bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of ZnCl2 on the spontaneous copolymerization of methyl acrylate with substituted 1,3‐dienes
Authors: Mikhael M. G. , Padias A. Buyle , Hall H. K.
Published: April 2003

The reactions of the mildly electron‐poor olefin methyl acrylate (MA) with three electron‐rich substituted hydrocarbon 1,3‐dienes, namely 2,3‐dimethyl‐1,3‐butadiene (DMB), 4‐methyl‐1,3‐pentadiene (MPD) and isoprene (IP) were investigated in 1,2‐dichloroethane in the presence of various amounts of zinc chloride at different temperatures. ZnCl2 complexes with the ester group of MA and increases the MA's electron‐poor character and therefore its tendency towards reactions with electron‐rich dienes. In the absence of ZnCl2, no reaction occurs between the investigated dienes and MA under the used reaction conditions. Both alternating copolymers and [4+2] cycloadducts formed spontaneously in the presence of ZnCl2 even at room temperature. The structure of the diene and its nucleophilicity control the product distribution. For the DMB and IP systems, raising the reaction temperature and increasing the ZnCl2 concentration enhance the overall reaction rate and in most cases also favor the cycloaddition over the copolymerization. IP is less reactive than DMB. With MPD only copolymer is formed because the two terminal methyl groups retard the concerted [4+2] cycloaddition. These results are in agreement with a postulated mechanism involving competition between the formation of a π‐allyl 2‐hexene‐1,6‐diradical, capable of initiating free radical copolymerization, and concerted [4+2] Diels‐Alder cycloaddition.
π Electron delocalization in pristine polyfuran: from the oligomers to the polymer
Authors: Hernández V. , Veronelli M. , Favaretto L. , Navarrete J. T. López , Jones D. , Zerbi G.
Published: April 2003

Chain‐length‐dependent π electron delocalization is analyzed in pristine oligofurans and polyfuran by means of Fourier transform Raman spectroscopy. Neutral polyfuran shows a large frequency dispersion with conjugation length and it has not yet reached saturation at the level of the hexamer. In spite of such a large π electron delocalization the polymer seems to show an unexpectedly good stability in air at room temperature. Regio‐defined poly(2,5‐difurans) could be good candidates for technological developments.
Full coverage of a hydroxy‐substituted poly(para‐phenylene) with first‐ and second‐generation dendritic wedges having isocyanate focal points
Authors: Karakaya B. , Claussen W. , Schäfer A. , Lehmann A. , Schlüter A.‐D.
Published: April 2003

Synthesis of the hydroxyethyl‐substituted poly(para‐phenylene) 2b employing Suzuki polycondensation is described. This PPP derivative is used as a matrix for the attachment of first‐ and second‐generation dendrons of the Fréchet‐type with isocyanate functions at the focal point. The degree of coverage is determined from NMR integration to be virtually 100% in both cases.
Synthesis of oligoanthrylenes and their photopolymerization in solution
Authors: Stein S. , Müllen K.
Published: April 2003

Trianthrylene compounds with film‐forming capabilities were synthesized in a three‐step procedure by means of transition‐metal catalyzed Grignard and Suzuki coupling reactions. Upon UV exposure, photopolymerization of the model compound 1,11‐di‐(9‐anthryl)undecane was observed in solution as well in the film due to [4+4] cycloaddition of the anthracene moieties. The soluble photopolymers were characterized by NMR spectroscopy and GPC analysis. As expected, irradiation of solutions of the trichromophoric hydrocarbons afforded crosslinked photoproducts which precipitated from solution. In the case of an analogous trianthryl derivative with tetraoxyethylene spacers, formation of a gel was observed due to cycloaddition of the anthracene groups. The film‐forming capabilities of trianthryl compounds in conjunction with UV‐induced photocrosslinking can be useful for photoresist applications and will be discussed in the following paper [1].
Photobleaching of oligoanthrylenes in the film state
Authors: Paul S. , Stein S. , Knoll W. , Müllen K.
Published: April 2003

Films of oligoanthrylenes are readily available by spin coating. Upon UV exposure, the properties (refractive index, fluorescence and solubility) of these films are changed due to [4+4] cycloaddition of the anthracene groups. This behavior appears to be useful for information recording purposes, which is demonstrated by surface plasmon and fluorescence microscopy. Although complete photobleaching of the films is not possible, effective photocrosslinking occurs for trichromophoric systems affording relief textures after development in ethanol/methylene chloride mixtures (negative tone photoresist). Furthermore, the reversibility of the solid state photodimerization of the anthracene moieties is discussed.
Enzyme‐mediated polymerization reactions: Peroxidase‐catalyzed polyphenol synthesis
Authors: Ayyagari M. , Akkara J. A. , Kaplan D. L.
Published: April 2003

Peroxidase‐catalyzed phenol polymerization in the presence of hydrogen peroxide has been extensively studied. The process offers many advantages over the conventional chemical process to produce phenol‐based resins. The enzymatic process avoids the use of formaldehyde and results in minimal formation of by‐products due to high specificity of the enzyme toward the reactants. A number of phenolic derivatives and aromatic amines can be polymerized in different reaction systems, such as bulk solvents, reversed micelles and Langmuir trough. The polymers produced produced exhibit morphology reflective of the templating effect of the medium used to prepare the materials. Polymer molecular weight and polydispersity can be controlled by suitable design of the reaction medium. Polymer characteristics such as structure, thermal and temporal stability, functionalization and processability are reviewed. Conductivity, nonlinear optical and related functional properties are discussed with regard to potential applications.
Synthesis and properties of interpenetrating networks from acrylates of d‐block elements
Authors: Gupta N. , Srivastava A. K.
Published: April 2003

Systematic synthesis of interpenetrating polymer networks (IPN) from poly(chromium acrylate) (PCrA) and zinc acrylate (ZnA) using divinyl benzene (DVB) as crosslinker has been carried out. Swelling studies and scanning electron microscopy (SEM) were performed to examine the extent of crosslinking and phase behavior of the IPN. The crosslinking decreases with the increase of linear polymer concentration and its molecular weight, respectively. On the other hand, it increases with the increase of concentration of crosslinking agent and monomer II, respectively. The IPN was found to be thermally stable up to 300 °C.
Alkylthio‐substituted oligothiophenes: the influence of the alkyl chain length on the solid‐state and solution properties of 4,4′‐bis(butylthio)‐2,2′‐bithiophene
Authors: Antolini L. , Folli U. , Goldoni F. , Iarossi D. , Mucci A. , Schenetti L.
Published: April 2003

A solid‐state (single crystal X‐ray, IR, DSC) and solution (1H NMR nuclear Overhauser effect (NOE) and longitudinal relaxation times (T1)) study of 4,4′‐bis(butylthio)‐2,2′‐bithiophene is reported. The two thienyl rings are coplanar and in an anti orientation in the solid state, whereas a low amount of syn form is present in solution. The n‐butylthio chain adopts a fully extended, nearly idealized, anti conformation in the crystal, with all the non‐H atoms of the whole molecule strictly coplanar, despite the molecular length, but does not show a preferred orientation in solution. The observed changes on passing from the solid to the solution state are indications of the potential solvatochromic and thermochromic properties of β‐butylthio‐substituted oligomers and polymers.
Copolymerization of ethyl cyanoacrylate and ethylene in the presence of zinc chloride or trifluoroacetic acid as complexing agent
Authors: Sperlich B. , Eisenbach C. D.
Published: April 2003

The free radical copolymerization of ethene and ethyl cyanoacrylate (ECA) in the presence of Lewis and Brønsted acids has been studied in detail. Both trifluoroacetic acid (TFA) and ZnCl2.Et2O were found to be useful complexing agents for synthesizing highly alternating copolymers of olefins and ECA. The influence of the complexing agents was quantified by determination of the copolymerization parameters r1 of ECA for ECA/ET copolymerization. The synthesized copolymers showed unusual thermal behavior with regard to their alternating structure. This was established by the semi‐crystallinity and the variation of the glass transition temperature with the degree of alternation.
Study of particle interaction in a highly concentrated latex by turbidimetry
Authors: Weiss A. , Pötschke D. , Ballauff M.
Published: April 2003

A study of the low‐angle region of the static structure factor S(q) (q = (4π/λ) sin(θ/2); θ: scattering angle, λ: wavelength of the radiation in the medium) of a concentrated (44 wt.%) poly(methyl‐methacrylate) (PMMA) latex by turbidimetry is presented. It is demonstrated that S(0), i.e., the structure factor extrapolated to vanishing scattering angle can be obtained in excellent accuracy up to the highest concentrations. Since S(0) reflects the balance between long‐range attractive and short‐range repulsive forces between the latex particles, this quantity can be used to assess the stability of the latex against flocculation. Special attention has been paid to the influence of polydispersity on S(0). The analysis of S(q) in the vicinity of q = 0 for the system under consideration indicates the absence of attractive forces between the particles.
Polyesters based on oxygen‐organosolv lignin
Authors: Evtugin D. V. , Gandini A.
Published: April 2003

Oxygen‐organoslov lignin (namely oxygen‐acetone) was introduced as a macromonomer into polyesterification systems including diacid chlorides and, optionally, oligoethyleneoxide glycols. It was concluded that the incomplete participation of phenolic hydroxy groups of lignin in these polycondensation reactions could lead to poor crosslinking as shown by the partial solubility of the final polyesters in polar solvents. This paper presents the synthesis, characterization and some properties of these materials.
Local dynamics in a thermotropic terpolyester as revealed by dynamic mechanical analysis, 2H NMR and dielectric spectroscopy
Authors: Wiesner U. , Spiess H. W. , Müller F. , Kremer F. , Lauprêtre F. , Halary J. L. , Monnerie L.
Published: April 2003

Dynamic mechanical, 2H NMR and dielectric spectroscopy techniques were used to identify the nature of the local motions involved in the secondary relaxations of a thermotropic aromatic terpolyester prepared from para‐hydroxybenzoic acid, hydroquinone and isophthalic acid. Three secondary relaxations, denoted β, γ, and δ, were detected. A β relaxation, pointed out by dynamic mechanical measurements, is quite close to the large amplitude π‐flip processes observed by 2H NMR. Correlated motions of the para‐substituted rings and adjacent carbonyl groups may also participate in the β process. Then, at lower temperatures, a γ process is detected by both dielectric and dynamic mechanical experiments. It is assigned to small amplitude oscillations of the isophthalic acid units of the HBA33 polymer. At high temperatures, a heavy overlap of broad rate distributions for the β and γ processes observed in the measurements precludes a more detailed analysis. A dielectric relaxation, denoted δ relaxation, is observed at very low temperatures. It likely comes from motions of a very small number of water molecules trapped in the structure of the terpolyester.
Dielectric relaxation and conductivity in polyelectrolyte—surfactant complexes
Authors: Antonietti M. , Maskos M. , Kremer F. , Blum G.
Published: April 2003

The dielectric and conductivity behavior of some selected solid polyelectrolyte‐surfactant complexes (PE‐surf) is characterized by broadband dielectric spectroscopy in the frequency range 10−2–107 Hz. Depending on phase‐morphology and volume fraction of alkyl‐tails, electrical conductivities at room temperature of up to 10−4 S/cm are found. In addition, the behavior at low temperatures is characterized by two distinct β‐relaxations which show an Arrhenius‐like activation, and their relaxation strength depends on temperature, in contrast to the standard behavior of dielectric media. The relaxations are assigned to surfactant movements, the number or strength of which increase with temperature, which are obviously important already well below the glass transition temperature of the ionic layers. Doping of a selected complex showing a rather high basic conductivity with LiClO4 results in a decrease of the conductivity, which is explained by an increase in the glass transition temperature of the ionic layer.
Molecular imprinting: An approach to “tailor‐made” synthetic polymers with biomimetic functions
Authors: Takeuchi T. , Matsui J.
Published: April 2003

The recent development of synthetic polymers with biomimetic functions prepared by molecular imprinting is reviewed in this article. Molecular imprinting is based on template polymerization in which polymers are prepared in the presence of a template molecule to be imprinted. Resultant polymers record the shapes and chemical properties of the templates in their matrixes and exhibit antibody‐like and enzyme‐like activities. The most significant advantage of this technique is its simplicity: complementary sites for the target molecules which are expected to be specific binding/catalytic sites can be constructed with the aid of molecular self‐assembly and no complicated synthesis is necessary. In this article, we present typical examples of molecularly imprinted polymers and especially focus on the effectiveness of molecular imprinted polymers as artificial antibodies and the potential as substrate‐selective catalysts.
The synthesis and polymerization of oxo‐crown ethers
Authors: Peeters E. , Janssen H. M. , van Zundert M. F. , van Genderen M. H. P. , Meijer E. W.
Published: April 2003

A novel synthetic route to and a polymerization procedure for oxo‐crown ethers 2, 11‐dioxo‐18‐crown‐6 (1), 2‐oxo‐12‐crown‐4 (2) and 2‐oxo‐21‐crown‐7 (3) are described. Cyclization of the ω‐hydroxycarboxylic acid precursors of 1—3 has been achieved by heating these precursors in the presence of a Lewis acid catalyst (CoCl2) and a template salt (MCl). Cyclization yields up to 82% were reached, using CsCl as template salt. Oxo‐crown ethers 1—3 have been polymerized using SnOct2 as catalyst, giving polymers with molecular weights of approximately 5 kg/mol and dispersities of ca. 1.8 (measured with polyethylene oxide standards). The polymerization of 2 was monitored with 1H‐NMR and SEC giving information about (a) the influence of monomer/catalyst ratio and temperature on polymerization rate and (b) the influence of temperature on molecular weight (distribution). The possibility of introducing endgroups into poly(2‐oxo‐12‐crown‐4) using SnOct2‐catalyzed polymerization was also studied.
SAXS studies on the deformation of macrolattices in block copolymers
Authors: Brandt M. , Ruland W.
Published: April 2003

Uniaxial stretching of SIS triblock copolymers produces ellipsoidal intensity distributions in SAXS. A quantitative evaluation of the axis ratio leads to the determination of the extension ratio of the macrolattices. A comparison with the extension ratio of the bulk indicates that a uniform deformation of the macrolattices has taken place. The angular dependence of the intensity distribution on the ellipsoid shows systematic deviations between calculated and observed values which are interpreted in terms of lattice distortions produced by local stresses. The relationship between these stresses and the mechanical anisotropy of the bcc macrolattices is investigated.
Linearity of heat capacity step near the onset of α glass transition in poly(n‐alkylmethacrylate)s
Authors: Hempel E. , Beiner M. , Renner T. , Donth E.
Published: April 2003

DSC measurements around the glass transition in the homologous series of seven poly(n‐alkylmethacrylate)s (alkyl=methyl, ethyl, propyl, butyl, pentyl, hexyl, octyl) are presented. The step height Δcp decreases linearly with the number of n‐alkyl C‐atoms in the side chain. The usual glass step in the DSC curves, e. g. for poly(methylmethacrylate), degenerates to a bend near poly(n‐octylmethacrylate). This finding is discussed as a result of a linear relation between the caloric relaxation strength Δcp and the temperature difference from the α onset Tonset in the splitting region of poly(n‐alkylmethacrylate)s, with Δcp → 0 for T → Tonset. The number of monomeric units per cooperatively rearranging region at Tg decreases from PMMA (Nα∼20) to PnOMA (Nα<5). This demonstrates that the cooperativity at the α onset in poly(n‐alkylmethacrylate)s is very small, as expected from a fluctuation approach to the glass transition.
Synthesis and ionic conductivity studies of solid polymer electrolytes based on modified alternating maleic anhydride copolymer with oligo(oxyethylene) side chains
Authors: Ding Liming , Shi Jing , Ma Dezhu , Dong Shaojun
Published: April 2003

Comb‐like polymers (CP) based on modified alternating methyl vinyl ether/maleic anhydride copolymer with oligo‐oxyethylene side chains of the type O(CH2CH2O)nCH3 have been synthesized and characterized, and complexed with LiNO3 to form an amorphous polymer electrolyte. CP/salt complexes showed conductivity up to 10−5 S/cm at room temperature. The temperature dependence of ionic conductivity suggests that the ion transport is controlled by segmental motion of the polymer, shown by linear curves obtained in Vogel–Trammann–Fulcher plots. The ionic conductivity maximum moves to a higher salt concentration as the temperature increases. IR results also indicate that the ester in CP might decompose at 140°C and reproduce the maleic anhydride ring.
Degree of branching in hyperbranched polymers
Authors: Hölter D. , Burgath A. , Frey H.
Published: April 2003

Topological considerations concerning the ratio of linear, imperfectly branched, dendritic and terminal units in hyperbranched polymers based on AB2, AB3 and ABm (m≥2) type monomers are summarized. The reaction of AB2 monomers with a core molecule of the structure Bf is also treated. For larger hyperbranched polymers based on AB2 monomers the fraction of terminal units has to be equal to the number of dendritic units. A general expression for the degree of branching (DB) is derived for AB2 systems, which is based on the number of dendritic and linear units. The expression is valid for low molecular weight as well as high molecular weight hyperbranched polymers in contrast to the commonly used expression based on dendritic, linear and terminal units. DB may not exceed 0.5 in hyperbranched polymers based on AB2 systems (0.44 in AB3 systems). Furthermore, a general expression for DB in hyperbranched polymers based on ABm monomers is derived. Consequences for signal ratios in NMR‐spectra of hyperbranched polymers are discussed. The expressions presented allow verification of NMR‐integration ratios obtained experimentally on the basis of model compounds.
Craze formation in amorphous polymers in relation to the flow and main transition
Authors: Starke J.‐U. , Schulze G. , Michler G. H.
Published: April 2003

Crazes were produced and analyzed in unnotched tensile bars of poly(styrene‐co‐acrylonitrile) (SAN) and polycarbonate (PC) in creep experiments above TVF (the Vogel temperature). The craze microstructure was investigated as a function of temperature (T) and load (σ) by means of small angle X‐ray scattering (SAXS) and transmission electron microscopy (TEM). Contrary to expectation, the scattering vector of maximum intensity (smax), which is inversely proportional to the distance between the fibrils of crazes, was not linearly dependent on σ at constant temperature. At the highest stresses (regime III), smax was independent of stress, and the average distance between the fibrils reaches a minimum value. At intermediate stresses (regime II), a strong increase of fibrillation energy Γ was detected, as the temperature was reduced. In the vicinity of TVF, Γ reached values of the order of the polymer chain fracture energy. At the lowest stresses (regime I), the energy of fibril formation was independent of temperature and corresponded to the van der Waals surface energy. The molecular motions during fibril formation may be linked to local stress‐induced flow processes of polymer chains (regime I) and α‐relaxations (regime II). Increasing stress restricts the range of mobility of macromolecules to shorter and shorter units and a transition from the formation of fibrillated crazes to homogeneous crazes or shear deformation processes occurs at the highest stresses (regime III). A pressure—temperature diagram was constructed from the transition between the regimes, particularly at negative pressure.
Polydimethylsiloxane‐cyclodextrin networks synthesized into a porous polystyrene gel – an investigation by energy filtering transmission electron microscopy
Authors: Du Chesne A. , Wenke K. , Lieser G. , Wenz G.
Published: April 2003

Crosslinked poly(styrene)‐poly(dimethylsiloxane)‐cyclodextrin systems are a new class of multicomponent polymer networks. They are prepared by swelling a polystyrene gel (PS) with the components of the poly(dimethylsiloxane)‐cyclodextrin network (PDMS(CDX)) and subsequent crosslinking. Electron spectroscopic imaging and elemental mapping are appropriate methods for the investigation of these polymer systems, which contain heteroatoms in one of their components. It is shown that PDMS(CDX) is uniformly distributed within PS. Interpenetration with PS is responsible for the stable anchoring of PDMS(CDX) and prevents phase separation.
Electrochemical characterization of polymer ion‐exchange bipolar membranes
Authors: Mafé S. , Ramírez P.
Published: April 2003

A bipolar membrane (BM) is a layered structure composed of one cation and one anion ion‐exchange layers joined together in series. Polymer BMs offer promising applications for many industrial processes (e. g., the use of bipolar electrodialysis for environmentally clean technologies and the treatment of salt‐water effluents) because of their unique electrochemical properties. The most important of these properties is the electric field enhanced (EFE) water dissociation which arises when an electric current is forced through the membrane. This phenomenon occurs at the bipolar junction of the BM, and its coupling with ion transport, though still poorly understood, is the basis of most of the potential applications of BMs. In this review, we will focus on recent work concerning the physical chemistry of BMs and give a general overview of their electrochemical properties, emphasizing both theoretical and experimental aspects. We will model first the electric double layer at the bipolar junction between the two ion‐exchange layers, and describe then the EFE water dissociation occurring in this junction. Later, we will present in detail a complete theoretical model for the coupling of ion transport and water dissociation in BMs, and show that this model is able to explain the experimental trends observed in the electrochemical characterization of polymer BMs by means of membrane potential, current–voltage curve, and impedance measurements.
Aromatic polymers obtained by precipitation polycondensation. 6. Morphology of polyketone particles
Authors: Zolotukhin M. G. , Calleja F. J. Balta , Rueda D. R. , Palacios J. M.
Published: April 2003

Syntheses of aromatic polyketones in the form of particles were performed using a very small monomer concentration (0.05 mol/1) by the precipitation polycondensation method. Some of these particles present highly ordered elongated needle‐like structures (whiskers) particularly for the all‐para polyketone samples. The use of isophthaloyl instead of terephthaloyl for the same low monomer concentration produces, in addition to the globular particles, bundles of ribbon‐like structures. The average size of the needle‐like particles is 1−5 μm in width and 150−250 μm in length. The factors controlling the morphology texture and size of the whiskers and ribbons are shown to be the polymer structure and the reaction conditions. Formation mechanisms are discussed.
Poly(di‐n‐pentylsilylene) copolymers containing diethyleneglycol‐diethylether side chains
Authors: Schwegler L. A. , Möller M.
Published: April 2003

Poly(dipentylsilylene) copolymers containing 4,7,10‐trioxadodecylmethylsilylene units as comonomer were synthesized via a Wurtz‐type coupling reaction from the corresponding dichlorosilanes. The copolymers were characterized by GPC and NMR spectroscopy. Solvent‐ and temperature‐dependent UV absorption was observed. The bulk polymers underwent broad endothermic transitions below room temperature, whose temperature and heat effect depended on the incorporation of comonomer. This suggested that the high‐temperature state can be described as a columnar mesophase corresponding to the well established case of the poly(dipentylsilylene). Correlated to this transition, the copolymers also showed thermochromic behavior at low temperatures. The materials could be oriented by shearing in the mesophase, which was demonstrated by polarized optical microscopy, polarized IR spectroscopy and UV spectroscopy.
Temperature dependence of a glass transition cooperativity
Authors: Korus J. , Hempel E. , Beiner M. , Kahle S. , Donth E.
Published: April 2003

The size of glass transition cooperativity for 11 polymers and glycerol is determined from heat capacity spectroscopy (HCS) and differential scanning calorimetry (DSC) by using a calorimetric fluctuation formula. The data cover in total the 0.25 ≤ x ≤ 0.95 part of the reduced temperature interval between the Vogel temperature and a cooperativity onset temperature. A steep cooperativity increase at lower temperature is observed. The data are consistent with the hypothesis that the temperature dependence can be described by the enlargement of a minimal cooperativity at the onset.
Effective conjugation length and UV/vis spectra of oligomers
Authors: Meier H. , Stalmach U. , Kolshorn H.
Published: April 2003

On the basis of an extended series of monodisperse oligomers of the dialkoxy‐substituted phenyleneethenylenes 1a–i the Eqs. (3) and (4) were conceived in order to determine the limiting values of the energies Ei and the wavelengths λi of the UV/vis absorption. The convergence of the Ei, and λi values with a growing number n of repeating units permits a precise prediction of the Ei,∞ and λi,∞ values of the corresponding polymer 1j as well as a statement about the overall effect of conjugation ΔEi and the effective conjugation length ECL. A great variety of different conjugated oligomers 2–14 can be evaluated by the same algorithm.
Block copolymers containing liquid crystalline segments
Authors: Mao G. , Ober C. K.
Published: April 2003

The interest in block copolymers containing liquid crystalline (LC) segments is due to the resulting interplay between mesophase formation and the microphase structure which creates opportunities in tailoring their nanostructure. This review summarizes recent literature reporting LC‐coil block copolymers with well controlled microphase morphologies produced using living methods. Developing applications are also described and include LC displays and low energy surfaces.
The influence of multivalent cations on negative thixotropy in aqueous glycerol solutions of partially hydrolyzed polyacrylamide
Authors: Bradna B. , Quadrat O. , Titkova L. , Dupuis D.
Published: April 2003

Negative thixotropic behavior in aqueous glycerol solutions of partially hydrolyzed polyacrylamide was studied at various concentrations of Na+, Ca2+ and Al3+ chlorides. A decrease in critical shear stresses and more intensive negative thixotropic behavior observed in the presence of multivalent cations were explained in terms of their stronger charge screening effect. This effect suppresses intermolecular electrostatic repulsions, which act against association of polymer molecules and, thus, against the occurrence of negative thixotropy.
Polythienylenevinylene as promoter of hole injection from ITO into bilayer light emitting diodes
Authors: Tak Y.‐H. , Mang S. , Greiner A. , Bässler H. , Pfeiffer S. , Hörhold H.‐H.
Published: April 2003

Due to the low oxidation potential of poly‐(2,5‐thienylenevinylene) (PTV) an ohmic contact for hole injection is established at an indium tin oxide (ITO)/PTV interface. It gives rise to space‐charge‐limited conduction in an ITO/PTV/Al diode. The ohmic nature of the ITO/PTV contact can be exploited to increase hole injection into multilayer organic light emitting diodes in which internal charge accumulation would otherwise lower majority carrier injection by virtue of electric field screening at the anode.
Electrospray ionization mass spectrometry as an analytical tool for non‐biological monomers, oligomers and polymers
Authors: Saf R. , Mirtl C. , Hummel K.
Published: April 2003

This paper reviews electrospray ionization mass spectrometry (ESI‐MS) as an analytical tool for the investigation of non‐biological materials. The fundamentals of the method are briefly described and principles of the interpretation of ESI mass spectra are explained. Differences in comparison to biochemical applications of ESI‐MS are discussed. Selected examples show how ESI‐MS can be used for the investigation of synthetic monomers, oligomers, and polymers, especially in cases where other analytical methods fail.
Textures and defects of the hexagonal columnar phase of phthalocyaninato‐poly(siloxane) derivatives (PCPS)
Authors: Ries R. , Lieser G. , Schwiegk S. , Wegner G.
Published: April 2003

Samples of alkyloxy derivatives of phthalocyaninato‐poly(siloxane) (PCPS) with various patterns of substitution were prepared by solution casting. After this history of treatment they form lyotropic hexagonal columnar mesophases. Textures and defects were analyzed in the “frozen” state (with the solvent evaporated) by optical and electron microscopy. With the exception of the space occupied by a single molecule, significant differences of the behavior in the liquid crystalline state were not found among the PCPS derivatives. The side chains of the samples under investigation are too short to be ordered but in the frozen liquid crystalline state the main chains are in register. Both optical and electron microscopy provide evidence for undulations of the molecular trajectories with preferential orientation. Defects typical of hexagonal columnar phases, e.g. walls of various origin and developable domains, where observed. Together with the undulations, transversal edge dislocations occur, as can be demonstrated by high resolution electron microscopy. Inserted lattice half‐planes enable the system to minimize the elastic energy of the highly persistent molecules in the bent director field.
Direct comparison of membrane interactions of model peptides composed of only Leu and Lys residues
Authors: Epand Raquel F. , Lehrer Robert I. , Waring Alan , Wang Wei , Maget‐Dana Régine , Lelièvre Dominique , Epand Richard M.
Published: April 2003

We compared the properties of two peptides of identical size and amino acid composition, Ac–(LKKL)5–NHEt and Ac–(KL)10–NHEt. Both are amphipathic, but only Ac–(LKKL)5–NHEt is a potent promoter of negative curvature. CD studies performed in the presence of lipids confirmed that under these conditions Ac–(LKKL)5–NHEt forms an α‐helix, and Ac–(KL)10–NHEt adopts a β structure. We studied their binding affinity by centrifugation and isothermal titration calorimetry techniques. The Ac–(LKKL)5–NHEt bound to zwitterionic and anionic liposomes, while Ac–(KL)10–NHEt interacted mainly with anionic liposomes. Ac–(LKKL)5–NHEt was more lytic than Ac–(KL)10–NHEt for zwitterionic palmitoyloleoylphosphatidylcholine (POPC) liposomes, and for liposomes composed of lipids extracted from either sheep or human erythrocytes (RBC). Both peptides had similar lytic and lipid mixing activities for liposomes containing anionic lipids. Both peptides were highly hemolytic, with Ac–(LKKL)5–NHEt active against sheep RBC and Ac–(KL)10–NHEt more active against human RBC. From their respective minimal effective concentrations (MECs) as antimicrobial agents, we judged Ac–(KL)10–NHEt to be 2 to 5‐fold more potent than Ac–(LKKL)5–NHEt in media that contained physiological concentrations of NaCl. Notwithstanding, both peptides had MECs <1 μg/mL for Escherichia coli and Pseudomonas aeruginosa and <4 μg/mL for Staphylococcus aureus and methicillin‐resistant Staphylococcus aureus. Although selectivity of antimicrobial peptides for bacterial membranes may result, in part, from the preferential display of anionic residues in these membranes, inability to interact with or bind to zwitterionic phospholipids offers no guarantee that the peptide will lack appreciable cytotoxicity for host cells. © 2003 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 71:
2–16, 2003
Transmembrane segment peptides with double D‐amino acid replacements: Helicity, hydrophobicity, and antimicrobial activity
Authors: Maeda Mitsuko , Melnyk Roman A. , Partridge Anthony W. , Liu Li‐Ping , Deber Charles M.
Published: April 2003

The adoption of a helical conformation in a membrane environment effectively increases the “apparent hydrophobicity” of a peptide segment by satisfying the backbone H‐bonding potential, thus stabilizing it in this environment. Here we sought to explore whether destabilizing the helical conformation would have a measurable effect on the apparent hydrophobicity of such segments in both aqueous and membrane‐mimetic environments. In order to uncouple peptide hydrophobicity from helicity, we used the prototypic KKAAAAAAAAAAAAWAAAAAAKKKKNH2 peptide as a template, and performed pairwise DD‐scanning mutagenesis over the length of the sequence. Studies on this library of 13 peptides show that the DD replacements at positions near the center of peptide sequence had the most significant effects on the peptides' retention time in high performance liquid chromatography experiments. Decreased retention times correlate well with decreased helicity as measured by CD spectroscopy in the aqueous environment. Trp fluorescence measurements indicated that the peptides displayed a significant red shift in LPC (but not LPG) with peptides having DD replacements near the middle of the peptide sequence, emphasizing the importance of the anionic membrane in promoting peptide insertion. When tested against a laboratory strain of Escherichia coli, antimicrobial activity of the DD‐peptides correlated with the apparent hydrophobicity but not with the overall micelle‐based helical content of the peptides per se. Further analysis of the DD‐positional dependence of the antimicrobial activity suggests that the presence of a local, uninterrupted stretch of helical structure (10–12 residues) may be a prerequisite for peptide biological activity. The overall findings support the notion that one should distinguish between the hydrophobicity of individual residues and the apparent hydrophobicity of the peptide as a whole, as the latter will ultimately have a greater influence on the properties of the full‐length species. © 2003 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 71: 77–84, 2003
Improved survival in women with BRCA‐associated ovarian carcinoma
Authors: Cass Ilana , Baldwin Rae Lynn , Varkey Taz , Moslehi Roxana , Narod Steven A. , Karlan Beth Y.
Published: April 2003

BACKGROUND

The objective of this study was to determine the clinical characteristics, treatment response, and frequency of p53 overexpression in Ashkenazi Jewish women with hereditary ovarian carcinoma.

METHODS

Seventy‐one Jewish women with epithelial ovarian carcinoma (EOC) were tested for the three BRCA founder mutations using single‐strand conformation polymorphism analysis, heteroduplex analysis, and protein truncation testing. Clinical and histopathologic data were reviewed retrospectively. In vitro chemoresistance was analyzed in 32 patients. Mutations of p53 were studied using immunohistochemical detection of p53 overexpression.

RESULTS

Thirty‐four of 71 Jewish patients with EOC (48%) had germline BRCA mutations (BRCA heterozygotes), including 22 BRCA1 mutations and 12 BRCA2 mutations. BRCA heterozygotes were younger compared with Jewish patients who had EOC without mutations (sporadic carcinoma; 50 years vs. 59 years, respectively; P = 0.01). BRCA1 heterozygotes were younger compared with BRCA2 heterozygotes (48 years vs. 57 years, respectively; P = 0.01). Histopathologic tumor features were similar; however, tumors with low malignant potential were seen only in women with sporadic carcinoma. Both groups had equivalent rates of surgical cytoreduction and similar median follow‐up (72 months). BRCA heterozygotes had higher response rates to primary therapy compared with patients who had sporadic disease (P = 0.01). In vitro chemoresistance predicted tumor response to platinum chemotherapy correctly in BRCA heterozygotes (P = 0.0096). BRCA heterozygotes with advance‐stage disease had improved survival compared with patients who had advanced stage sporadic carcinoma (91 months vs. 54 months, respectively; P = 0.046) and had a longer disease free interval (49 months vs. 19 months, respectively; P = 0.16). p53 overexpression was common in BRCA heterozygotes (80%).

CONCLUSIONS

BRCA1 heterozygotes developed EOC at a younger age compared with BRCA2 heterozygotes and women who had sporadic ovarian carcinoma. BRCA heterozygotes had a better response to platinum chemotherapy compared with women who had sporadic disease, which may have contributed to their improved prognosis. Cancer 2003;97:2187–95. © 2003 American Cancer Society.

DOI 10.1002/cncr.11310
Use of arsenic trioxide (As2O3) in the treatment of patients with acute promyelocytic leukemia
Authors: Lazo Guillermo , Kantarjian Hagop , Estey Elihu , Thomas Deborah , O'Brien Susan , Cortes Jorge
Published: April 2003

BACKGROUND

Approximately 20–30% of patients with acute promyelocytic leukemia (APL) who are treated with all‐trans retinoic acid (ATRA) and an anthracycline develop recurrent disease. It has been reported that arsenic trioxide (As2O3) is effective in this setting. The authors report the experience of The M. D. Anderson Cancer Center with As2O3 in the treatment of patients with recurrent APL.

METHODS

Twelve patients who developed recurrent APL after treatment with ATRA were included. Patients received intravenous As2O3 0.15 mg/kg per day until they achieved a complete remission (CR) or up to a maximum of 60 days. Their median age was 44 years (range, 26–72 years), and the median duration of first remission was 52 weeks (range, 23–292 weeks).

RESULTS

All 12 patients achieved a CR. The median time to achieve CR was 52 days (range, 27–75 days). Seven of 10 evaluable patients achieved a molecular remission (i.e., polymerase chain reaction [PCR] analysis was negative for the gene encoding fusion of the nuclear receptor for retinoic acid to the PML gene at the time of CR; 70% of patients; 95% confidence interval, 0.35–0.93), and all other patients had negative PCR results after they received postremission therapy. All patients received subsequent therapy: Four patients received As2O3 alone, six patients received As2O3 with other chemotherapeutic agents, and two patients received idarubicin plus ATRA without As2O3. Eight patients continued in CR after a median follow‐up of 24 months (range, 9–45 months). Side effects were mild, except for two patients who developed Grade 2 and 3 peripheral neuropathy, respectively; one of those patients required discontinuation of therapy.

CONCLUSIONS

As2O3 is effective and well tolerated therapy for patients with recurrent APL. Molecular remission may be achieved at the time of CR in the majority of patients, and remissions are durable. Cancer 2003;97:2218–24. © 2003 American Cancer Society.

DOI 10.1002/cncr.11314
Extranodal marginal zone B‐cell lymphoma of mucosa‐associated lymphoid tissue of the head and neck area
Authors: Wenzel Catharina , Fiebiger Wolfgang , Dieckmann Karin , Formanek Michael , Chott Andreas , Raderer Markus
Published: April 2003

BACKGROUND

Mucosa‐associated lymphoid tissue (MALT) lymphoma is a distinct entity with specific clinical and pathologic features that may affect diverse organs. MALT–lymphomas remain localized within their original environment for a long period of time. As recent data have demonstrated a relatively high rate of multiorgan involvement at diagnosis, the authors have retrospectively evaluated 36 patients presenting with MALT‐lymphoma in the head and neck area. The authors focused on patients' disease localization, initial treatment, clinical course, and follow‐up.

METHODS

Thirty‐six patients with a histologically verified diagnosis of an extranodal marginal zone B‐cell MALT‐lymphoma arising in the head and neck area were included in this retrospective analysis.

RESULTS

Treatment consisted of surgical resection as the sole treatment in 4 patients (11%), surgical resection with consecutive radiotherapy in 13 patients (36%), radiotherapy alone in 11 patients (31%), chemotherapy in 2 patients (6%), surgical resection plus radiotherapy and chemotherapy in 4 patients (11%), and combined radiation and chemotherapy in 1 patient (3%). Complete and partial disease remissions after initial treatment were achieved in 22 (61%) and 13 patients (36%), respectively, whereas one patient refused any therapy. Four patients (11%) were lost to follow‐up and 15 patients (43%) have had disease recurrence after a median time of 11 months (range, 3–80 months).

CONCLUSIONS

These data suggest that MALT‐lymphomas of the head and neck area are preferentially treated using local modalities such as radiation and/or resection. This practice, however, is associated with an unexpectedly high rate of dissemination or disease recurrence. Obtaining an initial complete response is crucial in these patients. According to previous data, the possibility of understaging in such patients cannot be ruled out. Clinical trials with application of systemic treatment are warranted for these patients. Cancer 2003;97:2236–41. © 2003 American Cancer Society.

DOI 10.1002/cncr.11317
Effect of stereotactic core needle biopsy on pathologic measurement of tumor size of T1 invasive breast carcinomas presenting as mammographic masses
Authors: Charles Melita , Edge Stephen B. , Winston Janet S. , Hurd Thelma C. , Driscoll Deborah L. , Stomper Paul C.
Published: April 2003

BACKGROUND

Stereotactic core needle biopsy (SCNB) may change the size of the tumor defined pathologically at excision. This may alter tumor stage and affect recommendations for adjuvant systemic therapy. This study evaluated the effect of SCNB on assessment of pathologic tumor size and staging for invasive breast carcinomas presenting as mammographic masses.

METHODS

The authors reviewed the mammographic and pathologic size of 138 mammographically detected invasive carcinomas manifested as a measurable mass lesion on mammography and as a 20 mm or smaller lesion on pathologic evaluation. Group A included 61 patients with SCNB before surgical excision and the Group B (the control group) included 77 patients who had surgical excision without SCNB. The size of the mammographic central mass was compared with the pathologic tumor size. The difference between the mammographic and pathologic size was determined and the findings in Group A and B were compared by the Mann–Whitney U test.

RESULTS

The mean mammographic size was 12.2 and 11.83 mm and the mean pathologic size was 9.85 and 9.87 mm for Groups A and B, respectively. The mean difference between mammographic and pathologic size in Groups A and B was 2.3 mm and 1.96 mm, respectively (P = not significant).

CONCLUSIONS

For soft tissue masses, the difference between mammographic size and pathologic size of invasive carcinoma at excision does not appear to be affected by the use of SCNB. Except in the circumstance of complete removal of the cancer by SCNB, the pathologic size and stage of the excised tumor after SCNB is not altered significantly by SCNB. Cancer 2003;97:2137–41. © 2003 American Cancer Society.

DOI 10.1002/cncr.11336
Adenosquamous histology predicts a poor outcome for patients with advanced‐stage, but not early‐stage, cervical carcinoma
Authors: Farley John H. , Hickey Kimberly W. , Carlson Jay W. , Rose G. Scott , Kost Edward R. , Harrison Terry A.
Published: April 2003

BACKGROUND

The objective of this study was to compare survival between patients with adenocarcinoma and patients with adenosquamous carcinoma of the cervix.

METHODS

Patients who were diagnosed with invasive cervical carcinoma from 1988 to 1999 were identified from the Automated Central Tumor Registry for the United States Military Health Care System. Clinical data, including race, age at diagnosis, histology, tumor grade, disease stage, lymph node status, treatment modality, and survival, were collected. Survival analysis was performed with Kaplan–Meier survival curves and compared using the log‐rank test.

RESULTS

A total of 273 women were identified, 185 women with a histologic diagnosis of adenocarcinoma (AC) and 88 women with a diagnosis of adenosquamous carcinoma (ASC). Among the women with ASC, only 5% had Grade 1 tumors, and 66% had Grade 3 tumors. By comparison, among the women with AC, 37% had Grade 1 tumors, and 26% had Grade 3 tumors (P < 0.001). There was no difference in the incidence of positive lymph nodes or in the number of patients who underwent radical hysterectomy as primary treatment between patients with ASC and patients with AC. More patients with ASC received radiation therapy (51% vs. 28%) or chemotherapy (29% vs. 12%) as treatment (P < 0.001). Patients who had tumors with ASC histology had a significantly decreased 5‐year survival rate compared with patients who had tumors with AC histology (65% vs. 83%; P < 0.002). When patients with early‐stage cervical carcinoma (International Federation of Gynecology and Obstetrics [FIGO] Stage I) were examined separately, there was no statistically significant difference in the 5‐year survival rate (AC, 89%; ASC, 86%; P = 0.644). However, when patients with advanced‐stage disease (FIGO Stages II–IV) were analyzed, ASC was associated with a significant decrease in median and overall survival (P = 0.01). When the results were analyzed by grade, patients who had tumors with ASC histology had a shorter survival compared with patients who had AC histology of any grade; however, this was a significant difference only for patients with Grade 1 tumors: The 5‐year survival rate for patients with Grade 1 AC was 93%, compared with 50% for patients with Grade 1 ASC (P < 0.01).

CONCLUSIONS

ASC histology appears to be an independent predictor of poor outcome in women with cervical carcinoma compared with their counterparts who have pure AC. The significant decrease in survival was observed only in patients with advanced‐stage cervical carcinoma. This decreased survival may be related mainly to the grade of ASC. Cancer 2003;97:2196–202. Published 2003 American Cancer Society.

DOI 10.1002/cncr.11371