bluuebunny/crossref_metadata_2025 huggingface dataset:
Carbocationic Polymerization
Authors: Puskas Judit E. , Kaszas Gabor
Published: October 2003

This article summarizes fundamental and general aspects of carbocationic polymerizations, with a historical overview and up‐to‐date references. Following general considerations, the basic elements of carbocationic polymerization, such as monomers, initiating systems, solvents, and temperature, are discussed. Special attention is given to carbocation stability and monomer nucleophilicity, and dynamic interactions. The section on the kinetics of carbocationic polymerization presents current understanding of the elementary reactions—initiation, propagation, termination, and transfer reactions, and copolymerization. Controlled (living) carbocationic polymerization is discussed in a separate section. Finally, industrial carbocationic polymerizations are reviewed.
Cellular Materials
Authors: Imeokparia Daniel D. , Suh Kyung W. , Stobby William G.
Published: October 2003

This article is concerned with the general theory of expansion, manufacturing processes, properties, and applications of foamed (cellular) plastics. The high strength‐to‐weight ratio, excellent insulating properties, and cushioning properties of cellular plastics have contributed to the development and growth of the broad range of cellular plastics in use. The total usage of foamed plastics in the United States has risen from 1.4 million metric tons in 1982 to 2.2 million metric tons in 1992 and has been projected to rise to about 3.1 million metric tons in 2002.

The manufacturing processes for cellular polymers are described in terms of three classified methods on the basis of cell growth and stabilization processes. The properties of cellular plastics, including mechanical, thermal, electrical, and environmental aging properties, are summarized. A general discussion is given on the properties of cellular plastic necessary in many applications such as the comfort cushioning, thermal insulation, packaging, structural components, buoyancy, electrical insulation, and space‐filling markets. A brief discussion is also given on the process economics, raw materials, and energy considerations for the commercial products of primary importance.
Cellulose
Authors: French Alfred D. , Bertoniere Noelie R. , Brown R. Malcolm , Chanzy Henri , Gray Derek , Hattori Kazuyuki , Glasser Wolfgang
Published: October 2003

This article covers nomenclature, sources, preparation, uses, microcrystalline cellulose, structural chemistry, reactions, solvents, and liquid crystals. Cellulose for commercial purposes comes mostly from wood and cotton, whereas cellulose for research comes from bacteria, algae, and ramie (also a textile fiber). Preparation includes pulping and purification, with an alternative method of steam explosion. The pore structure of cellulose is mentioned, along with the buildup of cellulose molecules into entire fibers. Emphasis is given to cellulose crystal structure. Recent research has provided structures with much better resolution for two crystal forms. Most native cellulose is a mixture of two crystalline phases. Cellulose solutions are important to the rayon and cellophane industries, and new solvents are of interest because they may lessen pollution and might permit commercial production of stronger cellulosic materials through the formation of liquid crystals. Figures include the chemical and physical structures of the molecule, including in solution, X‐ray diffraction patterns, the structure of a microfibril, and the unit cell structures of cellulose I–IV.
Cellulose Fibers, Regenerated
Authors: Woodings Calvin
Published: October 2003

Fibers manufactured from cellulose are either derivative or regenerated; historically they are designated man‐made fibers and distinguished from fibers based on synthetic organic polymers. A derivative fiber is one formed when a chemical derivative of a natural polymer, eg, cellulose, is prepared, dissolved, and extruded as a continuous filament, and the chemical nature of the derivative is retained after the fiber formation process. A regenerated fiber is one formed when a natural polymer, or its chemical derivative, is dissolved and extruded as a continuous filament, and the chemical nature of the natural polymer is either retained or regenerated after the fiber formation process. The difficulties of making solutions of natural cellulose from which fibers can be spun has led to most fabricated cellulosic fibers being regenerated from more readily soluble derivatives of cellulose. It is the technology of making these fibers that is the subject of this article.

Textile fibers and filaments composed of regenerated cellulose are called rayons. In Europe the fibers are now generally known as viscose; the term viscose rayon is used whenever confusion between the fiber and the cellulose xanthate solution (also called viscose) is possible. In addition to the viscose process, the cuprammonium rayon and direct dissolution processes are also covered. Fiber properties and environmental and commercial issues are discussed.
Chitin and Chitosan
Authors: Hudson Samuel M. , Jenkins David W.
Published: October 2003

Chitin is a structural polysaccharide widely found in nature. It occurs as highly ordered microfibrils in many species such as yeast, fungi, insects, and marine invertebrates. Chitin is a homopolymer of 1‐4 linked 2‐acetamido‐2‐deoxy‐β‐D‐glucopyranose, although some of the glucopyranose residues are deacetylated and occur as 2‐amino‐2‐deoxy‐β‐D‐glucopyranose. When chitin is deacetylated to more than 50% of the free amine form, it is referred to as chitosan. Biopolymerization of chitin is by the activated monomerN‐acetyl‐uridine diphosphate‐glucosamine by synthase enzymes. The isolation of chitin is commonly from the shell fish waste of the shrimp and crab industries. Chitin is insoluble in most common solvents, whereas chitosan dissolves in many common aqueous acid solutions. Industrially, chitin is mainly used as a powder and as a precursor to chitosan. Applications of chitosan are found in many primary industries such as agriculture, paper, textiles, and wastewater treatment. Chitosan has good film and fiber forming properties. Many medical and pharmaceutical uses of chitosan have been described. It has also become a popular nutritional dietary additive.
Chromatography, Size Exclusion
Authors: Dawkins John V. , Meehan Elizabeth
Published: October 2003

Developments in size exclusion chromatography for characterizing polymers are outlined. Particular attention is directed toward understanding the mechanisms that contribute to separations of polymers in both organic and aqueous eluents. In addition to identifying the details of an exclusion mechanism controlled by hydrodynamic volume, secondary mechanisms such as adsorption and ionic interactions are considered. Column performance defined by specific resolution is introduced together with the factors and experimental parameters that need to be assessed for high resolution and high speed separations. The application of polymeric stationary phases for use in high performance separations is described emphasizing the role of column packing parameters such as pore size and particle size distribution. An overview of instrumentation employed in current methodology is provided, focussing on technology for concentration and molecular weight sensitive detectors. The use of combinations of detectors for samples with more than one heterogeneity is briefly reviewed. Data treatment for conversion of chromatograms to molecular weight distributions is described, including a survey of a range of calibration methods. These treatments also permit the determination of average molecular weights.
Coatings
Authors: Wicks Zeno W.
Published: October 2003

Various aspects of coatings are covered: (1) film formation from solutions of thermoplastic polymers, thermosetting coatings, and latex coatings; (2) flow of resin solutions and of dispersed phase systems; (3) mechanical properties of coatings are discussed with emphasis on understanding the basic principles involved in formability, flexibility, and abrasion and mar resistance of films; (4) exterior durability, adhesion, and corrosion protection by coatings; (5) the chemistry and properties of the polymers and cross‐linkers used in binders; (6) solvent characteristics and volatile organic compound emissions; (7) color and gloss of films, pigment dispersion, and pigment volume relationships; and (8) the causes and possible remedies for film defects. Two hundred fifty‐seven references are provided.
Coextrusion
Authors: Dooley Joseph , Tung Harvey
Published: October 2003

Multilayer coextrusion of thermoplastic film and sheet is an important plastic fabrication process, providing large growth opportunities for the plastics industry, challenging such traditional materials as metals, glass, paper, and textiles. The attraction of coextrusion is both economic and technical. It is a single‐step process starting with two or more plastic materials that are simultaneously extruded and shaped in a single die to form a multilayer sheet or film, avoiding the costs and complexities of conventional multistep lamination and coating processes. Coextrusion readily allows manufacture of products with layers thinner than can be made and handled as an individual ply. Coextrusion has been used commercially to manufacture unique films consisting of hundreds of layers. This article summarizes coextrusion technology, including coextrusion dies, polymer specifications for coextrusion, recycling of multilayer scrap, and some commercial applications.
Colorants
Authors: Heitzman Scott
Published: October 2003

Color is an important component of plastics. Traditionally colorants in plastics were used to imitate the materials they may have been replacing: glass, wood, marble, and metals. Today the role of colorants has been expanded to include everything from a designers desired appearance or image to trademarking a product. In bright detergent bottles, the color in the packaging will not only attract customers to a shelf but also leave them with an image of how the product will perform. Colorants are also used to enhance the functional capabilities of plastics. Improving conductivity and uv resistance are a couple of examples.
Coloring Processes
Authors: Heitzman Scott
Published: October 2003

This article provides a basic understanding of how plastic materials are colored. A variety of colorants, equipment, and processes are briefly reviewed.
Combinatorial Methods for Polymer Science
Authors: Meredith Carson , Smith Archie P. , Crosby Alfred J. , Amis Eric J. , Karim Alamgir
Published: October 2003

This article presents recent advances in which combinatorial methodologies have been used for efficient measurement of chemical and physical properties of polymers over large regimes of variable space. Methodologies for both synthesis and characterization allow for both materials discovery and discovery of new models and structure–processing–property relationships. Polymer synthesis with combinatorial methods relies primarily on reactant mixing and diversity to create discrete libraries for investigating reactant structure and composition variations. In the future, techniques will be developed to allow library variation in processing variables like temperature, UV exposure, and pressure during synthesis. Several recent developments are presented in the combinatorial characterization of polymers, using high throughput libraries of films and coatings. As examples, four novel techniques are developed for preparing continuous gradient polymer libraries with controlled variations in temperature, composition, thickness, and substrate surface energy. The use of these new library techniques facilitates characterization of polymer blend phase behavior, thin‐film dewetting, block copolymer order–disorder transitions, and polymer adhesion.
Composites, Fabrication
Authors: Goldsworthy W. Brandt , Dawson Donna
Published: October 2003

As the value of fiber‐reinforced composite materials became apparent in the last half of the twentieth century, the processes used to fabricate parts from these materials evolved from operations relying on manual labor to manufacture by sophisticated, computer‐controlled equipment. Although hand lay‐up and spray‐up in open molds is still common for fabricating large nonstructural parts, the trend is to closed systems and automated production equipment designed to meet product application requirements. Early moves to automation included equipment for preforming the part shape from dry fiber reinforcements and devices for combining materials into sheet and bulk molding compounds that could be rapidly processed in compress presses or by automated injection‐molding machines. All these fabrication processes and other early forms have continued to evolve, and automated pultrusion, filament winding, tape laying, fiber placement, pulforming, and specialty dedicated machines have been invented. Over time, processing parameters have been refined and optimized, and computer controls have been developed that have enabled composites fabrication of primary structural elements for infrastructure, building construction, and other high volume markets.
Conformations and Configuration
Authors: Mattice Wayne L. , Helfer Carin A.
Published: October 2003

The rotational isomeric state model uses information about the bond lengths, bond angles, preferred torsional angles, and energies for short‐range intramolecular interactions to quickly produce numerical values for conformational‐dependent physical properties of chains unperturbed by the excluded volume effect. This article describes the rotational isomeric state model and gives several illustrative examples of its application to polymers.
Degradation
Authors: Billingham N. C.
Published: October 2003

The degradation of polymers under a wide range of conditions is reviewed. Purely thermal degradation, in inert atmospheric conditions, defines the ultimate stability of a polymer in the absence of other degradative influences. The mechanisms of degradation are shown to include depolymerization, random scission, and rearrangement of functional groups. Their relative importance is dependent upon temperature and polymer structure.

Degradation in air is more relevant to service use of polymers and is shown to involve the formation and reaction of hydroperoxides; effects on mechanical properties are reviewed.

Photo‐oxidation is shown to be dependent on whether the polymer is intrinsically light absorbing or absorbs via chromophoric impurities. Photoinitiated generation of radicals leads to oxidation chemistry accompanied by photolysis reactions of the products.

Degradation by high energy radiation, hydrolytic degradation, and degradation by microorganisms (biodegradation) are briefly reviewed, as are methods of accelerating degradation.
Dental Applications
Authors: Culbertson Bill M. , Kerby Ronald E.
Published: October 2003

The various types of monomers and polymers and methods of polymerization used in dentistry are discussed, along with brief attention given to new areas of promise for preparing better materials for dental applications. Polymeric materials discussed in this article include impression materials, dentures and denture liners, artificial teeth, crown and bridge materials, mouth protectors, maxillofacial materials, restoratives (filling materials), such as glass‐ionomers or glass polyalkenoates, composites and compomers, adhesives, cements, and sealants. While enormous progress has been made in developing improved materials for meeting oral health needs, it remains clear that there are still many opportunities for development of improved materials for use in dental applications.
Dielectric Relaxation
Authors: Williams Graham
Published: October 2003

The dielectric properties of polymers, as complex permittivity ɛ(ω) and complex conductivity σ(ω), measured in the frequency range 10−6to 1012Hz, give information on (1) the reorientational motions of chain dipoles and (2) the translational motions of charged species (ions, electrons). The theory of dielectric relaxation and charge conduction is outlined for dipolar and electrolyte systems and experimental dielectric data for amorphous, crystalline and liquid‐crystalline polymers, and polymer electrolytes are summarized.
Elasticity, Rubber‐like
Authors: Queslel J. P. , Mark J. E.
Published: October 2003

Long, flexible polymer chains with high mobility and weak interchain interactions may be covalently linked together to form network structures. These materials exhibit a unique behavior called rubber‐like elasticity, which is high and reversible deformability (up to 10 times the original dimension). The origin of elasticity at thermodynamic equilibrium is the decrease in entropy of the chains between cross‐linking points resulting from the extension. Elastomers therefore follow thermodynamic laws similar to those for gases. There is a minor intramolecular energetic component in the retractive force which can be extracted from thermoelasticity experiments and is related to conformational energy changes of the chains.

Most of the theoretical and experimental works in the field of rubber‐like elasticity have been devoted to the characterization of network structures. Molecular models based on statistical mechanics have been applied to the analysis of equilibrium properties such as stress–strain measurements in uniaxial extension and swelling by a solvent. The real behavior of rubbers is between the predictions of the simple affine and phantom models and is well represented by molecular models which include entanglement constraints. These models associated with topological descriptions of networks are powerful tools to describe network structures.
Thermoplastic Elastomers
Authors: Holden Geoffrey
Published: October 2003

Thermoplastic elastomers are a rapidly growing part of the polymer industry. They combine the physical properties of rubbers with the ability to be processed on equipment designed for thermoplastics. This gives them two advantages over conventional rubbers—processing is much faster and scrap is recyclable. In addition, thermoplastic elastomers can be used to formulate adhesives, compatibilize and modify other thermoplastics, and modify asphalts. There are several types of thermoplastic elastomers. The most important are styrenic block copolymers, multiblock copolymers, and hard polymer/elastomer combinations. Most thermoplastic elastomers are multiphase systems, with one or more hard phases and an elastomeric phase. The properties of individual thermoplastic elastomers depend on the properties and proportions of the individual phases and on their morphology. This article reviews and compares the structure, synthesis, and properties of thermoplastic elastomers of all types. It includes details of their commercial uses, trade names, and consumption.
Electrically Active Polymers
Authors: Zarras Peter , Irvin Jennifer
Published: October 2003

In the years since the discovery of conductivity in polyacetylene, a tremendous amount of research has been devoted to the synthesis, characterization, and application development of electrically active polymers. This article reviews the theory of conduction in these materials and discusses the syntheses of the major types of electrically active polymers. Electrical conductivities of these polymers are presented along with stability and mechanical and optical properties. The unique combinations of properties in these materials have led to a wide range of practical applications, which are also discussed.
Electronic Packaging
Authors: Weber William D.
Published: October 2003

This article describes the chemistry, formulation, and processing methods of a variety of polymeric materials used in the assembly of common types of first level electronic packages.
Electrooptical Applications
Authors: Dalton Larry R.
Published: October 2003

An overview of organic electronic electrooptic materials and the applications of those materials in prototype devices is given. This overview is set in the context of competing technologies. Quantum and statistical mechanical theoretical methods have recently provided significantly improved guidance in understanding organic electrooptic material structure/function relationships, leading to the systematic increase in electrooptic activity of such materials to values 15 times larger than the current commercial standard lithium niobate. In addition to discussion of electro‐optic activity, auxiliary properties of bandwidth, optical loss, thermal stability, photochemical stability, mechanical properties, and processability are discussed. Since the year 2000, substantial advances have been achieved in the processing of organic electrooptic materials and the integration with disparate materials, e.g., silicon photonics. For example, cycloaddition reactions have been employed to dramatically improve the thermal and photochemical stability of organic electrooptic materials. Integration of organic electrooptic materials with silicon photonic device structures have lead to new performance records, device concepts, and paves the way for the chipscale intergration of electronics and photonics. The fabrication of conformal and flexible devices have also been demonstrated with organic electrooptic materials and such materials have been amenable to production of complex photonic circuitry by nanoimprint/soft lithography techniques.
Ethylene Polymers,LDPE
Authors: Maraschin Norma
Published: October 2003

Low density polyethylene (LDPE) was the first thermoplastic polyolefin used commercially. It was discovered serendipitously in 1933 and was quickly utilized for radar sheathing during the war. LDPE, along with high density polyethylene (HDPE) and linear low density polyethylene (LLDPE), offers an unparalleled combination of low cost, ease of fabrication into a variety of end uses, and balance of physical properties. Polyethylene has displaced paper, metal, wood, and other materials of construction. LDPE is unique in its polymerization process. Free‐radical‐initiated polymerization is used to make LDPE, as compared to transition‐metal catalysis for HDPE and LLDPE. The free‐radical process leads to the unique molecular structure of LDPE: the presence of long‐chain branching. The long‐chain branching imparts unusual rheological behavior in both shear and extension. LDPE is used in a variety of applications, such as film, coating, molding, and wire and cable insulation. One of the reasons for its wide range of utility is its thermal stability and low toxicity.
Ethylene Polymers,LLDPE
Authors: Simpson D. M. , Vaughan G. A.
Published: October 2003

Ziegler–Natta‐catalyzed linear low density polyethylene (LLDPE) was first commercialized in the late 1970s. Unlike low density polyethylene (LDPE) produced in the high pressure process, Ziegler–Natta LLDPE has no long‐chain branching and has a narrower molecular weight distribution. LLDPE offers improved mechanical properties relative to LDPE. Metallocene‐catalyzed LLDPE(mLLDPE) resins, commercialized in the 1990s, are more compositionally homogeneous than LLDPE and have narrower molecular weight distributions. mLLDPE resins offer improved toughness properties relative to LLDPE. LLDPE resins are used in film, injection molding, blow molding, rotational molding, tubing, and wire and cable coating applications.
Extrusion
Authors: Rauwendaal Chris
Published: October 2003

Extruders are the most common machines in the plastics processing industry. Extruders are used not only in extrusion operations, but also in molding operations for example, injection molding and blow molding. Essentially every plastic part has gone through an extruder at one point or another; in many cases, more than once. In typical plastics extrusion processing a viscous melt under pressure is forced through a shaping die in a continuous stream. The feed stock may enter the extrusion device in the molten state, but more commonly it consists of solid particles that must be subjected in the extruder to melting, mixing, and pressurization. This article discusses extruders and the extrusion process in detail, including screw design, dies, mixing, melting, conveying, and degassing.
Fatigue Behavior of Polymers
Authors: Lesser Alan J.
Published: October 2003

Polymers and polymer‐based composites are increasingly displacing more traditional materials in a wide variety of engineering applications, and as such characterization of their fatigue behavior is of utmost importance. This article presents a general overview of the fatigue behavior of polymers. After a brief introduction that includes general terminology, the effects of test conditions (sample geometry, loading frequency, etc) are discussed. The effects of these conditions are also discussed in relevance to both the high cycle and low cycle fatigue behavior. Current models for predicting fatigue life are also reviewed, including cumulative damage theories and fatigue crack propagation models. Morphological and environmental effects are then discussed over a broad range of semicrystalline, amorphous, and modified polymer systems.
Fibers, Elastomeric
Authors: Boliek John E. , Denney Stacy A.
Published: October 2003

Elastomeric fibers are used commercially with hard fibers to provide stretch properties in textiles. The elastomeric polymer can be spun or cut into fibers that provide high elongation, low modulus, and good recovery from stretching. This article contains a description of the chemical composition, mechanical properties, and manufacturing methods of both natural and synthetic elastomeric materials. The economic aspects and commercial uses of the fibers in the textile industry are also described.
Films, Manufacture
Authors: Mount Eldridge M.
Published: October 2003

This article describes the methods and materials used in the commercial manufacture of polymer film products. Techniques for cast and oriented films using a variety of film‐making equipment are discussed and explained. The manufacturing process is broken down into a series of critical process steps to describe the function of each in the film‐making process and the impact of each on the film properties produced. Both extrusion and solvent‐based casting methods are described and a description of film‐finishing processes is given.
Fluorocarbon Elastomers
Authors: Worm Allan T. , Grootaert Werner
Published: October 2003

Fluorocarbon elastomers are fluorine‐containing cross‐linked amorphous polymers with a carbon–carbon backbone, which are designed for demanding service application in hostile environments. This article reviews the development history of fluorocarbon elastomers and the basic properties of the polymers. A brief manufacturing process for the polymers is presented along with processing information to convert the fluorocarbon elastomers into useful parts for various applications. Major uses and specifications for these uses are also presented.
Fracture
Authors: Kausch Hans‐Henning , Williams J. G.
Published: October 2003

Fracture of polymers is defined, and the essential phenomena of stable and unstable crack propagation are described and quantified using different concepts of fracture mechanics (linear elastic, confined plasticity, essential work of fracture). Particular attention has been given to a discussion of toughness and time‐dependent strength in terms of molecular parameters (eg, chain architecture, degree of entanglement, and molecular mobility) and of extrinsic variables (state of stress, rate of loading).
Gelatin
Authors: Keenan Thomas R.
Published: October 2003

The general subject, gelatin, is reviewed. Topics include the chemical composition and structure, physical and chemical properties, manufacturing methods, quality standards, analytical methods, and economic aspects.
Glass Transition
Authors: Bicerano Jozef
Published: October 2003

The glass transition is by far the most important one among the many transitions and relaxations observed in amorphous polymers. It has a drastic effect on the properties and processing characteristics of such polymers. It is important in semicrystalline polymers as well, but its role diminishes in importance with increasing crystalline fraction. The glass‐transition temperature (Tg) can be defined operationally asthe temperature at which the forces holding the distinct components of an amorphous solid together are overcome, so that these components are able to undergo large‐scale molecular motions, limited mainly by the inherent resistance of each component to such flow. The practical effects of the glass transition on the processing and performance characteristics of polymers, as well as the key aspects of its physics, are implicit in this definition.
Hardness
Authors: Calleja F. J. Baltá , Flores A.
Published: October 2003

Hardness is related to the resistance to local deformation of a material surface when indented, drilled, sawed, or abraded. Hardness is shown to be a mechanical property that provides a rapid evaluation of variations in polymer microstructure and morphology. Recent results concerning the microhardness of semicrystalline polymers and amorphous polymers relating to their structure are reviewed. The hardness of polymer glasses is first discussed in relation to their glass‐transition temperature. The development of structure during crystallization of glassy polymers as revealed by microhardness is brought up, and the hardness dependence on structural parameters such as the degree of crystallinity and the crystalline lamellar thickness is discussed. The close existing relationship between crystal hardness and melting temperature is presented. The correlation between microhardness of polymers and macroscopic mechanical properties (yield stress and Young's modulus) is highlighted. Some applications of the microhardness technique to polymer blends are also illustrated. In case of uniaxially oriented polymers, the indentation anisotropy is shown to provide information of the elastic response of the material along chain direction. Finally, the present review presents a comprehensive summary of the different methods used for the determination of hardness numbers, stressing the correlation between the hardness values resulting from different indenter geometries.
Heat Stabilizers
Authors: Mesch Keith A.
Published: October 2003

Halogenated polymers, particularly poly(vinyl chloride) (PVC) and poly(vinylidene chloride) (PVDE), require the use of heat stabilizers for effective processing. A variety of chemical classes are effective commercial heat stabilizers since they prevent the catastrophic degradation of these polymers at normal processing temperatures. The most effective class of heat stabilizers are the organotin mercaptides which can provide effective stabilization at dosages of the order of 1% or less of the PVC. Mixed metal products, consisting of combinations of calcium and zinc or barium, calcium and zinc soaps are used extensively in many flexible PVC applications. Heat stabilizers based on lead soaps and salts have been used commercially in PVC since the 1930s. Within the past few years. completely new heat stabilizer technologies, based on new organic compounds, have been introduced to the market for rigid PVC processing.

All heat stabilizers must provide several functions to stabilize PVC. They must neutralize hydrogen chloride, react with “defect sites” on the polymer to replace weakened carbon–chlorine bonds, prevent autoxidation effects, and disrupt conjugated polyenes on polymer. Reactive mechanisms for the major classes of technologies are reviewed. The heat stabilizers must be very cost‐effective in a highly competitive marketplace. Several suppliers and their major products are highlighted. Health and safety concerns for the major classes of heat stabilizers are also presented.
Hydrogels
Authors: Künzler Jay Friedrich
Published: October 2003

The area of hydrogel research has expanded dramatically in the last 10 years. This is due primarily to the fact that hydrogels have performed well for biomedical applications. This has been true for both the synthetic‐ and natural‐based hydrogels. This article focuses on the properties, classes, preparation, and application of hydrogels, with particular emphasis on the design of hydrogels for biomedical applications including ophthalmic, drug delivery, tissue engineering, and biosensors. Advances in the use of hydrogels to restore, augment, or replace the natural functions of the tissues and organs of the body are described.
Hyperbranched Polymers
Authors: Hult Anders
Published: October 2003

Hyperbranched polymers are polymers based on A

x

B‐monomers, ie, monomers having one B‐functionality and two or more A‐groups resulting in polymers with a potential branching point in each repeat unit. The properties of hyperbranched polymers have been shown to depend on several parameters, the most important ones ate the backbone and the end‐group structure in combination. The properties of hyperbranched polymers differ from linear polymers, for example, the solubility, which is much higher for hyperbranched polymers. Attachment of reactive end‐groups in various amounts leads to thermoset structures where the
T
g
and cross‐link density can be greatly varied for the same hyperbranched polymer.

A wide variety of hyperbranched polymers has been described in the literature. The synthesis of hyperbranched polymers can be done in several different ways. Classical condensation reactions are the most commonly used. The condensation reactions are either made in bulk or in solution where the A

x

B‐monomers are condensed by themselves or in combination with a B

y

‐core monomer. Another approach to the synthesis of hyperbranched polymers is the use of self‐condensing vinyl polymerization which is a way of using vinyl‐functional monomers to obtain hyperbranched polymers.
Impact Resistance
Authors: Yee Albert F. , Sue Hung‐Jue
Published: October 2003

The impact resistance of plastics is one of the most important tests for the practical use of these materials in various applications. The commonly used standard test methods and the testing equipment are described in some detail in this article. The test results are related to basic mechanical properties, where possible. In particular, a method for correlating notched impact results with a more rigorous test of energy release rate is described. A few examples of techniques for toughening plastics for greater impact or fracture resistance are given, along with the toughening mechanisms.
Injection Molding
Authors: Bozzelli John W.
Published: October 2003

Injection molding is an important thermal forming process for converting plastics, metals, ceramics, and wax into complex three‐dimensional products. Products range from large automotive body sections to microscopic gears and connectors. Applications appear limitless. Variations and extensions continue to evolve as this technology helps change the quality of life for the world's population. Injection molding consumed approximately 32 wt% of all plastics sold worldwide in the year 2000, roughly 4.95 × 107metric tons. This is an industry that will continue to grow and drive national economics.
Ionomers
Authors: Kim Joon‐Seop
Published: October 2003

Ionomers are polymers with low dielectric constants, containing a relatively small number of ionic groups, and they usually show unique physical properties, for example, two glass‐transition temperatures, small‐angle x‐ray scattering peaks, unusual transport properties, and high melt viscosity. Since the 1950s, the ionic interaction has been known as a very important factor in modifying polymer properties, and thus has received considerable attention from industrial as well as academic arenas. This overview begins with a brief discussion on three models of ionomers, ie, core–shell model, hard‐sphere model, and Eisenberg–Hird–Moore model, and then moves on to glass transitions. Styrene‐based ionomers, presently the best‐understood family of ionomers in terms of structure–morphology–property relationships, are described. There is a discussion of crystalline ionomers, block ionomers, and end‐capped ionomer systems. Three different types of plasticization using polar, nonpolar, and amphiphilic plasticizers are discussed. Some major applications of ionomers are selectively demonstrated very briefly.
Isocyanate‐Derived Polymers
Authors: Ulrich Henri
Published: October 2003

Homo‐ and copolymers derived from mono‐ and diisocyanates are treated in this article. Also, addition, condensation, and addition/condensation polymers derived from diisocyanates are included. Of commercial interest are segmented block copolyamide elastomers produced from methylene di‐p‐phenylene isocyanate (MDI) and macrodicarboxylic acids and dicarboxylic acids. This reaction polymerization is conducted in a vented extruder or in solution. Also, engineering plastics are obtained from diisocyanates and dicarboxylic acids. Poly(amide imides) and poly(imides) are produced from MDI and TDI (toluene diisocyanate) and trimellitic acid anhydride and isophthalic acid and dianhydrides, respectively. Heterocyclic polymers with useful high temperature properties made from MDI and suitable monomers by a polyaddition/condensation reaction are also included.
Lignin
Authors: Lebo Stuart E. , Gargulak Jerry D. , McNally Timothy J.
Published: October 2003

The word lignin is derived from the latin wordlignummeaning wood. It is one of the main components of all vascular plants and the second most abundant polymer in nature. This article describes the current understanding of the structure of this complex natural polymer. The number and types of different chemical bonds present in lignin are discussed as are the ways in which different lignins are identified and their distributions determined in plant tissues. Means for isolating lignin from wood are described, and the chemical and physical properties of the resulting lignins are reviewed. The various chemical and instrumental methods for characterizing isolated lignins are also discussed. The article concludes with a review of commercial lignin products, including a discussion of producers, production methods, modification reactions, and the many industries in which lignins are used.
Mass Spectrometry
Authors: Guttman Charles M.
Published: October 2003

The two most common methods used to place charged high mass molecules into the gas phase, electrospray ionization and matrix‐assisted laser desorption/ionization (maldi), are described. Because of its dominant use with synthetic polymers, the maldi method is described in detail, including sample preparation and data analysis and the problems this method poses. The time‐of‐flight mass spectrometry system is also described in detail since it is the most common in use today for synthetic polymers. A variety of applications of maldi to synthetic polymers is reviewed. This includes molecular mass distribution, molecular composition distribution of copolymers, polymer architecture, combinations of maldi‐tof‐ms with size exclusion chromatography and other forms of polymer chromatography, and the use of maldi in elucidating polymer chemical reaction mechanisms.
Membrane Technology
Authors: Baker Richard W.
Published: October 2003

During the past 40 years a number of large industrial and medical applications of membrane technology have been developed. Several tens of millions square meters of membrane are produced each year, and the total industry sales have grown to $2–3 billion in sales per year. Most of this industry is focused on the use of membranes as selective barriers for various separation processes. In some processes (microfiltration, ultrafiltration, dialysis), permeating species cross the membrane through tiny pores that block large solutes but allow others to permeate freely. In other processes (reverse osmosis, gas separation, pervaporation), the membrane pores are so small, about 5–10 Å in diameter, that they are within the range of thermal motions of the polymer chains that form the membrane materials. Separation then occurs because of differences in the solubility and mobility of the permeating solutes in the membrane material.

Early membranes were isotropic structures with uniform properties across the entire membrane, but now most membranes have an anisotropic structure consisting of a thin, dense selective layer, typically 0.1–2 μm thick, supported on a much more open, permeable layer (50–500 μm thick). This support layer provides sufficient mechanical strength to allow the membrane to be handled. By making the selective layer very thin, high permeation rates can be obtained. Even so industry processes often require very large membrane areas to perform the separation required; therefore, the technology to pack 10–100 m2of membrane in compact membrane modules of various designs has been developed. The techniques used to prepare membranes and membrane modules are described in this review.
Methacrylic Ester Polymers
Authors: Slone Robert V.
Published: October 2003

The commercially relevant and diverse chemistry of methacrylic ester polymers has encouraged their use in a remarkable variety of applications. Within this overview, particular attention is paid to the diversity of properties of methacrylic ester polymers and copolymers, the methods used to produce methacrylic ester polymers with specific properties, and the commercial applications of these materials.
Micromechanical Properties
Authors: Michler Goerg H.
Published: October 2003

An overview of successfully applicable techniques, particularly electron microscopy and scanning force microscopy, is given for the study of micromechanical mechanisms and properties in different polymers. Using modern developments in instrumentation, observation of realin situdeformation of structural details at the same place of a sample (eg, lamellae in polyethylenes) is possible.

Crazing formation in amorphous polymers (polystyrene, styrene–acrylonitrile, polycarbonate) and tough‐brittle transitions depending on deformation temperature are described. General mechanisms of toughening and, in particular, effects of rubber‐toughening (eg, role of particle size, shape, and particle cavitation) in amorphous (high impact polystyrene, acrylonitrile–butadiene–styrene) and semicrystalline polymers (toughened polyamide, polypropylene, and polyethylene blends) are discussed. Individual deformation steps are summarized in a “three‐stage mechanism of toughening.” Processes of deformation of amorphous, interlamellar regions, twisting and breaking off of lamellae in semicrystalline polymers can be directly shown. Unusually large plastic deformations can be revealed in di‐, tri‐, and star‐block copolymers with a new “thin layer yielding mechanism.”

Improved knowledge of micromechanical properties allows a deeper insight into the influence of morphology on mechanical properties and enables a defined modification of the morphology for improving the mechanical behavior of polymers for many practical applications, in a sense, “microstructural construction of polymers.”
Morphology
Authors: Bassett D. C.
Published: October 2003

Polymer morphology contains a uniquely detailed record of the history of a polymeric material, notably its crystallization and deformation and has been the key to understanding the fundamental aspects of such behavior. Early understanding gained from solution‐grown lamellae has been brought up to date for melt‐crystallized polymers. Spherulitic structure is now well characterized and is attributed to adjacent dominant lamellae repetitively branching and then diverging. The divergence is due to repulsion by cilia pressure and/or the nonparallel packing of initially rough surfaces. The differing environments and lamellar orientations within spherulites lead to an inherent, spatially varying, spread of properties characteristic of semicrystalline polymers. The latest findings, that fold surfaces generally transform behind the growth front and that a memory of the initial transverse morphology is retained on drawing to very high extensions, give key insights, respectively, into banded growth as a means of relieving surface stress and into the details of deformation.
Nomenclature
Authors: Schultz J. L. , Wilks E. S.
Published: October 2003

Polymer nomenclature is the naming of polymeric materials. The two principal approaches to nomenclature reflect the two methods used for graphical representation of polymers. Ideally, a structure‐based name should accompany a structure‐based representation of a polymer, while a source‐based name should accompany a source‐based representation. In practice, deviations from this ideal occur frequently, because the scientific community prefers structure‐based representations accompanied by source‐based names because they are easier to use. This article explains the principles of both structure‐based and source‐based nomenclature, and gives examples for a range of types, including regular linear single‐strand organic (random, statistical, block, graft, and modified), double‐strand organic (ladder and spiro), irregular single‐strand organic, inorganic, and coordination polymers. Stereochemistry in polymers is also covered. Nomenclature styles recommended by the International Union of Pure and Applied Chemistry and used by Chemical Abstracts Service are discussed.
Metal‐Containing Polymers
Authors: Abd‐El‐Aziz Alaa S.
Published: October 2003

The focus of this article is on the synthesis, properties, and applications of metal‐containing polymers. These polymers may be classified based on the types of metal–ligand bonding, and whether the metal is an integral part of the polymer backbone or pendent to the polymer backbone. The first class of polymers discussed are those with metals σ‐bonded to organic spacers in their backbones. Examples of metal–metal single and multiple bonds are also described. Metallocenes and coordination polymers are two classes of polymers where the metal is π‐coordinated to the organic ligands. The coordination of metals to porphyrins, phthalocyanines, Schiff base ligands, as well as to many other types of ligands are described. Another major class of polymers are those where the metal is pendent to the polymer backbone. These polymers include materials with metallic moieties π‐coordinated to unsaturated ligands in their backbones. Polymers with metallic moieties in their side chains are also described. A brief overview of star polymers and dendrimers is also included.
Phenolic Resins
Authors: Kopf Peter W.
Published: October 2003

Phenolic resins are a family of polymers and oligomers composed of a wide range of structures based on the various reaction products of phenols with formaldehyde. Applications vary from commodity construction materials to high technology applications in electronics and aerospace. Phenolic resins are prepared using acidic or basic catalysts. Weak Lewis acids, such as zinc acetate, are used for specialty resins. Phenolic novolaks are thermoplastic resins prepared from acid catalysts and a molar excess of phenol. They have a molecular weight of 500–5000 and a glass‐transition temperatureTgof 45–70°C. Novolak resins are typically cured with 5–15% hexamethylenetetramine as the cross‐linking agent. Resole‐type phenolic resins are produced with a molar ratio of formaldehyde to phenol of 1.2:1 to 3.0:1 and alkaline catalysts such as NaOH, Ca(OH)2, and Ba(OH)2. A typical resin has an initial molecular weight of 150 to perhaps 1500. For systems of unsubstituted phenols, the final cross‐link density is 150–300 atomic mass units per cross‐link. In 2001, worldwide consumption of phenolic resins exceeded 4 × 106t; slightly less than half of the total volume was produced in the United States, where the largest volume application is in plywood adhesives and accounts for ca 49% of U.S. consumption. As a mature industry, U.S. production of phenolic resins has paralleled the growth in the GNP. Applications for phenolic resins include coatings, adhesives, carbonless copy paper, molding compounds, bonded and coated abrasives, friction materials, foundry resins, laminates, air and oil filters, wood bonding, fiber bonding, composites, spherical fillers, and fibers. Factors contributing to the health and safety concerns of phenolic resins are related primarily to the presence of unreacted phenol and formaldehyde. Unreacted phenol in a resin can range from >10% for liquid resoles used in impregnation processes to <1% for novolaks intended for use as epoxy hardeners. Free formaldehyde can be 2–4% in liquid adhesives.