bluuebunny/crossref_metadata_2025_split huggingface dataset:
SAXS studies on the deformation of macrolattices in block copolymers
Authors: Brandt M. , Ruland W. 
Published: April 2003

AbstractUniaxial 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

AbstractDSC 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

AbstractComb‐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

AbstractTopological 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

AbstractCrazes 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

AbstractCrosslinked 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

AbstractA 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

AbstractSyntheses 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

AbstractPoly(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

AbstractThe 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

AbstractOn 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

AbstractThe 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

AbstractNegative 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

AbstractDue 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

AbstractThis 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

AbstractSamples 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

AbstractWe 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

AbstractThe 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

AbstractBACKGROUNDThe 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.METHODSSeventy‐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.RESULTSThirty‐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%).CONCLUSIONSBRCA1 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