. The size of microcrystals is evaluated to be from 2 to 20 μm. Moreover, one key fact has been found that the reaction temperature has a vital effect on the morphologies of the products.     

Ground state multiplicity of acylnitrenes: computational and experimental studies

The singlet—triplet energy splitting (ΔE _ST = E _S − E _T ) was calculated for formylnitrene (5) and for the syn- and anti-rotamers of carboxynitrene HOC(O)N (6) by the CCSD(T) method. Extrapolation of ΔE _ST to a complete basis set was calculated to be negative for 5 and strongly positive for 6. Similar results were obtained by the G2 procedure. The reason for the dramatic stabilization of the singlet state appeared to be a special bonding interaction between the nitrogen and oxygen atoms, which results in the structure intermediate between those of nitrene and oxazirene. It was found that the B3LYP/6-31G(d) method overestimates ΔE _ST by ∼9 kcal mol⁻¹ for 5 and by ∼7 kcal mol⁻¹ for 6. Taking into account this overestimation and the results of DFT calculations, it was concluded that benzoylnitrene has a singlet ground state. It was proved experimentally using photolysis of benzoyl azide in an argon matrix at 12 K that benzoylnitrene has a singlet ground state and its structure is similar to that of oxazirene. Nevertheless, these singlet intermediates have low barrier to the aziridine formation, which is traditionally considered to be a typical singlet nitrene reaction.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 519–526, March, 2005.