bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plastics Processing
Authors: Xanthos M. , Todd D. B. 
Published: July 2004

AbstractProcessing of plastics comprises a variety of operations involving flow and shaping of polymer melts into finished articles. For thermoplastic resins the most common processing operations are extrusion and molding. In extrusion, solid plastic resin is melted and then shaped in a continuous part of a defined cross section by screw‐conveying and forcing the melt to flow through a die. Die forming is used in pipe and tubing, film, sheet, wire, and cable coating. Molding involves such noncontinuous processes as injection molding, blow molding, rotational molding, and compression molding, in which three‐dimensional parts are made in a closed mold. Molded products are solid, hollow, or foamed. Other thermoplastics operations include thermoforming, calendering, and casting. In contrast to thermoplastics, thermosetting resins use low viscosity components which, through chemical reaction, produce the solid part in the mold. Common processing methods for thermoset systems are compression molding, transfer molding, and injection molding. Specialized techniques developed for fiber‐reinforced thermosets include open‐mold processing, pultrusion, resin transfer molding, and reaction injection molding. Specific processing methods for making low density articles from thermoset polyurethanes are described.
Electrochromic Polymers
Authors: Mortimer Roger J. 
Published: July 2004

AbstractAn electrochromic material is one where a reversible color change takes place upon reduction (gain of electrons) or oxidation (loss of electrons), on passage of electrical current after the application of an appropriate electrode potential. In this article the general field of electrochromism is introduced, with coverage of the types, applications, and chemical classes of electrochromic materials and the experimental methods that are used in their study. The main classes of electrochromic polymers are then surveyed, with descriptions of representative examples of electrochromic polymers based on transition metal coordination complexes, polymeric viologen systems, and conducting polymers.
Ring Opening Polymerization
Authors: Lecomte Ph. , Jérôme R. 
Published: July 2004

AbstractBiodegradable and biocompatible aliphatic polyesters have a great potential as biomaterials and environmentally friendly thermoplastics. An intensive research effort has been devoted to living or at least controlled ring opening polymerization (ROP) of lactones, lactides, and glycolides that contributes enormously to macromolecular engineering of these aliphatic polyesters. The recent progress in the field has been reviewed and discussed in terms of structure/nature of the polymerization promoters. A first section focuses on organometallic initiators and catalysts, with emphasis on the more efficient aluminum, tin, and yttrium alkoxides. Special attention is also paid to the steroselective ROP ofD,L‐ andmeso‐lactide into polylactide of controlled tacticity. Contamination of the final polyesters by metallic residues is a drawback, which is now tackled by grafting metal alkoxides onto solid supports. The second section is dedicated to ROP mediated by enzymes, which is a very attractive strategy. Finally, “all organic” processes have been recently worked out, which are very promising for the synthesis of aliphatic polyesters free from any metallic contaminants.
Crystallinity Determination
Authors: Runt James , Kanchanasopa Mantana 
Published: July 2004

Abstract
This article presents an overview of the most important experimental methods used to obtain degrees of crystallinity of semicrystalline polymers. Determination of relative and absolute crystallinites using wide‐angle X‐ray diffraction methods is presented first, accompanied by several examples from the literature. This is followed by discusssion of thermal analysis [in particular, differential scanning calorimetry (DSC)], probably the most widely used technique for crystallinity determination. Preferred procedures for determining crystallinites from DSC traces are also provided in brief. The use of vibrational spectroscopy (particularly FTIR) in this context is also reviewed, as is the use of several solid‐state NMR methods. The latter are illustrated by presenting selected examples and appropriate references.
Molecular Recognition in Dendrimers
Authors: Basu Subhadeep , Sandanaraj Britto S. , Thayumanavan S. 
Published: July 2004

AbstractDendrimers are ideal candidates for molecular recognition applications, and this article addresses that theme. Synthetic approaches for achieving various dendrimers are discussed, because these methodologies form the basis for designing dendrimers for molecular recognition. Dendrimers act as host macromolecules, where the binding events occur due to a variety of attractive forces. This article focuses mainly on hydrogen‐bonding‐based recognition and hydrophobic forces. Recognition based on hydrogen bonding has been reported both within dendritic interiors and as a method to modify the surface functionalities of dendrimers. Both of these aspects are covered. The binding of guest molecules due to hydrophobic pressure, ie, amphiphilic dendrimers, is discussed.
Molecular Self‐Assembly
Authors: Thibault Raymond J. , Rotello Vincent M. 
Published: July 2004

AbstractAfter a brief introduction to supramolecular polymers/polymerization that differentiates between main‐chain and side‐chain interactions, this article highlights recent work in the area of side‐chain supramolecular polymers. In particular, this article deals specifically with hydrogen bonding and aromatic π stacking recognition elements employed as pendant side chains, primarily through selected results by the authors. It is demonstrated that the side‐chain supramolecular motif is an effective and practical methodology for control over solution state polymer structure from the molecular level to the microscale. Specific noncovalent interactions provide an elegant means to reversibly control solution‐state polymer structure on the nano‐ and microscale, an efficient method for the incorporation and sensing of functional guest molecules, and also an effective means of reversibly functionalizing surfaces while maintaining charge neutrality. The “lock and key” nature, high directionality, and thermal response of these interactions make this a particularly attractive alternative to the fabrication of novel, functional materials. Also, the wealth of available interactions allows one to precisely tune form, function, and interaction strength of the assembling units providing for excellent control in materials processing.
Cyclodextrins
Authors: Ritter Helmut , Tabatabai Monir 
Published: July 2004

AbstractBecause of their polar hydrophilic outer shell and relatively hydrophobic cavity, cyclodextrins are able to form inclusion complexes with a wide variety of suitable hydrophobic molecules. This phenomenon leads to significant changes of the solubility and reactivity of the guest molecules without any chemical modification. Water‐insoluble molecules become completely water‐soluble by treatment with aqueous solution of native cyclodextrins or their derivatives, eg, methylated or hydroxypropylated cyclodextrins. Accordingly, a large number of applications have been found in many areas; eg, in food chemistry as well as in the pharmaceutical and cosmetic industries. Furthermore, cyclodextrins may be used in organic chemistry and also in polymer chemistry. Cyclodextrins (CDs) are produced in technical plants by enzymatically catalyzed degradation of starch.In this article, the synthesis of new monomers, their inclusion in cyclodextrin derivatives, and polymerization in aqueous medium are described.
Electropolymerization
Authors: Sarac A. Sezai 
Published: July 2004

AbstractElectronically conducting materials based on conjugated polymers have been applied in diverse items such as sensors, biomaterials, light‐emitting diodes, polymer actuators, rechargeable batteries, electromagnetic interference shielding, electroluminescent polymer displays, photodetectors, corrosion inhibition, flexible “plastic” transistors, and electrodes. The conductive films were grown by electrochemical polymerization of variety of heteroaromatic monomers. Monomers are electrochemically oxidized at a polymerization potential giving rise to radical cations. These radical cations (and monomers) are adsorbed onto the electrode surface and subsequently undergo a wide variety of reactions leading to the polymer network.Electrochemical polymerization of mainly nonconjugated, heterocyclic conjugated polymers of pyrrole, thiophene, carbazole, their derivatives, and their copolymers are reviewed. Applied characterization techniques are given. In addition to the conventional electrodes, electropolymerization of conjugated and nonconjugated systems on highly oriented pyrolitic graphite and carbon fiber, and their surface characterizations (spectroscopic and morphologic) are also discussed.
Flame Retardancy
Authors: Weil Edward D. 
Published: July 2004

AbstractFlame retardants believed to be in actual use or in serious commercial development are surveyed and classified by main chemical types: inorganic, halogenated (organic), phosphorus‐based, sulfur‐based, and nitrogen‐based. Based on weight, the inorganic category, dominated by alumina trihydrate, is the largest. Based on value (price), the bromine category is the largest, with tetrabromobisphenol A being the largest single compound, used extensively in electronic products. Both additive and reactive types are discussed. Factors favoring and limiting the use of each retardant are stated. Toxicological and environmental factors are discussed, and some cases where products have been withdrawn (recently pentabromodiphenyl ether, for example) are mentioned. Evidence for the value of flame retardants for life safety is given, so also are perceived environmental problems and regulatory restrictions. The use of high molecular weight additives or reactives is mentioned as a means for avoiding environmental concerns.
Computational Quantum Chemistry for Free‐Radical Polymerization
Authors: Coote Michelle L. 
Published: July 2004

AbstractThis article begins with an introduction to the basic principles of quantum‐chemical calculations, and also the calculation of reaction rates via transition‐state theory. This is followed by a brief practical discussion of the methods currently available for studying radical reactions. The article concludes with a description of some of the applications of quantum chemical calculations in the field of free‐radical polymerization, which illustrate the contribution that quantum chemistry has already made to our understanding of this process, and highlight its potential as a tool for solving further mechanistic problems in this field. It is beyond the scope of this article to provide a detailed mathematical description of quantum chemical methods. Rather, the aim is to provide the nonspecialist with a qualitative understanding of its inherent assumptions, and sufficient background information to initiate theoretical studies in the field of free‐radical polymerization, and to make informed judgments concerning the reliability of the procedures used.
Thermosets
Authors: Gotro Jeffrey , Prime R. Bruce 
Published: July 2004

AbstractThermosets are network‐forming polymers. Unlike thermoplastic polymers, chemical reactions are involved when producing or fabricating parts. As a result of these reactions the materials cross‐link and become “set,” ie, they can no longer flow or dissolve. In contrast to cross‐linked elastomers or rubbers, the glass‐transition temperature (Tg) of thermosets is generally above room temperature. They may contain additives such as catalysts to promote or accelerate cure. Most thermosets are used in filled or reinforced form to reduce cost, modify physical properties, act as a binder for particles or fibers, reduce shrinkage during cure, or to provide or enhance flame retardance. Epoxy resins are probably the best‐known members of the thermoset family whose members also include phenolic resins, unsaturated polyester, polyurethane, dicyanate, bismaleimide, acrylate, and many others. Topics covered in this article include thermosetting resin systems, cure and properties of thermosets, nanocomposites, residual stress, cure monitoring, and thermoset processes.
Rheological Measurements
Authors: Schoff Clifford K. , Kamarchik Peter 
Published: July 2004

AbstractThis article is concerned with the experimental measurement of rheological properties of both liquids and solids and the principles on which these measurements are based. The flow properties of a liquid are defined by its resistance to flow, ie, viscosity. This concept is defined and discussed in terms of both theoretical flow models and practical consequences. Temperature, thixotropic and other time‐dependent, and concentration effects are covered for dilute polymer solutions, melts, and dispersed systems. Techniques and viscometers for capillary, rotational, and moving‐body measurements are described. The rheological properties of viscoelastic solids are made up of a combination of permanent deformation and recoverable elastic deformation. Additionally, a number of liquids show elastic as well as flow behavior. Also described are additional techniques beyond those indicated for simple solids and liquids, which are needed for complete characterization of mechanical behavior of materials in terms of elasticity and viscoelasticity. Examples of such methods are the dynamic measurement of response to sinusoidal oscillatory motion; the measurement of flow with time after application of stress, ie, creep; and the measurement of the rate and degree of recovery after removal of stress, ie, creep recovery or recoil. Special topics such as the Weissenberg effect, time–temperature superposition, and electrorheological behavior are also discussed.
High Performance Fibers
Authors: Polk Malcolm , Vigo Tyrone L. , Turbak Albin F. 
Published: July 2004

AbstractThe preparation, processing, and properties of high performance fibers are critically reviewed. The principal classes of high performance fibers discussed are those derived from rigid‐rod polymers, gel spun fibers, modified carbon fibers, carbon‐nanotube fibers, ceramic fibers, and synthetic vitreous fibers. Rigid‐rod polymers are derived from lyotropic liquid crystalline polymers, such as the aramid Kevlar or thermotropic liquid crystalline polymers, such as Vectran. These fibers are generally characterized by remarkable unit tensile strength, modulus, and resistance to heat, flame, and chemical agents that normally degrade conventional fibers. Applications for these fibers are classified by structural aspects of the fiber, yarn, and fabric levels. Diversities in applications include uses in the aerospace, biomedical, civil engineering, construction, protective apparel, geotextile, and electronic areas.
Composite Foams
Authors: Gladysz Gary M. , Chawla K. K. 
Published: July 2004

AbstractComposite polymer foams are materials consisting of a polymer phase with voids and an additional solid or hollow phase distributed throughout the polymer. Conventional, single‐phase foams made by expanding polymers are excluded. Syntactic foams, made by incorporating hollow microspheres or microballoons in a binder phase, represent a special and important class of composite foam. With appropriate control of the size, morphology, and distribution of microballoons, syntactic foams can provide a wide range of properties. Addition of particles or fibers (long or short) provides another microstructural parameter to improve strength and damage tolerance of composite foams. Composite foams find a wide range of applications: offshore exploration of oil and gas, shielding against electromagnetic interference (EMI), thermal and acoustic insulation, damping, cores in sandwich construction, etc.
Polymer‐Supported Reagents
Authors: Bradley Mark , Galaffu Nicola 
Published: July 2004

AbstractThis article presents an overview of the materials commonly used in solid‐supported chemistry and their evolution. It begins with polystyrene–divinyl benzene based resins, includes reference to microgel and nanoparticles, and moves onto poly(ethylene glycol) (PEG)‐grafted resins. A review of alternative types of cross‐linker for polystyrene resins such as those based on polytetrahydrofuran and PEG is provided and alternative formats for polystyrene‐based resins such as plugs, discs, and films are discussed films. The final section covers aspects of alternative nonpolystyrene matrixes such as polyacrylamide–PEG‐based resins and cellulose.
Controlled Release Formulation, Agricultural
Authors: Wilkins Richard 
Published: July 2004

AbstractControlled release formulations (CRFs) are intended to improve the delivery of pesticides and related biologically active substances. The consequent improvement in efficiency reduces losses in use and has many benefits, such as reduction in exposure to both workers and the environment, particularly in minimizing leaching and evaporation. This article introduces the advantages of CRFs and provides a theoretical rationale for their use based on pseudo‐first‐order loss kinetics, which are typical for pesticide dissipation in the environment. Thus, the greater the loss rate, especially for pesticides of short duration, the greater the potential for improvement in delivery to the target pest. As a consequence of this principle, reduced levels of pesticide delivered efficiently can be as efficacious as higher amounts of conventional formulations.CRFs are classified as physical, chemical, or biological. The kinetics of release from CRFs is central to their successful use, and the mathematical basics of this are described. The mechanisms of release vary according to the type of formulation, and these are covered for physical and chemical types. Common release characteristics include first order, diffusion (square root of time) based, and zero order (constant). Release kinetics are usually measured under controlled laboratory conditions, but field determinations are preferable.The main groups of physical‐type formulations, such as reservoirs with release‐rate‐controlling membranes and without membrane and the monolith or matrix structures, are those based on microencapsulated liquid cores in sprayable concentrate formulations, and polymeric matrix methods that are often fabricated as granules. The polymers used and the approaches employed for designing these types of CRFs are introduced with emphasis on encapsulation methods, such as phase separation and interfacial polymerization. In addition, other formulation types are included, such as laminates, coated granules, microparticles, matrix granules (swellable and nonswellable), matrix devices for animal and public health protection, plastic films, and mulches. The biological approach to formulation based on living or dead genetically modified microorganisms containing proteinaceous toxins is also covered.
Cubic Liquid‐Crystalline Nanoparticles
Authors: Yang Da , Armitage Bruce , Marder Seth R. 
Published: July 2004

AbstractCubic liquid‐crystalline nanoparticles prepared from aqueous dispersions of cubic lipid–water phases are kinetically stable in the presence of certain dispersing agents. The properties of cubic nanoparticles from monoolein–water and other lipid–water systems have been examined with a variety of experimental techniques. The cubic nanoparticles can be stabilized by polymerization of the reactive lipids in cubic lipid assemblies. Several low‐energy‐input methods have been developed to facilitate the production and application of cubic nanoparticles. The ability to incorporate and deliver lipophilic, amphiphilic, and water‐soluble molecules in a controlled manner and the good biocompatibility of cubic nanoparticles make them excellent candidates for drug‐delivery applications.
Synthesis of antibacterial and antifungal cobalt(II), copper(II), nickel(II) and zinc(II) complexes with bis‐(1,1′‐disubstituted ferrocenyl)thiocarbohydrazone and bis‐(1,1′‐disubstituted ferrocenyl)carbohydrazone
Authors: Chohan Zahid H. , Khan Khalid M. , Supuran Claudiu T. 
Published: July 2004

AbstractThe condensation reaction of 1,1′‐diacetylferrocene with thiocarbohydrazide and carbohydrazide to form bis‐(1,1′‐disubstituted ferrocenyl)thiocarbohydrazone and bis‐(1,1′‐disubstituted ferrocenyl)carbohydrazone has been studied. The compounds obtained have been further used as ligands for their ligand and antimicrobial properties with cobalt(II), copper(II), nickel(II) and zinc(II) metal ions. The compounds synthesized have been characterized by physical, spectral and analytical methods and have been screened for antibacterial activity against Escherichia coli, Bacillus subtillis, Staphylococcus aureus, Pseudomonas aeruginosa and Salmonella typhi, and for antifungal activity against Trichophyton longifusus, Candida albicans, Aspergillus flavus, Microsporum canis, Fusarium solani and Candida glaberata using the agar well‐diffusion method. All the compounds synthesized have shown good affinity as antibacterial and antifungal agents, which increased in most of the cases on complexation with the metal ions. Copyright © 2004 John Wiley & Sons, Ltd.
Laser‐induced synthesis of iron–iron oxide/methylmethoxysilicone nanocomposite
Authors: Pola Josef , Bastl Zdeněk , Vorlíček Vladimír , Dumitrache Florian , Alexandrescu Rodica , Morjan Ion , Sandu Ion , Ciupina Victor 
Published: July 2004

AbstractThe IR laser irradiation of a gaseous mixture of iron pentacarbonyl–methoxytrimethylsilane–ethene in argon induces ethene‐photosensitized decomposition of iron pentacarbonyl into elemental iron and decomposition of methyltrimethoxysilane into species that polymerize into methylmethoxysilicone. These two concurrent gas‐phase processes allow formation of iron–iron oxide/methylmethoxysilicone nanocomposite. Spectral analyses and electron microscopy reveal the nanocomposite as consisting of iron clusters oxidized in outer layers and covered with the organosilicon polymer. The procedure shows its potential for gas‐phase synthesis of iron‐based clusters embedded in a polymer matrix. Copyright © 2004 John Wiley & Sons, Ltd.
Ion chromatography–inductively coupled plasma mass spectrometry determination of arsenic species in marine samples
Authors: Karthikeyan Sathrugnan , Hirata Shizuko 
Published: July 2004

AbstractArsenic speciation analysis in marine samples was performed using ion chromatography (IC) with inductively coupled plasma mass spectrometry (ICP‐MS) detection. The separation of eight arsenic species, viz. arsenite, monomethyl arsonic acid, dimethylarsinic acid, arsenate, arsenobetaine, tetramethylarsine oxide, arsenocholine and tetramethylarsonium ion was achieved on a Dionex AS4A (weaker anion exchange column) by using a nitric acid pH gradient eluent (pH 3.3 to 1.3). The entire separation was accomplished in 12 min. The detection limits for the eight arsenic species by IC–ICP‐MS were in the range 0.03–1.6 µ g l−1, based on 3σ of the blank response (n = 6). The repeatability and day‐to‐day reproducibility were calculated to be less than 10% (residual standard deviation) for all eight species. The method was validated by analyzing a certified reference material (DORM‐2, dogfish muscle) and then successfully applied to several marine samples, e.g. oyster, fish muscle, shrimp and marine algae. The low power microwave digestion was employed for the extraction of arsenic from seafood products. Copyright © 2004 John Wiley & Sons, Ltd.