bluuebunny/crossref_metadata_2025 huggingface dataset:
Weathering
Authors: Searle Norma D.
Published: October 2003

The irreversible changes in chemical and physical properties of polymeric materials exposed to the environment are caused by the combined action of all weather factors, including solar radiation, heat, moisture, oxygen, and atmospheric pollutants. However, the actinic radiation of the sun absorbed by materials is the critical factor. It initiates the chemical reactions that lead to degradation through its bond breaking capabilities. The wavelength specificity of degradation, and its material dependency are illustrated by the activation spectra of various types of polymers. The contributions of the other major environmental factors to weathering and various types of outdoor weathering tests are described. The significant advances in development of weatherable polymeric materials have increased the need for more rapid evaluations by both outdoor and laboratory accelerated tests. Their validity depends on how well they simulate the effects of exposure to end‐use environments in terms of failure modes, mechanism of degradation, and stability rankings of materials. The most important factor in good correlations between laboratory accelerated and outdoor weathering tests is adequate simulation of the spectral power distribution of the natural source over the full range of actinic wavelengths. The types commonly used in laboratory accelerated devices are compared with solar radiation and the effects of their deviations in the uv and visible regions are discussed. The effect of increased stress levels of irradiance, temperature, and moisture on acceleration factors and on correlation with natural weathering tests are described. Techniques for predicting lifetimes under natural weathering based on laboratory accelerated tests are reviewed.
X‐ray Microscopy
Authors: Ade H.
Published: October 2003

During the last few years near edge x‐ray absorption fine structure (nexafs) spectroscopy/microscopy has evolved into a useful characterization tool for polymer science, providing quantitative compositional mapping with minimal radiation damage at a spatial resolution of presently about 40 nm. This article reviews the spectroscopic principles of nexafs, discusses some polymer nexafs reference spectra to illustrate the underlying utility of nexafs spectroscopy to nexafs microscopy, and provides an overview of the state‐of‐the‐art of x‐ray microscopy instrumentation. Applications of nexafs microscopy are wide ranging and include mapping the composition of polymer thin films and their surfaces, as well as the composition of ultrathin sections of bulk materials ranging from polymer blends to multilayers. To date, nexafs microscopy is still a specialized technique that requires powerful synchrotron radiation sources, similar to established polymer science tools such as neutron and x‐ray small‐angle scattering and reflectivity.
Engineering Thermoplastics, Overview
Authors: Garbassi Fabio , Po Riccardo
Published: October 2003

This article provides a first key of access to engineering polymers. There is a compilation of materials classified as engineering thermoplastics, eg, cyclic olefin copolymers, syndiotactic polystyrene, acetal resins (polyoxymethylene), polyester resins [ie, poly(ethylene terephthalate), poly(butylene terephthalate), and poly(ethylene naphthalate)], polyarylates, liquid crystal polymers, poly(phenylene ether), polycarbonate, aliphatic and aromatic polyketones, acrylic resins, poly(phenylene sulfide), polysulfones, styrene copolymers, aliphatic and aromatic polyamide resins, polyimides, polyamide imide, polyphthalamide, polyetherimide, and fluoropolymers (polytetrafluoroethylene, ethylene–tetrafluoroethylene copolymers, fluorinated ethylene–propylene copolymers, perfluorovinylether–tetrafluoroethylene copolymers). For engineering thermoplastics in general, this article provides a short development history and a discussion of industrial production methods, physical, thermal, mechanical, electrical, and chemical properties, processing technologies, and some applications. Because property values can vary in a wide range, representative figures are reported, mostly from commercial data sheets compiled by producers; these data are available on‐line and are continuously updated. Some of the main properties are compared, on the frame of interpolymer competition.
Laser Light Scattering: Some Recent Developments
Authors: Chi Wu , Xiangjun Gong
Published: October 2003

This review summarizes some recent developments in the characterization of some special intractable macromolecules in solution by a combination of static and dynamic laser light scattering (LLS). Since both static and dynamic LLS are theoretically well established, we have limited this review on experimental details, such as the design of a high temperature LLS spectrometer, the clarification of polymer solutions, complementary apparatuses such as a novel differential refractometer, and portable particle sizer.
Ethylene Polymers,HDPE
Authors: Benham Elizabeth , McDaniel Max
Published: October 2003

Polyethylene (PE) is the most widely used plastic throughout the world, and high density polyethylene (HDPE) is the most widely used type of polyethylene. It was invented independently in the early 1950s in three different laboratories across the world. Commercial catalytic processes were quickly developed based on three different transition metals: chromium, molybdenum, and titanium. Today hundreds of different grades of HDPE are manufactured by several different commercial processes worldwide to meet the demands of applications too numerous to describe completely. HDPE properties can be made to vary widely for these specialized applications by manipulating its molecular structure, such as the molecular weight (MW), the MW distribution, the amount, type and placement of short‐chain branching, the end group composition, and the degree of long‐chain branching. These affect the stiffness of the polymer, the gloss or clarity, the impact, puncture and tear resistance, chemical resistance, electrical insulation properties, molding characteristics, and tensile properties. Common uses for HDPE include food packaging, bottles, bags, drums, fuel tanks and other automotive parts, pipe, film, geomembranes, toys, and filament.
Ethylene Polymers, Chlorosulfonated
Authors: Ennis Royce
Published: October 2003

Chlorosulfonated polyethylene, introduced in 1951, represents a family of chlorinated polymers based on various types of polyolefins and some prefunctionalized resins. They are usually prepared by simultaneous chlorination and chlorosulfonation in a homogeneous solution with an inert solvent. Introduction of chlorine atoms onto the polyolefin chain interrupts its regularity, converting the crystalline polymer into semiplastic, elastomeric, or rigid plastic consistency, depending on the level and distribution of chlorine atoms. The sulfonyl chloride group provides a site for a variety of cross‐linking reactions for thermoset applications. Raw polymer processing and vulcanizate mechanical properties depend on the base resin parameters of molecular weight, molecular weight distribution, and density, in addition to the chlorine and cross‐link type. When properly compounded and cross‐linked, these polymers give superior resistance to oil, heat, and ozone compared to most other elastomers, making them valuable in many automotive, construction, and coating applications. Specific adhesion characteristics of the sulfonyl chloride group and other functionality, eg, maleic anhydride graft, leads to special applications as primers and binders.
Ethylene Acrylic Elastomers
Authors: Wu Yun‐Tai , Stewart Mark A.
Published: October 2003

Ethylene acrylic elastomers have been successfully used in automotive underhood applications where heat and oil resistance are required. Additionally, ethylene acrylic elastomers offer excellent compressive stress relaxation, dynamic fatigue resistance, vibration dampening, and resistance to acid condensates, making it suitable for demanding applications including seals, gaskets, hoses, and torsional dampers. New products with improved properties are introduced to further enhance the performance range to meet future needs for improved fuel efficiency and higher exhaust gas emission standards.
Antifoaming Agents
Authors: Owen Michael J.
Published: October 2003

A review is presented of the materials used to control or eliminate foam in industrial processes and how they function. These materials are classified by their chemical type. Main active liquid‐phase components are hydrocarbon oils, polyethers, and silicone fluids; main solid‐phase components are waxy hydrocarbons and hydrophobic silica. Ancillary agents such as surfactants and carriers are also incorporated in some defoamer formulations. Sources of significant commercial defoamer products are listed. The theory of foaming and defoaming is outlined with emphasis on surface behavior such as entering, spreading, and dewetting phenomena. The role of dispersed hydrophobic solids is highlighted. Applications in various areas are briefly reviewed, including adhesives and sealants, chemical processing, cleaning compounds, construction, fermentation processes, fertilizers, food and beverages, leather, metal working, oil and petrochemicals, coatings, polymers, pulp and paper, textiles, and wastewater treatment. Economic and health and safety factors are considered. Test methods, such as pneumatic, dynamic, shaking, pour, stirring, and blending methods are also briefly reviewed.
Films, Orientation
Authors: Hanschen Tom P.
Published: October 2003

This review examines commercial methods of stretching polymeric films to achieve molecular orientation. Consideration is given to the initial extrudate and quenching methods. Stretching methods can be monoaxial, sequential biaxial, and simultaneous biaxial.
Phosgene
Authors: Dunlap Kenneth L.
Published: October 2003

Phosgene is a colorless liquid with a low boiling point. It is manufactured by the reaction of carbon monoxide and chlorine over activated carbon. It is a very toxic substance, and extensive safety procedures and equipment have been developed to help ensure its safe handling. Phosgene is an important and widely used intermediate for chemical synthesis. Its primary use is for the manufacture of polyisocyanates for the polyurethane industry. Phosgene is also used in the production of polycarbonate, chloroformates, agrochemicals, and intermediates for pharmaceuticals and dyestuffs.
Surface Properties
Authors: Koberstein Jeffrey T.
Published: October 2003

The properties of a polymer surface control many important industrial technologies because of their effects on such generic phenomena as wetting or spreading, adhesion, and release. The most important surface property for most applications is the surface tension, that is, the energy required to create an air–polymer interface or surface. This article reviews how the surface tension and other properties of an air–polymer interface depend on intrinsic factors such as the nature of the polymer, its end groups, and its molecular weight, as well as external factors such as temperature. Empirical methods for estimating surface tension and first principle methods for calculating surface tension are presented. Classical themodynamics pertaining to surface properties are presented to illustrate how surface tension is related to the work of adhesion and to the wetting of a polymer on a substrate. Surface properties are also described for heterogeneous polymers such as random, graft, and block copolymers; end‐functional homopolymers; and polymer blends. Theoretical frameworks and experimental data are presented to describe the following: the preferential surface segregation of the lowest energy component in these heterogeneous systems, how these segregation effects depend on molecular properties of the constituents, and how these systems reorganize when exposed to different environments. The most useful methods available for the measurement of polymer surface tension are discussed to conclude the article.
Perfluorinated Polymers, Tetrafluoroethylene–Perfluorovinyl Ether Copolymers
Authors: Gangal Subhash V.
Published: October 2003

Perfluoroalkoxy (PFA) fluorocarbon resins are designed to meet industry needs in chemical, electrical, and mechanical applications. These melt‐processible copolymers contain a fluorocarbon backbone in the main chain and randomly distributed perfluorinated ether side chains. A combination of excellent chemical and mechanical properties at evevated temperatures results in reliable, high performance service to the chemical processing and related industries. Chemical inertness, heat resistance, toughness and flexibility, stress‐crack resistance, excellent flex life, antistick characteristics, little moisture absorption, nonflammability, and exceptional dielectric properties are among the characteristics of these resins. These resins are produced by copolymerizing tetrafluoroethylene and perfluorovinyl ether in aqueous or nonaqueous media. The polymer is separated and converted into various forms, such as extruded cubes, powders, beads, or dispersions. PFA resins are fabricated by the conventional melt‐processing techniques used for thermoplastics. A general‐purpose grade is designed for a variety of molding and extrusion applications such as tubing, shapes, molded parts, and insulation for electrical wire and cables. Valves and fitting liners are made by a transfer‐molding process. Some grades of this polymer are suitable in semiconductor manufacturing, fluid handling systems for industry or life sciences, and instrumentation for precise measurements of fluid systems.
Perfluorinated Polymers, Tetrafluoroethylene–Ethylene Copolymers
Authors: Gangal Subhash V.
Published: October 2003

Copolymers of ethylene and tetrafluoroethylene (ETFE) have been studied for more than half a century. However, modified ETFE are the products of real commercial value because they have good tensile strength, moderate stiffness, high flex life, and outstanding impact strength, abrasion resistance, and cut‐through resistance.Electrical properties include low dielectric constant, high dielectric strength, excellent resistivity, and low dissipation factor.Thermal and cryogenic performance and chemical resistance are good. This family of polymers can be processed by conventional methods such as melt extrusion, injection molding, transfer molding, and rotational molding. These polymers are synthesized in aqueous, nonaqueous, or mixed medium with free‐radical initiators. The polymer is isolated and converted into extruded cubes, powders, and beads or a dispersion. The general‐purpose resin is used for insulating and jacketing low voltage power wiring for mass transport system, wiring for chemical plants, and control and instrumentation wiring. It is aslo used to produce sockets, connectors, and switch components. These resins porvide good service in seal glands, pipe plugs, corrugated tubing, fasteners, and pump vanes.
Modeling of Polymer Processing and Properties
Authors: Termonia Yves
Published: October 2003

Kinetic Monte‐Carlo lattice models are presented for the study of the effect of processing conditions on polymer structure and properties. These models clearly reveal the importance of molecular weight, molecular weight distribution, and density of entanglements in controlling the drawability of flexible polymers in the solid state. They have also been used to describe the processes of coagulation and quenching of a polymer solution and they are able to reproduce the wide variety of different polymer structures that can be obtained. Finally, turning to the processing of fibers into planar fibrous materials such as papers and nonwovens, it is shown that kinetic Monte‐Carlo models can be equally successful at predicting their mechanical and permeability properties.
Block Copolymers, Ternary Triblocks
Authors: Abetz Volker
Published: October 2003

This article deals with the self‐assembly of amorphous ABC block copolymers on different levels of hierarchy. After a short general introduction some theoretical background for microphase‐separated block copolymers is given, including the weak and strong segregation limits. Then the influence of the composition and topology on the morphologies of linear and star terpolymers are dealt with, and also the influence of chemical modifications of particular blocks on the morphology is discussed. Finally, the article concludes with investigations on superlattices formed by blends of microphase‐separated block copolymers. This higher level of structural hierarchy can lead to new symmetries such as noncentrosymmetric periodic lamellae or to morphologies showing macrophase separation within a microphase‐separated matrix.
Adhesive Compounds
Authors: Yorkgitis E. M.
Published: October 2003

Adhesives comprise one of the chief classes of polymer‐based products. Adhesive bonding is the method of choice for joining many materials, and adhesives see expanded use on a yearly basis because of their versatility and cost‐effectiveness. The market economics of adhesives is summarized and updated. Practical principles of adhesive bonding and formulation are briefly reviewed. Methods of dispensing or applying adhesives are explained in general terms. The many ways in which adhesives can be classified is covered with an emphasis on the physical forms and types of adhesives. The various chemistries used to make pressure‐sensitive, hot‐melt, solvent‐ and water‐based, structural, and natural product adhesives are described in some detail relative to the major constituents commonly used in each as well as the various minor constituents. The general advantages of each class of adhesive are provided. General comments on formulation and the role of the formulator in bringing adhesives to market concludes the article.
Initiators, Free‐Radical
Authors: Myers Terry N.
Published: October 2003

Most commercial free‐radical applications employ initiators such as peroxides and azo compounds. Lesser amounts of carbon–carbon initiators and photoinitiators and high energy ionizing radiation are also used commercially to generate free radicals. The chemical initiators are substances possessing labile oxygen–oxygen, carbon–nitrogen, or carbon–carbon covalent bonds that under certain thermal, chemical, or photochemical conditions undergo homolytic scission of the labile bond to produce free radicals. The free radicals produced are useful in many industrial chain reactions, eg, halogenations, additions to carbon–carbon double bonds, polymerizations of vinyl monomers, grafting reactions, curing of rubbers and unsaturated polymers, cross‐linking of polyolefins, modification of polyolefins, and reactive processing.

In this article free‐radical initiator decomposition pathways are reviewed. Initiator reactivity is related to chemical structure and to first‐order decomposition parameters such as temperature, frequency factor, and activation energy. Reactivity of derived free radicals is also related to structure and to the occurrence of secondary reactions such as β‐scission and induced decomposition. The energy and the chemical properties of the free radicals determine commercial utility; thus the interrelation of initiators, their kinetics, and the radicals produced provide guidelines for initiator selection.
Langmuir–Blodgett Films
Authors: Lee Christine M. , Talham Daniel R.
Published: October 2003

Langmuir–Blodgett (LB) films provide the opportunity to control the structure of thin films at the molecular level. LB films can be prepared from amphiphilic derivatives of a wide range of functional molecules. Preparation techniques are discussed in this article. The architectural control obtained from the LB technique allows arranging these molecules so that their optical, electrical, and chemical behavior can be controlled. Applications are numerous for such manipulations, and many conceivable uses have already been investigated. There is, yet, much room for improvement and adaptation in the method to prepare even more technologically advanced devices. LB films are the consequence of an age‐old observation, and the technique enjoys a promising future.
Piezoelectric Polymers
Authors: Harrison J. S. , Ounaies Z.
Published: October 2003

Piezoelectric polymers have been known to exist for more than 40 years, but in recent years they have gained notoriety as a valuable class of “smart materials.” This article details the current theoretical understanding of the origin of piezoelectric and ferroelectric phenomena in polymers and presents the state‐of‐the‐art in piezoelectric polymers and emerging material systems that exhibit promising properties. Key characterization methods, fundamental modeling approaches, and applications of piezoelectric polymers are discussed.
Polycarbosilanes
Authors: Matsumoto Kozo
Published: October 2003

This article is an overview of polycarbosilane science. Comprehensive reviews of poly(silylenemethylene)s, poly(silyleneethylene)s, poly(silylenetrimethylene)s, poly(silylene‐2‐butenylene)s, poly(silylenevinylene)s, poly(silyleneethynylene)s, and poly(silylenearylene)s are offered, with surveys of some other carbosilane polymers. A synopsis of carbosilane dendrimers is also provided.
Conductive Polymer Composites
Authors: Lu Daoqiang , Luo Shijian , Wong C. P.
Published: October 2003

Polymeric materials can be made electronically conductive by adding conductive filler. These materials are called electrically conductive polymer composites. Since their introduction, the electrically conductive polymer composites have been widely used for electromagnetic radiation shielding, heaters, antistatic articles, resistors, and assembling electronic device components, etc. This article reviews two special conductive polymer composites. One is electrically conductive adhesive, which is used to replace tin–lead solder for microelectronic packaging application. The other is conductive polymer composites with large positive temperature coefficients, which can be used for resettable fuses, self‐regulating heaters, etc.
Biotechnology Applications
Authors: Galaev I. Yu. , Mattiasson B.
Published: October 2003

Stimuli‐responsive polymers undergo reversible phase separation from aqueous solutions triggered by small changes in the environment. The polymers are used in bioseparation (affinity precipitation, aqueous two‐phase polymer systems, smart chromatographic matrices responding to temperature) for production of smart surfaces for the mild detachment of cultivated mammalian cells, as a “chemical valve” regulating porosity of the system, for production of reversibly soluble biocatalysts, as drug‐delivery systems, and for the development of bioanalytical systems.
Molecularly Imprinted Polymers
Authors: Hart Bradley R. , Shea Kenneth J.
Published: October 2003

Molecular imprinting is a method with which materials containing highly specific recognition sites with high affinities for a wide range of organic compounds can be made. Since its inception, the number and types of monomers and templates that have been used successfully has increased dramatically. In addition, our understanding of the mechanisms through which the materials operate is increasing. Some areas of application have become well developed and commercial applications are on the horizon. The applications discussed in this article include separation technology, sensors, catalysis, and antibody and receptor site mimics.
Magnetic Polymers
Authors: Rajca Andrzej
Published: October 2003

Technologically important magnetic properties, especially ferromagnetism, are associated with metallic and inorganic materials based on elements with partially filledd‐ andf‐shells. In the past 15 years, the realm of magnetic materials has been expanded to organometallics, organic molecular solids, and most recently, organic polymers. This article reviews recent advances in the area of organic polymers with magnetic properties, including recent discovery of magnetic ordering in a conjugated organic polymer.
Gene‐Delivery Polymers
Authors: Pack Daniel W.
Published: October 2003

Human gene therapy promises to provide unparalleled treatments for afflictions ranging from cystic fibrosis to cardiovascular disease to cancer. The development of safe and efficient methods for delivery of genetic material to specific cells within the body has been a limiting factor in implementation of this technology. Delivery methodologies have included the use of recombinant viruses and synthetic materials, especially cationic polymers. While viruses are by far the most efficient delivery vehicles currently available, polymers exhibit several properties—including very flexible chemistry, potential for biocompatibility, simplicity, and inexpensive synthesis—that make them excellent candidates for the gene delivery vehicles of the future. However, polymers are typically several orders of magnitude less efficient than viruses and are generally considered unacceptable for human gene therapy. Much work is underway to design and synthesize improved polymers for gene delivery applications. This article summarizes the important criteria for an ideal gene delivery vehicle in terms of the potential barriers that must be overcome. Further, the current state of the polymer‐mediated gene delivery field is reviewed and several new classes of polymers, specifically designed for human gene delivery, are described.
Liquid Crystalline Thermosets
Authors: Douglas Elliot P.
Published: October 2003

Liquid crystalline thermosets are a new class of materials currently under investigation in a number of research laboratories. Various types of these materials have been described, including liquid crystalline thermosets with epoxy, acrylate and methacrylate, maleimide and nadimide, vinyl, isocyanate and cyanate ester, and ethynyl end groups. These materials have two structural features, a cross‐linked network and liquid crystalline order, which can have a profound influence on each other. The formation of a network during the cross‐linking reaction can have a strong influence on the liquid crystalline structure of the final cured material. In addition, the liquid crystalline structure can have a strong influence on the kinetics of the cure reaction. The liquid crystalline structure also affects the properties of the cured material. For example, fracture toughness is increased and permeability to various liquids is decreased, although the nature of these changes depends on the liquid crystalline phase and the exact morphology of the system. Liquid crystalline thermosets may also be oriented using external fields, such as surfaces, electric fields, and magnetic fields. Orientation has the potential to provide a new processing route for thermosets, leading to unique properties unattainable with conventional thermosets.
Controlled Release Technology
Authors: Kumar Neeraj , Chaubal Mahesh , Domb A. J. , Majeti Ravi Kumar N. V.
Published: October 2003

Controlled release technologies present an invaluable scientific and practical tool for improving performance and safety of drugs. These technologies involve designing the system of materials/drugs/site of action in such a way that barriers surrounding the drug to deliver the latter act with efficacy and safety of the drug at the optimum time and the rate needed. Advances in polymer science have led to the development of several novel drug delivery systems. A proper consideration of surface and bulk properties can aid in designing of polymeric systems for various drug delivery applications. This article is an overview of polymeric controlled release technology starting from fundamentals to applications.
Structural Representation of Polymers
Authors: Schultz John L. , Wilks Edward S.
Published: October 2003

Representations of polymer structures, by both source‐based and structure‐based methodologies, are discussed, compared, and contrasted. The guidelines, called principles by Chemical Abstracts Service and recommendations by the International Union of Pure and Applied Chemistry, on how to represent polymers by both methodologies are explained. Examples are given of how source‐based and structure‐based representations of polymer structures are stored in Chemical Abstracts Service's Registry File, accessible via their Scientific and Technical Information Network, and guidance on how to search for different types of polymers is included. This article covers regular, single‐strand, organic polymers as well as more complex types such as post‐treated; alternating and other periodic; block, comb, and graft; double‐strand (ladder); cross‐linked; dendritic; hyperbranched; hyper‐cross‐linked; inorganic and quasi‐inorganic; oligomers and telomers; siloxanes and silicones; star and star‐block. Stereochemistry in polymers is discussed briefly.
Metallocenes
Authors: Wasserman Eric Paul
Published: October 2003

Ever since their discovery by Sinn and Kaminsky in 1979, the family of high activity homogeneous olefin polymerization catalysts known as “metallocenes” has been the subject of intense research and commercial development. While a structurally diverse group, metallocene catalysts are generally considered to have a few common features: a highly electrophilic, early transition metal or rare‐earth atom as the point of polymer chain attachment; a π‐bound cyclopentadienyl ring or isoelectronic analogue attached to this atom; and characteristically narrow distributions of polymer molecular weight and short‐chain branching. While polymerization of ethylene and propylene is reviewed in some detail, the nonpolymerization catalysis and (co)polymerization of functional monomers is also surveyed. The current commercial status of metallocene technology is also briefly discussed.
Heterophase Polymerization
Authors: Tauer Klaus
Published: October 2003

This article is an overview of heterophase polymerization techniques in liquid continuous media to prepare polymer dispersions. The common feature of heterophase polymerizations is the distinctive role that interfaces play during all stages and in all aspects of these processes. Accordingly, the heterogeneous nature and its influence on polymerization kinetics and product properties is emphasized rather than a successive treatment of various types of heterophase polymerization techniques such as suspension or emulsion polymerization. Thus, the focus is on colloid chemical and kinetic consequences of the compartmentalization during the polymerization processes.
Living Radical Polymerization
Authors: Klumperman Bert
Published: October 2003

Living Radical Polymerization (LRP) is the general name for a family of polymerization techniques. The techniques have in common that the propagating species is a free radical, and that an equilibrium exists between active (free radical) species and dormant species. Because of this equilibrium (nearly) all chains grow throughout the polymerization reaction. This leads to polymers with predetermined degree of polymerization and (usually) narrow molar mass distribution. A historical overview of the development of LRP is provided, and the three most important techniques are discussed in more detail. These three techniques are (1) nitroxide‐mediated polymerization (NMP), (2) atom transfer radical polymerization (ATRP), (3) reversible addition–fragmentation chain‐transfer–mediated polymerization (RAFT) The general kinetics and some boundary conditions for obtaining low polydispersity index (PDI) polymers are discussed. Further, the scope and limitations of the three major polymerization techniques are outlined.

Apart from the predetermined molar mass and the PDI, LRP is of particular interest in the synthesis of advanced architectures. These architectures include block copolymers, star‐branched polymers, telcchelic polymers, gradient or tapered copolymers, etc. Among the major advantages of LRP is the fact that most of the benefits of free‐radical polymerization (FRP) are retained. Thus, the possibility to (co)polymerize functional monomers (hydroxyl, epoxy, amide, anhydride, etc) and the possibility to polymerize under nondemanding conditions are typical for FRP as well as for LRP.
Ziegler–Natta Catalysts
Authors: Chadwick John C.
Published: October 2003

This article describes the development and characteristics of Ziegler–Natta catalysts for the polymerization of ethylene, propylene, and other alpha‐olefins. Particular emphasis is given to state‐of‐the‐art MgCl2/TiCl4/donor catalysts for polypropylene, including current insight into mechanistic aspects of Ziegler–Natta catalysis in relation to catalyst performance and polymer molecular composition and properties.

Ziegler–Natta catalysts are multisite systems, in which the nature and the distribution of the active species can be steered to give polymers having different tacticity and molecular weight distributions. MgCl2‐supported catalysts have almost totally replaced the TiCl3catalysts used previously and have enabled the development of cost‐efficient bulk and gas‐phase polymerization processes. Spherical particle morphology and controlled particle size and porosity have been achieved and this has played an important role in the widespread application of these catalysts.
Ethylene Copolymers
Authors: Guest Martin J. , Cheung Y. Wilson
Published: October 2003

Copolymerization of ethylene (E) and styrene (S) has been enabled by developments in metallocene catalysts. An overview of copolymerization chemistry shows that catalyst structure and polymerization conditions have major influences on the production efficiency, product composition, and copolymer microstructure. Copolymers produced have included those with alternating (ES)nsequences; when these sequences are stereoregular, they can crystallize. Ethylene and styrene have been copolymerized with additional monomers, including dienes and α‐olefins.

Ethylene–styrene copolymers have been primarily produced via solution polymerization techniques. To date, the copolymers of major interest are essentially atactic, and contain up to about 50 mol% styrene. These copolymers range from highly crystalline to essentially amorphous, dependent upon comonomer composition ratio. The structure–property relationships presented include thermal properties, viscoelastic behavior, mechanical properties, and rheology/processability. Materials engineering is important regarding the utility of poly(ethylene‐co‐styrene). The copolymers are compatible with bitumens, plasticizers, and tackifiers. Blend systems with copolymers as components and copolymer/filler composites are discussed. Potential markets/applications for poly(ethylene‐co‐styrene) have been identified from literature sources, and include foams.
Template Polymerization
Authors: Połowiński Stefan
Published: October 2003

Template polymerizationis defined asa process of polymer synthesis in which the monomer units are organized by a preformed macromolecule (template) and refers to one phase systems in which the monomer and template are soluble in the same solvent. The general characteristics of template polymerization, polycondensation, and copolymerization are discussed. Associated kinetic, molecular, and tacticity effects are also considered. Typical examples of template polymerization systems and products of template polymerization such as interpolymer complexes and ladder‐type polymers are presented. Possible applications are briefly described.
Phase Transformation
Authors: Binder Kurt , Müller Marcus
Published: October 2003

This article briefly summarizes some key theoretical concepts about phase transformations, discusses the extent to which they differ from related phenomena in other materials, and mentions a few typical experiments to introduce the main techniques used to study such phase transitions. Phase transformations of polymeric materials, such as unmixing of a polymer solution or polymer blend, or the crystallization of a polymer melt or its glass transition into an amorphous structure, are very common phenomena and have important applications.

Polymers in the solid state rarely reach full thermal equilibrium. Of course, all amorphous materials can be considered as frozen fluids, whereas polymers typically are semicrystalline, where amorphous regions alternate with crystalline lamellae, and the detailed structure and properties are history‐dependent. Such out‐of‐equilibrium aspects are out of the scope of the present article, which rather emphasizes general facts of the statistical thermodynamics of phase transitions and their applications to polymers in fluid phases.
Gel Point
Authors: Henning Winter H.
Published: October 2003

The liquid‐to‐solid transition in soft materials is marked by the gel point (GP). AT GP, long‐range connectivity in the material diverges to infinite size. The connectivity can have many origins, mostly either network formation or growth of glassy states that suppress the local mobility. Growth of connecticity is slow for most soft materials, while loss of connectivity (reverse gelation) can occur rather rapidly. Materials at their GP, called “critical gels” exhibit universal features that merge liquid and solid characteristics into a unique behavior: (
1
) stress requires an infinite time to relax and (
2
) relaxation occurs in a broad, self‐similar distribution of shorter modes. These features become apparent in rheological experiments that probe the long‐time behavior. The broadening of the spectrum has been attributed to two effects, the broadening of the cluster size distribution (molecular clusters, supramolecular clusters) and the branching of the clusters. Many soft materials, namely in food, pharmaceuticals, photographic media, adhesives, vibration dampeners, and superabsorbers (to name a few), are close to their GP, ie, they are liquids just before reaching their GP or they are solids that have barely passed the GP. The GP serves as reference for developing such materials.
Carbon Black
Authors: Wang Meng‐Jiao , Gray Charles A. , Reznek Steve R. , Mahmud Khaled , Kutsovsky Yakov
Published: October 2003

Carbon black is a generic term for an important family of products used widely to modify the mechanical, electrical, and other physical properties of the medium in which it is dispersed. It is the most widely used nano‐material, with particle dimensions ranging from tens of nanometers to a few hundred nanometers. It plays a major role in elastomers, plastics, paints and inks as a reinforcing agent, a black pigment, and an electrically conductive material. This article is an extensively revised and updated version of an article published in 1992. It provides a comprehensive review of the technical and commercial aspects of carbon black usage. The history of carbon black, its microstructure, chemical composition, morphology, surface activity, and characterization are discussed. The mechanism of carbon black formation and its manufacture, including oil‐furnace black process, thermal black process, acetylene black process, lampblack process, and impingement black process, is described. A separate section is included on newly developed surface modification technologies and related commercial applications. One section is devoted to the properties, applications, and markets of the two main types of carbon blacks, rubber grades, and special grades. The rubber grades are primarily used as a reinforcing agent in tire and other rubber products to improve their mechanical properties. Most of the special grades are manufactured to meet specific product specifications for imparting certain properties required by the end‐use products, such as dispersion, pigmentation, and electrical conductivity. The health, safety, and environmental section includes a summary of recent health studies.
Polyester Films
Authors: MacDonald W. A.
Published: October 2003

The manufacturing process for poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) films is described. The film properties of PET and PEN films are discussed and compared. The methods used to modify film properties such as coating, fillers, and coextrusion and how the properties of polyester films are exploited in application are described.
Silane Coupling Agents
Authors: Blum Frank D.
Published: October 2003

Silane coupling agents are often used to improve the properties of composite materials by modifying interfaces. The coupling agents typically contain trichloro, trimethoxy, or triethoxy groups attached to silicon at one end. These inorganic groups hydrolyze, condense, and adsorb at oxide interfaces to form a bond with the coupling agents. The other end of the molecule typically contains organofunctional groups that are chosen to react or to be compatible with an organic polymer resin. The coupling agents are particularly effective for improving the mechanical properties of composites when water is present. The appropriate selection of the coupling agent is of importance for optimal improvement of the mechanical properties of the composite materials. Factors to be considered are the type of chemical bonding desired, compatibility between the coupling agent layer and resin, and the mechanical properties of the interphase.
Environmentally Degradable Plastics
Authors: Stevens E. S.
Published: October 2003

The relationship between plastics and the environment is a topic of current interest to government agencies, the plastics industry, and the general public. During the 1990s, standardization organizations (ASTM, CEN, ISO) defined terms such as degradable, biodegradable, and compostable, and developed specifications for labeling prerequisites; ISO began to formulate life‐cycle assessment (LCA) programs. In some applications (eg, agricultural mulching film and compost bags) biodegradability and compostability serve intrinsic functional purposes; in others (eg, packaging, food service items, and consumer products) they allow disposal by composting, thereby avoiding incineration and landfilling.

Activated polyolefins degrade, but by current standards are not compostable. Petroleum‐based synthetics that are biodegradable and compostable include poly(vinyl alcohol), poly(glycolic acid), and polycaprolactone; synthetic copolyesters and poly(ester amides) are biodegradable, some are compostable. Commercialized polymers obtained from renewable resources (biomass) include cellulose, starch, poly(lactic acid), microbial polyhydroxyalkanoates, and polymerized vegetable oils. LCA has shown that many of these polymers have lower environmental impacts than conventional petroleum‐based plastics. Their properties can be varied through the use of derivitization, additives, and blends. Many other polymeric materials have been studied in the laboratory but not yet commercialized. The future prospects for green plastics depend on technological developments that enhance environmental attributes, improve performance, and lower costs.
Poly(p‐phenylenevinylene)
Authors: Wolf Michael O.
Published: October 2003

This article provides an overview of the methods by which PPV and some of its derivatives may be prepared, the physical and electronic properties of these materials, and the applications that are being explored.

Poly(p‐phenylenevinylene) (PPV) and its derivatives are polymers with potential applications in optoelectronic devices. PPV is a conjugated polymer. Many conjugated polymers are known and exhibit remarkably high electrical conductivities when oxidatively or reductively doped. Much of the early research on PPV focused on the relatively disappointing properties of the doped material; however, interest in this material was reawakened in 1990 when it was discovered that films of undoped PPV could be used as the emitting layer in organic electroluminescent (EL) devices. This discovery stimulated intense research in the area, including many fundamental studies of the properties of PPV and its derivatives, and extensive academic and industrial interest in the applications of the materials.
Nanocomposites, Metal‐Filled
Authors: Carotenuto G. , Nicolais L.
Published: October 2003

Because of surface effects and the dramatic changes in properties that occur when the critical length governing some phenomenon (eg, magnetic, structural) becomes comparable with size, metal clusters have unique characteristics (eg, plasmon absorption, near‐IR photoluminescence, superparamagnetism). The embedding of metal clusters into polymeric matrices represents a simple way to take advantage of mesoscopic metal characteristics. Polymer‐embedded metal clusters represent a new class of advanced composite materials that may find important applications in different technological areas.
Thermochromic Polymers
Authors: Seeboth Arno , Lötzsch Detlef
Published: October 2003

This paper presents an overview of the preparation, characterization, and potential application of thermochromic polymers. The termthermochromicdescribes materials which vary their color, color intensity, or transparency in response to temperature changes. Thermochromic effects have been observed in different types of polymer systems such as pure polymers, cross‐linked polymeric networks, polymer blends, and gels, whereby the origin of the thermochromic effect can be multifarious. The color can appear owing to absorption or owing to the physical effect of materials on light. The latter is called physical color and includes scattering and diffraction of light. Research in the field of thermochromic polymers has led to the discovery of novel effects producing thermochromism as well as to the development of thermochromic polymers with improved material properties. Moreover, rational design and optimization with a view to specific applications has started. Selected examples of the different classes of thermochromic polymers are presented and their characteristic material properties and potential applications are pointed out.
Imaging Applied to the Geologic Sciences
Authors: Arvidson Raymond E. , Guinness Edward A. , Stein Thomas , Niebur Curt , Larsen Kristopher
Published: October 2003

Geology can be defined as the study of the nature and dynamics of planetary surfaces and interiors. This field of endeavor has expanded greatly over the past few decades to include study not only of the Earth, but also of other objects in the solar system, focusing heavily on Earth's Moon, Venus, and Mars. Acquisition and analysis of imaging data have been central to increased understanding of planetary surfaces. In the case of the planets and satellites, imaging data have been of fundamental importance because of the very limited opportunities for human exploration, return of samples, or even detailedin‐situanalyses. For Earth, analyses of image data have been central to several emerging fields of interest. In this article, the focus is on key scientific objectives associated with the geology of the Earth and how appropriate imaging data sets will help meet those objectives. This focus is not meant to downgrade the importance of imaging in robotic or human exploration of the solar system. Rather it is meant to provide a coherent theme for the article and to delineate how imaging will help address a suite of fundamentally important objectives and challenges that face us over the next few decades.

The article begins with an overview of remote sensing as applied to geology, focusing on imaging applications. Summaries of objectives and tasks based in part on plans put together by the United States Geological Survey for the next decade follow. These plans both focus the key scientific areas of research within geology that have significant societal benefits and provide a coherent pathway for discussing uses of imaging in geology. Specific examples are given for the major objectives to illustrate the use of imaging techniques to address particular applications.