bluuebunny/crossref_metadata_2025_split huggingface dataset:
Antioxidants
Authors: Dexter Martin , Thomas Richard W. , King Roswell E. 
Published: October 2003

AbstractAntioxidants are used to retard the reaction of organic materials with atmospheric oxygen. Such reactions can cause degradation of the properties of the polymer, loss of flavor and development of rancidity in foods, and a change in lubricants. The need for antioxidants depends on the chemical composition of the substrate and the conditions of exposure. High concentrations of antioxidants, ie 0.5–2% based on the weight of the polymer, are used to stabilize polymers, such as natural rubber and polyunsaturated oils. Saturated polymers have greater oxidative stability and require relatively low concentrations of stabilizers, ie 0.01–0.05% based on the weight of the polymer. The mechanism by which an organic material undergoes autoxidation involves a free‐radical chain reaction. Thermally induced homolytic decomposition of peroxides and hydroperoxides to free radicals increases the rate of oxidation. Decomposition to nonradical species removes hydroperoxides as potential sources of oxidation initiators. The selection of an antioxidant or system of antioxidants is dependent upon the polymer and the anticipated end use. Low concentrations of antioxidants (<0.01%) are added to polyethylene and polypropylene after synthesis and prior to isolation so as to retard oxidation of the polymers exposed to air. Polyunsaturated elastomers are sensitive to oxidation. Antioxidants are added to the elastomers prior to vulcanization to protect the rubber during drying and storage. The oxidation of food containing fats and oils results in a loss of sensory appeal and eventually rancidness. FDA regulations covering the use of direct food additives are stringent and few new materials have been regulated. The most commonly used materials are butylated hydroxytoluenen‐propyl gallate, α‐tocopherol, and butylated hydroxyanisole. A number of antioxidants have been accepted by the FDA as indirect additives for polymers used in food applications.
Atomic Force Microscopy
Authors: Schiraldi D. A. , Poler J. C. 
Published: October 2003

AbstractInherently a surface characterization technique, atomic force microscopy (afm) has been utilized to describe the structure and composition of organic, inorganic, and hybrid polymer systems, ranging from thermosets to thermoplastics, and thermoplastic blends and alloys. Scales ranging from large phases, through lamellar crystals, to individual polymer chains (and repeat units within these chains) have been characterized using afm. Also characterized using afm methods have been thermomechanical properties of these polymers, and surface properties (tribology, hardness, adhesion) of these surfaces.
Biodegradable Polymers, Medical Applications
Authors: Kumar Neeraj , Ezra Aviva , Ehrenfroind Tirtsa , Krasko Michal Y. , Domb Abraham J. 
Published: October 2003

AbstractBiodegradable polymers have been used in medicine as surgical aids and orthopedic applications. They have been used as hemostats, absorbable sutures, bone fixation aids, nerve‐guided tubes, and for controlled drug delivery. The potential use of biodegradable polymers is in its initial stage as many more applications are expected to be developed in the years to come. The scientific work on biodegradable polymers have generated new polymeric materials and compositions that allow the development of new medical applications. For example, cardiovascular stents are now made from metals, whereas to keep vessel potency, a few months of lumen support might be sufficient. A biodegradable stent that will provide support for sufficient time estimated as a few month may provide a better solution to the problem of restenosis. In addition, a biodegradable stent may release antirestenosis agents embedded in the polymer body to the surrounding tissue. Biodegradable polymers are needed as scaffolds for tissue engineering, gene carriers in gene therapy, and as depot drug formulations for controlled drug delivery. This article touches upon all of these concepts and applications.
Bulk and Solution Polymerizations Reactors
Authors: Nauman E. Bruce 
Published: October 2003

Abstract
A great majority of polymers are made by bulk or solution polymerizations. Even when there is a competing process, such as gas‐phase or emulsion polymerization, it is likely that bulk or solution process will coexist in order to produce special product grades. A common feature of most bulk or solution polymerizations is the need to remove unreacted monomer, by‐products, and solvents from a highly viscous polymer melt (ref. to devolatilization). Temperature control is a key design issue for vinyl addition polymers while control of stoichiometry, including the removal of reaction by‐products, is the major design issue for condensation polymerizations. Most high volume polymers are made in continuous processes consisting of one or more reactors in series followed by a devolatilization system. Most designs are flexible so that many product grades, including random copolymers, can be made in the same equipment.
Butyl Rubber
Authors: Webb Robert N. , Shaffer Timothy D. , Tsou Addy H. 
Published: October 2003

Abstract

Butyl rubber and other isobutylene polymers in wide use include various homopolymers and copolymers. Low levels of unsaturation for subsequent cross‐linking are incorporated by copolymerization with isoprene. Halogenation at the unsaturation site provides additional cross‐linking mechanisms and covulcanization with highly unsaturated elastomers. Polymers containing star branches, conjugated‐diene sites, divinylbenzene, and brominated
p
‐methylstyrene have also been synthesized. Isobutylene polymers are polymerized by a cationic mechanism, using a Brønsted acid as an initiator and a Lewis acid as a coinitiator, eg, water and aluminum chloride. Molecular weights range from several hundred for terminally unsaturated polybutenes to over a million for elastomer grades.

The
T
g
of polyisobutylene is about −70°C, and the polymer is amorphous in the unstrained state. The polymers exhibit a broad damping peak and a low plateau modulus. They display an exceptionally low permeability to gases, and are widely used as air retention barriers in tires. Optimum physical properties are obtained by compounding with carbon black and other fillers. Various mechanisms are used to cross‐link the compounds into elastomeric vulcanizates. Sulfur is used to provide polysulfidic cross‐links, while resin and zinc oxide cure systems give carbon–carbon cross‐links. Besides inner tubes and innerliners, butyl rubbers are used in blends to improve cut‐growth resistance and wet‐skid resistance. Blends with thermoplastic resins improve toughness. Polyisobutylenes enjoy extensive use as adhesives and caulks, and are chemically modified for use in lubricants as dispersants.
Carbocationic Polymerization
Authors: Puskas Judit E. , Kaszas Gabor 
Published: October 2003

AbstractThis 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

AbstractThis 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

AbstractThis 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

AbstractFibers 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

AbstractChitin 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

Abstract
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

AbstractVarious 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

AbstractMultilayer 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

Abstract
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.
Combinatorial Methods for Polymer Science
Authors: Meredith Carson , Smith Archie P. , Crosby Alfred J. , Amis Eric J. , Karim Alamgir 
Published: October 2003

Abstract
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

AbstractAs 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

Abstract
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

AbstractThe 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

AbstractThe 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

AbstractThe 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.