Crystal Structures of Tetrakis‐(4‐chlorophenylthio)‐butatriene and Tetrakis‐(tert‐butylthio)‐butatriene

Tetrakis‐(4‐chlorophenylthio)‐butatriene (3a) and tetrakis‐(tert‐butylthio)‐butatriene (3b) were synthesized, and their crystal structures were determined. The compound 3a is monoclinic, space group P2₁/c, a=6.9785(8), b=8.6803(9), c=22.884(2) Å, β=93.887(6)^o, V=1383.0(3) ų, Z=2. The compound 3b is monoclinic, space group P2₁/n, a=11.0615(6), b=10.8507(4), c=11.2717(6) Å, β =116.427(2)^o, V=1211.5(1) ų, Z=4. The title compounds 3a and 3b reside on an inversion center so that only half of the molecule is crystallographically unique. Both compounds are not planar. The crystal structures of 3a and 3b have cumulated double bonds. The C7–C8–C8ⁱ and C5–C6–C6ⁱ angles that show the linearity in both structures, respectively, are 176.4(3)° in 3a and 175.6(2)° in 3b.     

pH‐Sensitive Polyacrylic Acid (PAA) Hydrogels Trapped with Polysodium‐p‐Styrenesulfonate (PSS)

The preparation of a new type of semi‐interpenetration network system of polyacrylic acid (PAA) hydrogel trapped with polysodium‐p‐styrenesulfonate (PSS) is presented. The structure and response properties of PAA/PSS were investigated by Fourier transform infrared (FTIR) analysis and pH and ionic intensity stimuli‐responsive measurement. The FTIR analysis proved the successful intermingling of PSS into PAA. The swelling behavior of PAA hydrogel in an alkaline environment was improved due to the addition of PSS. As the ionic concentration in solution increased, the swelling rate of PAA decreased after adding PSS. However, the swelling velocity of the pure PAA is quicker than that of the PAA/PSS samples since the PSS will enhance the entanglement of this hydrogel network and slow down the swelling velocity. Multi‐interactions between the PAA hydrogel network and trapped PSS chains, including electrostatic repulsive interaction, entanglement interaction, ionic intensity interaction, and osmotic pressure, were proposed to explain the earlier‐mentioned experimental phenomena.     

Nanostructured Thermosetting Blends of Phenolic Thermosets and Poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) Triblock Copolymer

The amphiphilic triblock copolymer, poly(ethylene oxide)‐block‐poly(propylene oxide)‐block‐poly(ethylene oxide) (PEO‐b‐PPO‐b‐PEO) was incorporated into novolac resin to prepare thermosetting blends. The morphology of the thermosetting blends was investigated by means of atomic force microscopy (AFM) and small‐angle x‐ray scattering (SAXS) and the nanostructures were obtained. It was identified that the reaction‐induced phase separation occurred in the blends of phenolic thermosets with the model poly(propylene oxide) (PPO), whereas poly(ethylene oxide) (PEO) was miscible with novolac resin after and before the curing reaction. In terms of miscibility and phase behavior of the subchains of the triblock copolymer with novolac resin, it was demonstrated that the formation of nanostructures in the thermosets followed a mechanism of reaction‐induced microphase separation.     

Influence of N‐Substitution on Electron Spin Resonance (ESR) Behavior of 2‐(2‐Nitrophenyl)‐1H‐benzimidazole Derivatives

Abstract

The synthesis of 2‐(2‐nitrophenyl)‐1H‐benzimidazole (1), 1‐benzoyl‐2‐(2‐nitrophenyl)‐1H ‐benzimidazole (2), and 1‐acetyl‐2‐(2‐nitrophenyl)‐1H‐benzimidazole (3) is reported. Stable radical anions (1 ^·?, 2 ^·?, and 3 ^·?) were generated by chemical reduction in DMSO and studied by ESR spectroscopy. The interpretation of the ESR spectra was done by means of computational simulation process. Hyperfine coupling constants were assigned by comparison with related compounds, and on the basis of calculation based on SCF INDO MO method in the unrestricted Hartree–Fock scheme.     

Steady–shear‐induced Isothermal Crystallization of Poly(L‐lactide) (PLLA)

The isothermal crystallization of poly(L‐lactide) (PLLA) under steady‐shear flow was investigated in situ using an optical polarizing microscope with a hot shear stage. The steady–shear‐induced crystalline morphology of PLLA, to a great degree, depends on the crystallization temperature. There is a critical temperature, 120°C, below which shear‐induced row nuclei enhance nucleation ability, leading to the improvement of crystallinity, and above which cylindrite structure is generated. Their numbers increase and size reduces with temperature owing to the better movement and relaxation behavior of chains in the presence of shear flow. The results of 2D wide‐angle x‐ray diffraction (WAXD), showing the oriented structure at high T _c , and differential scanning calorimetry (DSC), detecting the rising of T _m with increasing T _c , well confirm the effect of T _c on the crystallization of PLLA under shear flow.     

Electrochemical Synthesis and Structure of Poly(2‐methyl‐1‐naphthylamine) Films

A novel polymer, poly(2‐methyl‐1‐naphthylamine), which was synthesized electrochemically at various temperatures from a solution containing 2‐methyl‐1‐naphthylamine, acetic acid and sodium acetate, was characterized by IR spectroscopy. The structural conclusions were based on comparisons of polymer spectra with the IR‐spectrum of the monomer, 2‐methyl‐1‐naphthylamine. IR spectroscopy indicates that the electropolymerization proceeds via the –NH₂ groups and that the poly(2‐methyl‐1‐naphthylamine) structure consists of imine (–N?C) and amine (–NH–C) links between naphthalene rings as well as a free methyl groups in the chains. An analysis of the “substitution pattern” region in the polymer's spectra suggests that the polymer molecules were formed via mixed N–C(4), N–C(5) and N–C(7) linkages between repeated units. The ratio of between the 1645 and 1620 cm^? 1 peak areas decreases with increased temperature during synthesis, indicating that 25°C is the best temperature to obtain higher molecular weights.     

Thermal Behavior of Polyamide‐12 and Poly (Styrene‐Co‐Acrylonitrile) Blend

In this work, an unusual morphology of a mixture of polyamide‐12 (PA‐12) with a series of poly (styrene‐co‐acrylonitrile) (SAN) was obtained by solution casting and fast solvent evaporation. The prepared film was transparent although it contained many crystals. These crystals apparently prevented phase separation despite the instability of the PA‐12 and SAN mixtures below 180°C. In isothermal experiments, once the crystals were melted, phase separation began and the scattered intensity fit the Cahn–Hilliard theory. When the AN content in the SAN copolymer was less than 5%, the phase separation took place when only part of the crystals were melted at 180°C. However, due to the constraint of unmelted crystals, the growth rate of phase separation at this temperature was much slower.     

Polystyrene‐b‐Poly(Ethylene‐r‐butylene)‐b‐Polystyrene Triblock Copolymer/Organoclay Nanocomposites and Their Phase Characteristics

Abstract

Intercalated polymer/clay nanocomposites were prepared using a polystyrene‐b‐poly(ethylene‐r‐butylene)‐b‐polystyrene (SEBS) cylindrical triblock copolymer. Dynamic rheological measurements, x‐ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetry analysis (TGA) were conducted to investigate the internal structure and physical and phase characteristics of the nanocomposites. The XRD data confirmed that the interlayer distance between the anisotropic silicates increased due to the intercalation of SEBS into the clay interlayers. As the clay loading increased, the onset points of the order–disorder transition (ODT) and order–order transition (OOT) were found to decrease, whereas the thermal decomposition temperatures, monitored by TGA, increased with the clay loading.     

Conformational and Structural Analysis of 6‐(4‐Methoxy‐phenyl)‐1,5,7a‐triphenyl‐tetrahydro‐imidazo[1,5‐b][1,2,4]oxadiazol‐2‐one

Abstract

The cis stereochemistry of 6‐(4‐methoxy‐phenyl)‐1,5,7a‐triphenyl‐tetrahydro‐imidazo[1,5‐b][1,2,4]oxadiazol‐2‐one was studied by use of a PM3 semi‐empirical quantum mechanical model, and x‐ray crystallographic analysis. It crystallizes in the monoclinic space group P2 ₁ /n with a = 10.812(1) Å, b = 16.464(2) Å, c = 13.379(1) Å, α = 90.00°, β = 98.39(1)°, γ = 90.00°, V = 2356.07(4) Å³, Z = 4, D _calc = 1.3067 g cm^?3, F(0 0 0) = 976.41, and μ = 0.086 mm^?1. The structure was solved by direct methods and refined to R = 0.066 for 1257 independent reflections [I > 4σ (I)]. The results from x‐ray diffraction were seen to be generally consistent with the results from previously reported spectroscopic investigations, beside theoretical calculations, except for conformations of five‐membered fused heterocycles. Two inter‐ and intramolecular weak interactions in addition to carbon atoms (C1 and C3) with different chiralities were found in the structure. The conformational study was performed by randomly scanning the potential energy surface belonging to the title compound with respect to selected torsion angles.     

Poly(m‐Phenylene Isophthalamide) Ultrafine Fibers from an Ionic Liquid Solution by Dry‐Jet‐Wet‐Electrospinning

Ultrafine poly(m‐phenylene isophthalamide) (PMIA) fibers from PMIA solution in an ionic liquid via dry‐jet‐wet electrospinning technology are described. The morphology of the fibers with and without treatment in a coagulation water bath in the dry‐jet‐wet‐electrosinning process was observed by scanning electrical microscopy (SEM) and a high resolution optical microscope. The crystal structure of the fibers was analyzed by wide angle X‐ray diffraction (WAXD). The differences of morphologies and properties between the ultrafine fibers obtained by the electrospinning process and fibers from conventional wet‐spinning technology are discussed. The thermal properties of the ultrafine PMIA fibers were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).     

Structural Assignments of 1‐(β‐d‐Glucopyranosyl)‐1,2,3‐triazoles by 1H‐ and 13C‐NMR Study

The ¹H‐ and ¹³C‐NMR spectra of 1‐β‐d‐glucopyranosyl‐1,2,3‐triazole‐4,5‐dimethyl carboxylate, 1‐β‐d‐glucopyranosyl‐1,2,3‐triazole‐4,5‐dicarboxamide, ‐dialkylcarboxamide‐N‐nucleosides 4–18, and 6‐amino‐4H‐1‐(1‐β‐d‐glucopyranosyl)‐8‐hydroxy‐1,2,3‐triazolo[4,5‐e][1,3]‐diazepin‐4‐one 19 had been studied. Resonance signals and anomeric configurations were assigned by homo‐ and heteronuclear two dimensional methods (DQF‐COSY, HSQC, HMBC, HMQC, ROESY).     

Temperature‐Triggered Capture of Dispersed Particles Using a Laponite‐Poly(NIPAM) Temperature‐Responsive Surface

In this study a new method is investigated that enables a conductive surface to be modified so as to capture dispersed particles when the temperature is increased. Poly(NIPAM) (NIPAM is N‐isopropylacrylamide) was grafted from electrodeposited Laponite RD particles using surface‐initiated atom transfer radical polymerization (ATRP) to give a temperature‐responsive surface. This was used to capture dispersed polystyrene particles. In the first part of the study the conditions used to electrodeposit Laponite onto a carbon foam electrode were determined. The ability of the temperature‐responsive surface to capture dispersed polystyrene particles was investigated between 20 and 50°C. Temperature‐triggered particle capture was reversible or irreversible depending on the conditions used during ATRP. A high surface concentration of poly(NIPAM) on the particle electrodes is believed to increase the extent of polystyrene particle capture and also reversibility. A theoretical analysis in terms of interaction energy–distance curves is presented for the capture behavior. It is concluded that the temperature‐responsive surface has both electrostatic and steric contributions to the total interaction energy. The steric component (which originates from poly(NIPAM)) is temperature‐dependent and provides the basis for temperature‐triggered particle capture.     

Shear Effect on Morphology of Poly(Butylene Terephthalate)/Poly(Styrene‐co‐Acrylonitrile) Blends

Abstract

The shear flow effect on the morphology of poly(butylene terephthalate)(PBT)/poly(styrene‐co‐acrylonitrile)(SAN) was studied by a parallel plate type shear apparatus. In PBT/SAN = 20/80 blend, particle size of dispersed domains was governed by both break‐up and coalescence processes, and it was much affected by shear rate. The minimum particle size was observed at a certain shear rate. This phenomenon can be explained by the shear matching effect of PBT and SAN; that is, the viscosity ratio of PBT to SAN changed with shear rate and the finest morphology was obtained at the appropriate viscosity ratio. Similar behavior was also observed for PBT/SAN = 70/30 (PBT was the matrix), even though the particle size was larger than that of PBT/SAN = 20/80. For PBT/SAN = 10/90 blend, the sample showed a complicated appearance during shearing. A translucent region correlated to the fine morphology was observed more than twice with increasing shear rate. This phenomenon could not be explained by the viscosity matching effect only. It was affected by small changes in the balance of breaking‐up and coalescence effects.     

Effect of Non‐Ideal Mixed Solvents on Dimensions of Poly(N‐Vinylpyrrolidone) and Poly(Methyl Methacrylate) Coils

An addition of a small amount of non‐solvent tetrahydrofuran (THF) to good solvent water gave rise to a strong solvent power for poly(N‐vinylpyrrolidone) (PVP). It was found that PVP coils in mixtures of water and THF first swelled as the fraction of THF was increased, and then the coils contracted after a critical composition of the solvent mixture based on the measurement of dilute solution viscosities. It was reached that the power of the mixed solvents was not the simple average of the power of individual components. The influence of the non‐ideal mixing of water and THF on the power of these mixtures for PVP and the dimensions of PVP coils was taken into account. Especially the formation of pseudo‐clathrate hydrate structure with the composition φ _THF ≈ 0.44 was found to be an important factor to change the solvation and dimensions of PVP coils. Some other solvent mixtures for PVP and poly(methyl methacrylate) (PMMA) were also found to be non‐ideal mixtures. The viscosities of these solvent mixtures could show positive or negative deviation from the values obtained from the addition rule. It was shown again that the influence of the non‐ideality of these solvent mixtures on the dimensions of polymer coils was great. The action of mixed solvents changed the dimension of polymer coils, not only because of excluded volume effects but also because of the different molecular interactions present in these mixed solvents.     

Solvent Dependence of Tautomeric Equilibria of 1‐(o‐Substituted Phenyl)Barbituric and ‐2‐Thiobarbituric Acid Derivatives

Abstract

The enolisation tendencies of 1‐(o‐substituted phenyl)barbituric and ‐2‐thiobarbituric acid derivatives have been studied by observing the behaviour of the compounds in different solvents by ¹H and ¹³C NMR. It has been found that the enolisation tendencies of the thiobarbituric acid derivatives observed in polar solvents are greater than those of the barbituric acid derivatives. The ratio of keto–enol tautomers of thiobarbituric acid derivatives in DMSO and in DMF has been calculated.     

Poly(acrylamide‐co‐acrylic acid)/Poly(vinyl pyrrolidone) Polymer Blends Prepared by Dispersion Polymerization

The structure and properties of a three‐component system, a poly(acrylamide‐co‐acrylic acid)/poly(vinyl pyrrolidone) [P(AM‐co‐AA)/PVP] polymer blend prepared by dispersion polymerization, were studied. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that the resulting P(AM‐co‐AA) microspheres with diameters between 200–300 nm were well‐dispersed in the PVP matrix. Fourier transform infrared spectra (FTIR) showed that intermolecular hydrogen bonding interaction occurred between the dispersed phase and the continuous phase. The mechanical properties of P(AM‐co‐AA)/PVP polymer blends were also determined. With different mass ratios of acrylamide to acrylic acid, it was found that the blends had better mechanical properties with increased AA content.     

Spectrophotometric and 27‐Al NMR Characterization of Aluminum(III) Complexes with l‐Histidine

Abstract

The complex formation between l‐histidine (HHis) and aluminum(III) ion in water solutions was studied by UV spectrophotometric and 27‐Al NMR measurements at 298 K. UV spectra were measured on solutions in which the total concentration of histidine was from 15.0 to 50.0 mmol/dm³ and the concentration ratio of histidine to aluminum was varied from 3∶1 to 10∶1 in the pH range between 4.2 and 6.0. The spectra were taken in the wavelength interval 240–340 nm. Nonlinear least‐squares treatment of the spectrophotometric data indicates the formation of the complexes Al(HHis)³⁺, Al(His)²⁺, Al(HHis)His²⁺, and Al₂(OH)His⁴⁺ with the overall formation constants β_p,q,r: log β_1,1,1=11.90±0.04, log β_1,1,0=7.25±0.08, log β_1,2,1=20.1±0.1, and log β_2,1,1=5.92±0.12 (p, q, r are stoichiometric indices for metal, ligand, and proton, respectively). ²⁷Al‐NMR spectra were taken on solutions with the concentration of aluminum 50 mmol/dm³ and that of histidine 250 mmol/dm³. In the pH interval 5.0–6.1, two resonances at 9.5 ppm and 12.0 ppm were assigned to Al(HHis)²⁺ and Al(HHis)(His)²⁺ (or Al(OH)(HHis)₂ ²⁺), respectively.     

Synthesis and Characterization of Novel Poly(1‐Naphthylamine)‐Montmorillonite Nanocomposites Intercalated by Emulsion Polymerization

Nanocomposites of montmorillonite (MMT) with poly(1‐naphthylamine) (PNA) is investigated for the first time by emulsion polymerization using three different oxidants. Polymerization of PNA was confirmed by Fourier transformation infrared (FT‐IR) as well as UV‐visible spectra. The in situ intercalative polymerization of PNA within MMT layers was confirmed by FT‐IR, X‐ray diffraction, conductivity; scanning electron microscopy (SEM) as well as transmission electron microscopy studies. X‐ray diffraction revealed intercalated as well as exfoliated structures of PNA/MMT nanocomposites, which were compared with the reported polyaniline‐MMT nanocomposites. It was found that the increase in the concentration of PNA in the interlayer galleries of MMT led to destruction of the layered clay structure resulting in exfoliation of the nanocomposite. Conductivity of the nanocomposites was found to be in the range of 10^?3 to 10^?2 S cm^?1 which was found to be higher than the ones reported for polyaniline‐clay nanocomposites as well as PEOA‐OMMT nanocomposites at similar concentrations of intercalated species. The morphology of PNA/MMT nanocomposites was found to be governed by the nature of the oxidant used.     

Characterization of polymer thin films with small‐angle X‐ray scattering under grazing incidence (GISAXS)

FEMTO, a femtosecond (fs) X-ray source based on laser interaction with a relativistic electron beam, began operation in the fall of 2006. It is installed at the μXAS beamline of the Swiss Light Source (SLS) at the Paul Scherrer Institut, Villigen. “Laser slicing” of an electron beam has first been proposed and demonstrated at the ALS [] and has recently been implemented at BESSY [2 Khan, S. 2006. Phys. Rev. Lett, 97: 074801[Crossref], [Web of Science ®] , [Google Scholar]] to generate fs soft X-rays (1–2 keV) with variable polarization. FEMTO is the first undulator source providing tunable, fs hard X-rays in the range 4.5–12 keV for laser/X-ray pump-probe absorption and diffraction experiments.     

Non‐isothermal Melt Crystallization Kinetics for Poly(ethylene 2,6‐naphthalate) (PEN)/Montmorillonite Nanocomposites Prepared by Melt Intercalation

The nonisothermal crystallization behaviors for poly(ethylene 2,6‐naphthalate) (PEN) and poly(ethylene 2,6‐naphthalate) (PEN)/montmorillonite nanocomposites prepared by melt intercalation were investigated using differential scanning calorimetry (DSC). The Jeziorny, Ozawa, Ziabicki, and Kissinger models were used to analyze the experimental data. Both the Jeziorny and the Ozawa models were found to describe the nonisothermal crystallization processes of PEN and PEN/montmorillonite nanocomposites fairly well. The results obtained from the Jeziorny and the Ozawa analysis show that the montmorillonite nanoparticles dispersed into PEN matrix act as heterogeneous nuclei for PEN and enhance its crystallization rate, accelerating the crystallization, but a high‐loading of montmorillonites restrain the crystal growth of PEN. The analysis results from the Ziabicki and the Kissinger models further verify the dual actions stated above of the montmorillonite nanoparticles in PEN matrix.