bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of binary and ternary mobile phases in reversed‐phase high performance liquid chromatographic separation of chiral compounds
Authors: Gołkiewicz Władysław , Błażewicz Anna , Matosiuk Dariusz
Published: March 2004

The influence of the nature of typical organic modifiers, used in reversed‐phase systems diluted with water, on retention and selectivity of chiral acetylated diamines and acetonitriles possessing pharmacological activity was investigated. Linear, semilogarithmic relationships between the logarithm of the retention factor, k, of the enantiomer and the volume fraction, Φ, of the organic modifier in the binary aqueous‐organic eluent were established for chiral stationary phases. The slope of a plot of log k vs. the modifier volume fraction depends not only on the chemical structure of the chromatographed enantiomers, but also on the nature of the modifier. Moreover, the enantioselectivity of the studied racemates also depends on the nature and concentration of the modifier and is higher for a methanol mobile phase than for acetonitrile.
Separation techniques for the analysis of artists' acrylic emulsion paints
Authors: Scalarone Dominique , Chiantore Oscar
Published: March 2004

Emulsion paints are complex chemical systems. The main problems in their characterization are related to the similarities in polymer composition and to the presence of many different types of additives. Thus high resolution separations, sensitivity, and response specificity are required to identify simultaneously the polymer matrix and the minor components. Especially surfactants and pigments are thought to affect significantly the properties of the paint layers during ageing and their identification is the first step in evaluating the behaviour of these products in working conditions. Representative samples of acrylic emulsion paints for artists have been investigated by pyrolysis‐gas chromatography‐mass spectrometry (Py‐GC‐MS) and size exclusion chromatography‐Fourier transform infrared spectroscopy (SEC‐FTIR), and the results have been compared. All the analysed samples were bound in ethyl acrylate‐methyl methacrylate, poly(EA‐co‐MMA), or n‐butyl acrylate‐methyl methacrylate, poly(nBA‐co‐MMA), copolymers. Two types of nonionic surfactants, ethoxylated fatty alcohols and alkylaryl polyethoxylates, commonly used as emulsifiers and dispersive agents have been identified, together with a number of organic pigments.
Rapid and high‐resolution analysis of geometric polyprenol homologues by connected octadecylsilylated monolithic silica columns in high‐performance liquid chromatography
Authors: Bamba Takeshi , Fukusaki Ei‐ichiro , Nakazawa Yoshihisa , Kobayashi Akio
Published: March 2004

A Chromolith Performance octadecylsilyl (ODS) monolithic silica column (Merck) was compared with a conventional microparticulate ODS‐bonded silica column in the high‐performance liquid chromatography separation of natural polyprenols. A system comprising two connected monolithic columns afforded an equivalent separation at half the analysis time of the conventional method. Furthermore, ten connected columns achieved a tremendously high‐resolution separation, in which the complicated series of homologous polyprenols with geometric isomerism were fully separated.
Analysis of basic compounds at high pH values by reversed‐phase liquid chromatography
Authors: Stella Cinzia , Rudaz Serge , Mottaz Manuel , Carrupt Pierre‐Alain , Veuthey Jean‐Luc
Published: March 2004

Reversed phase high performance liquid chromatography (RPLC) is currently the method of choice for the analysis of basic compounds. However, with traditional silica materials, secondary interactions between the analyte and residual silanols produce peak tailing which can negatively affect resolution, sensitivity, and reproducibility. In order to reduce these secondary interactions, which comprise ion exchange, hydrogen bonding, and London forces interactions, chromatographic analyses can be carried out at low or high pH values where silanol groups and basic compounds are mostly uncharged. The chromatographic behaviour of a particular bidentate stationary phase, Zorbax Extend C18, was studied with a set of basic and neutral compounds. Thanks to a higher chemical stability than traditional silica based supports, analyses were carried out with a high pH mobile phase, which represents a good alternative to the acidic mobile phases generally used to reduce ion exchange interactions. The performance of this bidentate stationary phase was also compared with that of other supports and it was proved that it is advantageous to work with high pH mobile phases when analyzing basic compounds.
Approaches for the coating of capillary columns with highly phenylated stationary phases for high‐temperature GC
Authors: Mayer‐Helm Bernhard X. , Rauter Walfried , Rauchbauer Georg , Tomastik Christian , Bangert Herwig
Published: March 2004

Two highly phenylated tetramethyl‐p‐silphenylene–diphenylsiloxane copolymers were coated on fused silica capillary columns and used as stationary phases in GC. The copolymers offered new insights into the coating process and column preparation due to their physicochemical properties. The fused silica capillary surface had to be pretreated in various ways to achieve a homogeneous film and a well deactivated surface: etching with ammonium bifluoride; leaching with sodium hydroxide and hydrochloric acid; silylation with tetraphenyldimethyldisilazane and triphenylsilylamine. Droplet formation was observed on tetraphenyldimethyldisilazane silylated surfaces leading to capillary columns with low separation efficiency. The topology of inhomogeneous films was investigated by light microscopy, scanning electron microscopy, and Auger electron spectroscopy. It became apparent that the stationary phase did not form droplets but islands, which are connected by a wetting layer according to the Stranski‐Krastanov growth mode. Both copolymers are potential stationary phases for high‐temperature GC with promising properties. They offer a higher overall polarity than 75% phenyl, 25% methyl‐polysiloxanes in combination with increased thermal stability and reduced bleed levels.
Determination of volatile fatty acids in landfill leachates by ion‐exclusion chromatography
Authors: Yamamoto Atsushi , Yasuhara Akio , Kodama Shuji , Matsunaga Akinobu , Suzuki Shigeru , Mohri Shino , Yamada Masato
Published: March 2004

An ion‐exclusion chromatographic method with on‐line desalinization for the determination of volatile fatty acids in landfill leachates is described. Highly sensitive conductivity detection of the organic acids was achieved by using dilute p‐hydroxybenzoic acid solution as an eluent. Interference with mineral acids was reduced by treatment with barium chloride solution prior to desalinization. A silver‐loaded cation‐exchange guard column for the desalinization was installed in series with the analytical column to avoid the contamination of organic acids. This method features detection limits of 0.01 mg L–1 formic acid, 0.02 mg L–1 acetic acid, 0.05 mg L–1 propionic acid, and 0.1 mg L–1 butyric acid, respectively, with an injection of 20 μL sample. Application of the on‐line desalinization LC method is illustrated for leachate samples from a Japanese sanitary landfill.
A modified HPLC method for the determination of aspartic acid racemization in collagen from human dentin and its comparison with GC
Authors: Benešová Terezie , Honzátko Aleš , Pilin Alexandr , Votruba Jaroslav , Flieger Miroslav
Published: March 2004

The D/L ratio of aspartic acid enantiomers in proteins of low turnover is generally accepted as a reliable procedure for age determination. In our study, twelve samples of eyetooth dentin were analyzed for age determination. The pure insoluble collagen isolated from eyetooth dentin was obtained by an EDTA demineralization process. Free amino acids obtained after collagen hydrolysis were converted intoo‐phthaldialdehyde‐N‐acetyl‐L‐cysteine (OPA‐NAC) derivatives for HPLC analysis under modified conditions and into trifluoroacetic acid isopropyl esters for GC analysis, respectively. The modified HPLC procedure used phosphate buffer and acidified sample matrix prior to injection which resulted in suppression of peak tailing of both diastereomers, thus allowing achievement of both good selectivity and good resolution. To ensure the high accuracy of the developed method the other parameters, i. e. specificity, precision, linearity, LOD, and LOQ, were also determined. Nine collagen samples covering the age range of 18 to 84 years were used for the determination of coefficient of racemization (KR) and calculation of parameters for age estimation. The regression equations for the data set analyzed were as follows:KR= 0.0005 × age + 0.0262 (R 2= 0.9639) for HPLC, andKR= 0.0006 × age + 0.0319 (R 2= 0.9374) for GC, respectively.
Temperature optimization for improved determination of phosphatidylserine species by micro liquid chromatography with electrospray tandem mass spectrometric detection
Authors: Larsen Åsmund , Molander Paal
Published: March 2004

A sensitive method for determination of disaturated phosphatidylserine species in the presence of their monounsaturated analogs has been developed, using micro liquid chromatography coupled to electrospray ionization tandem mass spectrometry. The hydrophobic nature of the phosphatidylserine species required a combination of low‐eluting sample solvents and sub‐ambient temperatures in order to focus large sample volumes up to 20 μL. The samples were dissolved in 2‐propanol : hexane : water (20 : 10 : 4, v/v/v) prior to 1 : 9 dilution with ammonium formate buffer : 2‐propanol : tetrahydrofuran (30 : 55 : 15, v/v/v) and final 1 : 4 dilution with ammonium formate buffer (10 mM) : 2‐propanol : tetrahydrofuran (55 : 37.5 : 7.5, v/v/v). The analytical column was a 0.5×150 mm stainless steel column packed with 5 μm C30 particles, while the mobile phase contained ammonium formate buffer (10 mM) :  2‐propanol : tetrahydrofuran (30 : 55 : 15, v/v/v). A temperature program from 5°C (hold for 3 minutes) to 75°C at 8 K/min provided separation of the disaturated phosphatidylserine species from their monounsaturated analogs, making available a sensitive determination of the isobaric species. The mass limit of detection for dipalmitoyl phosphatidylserine was 100 pg, corresponding to a concentration limit of detection of 5 pg/μL when using an injection volume of 20 μL. This is an improvement by a factor of 20 as compared to previously reported numbers obtained with conventional LC columns. The within‐assay precision of dipalmitoyl phosphatidylserine was 11.9% RSD (n = 3), while the retention time precision was 4.1% RSD (n = 6).
Recognition of hepatotoxic homologues of Microcystin using a combination of selective adsorption media
Authors: Kubo Takuya , Hosoya Ken , Watabe Yoshiyuki , Tanaka Nobuo , Sano Tomoharu , Kaya Kunimitsu
Published: March 2004

Microcystin, a hepatotoxin produced by cyanobacteria, was chromatographically discriminated with newly prepared selective adsorption media. Since the name Microcystin refers to up to 70 different homologues, we have developed a novel technique to prepare selective recognition sites, based on the “Fragment Imprinting Effect”. The homologues of Microcystin can be individually discriminated from each other by antigen‐antibody assay as well as by C18‐based HPLC. This is mainly due to differences in the three dimensional structure of Microcystin homologues; however, differences in toxicity are relatively small among the homologues. Therefore we have to measure the total amount of Microcystin homologues present to determine contamination by Microcystins. We have demonstrated the first group recognition for Microcystin homologues through combination of two different selective adsorption media prepared by a fragment imprinting technique.
Laser even harmonics generation by a plasma embedded in a static electric field
Authors: Ferrante G , Zarcone M , Uryupin S A
Published: March 2004

Even order harmonics generation of the laser radiation due to electron-ion collisions in a plasma embedded in a constant electric field is investigated theoretically. Even harmonics are generated because the presence of a static electric field removes the invariance of the electron distribution function under the symmetry operation of velocity direction inversion. Efficiency generation dependencies are investigatedvsdifferent significant parameters as: harmonics number; the ratio of the electron quiver velocity to the thermal velocity; the orientation of the constant electric field with respect to the laser radiation electric field and its wavevector. It is shown that in the general case the polarization planes of different even harmonics are different and do not coincide with that of the generating laser radiation.
Symmetry point group description of second harmonic generation in
carbon nanotubes
Authors: De Dominicis L , Fantoni R , Botti S , Asilyan L S , Ciardi R , Fiori A , Appolloni R
Published: March 2004

The role played by symmetry properties of a carbon
nanotube in the generation of second harmonic radiation is studied
by using the formalism of irreducible representation of the
symmetry point group. Experimental results of second harmonic
generation in a carbon nanotube sample are discusses in view of
the theoretical prediction obtained.
Atom interferometer using two Stern-Gerlach magnets
Authors: Rubin K , Eminyan M , Perales F , Mathevet R , Brodsky K , Viaris de Lesegno B , Reinhardt J , Boustimi M , Baudon J , Karam J-C , Robert J
Published: March 2004

An atom interferometer using two Stern-Gerlach magnets as polariser and analyser is described. The interferometer was first operated with a thermal beam of ground state potassium atoms. In that case the beam splitters are two radio-frequency zones within a transverse homogeneous magnetic field building a coherent superposition of Zeeman states. Ramsey fringes are obtained by scanning the RF-frequency through the resonance profile. Pulsing the RF power allows to get the time-of-flight distribution of the beam. Atomic interference fringes (``Stern-Gerlach fringes'') are observed when the magnitude of an inhomogeneous magnetic field located in between the beam splitters is scanned. When the inhomogeneous field is also pulsed, the scalar Bohm-Aharonov effect is observed. The use of metastable helium atoms (He*23S) in place of potassium atoms is proposed. In addition to the usual advantages provided by metastable atoms of high internal energy, this atom offers the specific advantage to behave as an ideal spin-one particle. This allows us to greatly simplify the polarisation scheme of the interferometer. Possible applications involving transversally inhomogeneous magnetic fields are given and limitations due to the finite source size and angular aperture are discussed.
Excited-state absorption as a source of nonlinear thermo-induced lensing and
self-Q-switching in an all-fiber Erbium laser
Authors: Kir'yanov A V , Il'ichev N N , Barmenkov Yu O
Published: March 2004

A modeling of an all-fiber self-Q-switched Erbium laser
is developed, implying that the mechanism of self-Q-switching is
the power-dependent thermo-induced lensing in Erbium fiber that
stems from the excited-state absorption at the laser wavelength.
α-Alums: K,Rb,Tl and NH4Al(SO4)2⋅ 12H2O – a new family of χ(3)-active crystalline materials for Raman laser converters with large frequency shifts
Authors: Kaminskii A A , Haussühl E , Haussühl S , Eichler H J , Ueda K , Hanuza J , Takaichi K , Rhee H , Gad G M A
Published: March 2004

Efficient high-order stimulated Raman scattering was excited under picosecond pumping in the visible and near-IR in four crystals of the α-alum family - novel isotropic χ(3)-active crystalline materials. All observed Stokes and anti-Stokes lasing components were identified and attributed to the promoting ≈1000 cm-1vibration modes of these crystals. Their one-micron steady-state first Stokes Raman gain coefficients were estimated as well.
Two-photon absorption of F2
- color centers in LiF crystal at 1906 nm
Authors: Fedorov V V , Fedorov A V , Martyshkin D , Donegan J F , Mirov S B
Published: March 2004

We report room-temperature two-photon induced
fluorescence of the F2
- color centers in LiF crystal in
the ∼960-1300 nm spectral range. The fluorescence spectra and
kinetics were measured using the first (1.906 μm) and second
harmonics (0.953 μm) of a H2–Raman Shifted single
frequency Nd:YAG laser. The fluorescence spectra and kinetics
under two-photon (1.906 μm) and one-photon (0.953 μm)
excitation were identical. A nonlinear dependence of the
fluorescence intensity versus excitation energy of 1.906 μm
radiation was demonstrated. The two-photon absorption cross
section of F2
- color center was measured to be (0.9±
0.4) × 10-49 cm4 sec at 1.906 μ m.
Artificial Opals as Effect Pigments in Clear‐Coatings
Authors: Egen Marc , Braun Lydia , Zentel Rudolf , Tännert Klaus , Frese Peter , Reis Oliver , Wulf Martin
Published: March 2004

Summary: In this paper, we describe the use of artificial opals from polymer beads as effect pigments in transparent industrial and automotive coatings. For this purpose, we synthesized monodisperse colloids from fluorinated methacrylates by surfactant‐free emulsion polymerization. The fluorinated monomers, in combination with crosslinking, lead to a refractive index contrast, thermal stability, and solvent resistivity necessary for use as effect pigments. After crystallization of the monodisperse polymer beads, crystal flakes with iridescent colors can be obtained. The crystal flakes can act as effect pigments in various transparent industrial and automotive coatings. Due to photonic crystal behavior of effect pigments, color flops up to 100 nm are observed.

Crystal flakes of CS‐7 as effect pigments in a transparent coating. The diameter of the tube is 5 mm.

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Crystal flakes of CS‐7 as effect pigments in a transparent coating. The diameter of the tube is 5 mm.
Fire Retardance in Poly(butylene terephthalate). The Effects of Red Phosphorus and Radiation‐Induced Cross‐Links
Authors: Balabanovich Aliaksandr I. , Zevaco Thomas A. , Schnabel Wolfram
Published: March 2004

Summary: The combustion performance of poly(butylene terephthalate) (PBT) can be improved by the addition of red phosphorus provided it is intermolecularly cross‐linked upon irradiation with 60Co γ‐rays in the presence of triallyl cyanurate (TAC). At a content of 3 or 4 wt.‐% the latter significantly promotes cross‐linking in the presence of air. From combustion tests with samples containing red phosphorus (Pred) and having been γ‐irradiated in the presence of TAC it turned out that an improved fire resistance of PBT is achieved if the red phosphorus content is at least 12.5 wt.‐%. In this case test samples were self‐extinguishing and the UL 94 rating corresponded to V‐1. Product analysis and thermal gravimetric analysis revealed that Pred stimulates aromatization and charring. These processes involve the reaction of Pred with the polymer. 31P NMR spectroscopy revealed that the residue contained chemically bonded phosphorus.

Decomposition of anhydride groups resulting in phenyl radicals.

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Decomposition of anhydride groups resulting in phenyl radicals.
Investigation Into Poly(propylene)/Montmorillonite/Calcium Carbonate Nanocomposites
Authors: Tang Yong , Hu Yuan , Zhang Rui , Wang Zhengzhou , Gui Zhou , Chen Zuyao , Fan Weicheng
Published: March 2004

Summary: A novel method was used to prepare poly(propylene)/montmorillonite/calcium carbonate nanocomposites by melt‐mixing, using pristine montmorillonite (MMT), hexadecyltrimethylammonium bromide (C16), calcium carbonate (CaCO3) and a matrix in a twin‐screw extruder. Two different sizes of calcium carbonate were used (nanosized CaCO3 and micron‐sized CaCO3, the average sizes being 60 nm and 12 μm respectively). The nanocomposite structure was evidenced using X‐ray diffraction (XRD), transmission electron microscopy (TEM) and high resolution electronic microscopy (HREM). Tensile tests and Izod notch impact tests suggested that the incorporation of nanosized CaCO3 into PP/montmorillonite nanocomposites increased the mechanical properties of the composites, but the improvement in the micro‐sized CaCO3‐filled PP/montmorillonite nanocomposites was found to be minimal. The thermal stability and flammability properties were characterized by thermogravimetric analysis (TGA) and a cone calorimeter respectively.

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Effect of Short Chain Branching of LDPE on its Miscibility with Linear HDPE
Authors: Hameed Tayyab , Hussein Ibnelwaleed A.
Published: March 2004

Summary: The influences of short chain branching (SBC) on the melt miscibility of low‐density polyethylene (LDPE) with linear high‐density polyethylene (HDPE) were investigated by rheological methods. Two LDPE resins with different branch contents were blended with the same linear HDPE. Dynamic and steady shear measurements were carried out using a Rheometrics ARES rheometer at 190 °C. The rheology of the low‐SCB LDPE (9 CH3/1 000 C) blends with HDPE can be predicted by the linear additivity rule. Hence, blends were suggested to be completely miscible at all compositions. However, blends of the high branch content LDPE (SCB = 19 CH3/1 000 C) were completely immiscible. Also, the different viscous and elastic properties of all the immiscible blends were much higher than the corresponding values for the more viscous and elastic blend component. The ratio of interfacial tension to droplet radius was estimated from Scholz et al. model as ≈1 500 N · m−2. The level of SCB in LDPE was found to have a strong influence on its miscibility with linear HDPE.

Cole‐Cole plot for blends of LDPE1 with HDPE.

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Cole‐Cole plot for blends of LDPE1 with HDPE.
Nanoporous Low Dielectric Cyclosiloxane Bearing Polysilsesquioxane Thin Films Templated by Poly(ε‐caprolactone)
Authors: Hyeon‐Lee Jingyu , Lyu Yi Yeol , Lee Mong Sup , Hahn Jun‐Hee , Rhee Ji Hoon , Mah Sang Kook , Yim Jin‐Heong , Kim Sang Youl
Published: March 2004

Summary: Dielectric cyclosiloxane bearing polysilsesquioxanes (CS‐PSSQs) were prepared by acid catalyzed polymerization using 2,4,6,8‐tetramethyl‐2,4,6,8‐tetra(trimethoxysilylethyl)cyclotetrasiloxane. The molecular weight, and content of the functional end‐groups of the CS‐PSSQs were found to be dependent on the process parameters, such as the molar ratio of water and catalyst to the OCH3 group of the silane monomer, the amount of solvent, and the poly(ε‐caprolactone) (PCL) content, etc. Based on these CS‐PSSQ prepolymers, nanoporous organic/inorganic hybrid thin films were fabricated by spin‐coating mixtures of these prepolymers with star‐shaped PCL on the silicon substrate, and subsequently heating them at 150 and 250 °C for 1 minute each and then at 420 °C for 1 hour. A dielectric constant as low as 2.28 was achieved for the nanoporous PCL/CS‐PSSQ (3:7 v/v) film, along with low moisture absorption in ambient and water conditions, primarily due to the presence of hydrophobic moieties such as ethylene and methyl groups of the polymer and nano‐sized hydrophobic pores inside the matrix, resulting in the film having stable dielectric properties. Moreover, the PCL/CS‐PSSQ (3:7 v/v) nanohybrid film revealed a nanoporous structure containing ca. 1.52 nm of average‐sized mesopores, as measured by the N2 adsorption method. The CS‐PSSQ‐only film showed high mechanical strengths having an elastic modulus and hardness of 6.64 and 0.88 GPa, respectively, for the 7 500 Å thick film and 2.41 and 0.38 GPa, respectively, for the PCL/CS‐PSSQ (3:7 v/v) film. In addition, the crack velocity of the CS‐PSSQ‐only film was found to be ca. 10−11 m · s−1 in ambient conditions and an aqueous environment, probably due to the enhanced hydrophobicity and mechanical toughness of the incorporated methyl group, siloxane unit and ethylene moieties in the polymer matrix.

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Synergistic Effect of the Charring Agent on the Thermal and Flame Retardant Properties of Polyethylene
Authors: Hu Xiao‐Ping , Li Ya‐Lan , Wang Yu‐Zhong
Published: March 2004

Summary: A new charring agent (CA), a derivative of triazines, was synthesized. The flame retardancy and thermal behavior of a new intumescent flame‐retardant (IFR) system for PE (PE‐IFR) were investigated by limited oxygen index (LOI), UL‐94 test, thermogravimetric analysis (TGA), and FTIR spectroscopy. The TG curves shows that the amount of residue of IFR‐PE system are largely increased compared to those of PE at temperatures ranging from 350 to 700 °C. The new PE‐IFR system can apparently reduce the amount of decomposing products at higher temperatures and promotes the formation of carbonaceous charred layers. It showed a distinct synergistic flame retardant effect (SE) between nitrogen and phosphorus. The flame retardant PE composition was optimized to achieve a LOI value of 31.2 and UL‐94 V‐0 performance with the synthesized charring agent, ammonium polyphosphate (APP).

TG curves of PE, APP, CA, and different PE/CA/APP systems.

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TG curves of PE, APP, CA, and different PE/CA/APP systems.
Copper Removal in Atom Transfer Radical Polymerization through Electrodeposition
Authors: Nasser‐Eddine Mohamad , Delaite Christelle , Dumas Philippe , Vataj Rame , Louati Alain
Published: March 2004

Summary: We describe the removal of copper from atom transfer radical polymerization (ATRP) through electrochemistry. tert‐Butyl methacrylate ATRP initiated by a PEO macroinitiator was run with CuBr complexed by N‐alkyl‐2‐pyridylmethanimine (Schiff base) or 2,2′‐bipyridyl (bpy) as catalyst. Voltammetry experiments using a CuBr/(Schiff base N‐morpholine‐2‐pyridylmethanimine)2 complex on a Pt electrode shows an oxidation peak of the ligand at 1.2 V permitting the oxidative destruction of the complex and so the elimination of copper. Using a Hg electrode, it is possible to directly reduce these complexes (at −2.1 V for the morpholine‐2‐pyridylmethanimine, −2.19 V for the butyl‐2‐pyridylmethanimine, and −2.25 V for the bpy). This complex reduction, followed by the formation of a copper amalgam, leads to the quantitative removal of copper and proceeds without polymer degradation.

The electrochemical removal of copper from the ATRP reaction.

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The electrochemical removal of copper from the ATRP reaction.
Phase Behavior of Poly(butyl acrylate) Networks in Nematic Liquid Crystal Solvents
Authors: Vendamme Richard , Bouchaour Tewfik , Pakula Tadeusz , Coqueret Xavier , Benmouna Mustapha , Maschke Ulrich
Published: March 2004

Summary: This paper reports the phase behavior of photochemically crosslinked poly(butyl acrylate) networks in nematic liquid crystal (LC) solvents. The swelling properties are studied as a function of temperature for two low molecular weight nematic LCs, 4‐cyano‐4′‐pentylbiphenyl (5CB) and the eutectic mixture of cyanoparaphenylenes (E7). Chemically crosslinked polymer networks were formed by the UV radiation of initial solutions of the reactive monomer, butyl acrylate, a crosslinker (hexanediol diacrylate), and a photoinitiator. To obtain different network densities, the ratio of butyl acrylate to hexanediol diacrylate was varied prior to polymerization/crosslinking reactions. Immersion in an excess of the LC solvent allowed for the measurement of size increase by polarized optical microscopy in terms of temperature. Length, width, and diagonal ratios were calculated considering swollen to dry network states of the samples. In general, swelling leads to an increase in the network size by increasing the temperature with a significant dependence on the degree of crosslinking. A large shift in the swelling ratio was found in the vicinity of the nematic to isotropic transition temperatures of the LCs.

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Relationships Between the Crystal Structures and the Multiple Melting Behaviors of Poly(ethylene 2,6‐naphthalate)
Authors: Gao Xia , Hou Weimin , Zhou Jianjun , Li Lin , Zhao Liqun
Published: March 2004

Summary: Poly(ethylene 2,6‐naphthalate) (PEN) can crystallize either from the glassy state or from the melt state. When crystallized from the glassy state, the sample was quenched from the melt in liquid nitrogen and then annealed at certain crystallization temperatures. When crystallized from the melt state, the sample was cooled to a preset temperature from the melt and then annealed for a certain time. The crystal modifications, morphologies and melting behaviors of PEN were investigated by means of wide‐angle X‐ray diffraction (WAXD), polarized optical microscopy (POM), small‐angle light scattering (SALS) and differential scanning calorimetry (DSC). The results show that an α crystal modification of PEN was obtained when PEN crystallized from the glassy state, whilst a β crystal modification was obtained when PEN crystallized from the melt state at a higher temperature. An hedritic morphology of PEN crystal was obtained with only one melting peak observed in DSC curves when PEN was crystallized at a higher temperature from either the glassy state or the melt state. The α crystal modification could also be obtained when PEN was crystallized at a lower temperature from the melt. Spherulitic or banded spherulitic morphologies of PEN crystals, exhibiting multiple melting peaks in DSC curves, were observed when PEN was crystallized at a lower temperature. The multiple melting behaviors of PEN crystals may be associated with spherulitic structures composed of lamellae of varying thickness.

WAXD patterns of PEN isothermally crystallized from different states.

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WAXD patterns of PEN isothermally crystallized from different states.
Cover Picture: Macromol. Mater. Eng. 2/2004
Authors: Egen Marc , Braun Lydia , Zentel Rudolf , Tännert Klaus , Frese Peter , Reis Oliver , Wulf Martin
Published: March 2004

Cover: The picture on the cover shows “artificial polymer opals”, which can be used as effect pigments in clear coatings. Shown is an EM picture, a dispersion of the opaline flakes and coated steel plates.

Further details can be found in the Full Paper by M. Egen, L. Braun, R. Zentel,* K. Tännert, P. Frese, O. Reis, and M. Wulf on page 158.
Estimates for norms of resolvents and an application to the perturbation of spectra
Authors: Bandtlow Oscar F.
Published: March 2004

Let A belong to the Schatten‐von Neumann ideal Sp for 0 < p < ∞. We give an upper bound for the operator norm of the resolvent (zI – A)–1 of A in terms of the departure from normality of A and the distance of z to the spectrum of A. As an application we provide an upper bound for the Hausdorff distance of the spectra of two operators belonging to Sp. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Solutions with boundary‐layers and spike‐layers to singularly perturbed quasilinear Dirichlet problems
Authors: Guo Zongming
Published: March 2004

The structure of nontrivial nonnegative solutions to singularly perturbed quasilinear Dirichlet problems of the form –ϵΔpu = f(u) in Ω, u = 0 on ∂Ω, Ω ⊂ RN a bounded smooth domain, is studied as ϵ → 0+, for a class of nonlinearities f(u) satisfying f(0) = f(z1) = f(z2) = 0 with 0 < z1 < z2, f < 0 in (0, z1), f > 0 in (z1, z2) and $ \underline {\lim} _{u \to 0_{+}} $f(u)/up–1 = –∞. It is shown that there are many nontrivial nonnegative solutions with spike‐layers. Moreover, the measure of each spike‐layer is estimated as ϵ → 0+. These results are applied to the study of the structure of positive solutions of the same problems with f changing sign many times in (0,∞). Uniqueness of a solution with a boundary‐layer and many positive intermediate solutions with spike‐layers are obtained for ϵ sufficiently small. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Tilings, packings, coverings, and the approximation of functions
Authors: Hinrichs Aicke , Richter Christian
Published: March 2004

A packing (resp. covering) ℱ of a normed space X consisting of unit balls is called completely saturated (resp. completely reduced) if no finite set of its members can be replaced by a more numerous (resp. less numerous) set of unit balls of X without losing the packing property (resp. covering property) of ℱ. We show that a normed space X admits completely saturated packings with disjoint closed unit balls as well as completely reduced coverings with open unit balls, provided that there exists a tiling of X with unit balls.

Completely reduced coverings by open balls are of interest in the context of an approximation theory for continuous real‐valued functions that rests on so‐called controllable coverings of compact metric spaces. The close relation between controllable coverings and completely reduced coverings allows an extension of the approximation theory to non‐compact spaces. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Estimates of difference norms for functions in anisotropic Sobolev spaces
Authors: Kolyada V. I. , Pérez F. J.
Published: March 2004

We investigate the spaces of functions on ℝn for which the generalized partial derivatives Dkf exist and belong to different Lorentz spaces L . For the functions in these spaces, the sharp estimates of the Besov type norms are found. The methods used in the paper are based on estimates of non‐increasing rearrangements. These methods enable us to cover also the case when some of the pk's are equal to 1. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Generalized random recursive constructions and geometric properties of random fractals
Authors: Liu Yan‐Yan , Wen Zhi‐Ying , Wu Jun
Published: March 2004

We study random recursive constructions in which the contracting vectors have different distributions at different stages. With such constructions, the one parameter family of martingales are introduced and the probabilistic behaviours of the limit random objects (not identically distributed) are discussed. We prove that the random fractal associated with such construction has a constant Hausdorff dimension almost surely and give an explicit formula to determine it. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
On the central limit theorem for the stationary Poisson process of compact sets
Authors: Pawlas Zbyněk , Beneš Viktor
Published: March 2004

Stochastic geometry models based on a stationary Poisson point process of compact subsets of the Euclidean space are examined. Random measures on ℝd, derived from these processes using Hausdorff and projection measures are studied. The central limit theorem is formulated in a way which enables comparison of the various estimators of the intensity of the produced random measures. Approximate confidence intervals for the intensity are constructed. Their use is demonstrated in an example of length intensity estimation for the segment processes. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Asymptotic analysis of nonselfadjoint operators generated by coupled Euler‐Bernoulli and Timoshenko beam model
Authors: Shubov Marianna A. , Peterson Cheryl A.
Published: March 2004

In the current paper, we present a series of results on the asymptotic and spectral analysis of coupled Euler‐Bernoulli and Timoshenko beam model. The model is well‐known in the different branches of the engineering sciences, such as in mechanical and civil engineering (in modelling of responses of the suspended bridges to a strong wind), in aeronautical engineering (in predicting and suppressing flutter in aircraft wings, tails, and control surfaces), in engineering and practical aspects of the computer science (in suppressing bending‐torsional flutter of a new generation of hard disk drives, which is expected to pack high track densities (20,000+TPI) and rotate at very high speeds (25,000+RPM)), in medical science (in bio mechanical modelling of bloodcarrying vessels in the body, which are elastic and collapsible). The aforementioned mathematical model is governed by a system of two coupled differential equations and a two parameter family of boundary conditions representing the action of the self‐straining actuators. This linear hyperbolic system is equivalent to a single operator evolution equation in the energy space. That equation defines a semigroup of bounded operators and a dynamics generator of the semigroup is our main object of interest. We formulate and proof the following results: (a) the dynamics generator is a nonselfadjoint operator with compact resolvent from the class 𝔖p with p > 1; (b) precise spectral asymptotics for the two‐branch discrete spectrum; (c) a nonselfadjoint operator, which is the inverse of the dynamics generator, is a finite‐rank perturbation of a selfadjoint operator. The latter fact is crucial for the proof that the root vectors of the dynamics generator form a complete and minimal set. In our forthcoming paper, we will use the spectral results to prove that the dynamics generator is Riesz spectral, which will allow us to solve several boundary and distributed controllability problems via the spectral decomposition method. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Amphiphilic Comb‐Like Poly(oxyethylene) and Its Complexes with LiClO4: Synthesis and Mesomorphic Behavior
Authors: Kim Jong‐Uk , Cha Sang‐Ho , Lee Jong‐Chan
Published: March 2004

Summary: We prepared an amphiphilic, comb‐like poly(oxyethylene) containing decyl‐tri(oxyethylene) amphiphiles in the side chain using a polymer analogous reaction to obtain a novel nonionic amphiphilic polymeric system with high molecular weight. The amphiphilic comb‐like poly(oxyethylene) itself only showed a side‐chain crystalline phase below its melting temperature of −31 °C. When the polymer was mixed with lithium perchlorate, a smectic liquid‐crystalline phase appeared. The ordered phases of the polymer and the polymer mixture were studied by differential scanning calorimetry, polarized optical microscopy, and X‐ray diffraction.

POM image (200 X) of D3OTP1 at room temperature.

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POM image (200 X) of D3OTP1 at room temperature.
Mesogeneous Catalysts: A New Concept in Nanotechnology
Authors: Rodríguez Rogelio , Nava Rufino , Halachev Todor , Castaño Victor M.
Published: March 2004

Summary: A novel type of catalysis, neither homogeneous nor heterogeneous, is presented. This new “mesogeneous catalysis” combines the high efficiency characteristic of the homogeneous process with the advantages of the heterogeneous one (i.e., the possibility of removing and reusing the catalyst and obtaining catalyst‐free products). The reactions are performed on the surface of nano‐particles, where catalytic‐active sites have been previously chemically anchored by a short dangling organic chain, thus forming a nanohybrid system.

Methanol produced by the different catalysts, after 60 min.

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Methanol produced by the different catalysts, after 60 min.
The Critical Lowest Molecular Weight for PEG to Crystallize in Cross‐Linked Networks
Authors: Qiao Congde , Jiang Shichun , Dong Dewen , Ji Xiangling , An Lijia , Jiang Bingzheng
Published: March 2004

Summary: Poly(ethylene glycol) (PEG) networks were synthesized by γ‐irradiation. The crystalline behavior of PEG was investigated by differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD). It was shown that the crystallinity of PEG is dramatically lower in the cross‐linked networks than in pure PEG. When the molecular weight of PEG in the networks decreased to 1 000, it could not crystallize at all. Moreover, we also found that the melting temperature of PEG is greatly affected by the presence of a cross‐linked network.

The DSC curves of PEG ($\overline M _{\rm w}$ = 1 500) and the corresponding cross‐linked PEG.

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The DSC curves of PEG ($\overline M _{\rm w}$ = 1 500) and the corresponding cross‐linked PEG.
Synthesis of a Novel Oligoaniline: “Dumbbell‐Shaped” Oligoaniline
Authors: Yu Youhai , Mao Huaping , Chen Liang , Lu Xiaofeng , Zhang Wanjin , Wei Yen
Published: March 2004

Summary: A new kind of aniline oligomer with a “dumbbell” shape was synthesized through a simple oxidative coupling reaction with a new rigid aromatic amine as starting material. The oligomer was characterized with mass spectrometry, IR and NMR spectroscopies. Its redox property was checked by cyclic voltammetry and chemical oxidation/reduction process was monitored by UV spectroscopy. We found it has a reversible electrochemical property like common oligoanilines. Combined with its well‐defined structure, it is expected to act as a model compound for a molecular electronic switch.

The “dumbbell‐shaped” oligoaniline compound synthesized here.

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The “dumbbell‐shaped” oligoaniline compound synthesized here.
Synthesis and Characterization of Amphiphilic Poly(caprolactone) Star Block Copolymers
Authors: An Sung Guk , Cho Chang Gi
Published: March 2004

Summary: Novel, star‐shaped, amphiphilic block copolymers composed of fully degradable poly(caprolactone) were synthesized by sequential addition polymerization. In the first step, four‐arm macroinitiators were produced by ring‐opening polymerization of caprolactone by initiation with pentaerythritol. Then, block copolymers were synthesized by sequential addition of 4‐(2‐benzyloxyethyl)‐ε‐caprolactone to the four‐arm macroinitiators. Star‐shaped, amphiphilic block copolymers containing poly(caprolactone)‐block‐poly[4‐(2‐hydroxyethyl)caprolactone] segments were obtained by catalytic debenzylation.

Four‐arm amphiphilic polycaprolactone star block copolymer.

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Four‐arm amphiphilic polycaprolactone star block copolymer.
Photoregulated Sol‐Gel Transition of Novel Azobenzene‐Functionalized Hydroxypropyl Methylcellulose and Its α‐Cyclodextrin Complexes
Authors: Zheng Peijie , Hu Xiao , Zhao Xiongyan , Li Lin , Tam Kam Chiu , Gan Leong Huat
Published: March 2004

Summary: Novel azobenzene‐functionalized hydroxypropyl methylcellulose (AZO‐HPMC) polymers and their α‐cyclodextrin (α‐CD) complexes have been prepared. These polymers show interesting sol‐gel transition behavior in aqueous solutions. In the absence of α‐CD, the gelation temperature increases after UV irradiation, while in the presence of α‐CD, the gelation temperature decreases after UV irradiation. The difference in the gelation temperatures between the trans and cis samples of AZO‐HPMC opens a wide operating window for reversible regulation of the sol‐gel transition behavior by photoirradiation.

The UV‐induced cis/trans isomerism of azobenzene‐functionalized hydroxypropyl methylcellulose and its α‐cyclodextrin complexes.

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The UV‐induced cis/trans isomerism of azobenzene‐functionalized hydroxypropyl methylcellulose and its α‐cyclodextrin complexes.
Thermotropic Liquid‐Crystalline Polymer Derived from Natural Cinnamoyl Biomonomers
Authors: Kaneko Tatsuo , Matsusaki Michiya , Hang Tran Thi , Akashi Mitsuru
Published: March 2004

Summary: The compound 4‐hydroxycinnamic acid (4HCA), a natural biomonomer, is polymerized by melt polycondensation to yield a liquid‐crystalline biopolymer (P4HCA) with UV reactivity. L929 cells were successfully incubated on P4HCA films at 37 °C.

Structure of poly(4‐hydroxycinnamic acid) (P4HCA) and its crossed‐polarizing optical micrograph in the nematic state. Inset image: optical micrograph of L929 mouse fibroblasts adhered on P4HCA film after 24 h incubation at 37 °C.

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Structure of poly(4‐hydroxycinnamic acid) (P4HCA) and its crossed‐polarizing optical micrograph in the nematic state. Inset image: optical micrograph of L929 mouse fibroblasts adhered on P4HCA film after 24 h incubation at 37 °C.
Preparation of Main‐Chain‐Type Quinolinol Polymers by Organometallic Polycondensation
Authors: Iijima Takayuki , Yamamoto Takakazu
Published: March 2004

Summary: New main‐chain‐type polymers of 8‐quinolinol were prepared by organometallic polycondensation. They had a poly(aryleneethynylene)‐type structure and exhibited photoluminescence with a peak at about 470 nm and quantum yields of 21–39%. Metal ions such as Zn2+ and Al3+ modified the photoluminescence.

Structure of the three main‐chain‐type polymers of 8‐quinolinol synthesized and studied here.

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Structure of the three main‐chain‐type polymers of 8‐quinolinol synthesized and studied here.
A Tandem Catalytic System for the Synthesis of Ethylene–Hex‐1‐ene Copolymers from Ethylene Stock
Authors: Ye Zhibin , AlObaidi Fahad , Zhu Shiping
Published: March 2004

Summary: A tandem catalytic system, composed of (η5‐C5H4CMe2C6H5)TiCl3 (1)/MMAO (modified methyl aluminoxane) and [(η5‐C5Me4)SiMe2(tBuN)]TiCl2 (2)/MMAO, was applied for the synthesis of ethylene–hex‐1‐ene copolymers with ethylene as the only monomer stock. During the reaction, 1/MMAO trimerized ethylene to hex‐1‐ene, while 2/MMAO copolymerized ethylene with the in situ produced hex‐1‐ene to poly(ethylene–hex‐1‐ene). By changing the catalyst ratio and reaction conditions, a series of copolymer grades with different hex‐1‐ene fractions at high purity were effectively produced.

The overall strategy of the tandem 1/2/MMAO catalytic system.

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The overall strategy of the tandem 1/2/MMAO catalytic system.
Suppression of Thermochromism in a Poly(di‐n‐hexylsilane)‐Zirconia Hybrid
Authors: Matsuura Yukihito , Inoue Hiroshi , Matsukawa Kimihiro
Published: March 2004

Summary: Poly(di‐n‐hexylsilane) (PDHS)‐containing zirconia hybrid thin films were prepared by a sol‐gel reaction of PDHS copolymers and zirconium alkoxide, and it was found that the thermochromic properties of PDHS due to the transformation of the SiSi main chain were suppressed in the PDHS‐zirconia hybrid thin film.

Structure of poly(di‐n‐hexylsilane)‐zirconia hybrid.

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Structure of poly(di‐n‐hexylsilane)‐zirconia hybrid.
Smectic A Elastomers with Uniform Homeotropic Orientation Obtained by Applying a Biaxial Mechanical Field
Authors: Nishikawa Etsushi , Yamamoto Jun , Yokoyama Hiroshi , Finkelmann Heino
Published: March 2004

Summary: The orientation behavior of a smectic A elastomer is investigated by applying a biaxial mechanical field to the elastomer in a swollen state. The network is composed of a siloxane‐polymer backbone, a bi‐functional cross‐linker, and a monomer with a perfluorinated tail. In this work, biaxial deformation is successfully achieved to macroscopically orient the smectic A phase in a uniform, homeotropic fashion. We describe the orientation process in detail and discuss the microstructure of the smectic A phase organized in the monomer, the linear polymer, and the elastomer determined by using X‐ray diffraction data.

A photograph of the oriented smectic A elastomer E4F (above) and a schematic model of its homeotropic orientation (below).

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A photograph of the oriented smectic A elastomer E4F (above) and a schematic model of its homeotropic orientation (below).
Double Yielding in a Styrene/Butadiene Star Block Copolymer
Authors: Adhikari Rameshwar , Buschnakowski Matthias , Henning Sven , Goerlitz Sylvia , Huy Trinh An , Lebek Werner , Godehardt Reinhold , Michler Georg Hannes , Lach Ralf , Geiger Kalman , Knoll Konrad
Published: March 2004

Summary:The morphology and tensile deformation behaviour of a highly asymmetric styrene/butadiene star block copolymer (polystyrene (PS) content = 74%) containing random PS‐co‐PB (polybutadiene) copolymer as a rubbery phase were investigated. The existence of double yielding, similar to that observed in some semicrystalline polymers, was detected in this nanostructured amorphous polymer. The observed phenomenon may be correlated with two different micromechanical processes taking place at the initial stage of deformation.

The stress‐strain curve of the star block copolymer prepared here (each curve represents a different method). The two yield points are clearly visible (labelled I and II).

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The stress‐strain curve of the star block copolymer prepared here (each curve represents a different method). The two yield points are clearly visible (labelled I and II).