bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermodynamic Properties of Polymers
Authors: Wunderlich Bernhard , Pyda Marek
Published: July 2004

The equilibrium properties of polymers and the changes occurring on going to nonequilibrium states are discussed. For example, the typical semicrystalline polymer is treated as a globally metastable structure of two or three nanophases with possible local equilibria (crystal/amorphous or crystal/amorphous/rigid amorphous). The transitions are explored experimentally by classical calorimetry and temperature‐modultated calorimetry. The heat capacity is taken as the basic thermodynamic property and linked to the different types of molecular motion in terms of small‐amplitude vibrational motion and large‐amplitude conformational motion. The low frequency vibrations are the skeletal vibrations and can be fitted to the low temperature heat capacities with one‐, two‐, and three‐dimensional Debye functions. The high frequency vibrations are treated as group vibrations, easily available as group vibrations from normal‐mode analyses of the polymer or related compounds. Data for almost 100 polymers are presented from the ATHAS data bank. The large‐amplitude, conformational motion can be linked to the deviation of the experimental heat capacity from the vibrational heat capacity and allowed to discuss the more mobile phases. The integral thermodynamic functions, enthalpy, entropy, and free enthalpy are then derived from the heat capacities and linked to the phase transitions and chemical thermodynamics (melting/crystallization, glass transition, mixing/demixing, and polymerization/depolymerization). The bibliography establishes the link to classical thermodynamics data and theory sources with 163 references.
N‐Vinylamide Polymers
Authors: Login Robert B.
Published: July 2004

N‐Vinyl lactams and their corresponding polymers and copolymers have received considerable attention in the academic literature and significant commercial success. However, until recently this interest centered onN‐vinyl pyrrolidinone and its polymers and copolymers.N‐Vinyl caprolactam is now emerging commercially because copolymerization withN‐vinyl pyrrolidinone results in copolymers with high levels of lactam functionality but with controlled hydrophobicity desired in many hair‐fixative products designed to resist drop in high humidity environments. Polyvinylpyrrolidinone (PVP) is a unique water‐soluble polymer that forms lustrous, continuous films on dry‐down that are very adhesive because of hydrogen bonding to substrates such as skin and hair. This adhesive characteristic also results in a wide variety of useful applications such as pharmaceutical tablet binding, hot‐melt, and paper‐adhesive applications. PVP is relatively nontoxic and contributes mildness to formulations. PVP will also complex with a variety of small and large molecules because the pyrrolidinone carbonyl group can accept a proton in the presence of large anions, becoming pseudocationic. In addition, because of lactam polarity where significant charge can appear on the nitrogen and oxygen atoms, it can interact with electron‐rich aromatics. Ligands such as anionic dyes and surfactants or triiodide or phenolic or polynuclear aromatics or polyacids, etc, will interact and complex with PVP. PVPHI3or povidone–iodine is probably the most successful of these complexes, retaining a reservoir of iodine even in dilute solution, affording fresh germicidal iodine as free iodine is consumed. Cross‐linked PVP or crospovidone can be employed to remove bitter tannins (phenolics) from beer and wine. Dry crospovidone can be compressed because of interhydrogen bonding, only to rapidly swell when exposed to moisture. For this reason, it has achieved success as a tablet disintegrant.
Water‐Soluble Polymers
Authors: McCormick Charles L. , Lowe Andrew B. , Ayres Neil
Published: July 2004

Water‐soluble (co)polymers represent a diverse class of macromolecules ranging from naturally occurring biopolymers such as polysaccharides and most polypeptides to wholly man‐made materials. Such materials have found a wide‐range of applications. In this article we detail the synthesis and solution characteristics of both natural and synthetic polymers. Emphasis is placed on polynucleotides, polypeptides, and polysaccharides for naturally occurring polymers, while the discussion regarding synthetic materials is divided into sections dealing with neutral, anionic, cationic, and zwitterionic species. Special attention is given to recent advances in synthetic methodologies which now allow the tailoring of synthetic materials with precisely controlled microstructures, predetermined molecular weights, narrow molecular weight distributions, and complex topologies.

Finally, we detail some of the self‐assembly characteristics of both high molecular weight statistical copolymers and lower molecular weight block copolymers in aqueous media with an emphasis on those materials which undergo phase transitions and/or conformational changes in response to an applied stimulus.
Xylylene Polymers
Authors: Beach W. F.
Published: July 2004

Pinhole‐free coatings of outstanding conformality and thickness uniformity are produced by exposing a substrate to a controlled deposition of pure gaseous monomer through the unique chemistry ofp‐xylylene, which is thermally stable but very reactive toward polymerization with other like molecules, in a process known as vapor deposition polymerization (VDP). A high molecular weight coating of poly(p‐xylylene) (PPX) is produced. Recent VDP developments are stressed in the article.

The convenient generation of the extremely reactive monomer is accomplished by thermal cleavage of its stable dimer,cyclo‐di‐p‐xylylene (DPX), commercially in the Gorham process. The PPXs formed as coatings in the Gorham process are referred to generically as parylenes. Parylene N, Parylene C, and Parylene D are polymer coatings produced by the Gorham process using the dimers DPXN, DPXC, and DPXD, respectively. These dimers are the feedstocks for the coating process. The Parylene C monomer, chloro‐p‐xylylene, has become the de facto performance standard owing to its room‐temperature volatility. VDP processes using means other than pyrolytic cleavage of DPX to generate reactive monomer, none practiced commercially, include photopolymerization and plasma polymerization, as well as imidization to produce polyimide films.

Manufacture of commercial DPXN is through two routes: direct pyrolysis ofp‐xylene and the Hofmann elimination route. DPXC and DPXD are prepared from DPXN by chlorinating. Thermodynamic considerations of the parylene process by VDP are covered. The importance of the physical processes of condensation and diffusion in VDP are treated, as is the propagation reaction.

VDP produces films of uniform thickness having excellent conformality and purity. Electrical properties merit their use in electronic construction. Barrier, spectral, and optical properties are also useful. Crystallinity determines important properties of mechanical strength at elevated temperatures and solvent resistance, which constitute the principal advantages of PPX materials. Uses include circuit boards, hybrid circuits, semiconductors, capacitors, the bathythermograph, medical uses (as in pacemakers), artifact conservation, and in laser fusion targets. They are also used as barrier coatings, in corrosion control, and as dry lubricants. The dimers present little concern in handling and storage to an experienced operator. In ancillary operations such as cleaning or adhesion promotion, suitable precautions given in manufacturers' Material Safety Data Sheets should be observed.
Drag Reduction
Authors: Singh Ram Prakash
Published: July 2004

Turbulent drag reduction in fluid flow by additives has been an exotic field of research ever since its reported discovery in 1949. Various technical applications have been envisaged both for polymeric and surfactant drag reduction. Some successful applications include increased flow of oil and other fluids through pipelines, improved fire fighting and irrigation, improved flow in storm sewers, and flow augmentation by drag reducers in pipeline transport of sediments and slurries. Other possible applications include district heating circuits, industrial and agricultural sprays, and slow‐release fertilizers and pesticides. However, the mechanism of drag reduction still eludes exact explanation mainly because of the inability to characterize polymers, surfactants, and their interactions at molecular or micellar levels in turbulent flows.

The main features of polymeric and surfactant homogeneous and heterogeneous drag reduction have been investigated by two‐component laser‐Doppler velocity meter in fully developed, well‐mixed, low concentration (1–2 ppm) drag‐reducing channel flows. Advances in computer technology have led to improved accuracies and reliability of experimental techniques and made possible direct numerical simulation of drag‐reducing turbulent flows. The role of extensional viscosity and elasticity of drag reducers is being keenly debated for the origin of drag reduction in theoretical and experimental investigations. A better understanding is emerging. Some synergistic effects have been observed in combining passive drag‐reducing devices such as riblets with polymers surfactants. Similar observations have been made in combination with microbubbles. This article provides an overview of the latest salient developments in materials, mechanisms, and applications in the field of polymeric drag reduction of various forms and geometries.
Mechanical Performance of Plastics
Authors: Brostow Witold , Singh Ram Prakash
Published: July 2004

We discuss methods of prediction of long‐term performance and reliability of polymer‐based materials from short‐term tests. The methods include prediction of slow crack propagation and also predictions based on correspondence principles including the stress–time correspondence. The amount of experimentation needed for reliable predictions is much lower than generally believed. For instance, experiments at two stress levels for a four‐phase polymer liquid crystal are sufficient for creation of a master curve. We cover briefly tribology, including friction, scratch resistance, and wear resistance. When appropriate, we illustrate mechanical and tribological processes by results of computer simulations.
Nanocomposites, Layer‐by‐Layer Assembly
Authors: Kotov Nicholas A. , Mamedov Arif A. , Guldi Dirk M. , Prato Maurizio , Wicksted James , Hirsch Andreas
Published: July 2004

Layer‐by‐layer assembly with polyelectrolytes (LBL) is one of the most powerful methods of preparation of nanocomposites. The current practice and future prospects of LBL‐made materials is reviewed. One of the most fundamentally interesting and practically relevant applications of LBL is the preparation of ultrastrong materials. The mechanical failure of hybrid materials made from polymers and single wall carbon nanotubes (SWNT) is primarily attributed to poor matrix–SWNT connectivity and severe phase segregation. Both problems can be successfully mitigated when the SWNT composite is made following the protocol of layer‐by‐layer assembly. This deposition technique prevents phase segregation of the polymer/SWNT binary system, and after subsequent cross‐linking, the nanometer‐scale‐uniform composite with SWNT loading as high as 50 wt% can be obtained. The free‐standing SWNT/polyelectrolyte membranes delaminated from the substrate are exceptionally strong with tensile strength approaching that of hard ceramics. Considering the lightweight nature of SWNT composites the prepared free‐standing membranes can serve as unique components for a variety of long‐lifetime devices.
Tissue Engineering
Authors: Ma Peter X.
Published: July 2004

Tissue engineering, still in its infancy, has shown great promise in developing novel therapies to tissue losses and organ failures. Scaffolds play a pivotal role in tissue engineering. Biodegradable polymers are the primary choice of materials for tissue engineering scaffolds. In this article, the principles of tissue engineering are discussed in relation to polymer science and engineering. The most frequently used polymers in tissue engineering are briefly reviewed. These include synthetic and natural polymers for porous scaffolds and hydrogel scaffolds. Their structure and important properties in relation to scaffold function are discussed. Important polymer processing techniques in the context of scaffold fabrication are also reviewed. These include the textile technologies, particulate‐leaching techniques, phase separation techniques, rapid prototyping, and other novel 3‐D fabrication techniques.
Wood Composites
Authors: Matuana Laurent M. , Heiden Patricia A.
Published: July 2004

The term wood composites is a general one that describes a wide range of products having some combination of wood element(s) held together by an adhesive “binder.” The wood composites industry is growing rapidly from both a steadily increasing demand for existing products and an increasing demand for new products to be used in new applications. This article describes the types of wood elements and major wood adhesives that are employed by the wood composites industry today, and major wood composite products that are currently marketed. An overview of current research directions and the forces driving this research is also presented, including research into alternative adhesive systems, adhesive modifications, improved processes, and lignocellulosic alternatives to wood.
Poly(ethylene naphthalate) (PEN)
Authors: Sakellarides S. L.
Published: July 2004

Poly(ethylene naphthalate) (PEN) is a thermoplastic polyester with performance properties superior to that of poly(ethylene terephthalate) (PET). With its higher stiffness, moisture, gas, and light barrier, as well as thermal, electrical, and chemical resistance, PEN extends polyester's application range into more demanding end uses in a variety of areas such as rigid and flexible packaging, industrial fiber, and film for electrical, light management, data storage, and imaging applications. This article summarizes PEN's key material properties, resin preparation and fabrication, and representative examples of end‐use applications published to date.
Photopolymerization, Free Radical
Authors: Cai Ying , Jessop Julie L. P.
Published: July 2004

Free‐radical photopolymerizations, which use light energy to initiate chain‐producing reactions, have many advantages over thermal polymerizations, including solvent‐free systems, spatial and temporal control of initiation, and high speed processing capabilities. This article provides an overview of the components, kinetics, and applications of free‐radical photopolymerization systems. Two general classes of photoinitiator systems (unimolecular and bimolecular) are discussed, as well as systems that have been developed to meet the demands of specific applications. (Meth)acrylates, which are the most widely used monomers in photopolymerization processes, and other commercially important free‐radical monomers, are described. The kinetic treatment of free‐radical photopolymerizations is outlined, with special emphasis on the photoinitiation step and its impact on the rate of polymerization expression. Kinetic modeling concerns in reaction systems containing monomers with more than one reactive group and in systems utilizing specialized polymerization methods are also considered. Finally, applications for free‐radical photopolymers in the automotive, electronic, medical, optical, graphic arts, flooring, and furniture industries are presented. This article provides the scientist or engineer with fundamental considerations of free‐radical photopolymerizations, along with references for more advanced topical research.
Plastics Processing
Authors: Xanthos M. , Todd D. B.
Published: July 2004

Processing 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

An 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

Biodegradable 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

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

Dendrimers 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

After 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

Because 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

Electronically 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

Flame 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

This 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

Thermosets 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

This 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

The 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

Composite 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

This 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

Controlled 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

Cubic 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

The 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

The 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

Arsenic 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.
Supramolecular structures and properties models of macrocyclic polymer complexes
Authors: Mubarak Ahmed T. , El‐Assiery Saeed A.
Published: July 2004

Two novel supramolecular complexes of types [Ru(L)(H2L)Cl·OH2] and [Ru(HLn)Cl3] (where H2L is a potential tetradentate ligand derived from hydrazine hydrate and diethyl malonate, and HLn is a potential bidentate ligand derived from coupling of allyl azo‐β‐diketone) have been synthesized and characterized by elemental analysis, conductance and magnetic measurements, followed by 1H NMR, to determine the effect of substituents on the intramolecular hydrogen bond. The electronic properties and models of the bonding of ligands and complexes were investigated by UV–Vis and IR spectroscopies. The first type of complex contains terminal hydrazinic nitrogen atoms with an unshared electron pair and may take part in nucleophilic condensations. Therefore, the reactions of allyl‐β‐diketone complexes with malonic dihydrazide have also been studied, as these cause ring closure and formation of supramolecular macrocyclic ligand complexes. The wavelengths of the principal electronic absorption peaks have been accounted for quantitatively in terms of crystal field theory, and various parameters have been evaluated. On the basis of the electronic spectra, an octahedral geometry has been established for the polymer complexes C. The macrocyclic polymer complexes D are pentacoordinate, and a trigonal‐bipyramidal environment (D3h) is suggested for the ruthenium(III) ion. The effect of the Hammett constant on the ligand field parameters is also discussed. Copyright © 2004 John Wiley & Sons, Ltd.
Solid‐state NMR study of [(Ph3SnF)2(Ph3SnO2PPh2)], a novel coordination polymer prepared from Bu4N[Ph3SnF2] and [Ph3SnOPPh2OSnPh3](O3SCF3)
Authors: Beckmann Jens , Dakternieks Dainis , Duthie Andrew , Mitchell Cassandra , Ribot François , d'Espinose de la Caillerie Jean Baptiste , Revel Bertrand
Published: July 2004

The coordination polymer [(Ph3SnF)2(Ph3SnO2PPh2)] (3), prepared by the reaction of [Ph3SnOPPh2OSnPh3](O3SCF3) (4) with Bu4N[Ph3SnF2] (5), was investigated by multinuclear magic angle spinning magnetic resonance spectroscopy and the results compared with those of the polymeric parent compounds Ph3SnF (1) and Ph3SnO2PPh2 (2). The crystal structure of 4 was determined by X‐ray crystallography. Copyright © 2004 John Wiley & Sons, Ltd.
Regioselective synthesis of symmetrical pyridyl selenium compounds by bromine–magnesium exchange of bromopyridines using isopropyl magnesium chloride: X‐ray crystal structure of 2,2′,5,5′‐tetrabromo‐3,3′‐dipyridyldiselenide
Authors: Bhasin K. K. , Arora Veena
Published: July 2004

2,2′‐Dipyridyl‐3,3′‐dipyridyl,5,5′‐dipyridyl‐diselenides have been synthesized by a convenient method employing non‐cryogenic conditions. Various bromopyridines (2‐Bromopyridine, 2,5‐dibromopyridines and 2,3,5‐Tribromopyridines) undergo selective monobromine–magnesium exchange to yield the corresponding pyridyl magnesium chlorides at room temperature upon treatment with iPrMgCl. The resulting pyridyl magnesium chloride is quenched with elemental selenium, which upon further oxidation affords the above diselenides in good yields. The compounds prepared using this methodology have been characterized by elemental analysis, IR, NMR (1H, 13C, 77Se) and mass spectral analysis. The molecular structure of 2,2′,5,5′‐Tetrabromo‐3,3′‐dipyridyldiselenide has been established by single‐crystal X‐ray diffraction analysis. It exists as a dimeric form due to the non‐bonding interactions between the selenium of one pyridine moiety and the hydrogen of the other. Copyright © 2004 John Wiley & Sons, Ltd.
Synthesis, structure characterization and larvicidal activity of some tris‐(para‐substitutedphenyl)tins
Authors: Song Xueqing , Duong Quyen , Mitrojorgji Edlira , Zapata Alejandra , Nguyen Nhuvu , Strickman Daniel , Glass Jacqulin , Eng George
Published: July 2004

A series of tris‐(para‐substitutedphenyl)tins (X − C6H4)3SnY, where X = Cl, F, CH3 and SCH3 and Y = Cl, OH and OAc, was synthesized. The structures of the compounds were primarily characterized by Mössbauer spectroscopy. Based on the spectroscopic data, the chloride derivatives were determined to be four‐coordinated monomers and the acetate and hydroxide compounds were found to be five‐coordinated polymers. The compounds were screened against the second larval instar of the Anopheles stephensi and Aedes aegypti mosquitoes. For the An. stephensi larvae, the compounds that had the highest toxicity were those that contained a single atom substituent on the phenyl ring, and the least effective compounds contained the SCH3 substituent. Toxicity was more dependent on the ring substituent than on the anion attached to the tin atom. Quantitative structure–activity relationships could be generated between the toxicity of the compounds and the surface area of the molecule, indicating that the toxicity was related to the size of the substituent on the ring. In the case of the Ae. aegypti, the toxicity was also more dependent on the ring substituent than on the anion group. However, the size of the substituent on the ring was not found to be the dominant factor in the toxicity of these compounds. Copyright © 2004 John Wiley & Sons, Ltd.
Synthetic and antimicrobial studies on new gold(I) complexes of imidazolidin‐2‐ylidenes
Authors: Özdemir İsmail , Denizci Akın , Öztürk H. Tansel , Çetinkaya Bekir
Published: July 2004

Six new 1,3‐diorganylimidazolidin‐2‐ylidene (NHC) gold(I) complexes of the type [Au(NHC)2]+ (1–6), were synthesized by reacting [AuCl(PPh)3] with 1,3‐dimesitylimidazolidin‐2‐ylidene or bis(1,3‐dialkylimidazolidin‐2‐ylidene). The complexes 1–6 were fully characterized by elemental analyses and spectroscopic data. The placement of mesityl or para‐substituted benzyl groups on the nitrogen atoms of the ring of the complexes leads to the particularly active antibacterial agents evaluated in this work. It is worth noting that the p‐methoxybenzyl derivative (2) inhibited the growth of Pseudomona aeruginosa, Staphylococcus epidermidis, Staphylococcus aureus and Enterococcus faecalis with minimum inhibitory concentration (MIC) values of 3.12 µg ml−1, 6.25 µg ml−1, 3.12 µg ml−1 and 3.12 µg ml−1 respectively. In contrast, the analogous p‐dimethylaminobenzyl derivative (3) is effective only against Escherichia coli (MIC = 3.12 µg ml−1). Copyright © 2004 John Wiley & Sons, Ltd.
New insights into the degradation mechanism of poly(vinyl chloride), part II. Limited polyene sequence length during degradation and synergism between costabilizers
Authors: Santamaría E. , Edge M. , Allen N. S. , Harvey H. B. , Mellor M. , Orchison J.
Published: July 2004

Fluorescence spectroscopy has shown that the limited sequence length exhibited during the thermal degradation of poly(vinyl chloride) (PVC) was the result of an HCl readdition/splitting off equilibrium, especially in unstabilized PVC formulations. In the case of stabilized PVC, the type and mechanistic action of the stabilisers seemed to play an important role in HCl re‐addition. The possibility of a synergistic effect taking place between costabilisers for PVC, namely N‐phenyl‐3‐acetyl pyrrolidine‐2,4‐dione (P24D) and its derivative N‐isopropyl‐n‐phenyl‐3‐(1‐iminoethyl) pyrrolidine‐2,4‐dione (P24D‐d) has also been investigated by means of statistical design, degrading the samples at 170°C in air and measuring the induction time (Ti) of the degraded polymer. The results reveal that the stabilising efficiency is not only affected by the presence of the metal soap, but also by the nature of the substituents in the P24D derivatives. It may be concluded that P24D‐d on degradation operates as a “reservoir” for P24D, extending the Ti to higher values compared to their individual performances and giving rise to a synergistic combination. The ability of the costabiliser to form a keto‐enol tautomerism as well as its ability to interact with the PVC and the metal soap play a crucial role in controlling their stabilising effectiveness in the polymer. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2744–2763, 2004
Enhancing the strength of polypropylene fibers with carbon nanotubes
Authors: Moore Eric M. , Ortiz Diana L. , Marla Vishnu T. , Shambaugh Robert L. , Grady Brian P.
Published: July 2004

Single‐walled carbon nanotubes were added to two different grades of polypropylene to produce composites. The composites were then melt‐spun into fibers, and the fibers were tested with both a conventional tensile pull tester and dynamic mechanical analysis. The changes in tensile properties were related to the grade of polypropylene used. In addition to fibers being made from the mixes, coarse extrudates (i.e., undrawn, gravity‐spun filaments) were also produced. Density measurements on these extrudates showed that the addition of nanotubes increased the composite density in a highly nonlinear manner, which suggested interaction between the polypropylene and the carbon nanotubes. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2926–2933, 2004