Preparation and stress-strain properties of aba block copolymers of α-methylstyrene and butadiene

ABA-type “tapered” block copolymers of α-methylstyrene (monomer A) and butadiene were prepared using four commercially available dilithio initiators. Polymerizations were run at 25°C in benzene solvent, or at 40°C with butadiene dissolved in neat α-methylstyrene. Although α-methylstyrene has a rather low ceiling temperature, triblock copolymers could be made at these temperatures by using α-methylstyrene concentrations well in excess of the [M]_e values at the respective temperatures. Its concentration was such that molecular weights of at least 15,000–20,000 for the A blocks could be attained. The course of the copolymerization at 40°C was followed, showing that copolymers containing about 40% α-methylstyrene could be formed in 4–8 hr, depending on the initiator used. They showed the usual behavior of triblock thermoplastic elastomers, with tensile strengths > 3000 lb/in.² at 24°C. However, because of the high T_g of poly(α-methylstyrene) (172°C), they also had tensiles of several hundred lb/in.² at 100°C, unlike comparable polymers with polystyrene end blocks, which have practically no strength at this temperature. Microstructures of polybutadienes made with these initiators are also given.     

Geminale Substituenteneffekte. VIII. Standardbildungsenthalpien von Acetalen

Geminal Substituent Effects. VIII. Enthalpies of Formation of Acetals The standard enthalpies of combustion ΔH_c° (1 or c) of the α-phenyl-substituted acetals ( 1 ) and diacetals ( 2 ) were measured calorimetrically. The enthalpies of vaporisation or sublimation ΔH_vap or ΔH_sub of 1–2 were obtained from the temperature function of the vapor pressure measured in a flow system, and the standard enthalpies of formation are obtained thereof: ΔH°_f (1 or c) and ΔH_f° (g) (in kJ mol⁻¹) for 1a = −308.40 ± 0.52(1), −248.94 ± 0.88; 1b = −343.48 ± 0.72 (1), −288.5 ± 1.5; 1c = −267.4 ± 1.3 (1), −205.3 ± 1.3; 1d = −343.8 ± 2.1 (c), −261.9 ± 2.2; 1e = −397.02 ± 0.86 (c), −311.3 ± 1.2; 1f = −414.52 ± 0.80 (1), −350.68 ± 0.86; 2a = −564.8 ± 2.4 (c), −467.1 ± 2.5; 2b = −547.6 ± 1.6 (c), −414.9 ± 2.7; 2c = −717.1 ± 7.5 (c), −587.0 ± 8.0. The results are combined into values of two strain free group increments CH[20, C_Ph] = −59.7 and C[20, C_Ph, C] = −71.3 kJ mol⁻¹; and compared to the aliphatic series of acetals.     

Oxidative coupling of 2,6‐dimethylphenol catalyzed by copper(II) complexes in aqueous solution

The oxidative coupling reaction of 2,6‐dimethylphenol (DMP) with H₂O₂ catalyzed by four copper(II) complexes was investigated in Tris‐HNO₃ buffer solution at 25°C. The kinetics of formation of diphenoquinone (DPQ, 4‐(3,5‐dimethyl‐4‐oxo‐2,5‐cyclohexadienylidene)‐2,6‐dimethyl‐2,5‐cyclohexadienone) from DMP was studied in detail. The kinetic parameters k₂ and K_m were obtained in the pH range of 6.0–9.0. The copper(II) complexes exhibited the optimal catalytic activity at around pH 7.0. The pH effect was reasonably explicated by the catalytic kinetic model suggested in this work. The catalytic mechanism was discussed. The deprotonized associated radical LCu^I(OH^?)‐^?OOH was suggested as the possible predominant species to oxidize DMP. The C? C and C? O coupling products were analyzed and the ratio of poly (2,6‐dimethyl‐1,4‐phenylene ether) (PPE) to DPQ was also evaluated. Both in weak acidic (pH < 6.5) and in alkaline aqueous solution (pH > 8) were suitable to the C? O coupling reaction in our catalytic systems. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Renewable Aliphatic Polyesters from Fatty Dienes by Acyclic Diene Metathesis Polycondensation

Three renewable, linear, aliphatic polyesters were prepared by Acyclic diene metathesis (ADMET) polymerization of α,ω-dienes derived from fatty acids. Condensation of 9-decenoic acid with allyl 9-decenoate, ethylene glycol, and 9-decen-1-ol proceeded in high conversion (≥94%) and purity (>99%) to give α,ω-dienes suitable for subsequent polycondensation. Polymerization was achieved using 1.0 mol% Hoveyda-Grubbs second-generation metathesis catalyst in combination with 2.0 mol% 2,6-dichloro-1,4-benzoquinone as an isomerization inhibitor under vacuum to drive equilibria toward polymer formation via ethene removal. Polymerization in the presence of solvent promoted ring-closing metathesis (RCM) at the expense of polymer, with cyclization increasing as the concentration of monomer decreased. Thus, ADMET polymerizations were performed in bulk to mitigate RCM. The resulting polymers with M _n and Ð that ranged from 6.6 to 8.9 kDa and 1.75–2.14, respectively, contained 76% or more of renewable carbon content and exhibited atom and carbon economies of greater than 84%. Melt (T _m) and crystallization (T _c) temperatures were 20.8–48.4 °C and 3.8–37.6 °C, respectively, and increased as ester density decreased within polymer structures. Sub-ambient glass transitions ranged from −10.3 to −50.0 °C. Lastly, the polymers were thermally stable below 320 °C, as 10% mass loss (T₁₀) occurred above 340 °C, which indicated that they existed as liquids for at least 319 °C (T₁₀ − T _m) before decomposing.     

Effect of MgO calcination temperature on the reaction products and kinetics of MgO–SiO2–H2O system

MgO-based binders have been widely studied for decades. Recently, the MgO–SiO₂–H₂O system was developed as a novel construction material, however, its reaction mechanism remains unclear. This paper investigated the reaction products and kinetics of MgO/silica fume (SF) pastes with MgO calcinated at different temperatures. The results indicate that MgO presented larger grain size after calcination at higher temperature. Mg(OH)₂ and magnesium silicate hydrate (M–S–H) gel were formed when using MgO calcined at 850, 950, and 1050°C. However, only M–S–H gel was formed when using MgO calcined at 1450°C. The reaction kinetics of MgO could be described using α = 1 − e^−k*t. The reaction rate of MgO increased with decreasing calcination temperature, increasing SF dosage, and the addition of sodium hexametaphosphate. Only M–S–H gel was formed when the reaction rate of MgO was below the demarcation line (about 0.250 × 10⁻⁶ s⁻¹), and the corresponding demarcation area was around 14 days.     

Micellar-Promoted Stereospecific Hydrolysis of Amino Acid Esters Catalyzed by Peptide-Like Nucleophiles

The efficiency of peptide-type nucleophiles (Z-L-Leu-L-His ( 2a ), Z-D-Leu-L-His ( 2b , Z-L-His-L-Leu ( 2c ), Z-L-Ala-L-His-OMe ( 2d ), Z-L-Leu-L-His-OMe ( 2e ), Z-L-Phe-L-His-OMe ( 2f ), Z-L-Leu-L-His-L-Leu ( 3a ), Z-D-Leu-L-His-L-Leu ( 3b ), and Z-L-Leu-L-Leu-L-His ( 3c )) in the stereospecific hydrolysis of p-nitrophenyl N-acyl-phenylalanates ( 4a -b) was examined at 10–30°C (pH 7.68) in an solution of hexadecyltrimethylammonium bromide ( 5 ). The hydrophobic and chiral amino acid group which is adjacent to the nucleophilic L-histidine part in 2a -f (or 3a-c ) was found to play an important role in determining the closeness of approach between the reactive nucelophile and substrate. The nucleophiles 2a and 3a gave high reactivity and stereospecificity in the hydrolysis of 4b possessing a long N-acyl chain, and the maximum enantiomer rate ratio (L/D), 16.1 (25°C) or 26.2 (10°C), was obtained with mixed micelles of 3a and 5. The structural effect of the nucleophiles on the stereospecific esterolysis of 4a-b is also discussed in detail on the basis of kinetic parameters (K_b/N, k_m, ΔH^‡, and ΔS^‡).     

Reaktivität und Selektivität bei der Oxidation von Styrolderivaten,II. Untersuchungen zur Oxidation von p-substituierten α-Methylstyrolen

Reactivity and Selectivity in the Oxidation of Styrene Derivatives, II. Studies on the Oxidation of p-Substituted α-Methylstyrenes The liquid phase oxidation of p-substituted (Br-, Cl-, t-Bu-, MeO-, CF₃-) α-methylstyrenes and of α,p-dimethoxystyrene with pure oxygen was investigated in chlorobenzene solution and in presence of cumene and of cumene hydroperoxide in the temperature range 65–125°C. The product yields were determined gaschromatographically. The differences of the activation energies of the epoxide formation and the parallel reactions amount to 19–48 kJ/mol. The epoxide selectivity increases with increasing temperature and concentration of olefine. The relative chain propagation constants k_p (CC) were determined by competitive oxidation with cumene. The k_p(CC) values of p-substituted α-methylstyrenes can be correlated by the Hammett equation with both σ and σ⁺ substituent constants.     

Polymerization of α,β-unsaturated carbonyl monomers initiated by 9-borabicyclo [3.3.1] nonane

9-Borabicyclo[3.3.1]nonane (9-BBN) initiated the polymerization of α,β-unsaturated carbonyl monomers such as ethyl acrylate (EA) without an oxidant at low temperatures (to −90°C) under argon. Hydroquinone and 2,6-di-tert-butyl-p-cresol had little effect on the polymerization, indicating that the propagating chain end is not a free radical. The rate of polymerization was found to be proportional to [9-BBN]^1.0 and [EA]^1.5. Electron spin resonance measurements using 5,5-dimethyl-1-pyrroline-N-oxide as a spin trap showed the absence of any radical species under polymerization conditions. No copolymerization of EA with styrene occurred. On the basis of the results obtained, this polymerization was assumed to proceed via a non-radical mechanism.     

Study on Selective Dimerization of α-Methylstyrenes Promoted by Ionic Liquids

The catalytic systems composed of ionic liquids containing BF₄⁻ anion and HBF₄ showed high catalytic activity to produce 4-methyl-2,4-diphenyl-1-pentene (MDP-1) or 1,1,3-trimethyl-3-phenylindan (TPI) under different temperature conditions. Up to 90.8% selectivity to MDP-1 with a 98.7% conversion of α-methylstyrene was obtained at 60 °C in the presence of [HexMIm]BF₄–HBF₄, while exclusive TPI was yielded when the reaction temperature increased to 120 °C. Further studies showed that another ionic liquid, [BMIm]Cl · 2AlCl₃, could act as an excellent catalyst and solvent for the dimerization of α-methylstyrene to produce TPI. The dimerization of α-methylstyrene catalyzed by [HexMIm]BF₄–HBF₄ and [BMIm]Cl · 2AlCl₃ performed the same reaction mechanism and the proton was the active species.     

New polymer syntheses. IX. Synthesis and properties of new conducting polyazomethine polymers containing main chain cycloalkanone and pyridine moieties

Novel polyazomethines containing cycloalkanones or pyridine moieties were synthesized by the polycondensation of 2,5‐bis(m‐aminobenzylidene)cyclopentanone (BMAP, IV), 2,6‐bis(m‐aminobenzylidene)cyclohexanone (BMAH, V), 2,6‐bis(p‐aminobenzylidene)cyclohexanone (BPAH, VI), and 2,6‐bis(m‐aminostyryl)pyridine (BMAS, VIII) diamines with terephthalaldehyde in EtOH at 25°C. These polymers were yellow to orange in color, had reduced viscosities up to 1.42 dL/g, and had electric conductivities as high as 10⁻¹¹–10⁻¹² S cm⁻¹. All the polyazomethines were insoluble in common organic solvents but dissolved completely in concentrated sulfuric acid. However, they were readily hydrolyzed in concentrated H₂SO₄. X‐ray diffraction diagrams showed that the crystallinities of the polyazomethines were low. These azomethine polymers showed high thermal and thermooxidative stability and exhibited no appreciable decomposition up to 400°C in air. The electronic spectra of the polymers indicated a large bathochromic shift of the π–π* absorption band (∼360 nm) that was due to the presence of CN bonds in the polymer main chain. Doping with iodine dramatically raised the conductivity and produced dark brown to black colored semiconductive polymers with a maximum conductivity on the order of 10⁻⁷ S cm⁻¹. Furthermore, the morphology of selected examples of the four polyazomethines was examined by scanning electron microscopy. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1218–1229, 2000     

Predictions based on Munsell notation. I. Perceptual color differences

For every pair of colors (j, k), the observers selected a pair of Munsell grays (N_a, N_b) such that the lightness difference matched the color difference in size, and the scaled value of color difference was defined as d_jk = V_a − V_b. On the basis of these data, where (j, k) are limited in the range that can be matched by d_jk < 4.0 V, the procedure was presented to define predicted values d̃_jk for Munsell colors (J, K) between 4V and 7V directly from Euclidean d̂_jk between points P_j and P_k in the current Munsell solid. The procedure is more practical than the multidimensional scaling representation. Inter‐point d̂_jk are measured in the units of C in the (H, C) plane and the contributions d̂_jk of 1C and 1V differences are assumed to be 1 and 2.3. Precision of predictions, RMS = {mean of d_jk − d̃_nk)²}^0.5, is 0.3 V (0.8 C) for 2‐D color differences (V_j = V_k). For the set of data on 3‐D color differences used in the present study, RMS = 0.6 V (1.7 C). These were compared with the precision of predictions by Judd, Adams–Nickerson formulae, CIE 1976(L*, u*, v*), and CIE94. © 1999 John Wiley & Sons, Inc. Col Res Appl, 24, 10–18, 1999     

Kinetics study of isothermal nicotine release from poly(acrylic acid) hydrogel

The isothermal kinetic of the release of nicotine from a poly(acrylic acid) (PAA) hydrogel was investigated at temperature range from 26°C to 45°C. Specific shape parameters of the kinetic curves, the period of linearity and saturation time were determined. The change in the specific shape parameters of the kinetic curves with temperature and the kinetic parameters of release of nicotine E_a and ln A were determined. By applying the “model fitting” method it was established that the kinetic model of release of nicotine from the PAA hydrogel was [1 − (1 − α)^1/3] = k_Mt. The limiting stage of the kinetics release of nicotine was found to be the contracting volume of the interaction interface. The distribution function of the activation energy was determined and the most probable values of activation energies of 25.5 kJ mol⁻¹ and 35 kJ mol⁻¹ were obtained. Energetically heterogeneity of the interaction interface was explained by the existence of the two different modes of bonding the nicotine molecules onto the hydrogel network by hydrogen bond and electrostatic forces. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Zur Kupplung von 4-substituierten 2-Pyrazolin-5-onen mit p-Chinondiiminkationen; Nachweis isokinetischer Beziehungen

On the Coupling of 4-Substituted 2-Pyrazoline-5-ones with Quinone Diimine Cations; Detection of Isokinetic Relations The temperature dependence of the rate constant k_K of the coupling reaction between pyrazoline-5-ones 1a – i and quinone diimine cations 2a , b is determined in dependence of the substituents at the coupling position (R³:  H,  NN Ar, CHAr–pyrazoline-5-one). The activation enthalpies are between 7 and 60 kJ mol⁻¹ and the activation entropies between −132 and −19 J mol⁻¹ K⁻¹. An isokinetic relation with β = 106°C is found and a rate determining combination of the carbanions of 1a – i with 2a , b is proposed. Contrary to this, the 2-pyrazolin-5-ones 1j – l , n (R³:  S CNH₂NR) obey an isokinetic relation with β = −45°C. Taking into consideration the activation parameters, the low dependence of k_K on the ionic strength, and the decrease of k_K with the increase of the pK values of the couplers, a rate determining splitting off of R³ is assumed.     

Structure and magnetism of a trinuclear CuII–GdIII–CuII complex derived from one-pot reaction with 2,6-di(acetoacetyl)pyridine

A unique 3d–4f mixed metal trinuclear compound, [Cu₂Gd(L)₂(NO₃)₂]NO₃ (1; H₂L=2,6-di(acetoacetyl)pyridine), is derived from a ‘one-pot’ reaction with H₂L,Cu(NO₃)₂·3H₂O and Gd(NO₃)₃·5H₂O. Two L²⁻ providing one central 2,6-diacylpyridine site and two terminal 1,3-diketonate sites hold two Cu^II ions and Gd^III ion and form a linear Cu–Gd–Cu trinuclear core. This compound shows ferromagnetic interaction between Cu^II and Gd^III.     

Nitridation of silicon powder studied by XRD, 29Si MAS NMR and surface analysis techniques

The nitridation of elemental silicon powder at 900–1475 °C was studied by X-ray photoelectron spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES), XRD, thermal analysis and ²⁹Si MAS NMR. An initial mass gain of about 12% at 1250–1300 °C corresponds to the formation of a product layer about 0·2 μm thick (assuming spherical particles). XPS and XAES show that in this temperature range, the surface atomic ratio of N/Si increases and the ratio O/Si decreases as the surface layer is converted to Si₂N₂O. XRD shows that above 1300 °C the Si is rapidly converted to a mixture of α- and β-Si₃N₄, the latter predominating >1400 °C. In this temperature range there are only slight changes in the composition of the surface material, which at the higher temperatures regains a small amount of an oxidised surface layer. By contrast, in the interval 1400–1475 °C, the ²⁹Si MAS NMR chemical shift of the elemental Si changes progressively from about −80 ppm to −70 ppm, in tandem with the growth of the Si₃N₄ resonance at about −48 ppm. Possible reasons for this previously unreported change in the Si chemical shift are discussed. ©     

Microcrystalline-cellulose hydrolysis with concentrated sulphuric acid

The effects of temperature (25–40°C), H₂SO₄ concentration (31–70% (w/v)) and the acid/substrate relationship (1–5 cm³ of H₂SO₄ per g⁻¹ of cellulose) on the solubilization rate of microcrystalline cellulose and on the glucose production rate have been analysed. The solubilization process was by determining reducing groups present in solution. For acid/substrate relationships of more than 1 cm³ g⁻¹ and H₂SO₄ concentrations of greater than 62% (w/v), the acid promoted the total solubilization of the cellulose in the form of chains with a low degree of polymerization within 4 h. The solubilization demonstrated zero-order kinetics in which the specific rate and time of total solubilization are a function of the variables in operation. Glucose was produced according to a mechanism of two consecutive first-order pseudo-homogeneous reactions. The values of the kinetic constants k₁ and k₂ have been correlated with temperature, the H₂SO₄ concentration and the acid/substrate relationship.     

Autoxidation of methyl linoleate initiated by the ozonide of allylbenzene

Allylbenzene ozonide (ABO), a model for polyunsaturated fatty acid (PUFA) ozonides, initiates the autoxidation of methyl linoleate (18∶2 ME) at 37°C under 760 torr of oxygen. This process is inhibited by d-α-tocopherol (α-T) and 2,6-di-ert-butyl-4-methylphenol (BHT). The autoxidation was followed by the appearance of conjugated diene (CD), as well as by oxygen-uptake. The rates of autoxidation are proportional to the square root of ABO concentration, implying that the usual free radical autoxidation rate law is obeyed. Activation parameters for the thermal decomposition of ABO were determined under N₂ in the presence of radical scavengers and found to be E_a=28.2 ±0.3 kcal mol⁻¹ and log A=13.6±0.2; k_d (37°C) is calculated to be (5.1±0.3)×10⁻⁷ sec⁻¹. Autoxidation data are also reported for ozonides of 18∶2 ME and methyl oleate (18∶1 ME).     

Properties of coal tar characterized by slight pyrolysis

The behavior of coal tars with different levels of pyrolysis in thermal fractionation is compared in the laboratory. The properties and group composition of the nonboiling residues (medium-temperature pitch) obtained by the distillation of coal tars at different temperatures, in comparable conditions, is investigated. The results indicate that the distillation of tars characterized by slight pyrolysis is accompanied by vigorous destruction processes, also affecting the α₁ fraction (t = 335–350°C), with subsequent reactions among the destruction products, leading to active increase in the α₁ and α₂ fractions (t ≥ 350°C). This is a significant difference between tars characterized by light pyrolysis and considerable pyrolysis.     

Humid aging of polyetherimide. I. Water sorption characteristics

The sorption and desorption kinetics of water into polyetherimide (ULTEM 1000) were studied at various temperatures ranging from 20 to 100°C. The water equilibrium concentration increases slightly with temperature from 1.39% (by weight) at 20°C to 1.50% at 100°C. The solubility coefficient, S, calculated from these data, and the water vapor pressure decrease with temperature. The calculated heat of dissolution H_s is close to −43 kJ mol⁻¹, which explains the low effect of temperature on the equilibrium concentration. The diffusion coefficient, D, varies from about 1.10⁻¹² m² · s⁻¹ at 20°C to about 16.10⁻¹² m² · s⁻¹ at 100°C. The apparent activation energy of diffusion, E_D, and the heat of dissolution, H_s, of water in the polymer have opposite values (respectively, +43 and −42 kJ · mol⁻¹). From this observation and a comparison of these data with water diffusion characteristics in other glassy polar polymers, it is hypothesized that the transport rate of water is kinetically controlled by the dissociation of water–polymer complexes. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1439–1444, 2000     

Synthesis of 5-ethoxymethylfurfural from glucose catalyzed by porous tetra-component metal oxides solid acid

The production of 5-ethoxymethylfurfural (EMF) from cheap and abundant glucose feedstock has attracted a great deal of attention because of its potential applications. Herein, three porous tetra-component metal oxide solid acid catalysts (SO₄²⁻/ZFSA-A, SO₄²⁻/ZFSA-F-10, SO₄²⁻/ZFSA-F-20) containing both Brønsted and Lewis acid sites have been successfully synthesized and can efficiently catalyze the synthesis of EMF from glucose. Particularly, the SO₄²⁻/ZFSA-A, SO₄²⁻/ZFSA-F-10, and SO₄²⁻/ZFSA-F-20 catalysts were prepared under the template of sodium alginate, 10% F127, and 20% F127, respectively. The prepared catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), N₂-adsorption–desorption isotherm, X-ray photoelectron spectroscopy (XPS), thermogravimetry (TG), temperature-programmed desorption of ammonia (NH₃-TPD), and pyridine infrared spectra (Py-FTIR). The characterization results indicated that all three catalysts have a porous structure. The pore distribution of the SO₄²⁻/ZFSA-A catalyst is mainly macroporous and mesoporous, while the SO₄²⁻/ZFSA-F-10 and SO₄²⁻/ZFSA-F-20 catalysts are mainly mesoporous. The SO₄²⁻/ZFSA-F-20 catalyst exhibited the highest catalytic performance due to its large specific surface area, desirable mesoporous structure, high total acidity (especially strong and super strong acidity), and appropriate Lewis/Brønsted acid ratio. By applying SO₄²⁻/ZFSA-F-20, the formation of EMF from glucose was successfully catalyzed and EMF was obtained at a yield of 34.56% after 12 h at 160°C. This yield is much higher compared with most other results achieved by solid acids catalysis. In addition, the reaction parameters such as reaction temperature, reaction time, glucose amount, and catalyst dosage were shown to have a significant effect on the catalytic performance. Notably, the SO₄²⁻/ZFSA-F-20 catalyst exhibited good reusability, as its activity did not significantly diminish after four rounds of repeated experiments and was successfully reactivated after calcination.