bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis of 2′‐O‐β‐d‐Ribofuranosylnucleosides
Authors: Mikhailov Sergey N. , Efimtseva Ekaterina V. , Rodionov Andrei A. , Bobkov Georgii V. , Kulikova Irina V. , Herdewijn Piet
Published: January 2007

A simple and efficient method for the preparation of 2‐O‐β‐D‐ribofuranosylnucleosides, minor tRNA components, is described in this unit. The method consists of condensation of a small excess of 1‐O‐acetyl‐2,3,5‐tri‐O‐benzoyl‐β‐D‐ribofuranose activated with tin tetrachloride with N‐protected 3,5‐O‐tetra‐isopropyldisiloxane‐1,3‐diyl‐ribonucleosides in 1,2‐dichloroethane. Subsequent deprotection produces 2‐O‐β‐D‐ribofuranosylnucleosides in an overall yield of 46% to 72%.
Preparation of 2′‐Deoxy‐2′‐Methylseleno‐Modified Phosphoramidites and RNA
Authors: Micura Ronald , Höbartner Claudia , Rieder Renate , Kreutz Christoph , Puffer Barbara , Lang Kathrin , Moroder Holger
Published: January 2007

The derivatization of nucleic acids with selenium is a useful approach to facilitate phase determination during three‐dimensional structural analysis by X‐ray crystallography. This unit describes (1) the synthesis and characterization of 2′‐deoxy‐2′‐methylseleno (2′‐Se‐methyl) nucleosides and their corresponding 3′‐O‐(2‐cyanoethyl)‐N,N‐diisopropylphosphoramidite derivatives, (2) the site‐specific incorporation of 2′‐Se‐methyl ribonucleosides into oligoribonucleotides by chemical RNA solid‐phase synthesis, and (3) the enzymatic ligation of Se‐containing RNA oligonucleotides to produce a biologically relevant RNA sequence.
Using Morpholinos to Control Gene Expression
Authors: Moulton Jon D.
Published: January 2007

Morpholino oligonucleotides are stable, uncharged, water‐soluble molecules used to block complementary sequences of RNA, preventing processing, read‐through, or protein binding at those sites. Morpholinos are typically used to block translation of mRNA and to block splicing of pre‐mRNA, though they can block other interactions between biological macromolecules and RNA. Morpholinos are effective, specific, and lack non‐antisense effects. They work in any cell that transcribes and translates RNA, but must be delivered into the nuclear/cytosolic compartment to be effective. Morpholinos form stable base pairs with complementary nucleic acid sequences but apparently do not bind to proteins to a significant extent. They are not recognized by any proteins and do not undergo protein‐mediated catalysis; nor do they mediate RNA cleavage by RNase H or the RISC complex. This work focuses on techniques and background for using Morpholinos.
Analysis and Management of Microarray Gene Expression Data
Authors: Grant Gregory R. , Manduchi Elisabetta , Stoeckert Christian J.
Published: January 2007

Microarray experiments require careful planning and choice of analysis tools in order to get the most out of the data generated, especially considering the associated significant cost and effort. Microarray experiments also require careful documentation, often residing in local databases and/or submitted to public repositories. An often bewildering assortment of choices is available for experimental design, data preprocessing, data analysis (e.g., differential gene expression, classification), and data management. This unit covers the basic steps and common applications for planning, data processing, and data management of microarray experiments, and provides guidance to making choices based on the goals and practical realities of the experiment, as well as the authors' experience in this area.
Evaluation of Glucose Homeostasis
Authors: Heikkinen Sami , Argmann Carmen A. , Champy Marie‐France , Auwerx Johan
Published: January 2007

Obesity and dyslipidemia are often found in association with insulin resistance (IR). These components combined with hypertension characterize the most common endocrine disorder in humans, the metabolic syndrome. Thus, in addition to profiling body weight evolution and lipid metabolites, glucose tolerance (a reflection of IR) and insulin sensitivity should also be considered as part of any metabolic phenotyping protocol. The ability to measure IR and glucose tolerance is important not only in the quest to fully understand the pathogenesis of the metabolic syndrome in the mouse, but also to test the effects of potential interventions. This unit presents a variety of tests used for this purpose, including direct blood glucose measurements, insulin measurement by ELISA, the homeostatic model assessment, glucose tolerance and insulin sensitivity tests, and the euglycemic clamp.
Techniques for Mammalian Cell Tissue Culture
Authors: Phelan Mary C.
Published: January 2007

This unit opens with detailed discussions on the latest principles of sterile technique and preparation of culture media. Step‐by‐step protocols describe trypsinizing and subculturing monolayer cultures, passaging suspension cultures, freezing and thawing cells, counting cells using a hemacytometer, and preparing cells for transport.
Population‐Based Case‐Control Association Studies
Authors: Hancock Dana B. , Scott William K.
Published: January 2007

This unit provides an overview of the design and analysis of population‐based case‐control studies of genetic risk factors for complex disease. Considerations specific to genetic studies are emphasized. The unit reviews basic study designs, differentiating case‐control studies from others, discusses selection of genetic markers for use in studies, introduces basic methods of analysis of case‐control data, and discusses measures of association and impact. Controlling for confounding (including population stratification), consideration of multiple loci, and haplotype analysis are briefly discussed. Readers are referred to basic texts on epidemiology for more details on general conduct of case‐control studies.
Using BLAST for Performing Sequence Alignment
Authors: Healy Matthew D.
Published: January 2007

BLAST is a widely used genetic sequence comparison program developed at the National Center for Biotechnology Information (NCBI). In this unit, three Basic Protocols and one Support Protocol are provided for general‐purpose BLAST searches on the NCBI and ENSEMBL Web‐accessible BLAST servers. Key parameters affecting how the search algorithm works are reviewed, with advice on modifying search parameters for specific situations. Many other public and private Web sites offer BLAST interfaces which may differ from those described in this unit, but the general principles will be similar. The Support Protocol describes how to obtain sequences in various formats from NCBI for use in BLAST searches. It is emphasized that no algorithm can be a substitute for biological understanding; performing a BLAST search takes only a few minutes but understanding the implications of the results takes much longer.
Preparation of Cells from Formalin‐Fixed, Paraffin‐Embedded Tissue for Use in Fluorescence In Situ Hybridization (FISH) Experiments
Authors: Weremowicz Stanislawa , Schofield Deborah E
Published: January 2007

Numerical and structural chromosome abnormalities can be accurately detected in cells from archived tissues using fluorescence in situ hybridization (FISH). This unit describes two common approaches to performing FISH in formalin‐fixed, paraffin‐embedded tissue. The first approach utilizes 4 to 6 µm tissue sections in cases for which preserving tissue morphology is necessary, and the second involves extraction of intact nuclei from 50 µm tissue sections. To interpret FISH results using 4 to 6 µm sections, an adequate number of nuclei must be evaluated to perform statistical analysis. Evaluation of 30 to 50 nuclei from the single cell suspension generally gives an interpretable result.
Overview of Flow Cytometry Instrumentation
Authors: Dean Phillip N. , Hoffman Robert A.
Published: January 2007

This unit describes the technology in general, to give a feel for the interplay between the various parts of a flow cytometer. Topics include cell preparation, detectors, analysis, and sorting. A brief chronology of flow instrumentation development illustrates the long history of the field.
Standard Safety Practices for Sorting of Unfixed Cells
Authors: Schmid Ingrid , Lambert Claude , Ambrozak David , Perfetto Stephen P.
Published: January 2007

Cell sorting of viable biological specimens has become widespread in laboratories involved in basic and clinical research. As these samples can contain infectious agents, precautions to protect instrument operators and the environment from hazards arising from the use of sorters are paramount. This unit presents a revised and updated version of the biosafety guidelines for sorting of unfixed cells established in 1977 by the International Society of Analytical Cytology (ISAC), whose recommendations have become recognized worldwide as the standard practices and safety precautions for laboratories performing viable cell‐sorting experiments. The unit contains background information on the biohazard potential of sorting and the hazard classification of infectious agents as well as recommendations on (1) sample handling, (2) operator training and personal protection, (3) laboratory design, (4) cell sorter setup, maintenance, and decontamination, and (5) testing the instrument for the efficiency of aerosol containment.
Optimized Whole‐Blood Assay for Measurement of ZAP‐70 Protein Expression
Authors: Shankey T. Vincent , Forman Meryl , Scibelli Paul
Published: January 2007

Chronic lymphocytic leukemia (CLL) is characterized by a clonal expansion of small lymphocytes commonly expressing cell surface markers (CD5 and CD19) that are consistent with a population of B lymphocytes. This unit describes a technique to measure ZAP‐70 protein expression in whole‐blood specimens from CLL samples. The protocols presented include an optimized fixation/permeabilization technique that allows labeling of cell surface markers and intracellular ZAP‐70 protein with significantly improved signal‐to‐noise ratio, an optimized combination of antibodies‐fluorophores to maximize ZAP‐70 expression levels, standardized methodology for instrument setup, including compensation, to improve inter‐ and intra‐laboratory reproducibility, and a method to index ZAP‐70 protein expression levels to internal positive and negative cell populations. Residual normal T and B cells function as internal positive and negative controls. These are used to index ZAP‐70 protein expression levels in the CLL population.
Isolation of Myelin
Authors: Larocca Jorge N. , Norton Williams T.
Published: January 2007

The methods used to prepare myelin involve homogenization of the tissue in isotonic sucrose solution, followed by the isolation of myelin membranes by a series of steps that include density gradient centrifugation and differential centrifugation. Homogenization of nervous tissue in isotonic sucrose causes the myelin sheath to peel from the axon and form relatively large myelin vesicles. The large size of the myelin vesicles, together with the fact that myelin membrane has a lower density than other biological membranes, make differential centrifugation and density gradient centrifugation the main tools for the isolation of this membrane. Three protocols are outlined in this unit: isolation of a highly‐purified myelin fraction from the central nervous system (CNS); separation of a highly‐purified CNS myelin fraction into subfractions of different densities; and isolation of myelin from the peripheral nervous system (PNS).
Preparation of Extracellular Matrices Produced by Cultured and Primary Fibroblasts
Authors: Beacham Dorothy A. , Amatangelo Michael D. , Cukierman Edna
Published: January 2007

Fibroblasts secrete and organize extracellular matrix (ECM), which provides structural support for their adhesion, migration, and tissue organization, besides regulating cellular functions such as growth and survival. Cell‐to‐matrix interactions are vital for vertebrate development. Disorders in these processes have been associated with fibrosis, developmental malformations, cancer, and other diseases. This unit describes a method for preparing a three‐dimensional matrix derived from NIH‐3T3 cells; the matrix is three‐dimensions, cell and debris free, and attached to a two‐dimensional culture surface. Cell adhesion and spreading are normal on these matrices. This matrix can also be compressed into a two‐dimensional matrix and solubilized to study the matrix biochemically.
Identification and Analysis of Multiprotein Complexes Through Chemical Crosslinking
Authors: Melcher Karsten , Chen Hung‐Ta
Published: January 2007

Chemical crosslinking provides information about protein‐protein interactions in the context of intact protein complexes; therefore, it is particularly suited to the analysis of multiprotein complexes. Rather than a single distinct technique, chemical crosslinking represents a smorgasbord of techniques that differ significantly both in chemistry and in scope. This unit will attempt to guide the reader through the complexities of crosslinking to find the most suitable approach for a given biological question. Sample protocols for two crosslinking methods considered to be particularly useful for the analysis of large multiprotein complexes are provided: His6‐mediated crosslinking and photoinducible label transfer crosslinking.
The Fluorescent Protein Color Palette
Authors: Olenych Scott G. , Claxton Nathan S. , Ottenberg Gregory K. , Davidson Michael W.
Published: January 2007

Advances in fluorescent protein development over the past 10 years have led to fine‐tuning of the Aequorea victoria jellyfish color palette in the emission color range from blue to yellow, while a significant amount of progress has been achieved with reef coral species in the generation of monomeric fluorescent proteins emitting in the orange to far‐red spectral regions. It is not inconceivable that near‐infrared fluorescent proteins loom on the horizon. Expansion of the fluorescent protein family to include optical highlighters and FRET biosensors further arms this ubiquitous class of fluorophores with biological probes capable of photoactivation, photoconversion, and detection of molecular interactions beyond the resolution limits of optical microscopy. The success of these endeavors certainly suggests that almost any biological parameter can be investigated using the appropriate fluorescent protein–based application.
Using the NCBI Map Viewer to Browse Genomic Sequence Data
Authors: Wolfsberg Tyra G.
Published: January 2007

This unit includes an introduction to the Map Viewer, which describes how to perform a simple text‐based search of genome annotations to view the genomic context of a gene, navigate along a chromosome, zoom in and out, and change the displayed maps to hide and show information. It also describes some of NCBI's sequence‐analysis tools, which are provided as links from the Map Viewer. The Alternate Protocols describe different ways to query the genome sequence, and also illustrate additional features of the Map Viewer. Alternate Protocol 1 shows how to perform and interpret the results of a BLAST search against the human genome. Alternate Protocol 2 demonstrates how to retrieve a list of all genes between two STS markers. Finally, Alternate Protocol 3 shows how to find all annotated members of a gene family
Using the Ensembl Genome Server to Browse Genomic Sequence Data
Authors: Fernández‐Suárez Xosé M. , Schuster Michael K.
Published: January 2007

The Ensembl genome Web browser (http://www.ensembl.org) provides a comprehensive source of automatic annotation of the human genome sequence (as well as other species of biomedical interest), with confirmed gene predictions that have been integrated with external data sources. This unit describes how to use the Ensembl browser, how to find your gene or protein of interest and get information and external links about them, and how to use the comparative genomic data.
Structure‐Based pKa Calculations Using Continuum Electrostatics Methods
Authors: Fitch Carolyn A. , García‐Moreno E. Bertrand
Published: January 2007

Electrostatic free energy is useful for correlating structure with function in proteins in which ionizable groups play essential functional roles. To this end, the pKa values of ionizable groups must be known and their molecular determinants must be understood. Structure‐based calculations of electrostatic energies and pKa values are necessary for this purpose. This unit describes protocols for pKa calculations with continuum electrostatics methods based on the numerical solution of the linearized Poisson‐Boltzmann equation by the method of finite differences. Critical discussion of key parameters, approximations, and shortcomings of these methods is included. Two protocols are described for calculations with methods modified empirically to maximize agreement between measured and calculated pKa values. Applied judiciously, these methods can contribute useful and novel insight into properties of surface ionizable groups in proteins.
Common File Formats
Authors: Leonard Shonda A. , Littlejohn Timothy G. , Baxevanis Andreas D.
Published: January 2007

This appendix discusses a few of the file formats frequently encountered in bioinformatics. Specifically, it reviews the rules for generating FASTA files and provides guidance for interpreting NCBI descriptor lines, commonly found in FASTA files. In addition, it reviews the construction of GenBank, Phylip, MSF and Nexus files.
Do better stories make better memories? Narrative quality and memory accuracy in preschool children
Authors: Kulkofsky Sarah , Wang Qi , Ceci Stephen J.
Published: January 2007

The present study examines how the quality of children's narratives relates to the accuracy of those narratives. Sixty‐one 3‐ to 5‐year‐olds played a novel game with a researcher in their schools. Children were questioned in an interview that included an open‐ended free recall prompt followed by a series of directed questions. Children's narratives were coded for volume, complexity and cohesion as well as for accuracy. Correlational results showed that overall, narrative skills enable the reporting of more information, while decreasing the proportion of information that was accurate. These results appeared to be driven by a quantity‐accuracy trade‐off; in an ensuing regression analysis with all narrative variables entered into the model, volume was associated with decreases in accuracy while narrative cohesion was associated with increases in accuracy. We discuss the results in terms of their relationship to the development of autobiographical memory as well as implications for forensic contexts. Copyright © 2007 John Wiley & Sons, Ltd.
Low‐Operating‐Voltage Organic Transistors Made of Bifunctional Self‐Assembled Monolayers
Authors: Mottaghi M. , Lang P. , Rodriguez F. , Rumyantseva A. , Yassar A. , Horowitz G. , Lenfant S. , Tondelier D. , Vuillaume D.
Published: January 2007

Self‐assembled monolayers (SAMs) are molecular assemblies that spontaneously form on an appropriate substrate dipped into a solution of an active surfactant in an organic solvent. Organic field‐effect transistors are described, built on an SAM made of bifunctional molecules comprising a short alkyl chain linked to an oligothiophene moiety that acts as the active semiconductor. The SAM is deposited on a thin oxide layer (alumina or silica) that serves as a gate insulator. Platinum–titanium source and drain electrodes (either top‐ or bottom‐contact configuration) are patterned by using electron‐beam (e‐beam) lithography, with a channel length ranging between 20 and 1000 nm. In most cases, ill‐defined current–voltage (I–V) curves are recorded, attributed to a poor electrical contact between platinum and the oligothiophene moiety. However, a few devices offer well‐defined curves with a clear saturation, thus allowing an estimation of the mobility: 0.0035 cm2 V–1 s–1 for quaterthiophene and 8 × 10–4 cm2 V–1 s–1 for terthiophene. In the first case, the on–off ratio reaches 1800 at a gate voltage of –2 V. Interestingly, the device operates at room temperature and very low bias, which may open the way to applications where low consumption is required.
Transparent Mesoporous Nanocomposite Films for Self‐Cleaning Applications
Authors: Allain E. , Besson S. , Durand C. , Moreau M. , Gacoin T. , Boilot J.‐P.
Published: January 2007

A versatile approach is studied for the elaboration of TiO2 based photocatalytic coatings for self‐cleaning applications on transparent substrates. The basic principle of the synthesis relies on the use of preformed TiO2 colloidal particles that are further dispersed within a transparent silica binder with a mesoporous structure. Film porosity in the nanometer range is controlled by achieving the sol–gel silica condensation around self‐organized micellar assemblies of a templating copolymer surfactant. The latter also acts as a stabilizer for the TiO2 particles, thus preserving their high dispersion within the film so that excellent optical properties are maintained even for high TiO2 loading (up to 50 %). Studies of photodegradation kinetics show that such mesoporous films are at least 15 times more active than films synthesized with a usual microporous silica binder. Moreover, the measured quantum‐yield efficiency (1.1 %) is found to be among the highest reported up to now. Improved photoactivity of the films is discussed as resulting from the closer proximity between the organic molecules and the surface of the TiO2 crystallites as well as the improved diffusion rate of water and oxygen through the interconnected pore network.
Thioether‐bridged Mesoporous Organosilicas: Mesophase Transformations Induced by the Bridged Organosilane Precursor
Authors: Liu J. , Yang Q. , Zhang L. , Jiang D. , Shi X. , Yang J. , Zhong H. , Li C.
Published: January 2007

The achievement of structural control over thioether‐bridged mesoporous organosilicas is reported. The mesoporous materials have been synthesized by co‐condensation of bis[3‐(triethoxysilyl)propyl]tetrasulfide (TESPTS) and tetramethoxysilane (TMOS) in acetic acid/sodium acetate buffer solution (HAc–NaAc, pH 4.4), using the nonionic surfactant P123 as a template. The mesostructure of the material is mainly controlled by the molar ratio of TESPTS/TMOS in the initial gel mixture. A mesophase transformation, progressing from a highly ordered 2D hexagonal structure via a vesiclelike structure to a mesostructured cellular foam, can be clearly observed when the molar ratio of TESPTS/TMOS is increased in increments. Solid‐state NMR results show that TESPTS is not completely hydrolyzed and condensed at the applied buffer conditions. At low concentrations, the unhydrolyzed TESPTS can penetrate into the core of the surfactant micelles and change the packing parameter of the P123 surfactant. Above a certain concentration, the TESPTS can form a microemulsion with P123 surfactant molecules. Therefore, the vesiclelike structure or cellular foam structure can be synthesized by simply controlling the molar ratio of TESPTS/TMOS. This approach provides a novel method for the facile synthesis of organic–inorganic hybrid materials with a controllable mesostructure under mild synthetic conditions.
Long K‐Doped Titania and Titanate Nanowires on Ti Foil and FTO/Quartz Substrates for Solar‐Cell Applications
Authors: Cheung K. Y. , Yip C. T. , Djurišić A. B. , Leung Y. H. , Chan W. K.
Published: January 2007

Potassium‐doped titania and titanate nanowires are fabricated by moisture‐assisted direct oxidation of titanium. The influence of the fabrication conditions on nanowire structure and morphology is investigated. It is shown that the presence of potassium is essential for nanowire formation, while the nanowire structure and morphology are strongly dependent on the fabrication temperature. The longest nanowires (ca. 10 μm) are obtained at 650 °C. At this substrate temperature, nanowires could be produced over a large substrate area both by oxidation of the Ti foil as well as by depositing a Ti film on the substrate (quartz or fluorine‐doped tin oxide (FTO)/quartz). Photovoltaic cells based on these nanowires are fabricated. The cell performance is dependent on the nanowire fabrication temperature and the substrate used, as well as on the annealing environment. Short‐circuit current densities of Isc = 3.05 mA cm–2 and Isc = 4.97 mA cm–2 could be obtained for Ti foil and FTO/quartz substrates, respectively, while the corresponding power‐conversion efficiencies are η = 0.93 % and η = 1.88 % (under AM 1.5 illumination, 100 mW cm–2; AM: air mass).
Highly Ordered 2D Hydrogen‐Bonded Structures of a Tetralactam Macrocycle on the Au(111) Surface
Authors: Kossev I. , Reckien W. , Kirchner B. , Felder T. , Nieger M. , Schalley C. A. , Vögtle F. , Sokolowski M.
Published: January 2007

Monolayers of a tetralactam macrocycle, which are commonly used as building blocks in the synthesis of rotaxanes or catenanes, are deposited on a Au(111) surface by using vapor deposition. Due to self‐organization, 2D highly ordered supramolecular networks form. From scanning tunneling microscopy (STM) and concomitant density‐function theory calculations, two structurally different phases are found. In both phases, pairs of hydrogen bonds between the amide groups of next‐neighbor macrocycles are responsible for the structural arrangement of the macrocycles. The structure of both phases differs from that of bulk lattice planes, which reveals that the Au(111) surface acts as a template for the growth of the specific 2D structures. These networks of tetralactam macrocycles possibly open a route to study mechanical interlocking processes or guest/host interactions of the molecules in further detail by using STM.
Nanostructure of potato starch. II. Structure of a highly crystalline gel obtained by retrogradation using X‐ray diffraction techniques
Authors: Bayer R. K. , Baltá‐Calleja F. J.
Published: January 2007

A highly crystalline gel (65% crystal portions) was prepared by retrogradation of injection‐molded potato starch in humid atmosphere. The different components of the nanostructure were identified by means of successive melting processes using “in situ” simultaneous wide and low angle X‐ray diffractions. At low temperatures, structural changes such as annealing phenomena or evaporation of water, giving rise to a thickening of the gel, are observed. In the range of 55–75°C, a first transition due to melting of a layered structure of concentric sphere‐like alternating crystalline and amorphous lamellar shells (amylopectine, AP, being the crystalline component) is detected. Analysis of results reveals that the AP crystallization contributes 25% to the overall crystal fraction. A spherulitic structure of alternating radial lamellae from amylose (AM) or AP melts in a higher temperature region between 75 and 86°C. This modification represents the major contribution to crystallinity of about 40%. Unexpectedly, the crystalline blocks of such a structure are abnormally anisometric; i.e., they are thicker than their width. This has been related to a contraction of the AMAP‐co‐spherulite due to an excessive growth of the AP‐shell crystals. The anisometry of the blocks of the AMAP lamellae vanishes at the beginning of the melting of the AP shell crystals, just when the total crystallinity decreases below 50% at 60°C. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 689–696, 2007
Measurement of AC conductivity and dielectric properties of flexible conductive styrene–butadiene rubber‐carbon black composites
Authors: Mohanraj G. T. , Chaki T. K. , Chakraborty A. , Khastgir D.
Published: January 2007

Flexible conductive polymer composites were prepared using styrene–butadiene rubber (SBR) as a matrix and conductive carbon black as filler. The filler loading was varied from 10 to 60 phr. The effect of frequency, filler loading, temperature, and applied pressure on the AC conductivity, permittivity, and loss factor of the composites was studied. The AC conductivity of low and high loaded composites was found to be frequency dependent and independent respectively. The permittivity and the loss factor were continuously decreasing with increasing frequency. The increase in filler loading increased the AC conductivity, dielectric constant, and loss factor of the composites. Increase in temperature imposed increase in conductivity and permittivity of the composites. With increasing applied pressure the properties showed exponential increase. The effect of time under a constant compressive stress was studied and dielectric relaxation times were evaluated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 986–995, 2007
Influence of extrusion, stretching and poling on the structural and piezoelectric properties of poly (vinylidene fluoride‐hexafluoropropylene) copolymer films
Authors: Huan Yan , Liu Yayan , Yang Yifei , Wu Yanan
Published: January 2007

Three types of poly (vinylidene fluoride‐hexafluoropropylene) (PVDF–HFP) copolymer films were prepared by extrusion, stretching as well as simultaneously stretching and static electric field poling (SSSEP), respectively, and measured by the differential scanning calorimetric, wide angle X‐ray diffraction, fourier transformation infrared‐attenuated total reflection, and Dynamic mechanical analysis. The experimental results showed that the films prepared by stretching and SSSEP have higher crystallinity and β phase than by extrusion. SSSEP improved the chain orientation enormously both in crystalline and amorphous regions, resulting in the highest storage modulus. Because of the lower β phase content, the extruded films exhibited the lowest piezoelectric coefficient d33. For the stretched and SSSEP films, although the β phase content was similar, the d33 was distinct because of the different potential energy for the rotation of the dipoles. In addition, the SSSEP films gave the maximum d33 (24 pC/N), higher than the other PVDF–HFP copolymer films that have been reported. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 858–862, 2007
Effect of rubber particle cavitation on the mechanical properties and deformation behavior of high‐impact polystyrene
Authors: Serpooshan V. , Zokaei S. , Bagheri R.
Published: January 2007

Rubber particle cavitation has been the focus of many investigations because it dramatically affects the mechanical properties of polymeric blends. In this work, the effect of rubber particle cavitation on the mechanical behavior of high‐impact polystyrene was studied. The extent of cavitation in rubber particles was varied via different thermal contraction/expansion cycles in the range of −100 to 23°C. Tensile, creep, and Charpy impact tests were conducted to evaluate the effects of the degree of cavitation on the general mechanical properties. The notch‐tip damage zone and deformation micromechanisms were also investigated by a transmitted optical microscopy technique to reveal the effects of cavitation on toughness. The results of this investigation illustrate a close relationship between the degree of rubber particle cavitation and the mechanical performance of high‐impact polystyrene. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1110–1117, 2007
Synthesis and characterization of poly(allyl methacrylate) obtained by γ‐radiation
Authors: K. Vardareli Tuğba , Usanmaz Ali
Published: January 2007

Allyl methacrylate was polymerized by γ‐radiation under vacuum in solution and atom transfer radical polymerization (ATRP) methods and also in the presence of atmospheric oxygen in bulk. The kinetic curve is S‐type with a longer induction period, because of the presence of oxygen, in bulk polymerization. The curve for the solution polymerization is almost linear with a short induction period. The rate started to decrease after about 60% conversion and reached to a limiting conversion of 100%. The polymerization by ARTP method using γ‐radiation as initiator instead of conventional heating method gave a kinetic curve of linear character up to about limiting conversion of 100%. The polymers obtained were mostly gel type with linear chain fractions at lower conversions. The polymer characterizations were carried out by FTIR, differential scanning calorimetry, NMR, TGA, and XRD methods. The polymers were shown to proceed by the opening of vinyl groups. The allyl groups caused a limiting crosslinking, but 98–99% of the allyl groups are shown by FTIR and NMR, unchanged during the polymerization. The cyclic type polymer formation was not likely taking place. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1076–1083, 2007
Formation of polymethylsiloxanes with alkyl side groups
Authors: Mukbaniani O. , Titvinidze G. , Tatrishvili Tamara , Mukbaniani Nino , Brostow Witold , Pietkiewicz Dorota
Published: January 2007

Hydrosilylation of α,ω‐bis(trimethylsiloxy)methylhydrosiloxane to alkenes in the presence of a catalyst was performed at several temperatures (30–70°C). Comb‐type methylsiloxane oligomers with various alkyl substituted groups in the side chains have been obtained. Not all active ≡SiH groups participate in the reaction. The reaction order, activation energies, and rate constants have been determined. The synthesized oligomers were characterized by 1H, 13C, 1H COSY NMR, and FTIR spectroscopy. Calculations using the quantum‐chemical semiempirical AM1 method for modeling reaction between methyldimethoxysilane [Me(MeO)2SiH] and hexene‐1 were performed to evaluate possible reaction paths. For all initial, intermediate, and final products, enthalpies of formation as a function of the distance between ≡CSi≡ bonds are calculated. The hydride addition is energetically more favorable according to the anti‐Markovnikov rule than according to the Markovnikov rule. Comb‐type oligomers were characterized by gel‐permeation chromatography, differential scanning calorimetry, thermogravimetry, and wide‐angle X‐ray diffractometry. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1176–1183, 2007
Structure–property relationships in acrylate/epoxy interpenetrating polymer networks: Effects of the reaction sequence and composition
Authors: Nowers Joseph R. , Costanzo Joseph A. , Narasimhan Balaji
Published: January 2007

Interpenetrating polymer networks (IPNs) of poly(ethylene glycol) 200 diacrylate and diglycidyl ether of bisphenol A were formed over a range of compositions and with different reaction sequences. We controlled the reaction sequence by thermally initiating the cationic epoxy polymerization, photoinitiating the free‐radical acrylate polymerization, and changing the processing order. The reaction was monitored by attenuated total reflectance Fourier transform infrared spectroscopy, photo differential scanning calorimetry. and modulated differential scanning calorimetry (mDSC). The glass‐transition temperature was estimated from mDSC. Mechanical and rheological tests provided the strength and hardness of the materials. Morphology and phase separation were explored with optical and scanning electron microscopy. All of the physical properties were dependent on IPN composition. Some properties and the morphology were dependent on the reaction sequence. Significant differences in glass‐transition temperature were observed at the same composition but with different reaction sequences. Even with minimal structure, correlations existed between the morphology and material properties with partially phase‐separated samples exhibiting maximum damping. The rapid reaction allowed minimal phase separation, yet different reaction sequences resulted in significantly different properties. This systematic study indicated that the relationships between phase morphology, processing, and the physical properties of IPNs are complex and not predictable a priori. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 891–901, 2007
Synthesis and characterization of novel two‐component conjugated polythiophenes with 3‐octyl and 3‐isooctylthiophene side chains
Authors: Feng Weidong , Qi Zhengjian , Sun Yueming
Published: January 2007

With copolymerization functionalization, a novel solution‐processable polymer, poly{(3‐octylthiophene)‐co‐[3‐(2‐ethyl‐1‐hexyl)thiophene]} (P3OTIOT), combining the electrochemical properties of poly(3‐octylthiophene) (P3OT) and poly[3‐(2‐ethyl‐1‐hexyl)thiophene] (P3IOT) was synthesized by the FeCl3‐oxidative approach. The characterization of the polymers included Fourier transform infrared, 1H‐NMR, gel permeation chromatography, thermogravimetric analysis (TGA), ultraviolet–visible spectroscopy, and photoluminescence (PL). P3OTIOT had excellent solubility in common organic solvents. Investigations of the optical properties showed that the optical band‐gap energy of P3OTIOT was similar to that of P3OT (2.43 eV) at 2.45 eV and 6% lower than that of P3IOT in CHCl3 solutions. The bandwidth of the P3OTIOT absorption approached that of P3OT, ranging from 370 to 570 nm, and the emission maximum of P3OTIOT was only 50 nm blueshifted with respect to that of P3OT. However, the PL intensity of P3OTIOT was 7 times higher than that of P3OT. TGA studies showed that P3OTIOT had very good thermal stability, losing 5% of its weight on heating to 300°C. It is suggested that P3OTIOT has low band‐gap energy, a high PL quantum yield, and processability. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1169–1175, 2007
Evaluation of carbonization tar in making high performance polyacrylonitrile‐based carbon fibers
Authors: Wang Yan‐Xiang , Wang Qiang
Published: January 2007

The polyacrylonitrile carbonization tar is discussed in detail by using gas chromatographic‐mass spectrometer and electron paramagnetic resonance. It is a viscous liquid that constitutes complicated condensed components resulting from polymer decomposition. It was demonstrated that the predominant products were acrylonitrile dimer and trimer species with trifle cyclohexane and cyclopentane. Moreover, the fragmentation course occurred in temperature range of 400–600°C and decomposed in 525°C most drastically. The formation of the tar could be regarded as random fragmentation of linear chain segments among ladder structures accompanying with secondary decomposition. After adjusting the middle temperature carbonization technology, depending on the components and formation of tar, the high performance carbon fibers were obtained that had tensile strength of 4.2–4.5 Gpa, elongation at break 1.7%–1.8%, modulus 235–240 Gpa. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1255–1259, 2007
Reducing volume shrinkage by low‐temperature photopolymerization
Authors: Lu Bo , Xiao Pu , Sun Mengzhou , Nie Jun
Published: January 2007

Low‐volume‐shrinkage poly(triethylene glycol dimethacrylate) was made by photopolymerization at a low temperature. The final double‐bond conversion and dynamic mechanical analysis indicated the optimal cure temperature to be −40°C, at which a cured sample had less volume shrinkage than samples cured at room temperature but similar mechanical properties. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1126–1130, 2007
Effect of an organoclay on the reaction‐induced phase‐separation kinetics and morphology of a poly(ether imide)/epoxy mixture
Authors: Peng Mao , Li Dasong , Chen Ying , Zheng Qiang
Published: January 2007

Organically modified layered silicates with a hydroxyl‐substituted quaternary ammonium surfactant as the modifier were incorporated into a mixture of poly (ether imide) and epoxy with 4,4′‐diaminodiphenyl sulfone as the hardener. The influence of the organically modified layered silicates on the reaction‐induced phase‐separation kinetics and morphology of the poly(ether imide)/epoxy mixture was investigated with time‐resolved small‐angle light scattering, phase‐contrast microscopy, and scanning electron microscopy. The phase‐separation kinetics were analyzed by means of the temporal evolution of scattering vector qm and scattering intensity Im at the scattering peak. The organically modified layered silicates obviously facilitated an earlier onset of phase separation but reduce the phase‐separation rate and greatly retarded the domain‐coarsening process in the late stage of spinodal decomposition. The temporal evolution of both qm and Im followed the power law qm ∼ (t − tos)−α and Im ∼(t − tos)−β, where t is the reaction time, tos is the onset time of phase separation, and α and β are growth exponents. For the samples filled with organically modified layered silicates, α crossed over from 0 to about 1/3, following Binder–Stauffer cluster dynamics, and an interconnected phase structure was observed for cure temperatures ranging from 120 to 230°C. For the unfilled samples, the interconnected phase structure was observed only at cure temperatures below 140°C. At temperatures above 150°C, α crossed over from 0 to 1/3 < α ≤ 1 under the interfacial tension effect, following Siggia's theory, and the domain‐coarsening rate was very fast; this resulted in macroscopic epoxy‐rich domains. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1205–1214, 2007
Crosslinking of poly(silyl ester)s containing fumaryloxyl units in the main chain and characteristics of the crosslinked products
Authors: Han Nianfeng , Liu Zonglin , Zhou Dejie , Jin Liqiang , Shi Congwen
Published: January 2007

Two unsaturated poly(silyl ester)s that contained innoxious fumaryloxyl units in the main chain were prepared by the polycondensation reaction of 1,5‐dichloro‐1,1,5,5‐tetramethyl‐3,3‐diphenyltrisiloxane or 1,3‐dichlorotetramethyldisiloxane with di‐tert‐butyl fumarate under nitrogen at 100°C for 1–3 days. To investigate the crosslinking reaction of the unsaturated poly(silyl ester)s, the two unsaturated poly(silyl ester)s were crosslinked in the presence of 2,2′‐azobisisobutyronitrile as a radical initiator. After the crosslinking, the unsaturated poly(silyl ester)s, which were viscous liquids, turned into solid products. The characterization of the two poly(silyl ester)s and the crosslinked products included infrared spectroscopy, 1H‐NMR spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. Comparisons were made between the linear poly(silyl ester)s and the crosslinked poly(silyl ester)s. After the crosslinking, the important resonance signal for ethenylene (CC) disappeared, and this showed that the crosslinking reaction was carried out progressively. The glass‐transition temperatures of the crosslinked poly(silyl ester)s were higher than those of the uncross‐ linked poly(silyl ester)s, and the thermal stability of the crosslinked poly(silyl ester)s was better than that of uncrosslinked poly(silyl ester)s. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1221–1225, 2007
Synthesis and characterization of polyimide–silica nanocomposites using novel fluorine‐modified silica nanoparticles
Authors: Mo Te‐Cheng , Wang Hong‐Wen , Chen San‐Yan , Dong Rui‐Xuan , Kuo Chien‐Hung , Yeh Yun‐Chieh
Published: January 2007

Polyimide–silica nanocomposites were synthesized with 4,4′‐oxydianiline, 4,4′‐(4,4′‐isopropylidenediphenoxy)bis(phthalic anhydride), and fluorine‐modified silica nanoparticles. Fluorinated precursors such as 4″,4‴‐(hexafluoroisopropylidene)bis(4‐phenoxyaniline) (6FBPA) and 4,4′‐(hexafluoroisopropylindene)diphenol (BISAF) were employed to modify the surface of the silica nanoparticles. The microstructures and thermal, mechanical, and dielectric properties of the polyimide–silica nanocomposites were investigated. An improvement in the thermal stability and storage modulus of the polyimide nanocomposites due to the addition of the modified silica nanoparticles was observed. The microstructures of the polyimide–silica nanocomposites containing 6FBPA‐modified silica exhibited more uniformity than those of the nanocomposites containing BISAF‐modified silica. The dielectric constants of the polyimide were considerably reduced by the incorporation of pristine silica or 6FBPA‐modified silica but not BISAF‐modified silica. The addition of a modifier with higher fluorine contents did not ensure a lower dielectric constant. The uniformity of the silica distribution, manipulated by the reactivity of the modifier, played an important role in the reduction of the dielectric constant. Using 6FBPA‐modified silica nanoparticles demonstrated an effective way of synthesizing low‐dielectric‐constant polyimide–silica nanocomposites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 882–890, 2007
Entropy–enthalpy compensation in solution properties of solutes at infinite dilution in nonpolar polymers
Authors: Huang Jan‐Chan
Published: January 2007

The knowledge of the Flory–Huggins interaction parameter, χ, between organic liquids and polymers is very important in the study of their miscibility. From the temperature dependency of χ the enthalpy and residual entropy of solution can be determined. In this study literature data of thirty‐two solutes, ranging from alkanes to alcohols, at infinite dilution in isotatic polypropylene, poly(ethyl ethylene), and poly(dimethylsiloxane), were tested and linear entropy–enthalpy compensation was observed. The plot of residual free energy versus enthalpy of solution was also linear, with a lower correlation coefficient than the entropy–enthalpy plot. The range of enthalpy of solution was wider than those of the size corrected free energy of solution. In nonpolar solvents the enthalpy of solution reflected largely the interaction within the solute liquid state, and showed a linear trend with respect to solute cohesive energy density for n‐alcohols. The wide range of enthalpy of solution suggests the use of a two‐dimensional solubility parameter model to correlate the enthalpy of solution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1241–1247, 2007
Formation of poly(vinyl alcohol)‐titanium lactate hybrid nanofibers and properties of TiO2 nanofibers obtained by calcination of the hybrids
Authors: Nakane Koji , Yasuda Kaori , Ogihara Takashi , Ogata Nobuo , Yamaguchi Shinji
Published: January 2007

New organic‐inorganic hybrid nanofibers, poly(vinyl alcohol) (PVA)‐titanium lactate (TL) hybrid nanofibers, were formed by electrospinning employing water as a solvent. Anatase‐type TiO2 nanofibers were obtained by calcination of the hybrid nanofibers in air. The fiber diameters of the PVA‐TL hybrid nanofibers was 200–350 nm, and the fiber diameter of the TiO2 nanofibers was 70–80% of that of the PVA‐TL hybrid nanofibers. The specific surface area and average pore diameter of the TiO2 nanofiber calcined at 500°C for 5 h were 21.0 m2/g and 7.4 nm, respectively. The photocatalytic decomposition of methylene blue using the TiO2 nanofibers was also investigated. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1232–1235, 2007
Temperature and pH sensitive star‐shaped material for the controlled release of coenzyme A
Authors: Guo Bao‐Lin , Yuan Jin‐Fang , Gao Qing‐Yu
Published: January 2007

A novel star‐shaped copolymer was prepared by tolulene diisocyanate (TDI) trimer, poly(ethylene oxide) (PEO), P(2‐(dimethylamino)ethyl methacrylate) (PDMAEMA), and 2‐hydroxyethylacrylate (HEA) with TDI trimer as core and PEO, PDMAEMA as arm chains by addition of functional groups and copolymerization. The structure of the star‐shaped copolymer was characterized by FTIR, 1H NMR, and UV, and the molecular weight and polydispersity were determined by gel permeation chromatography (GPC). Their aqueous solution properties and controlled coenzyme A (Co A) delivery were also studied. The results showed that the copolymer had better temperature sensitivity and pH sensitivity. The release of Co A from the copolymer was dependent on the release medium such as concentration of the polymer, pH, and temperature in the aqueous solution. The higher concentration of the copolymer absorbed more Co A than the lower one. The increasing temperature accelerated Co A release from the copolymer. The pH of the solution had significant impact on the release of Co A from the copolymer. The results suggested that the novel copolymer could be used as a drug delivery carrier. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1279–1284, 2007