Polymeric materials elastomers

A rubber or elastomer is a polymer with viscoelasticity [1-3], Since rubbers are amorphous polymers above the glass transition temperature, considerable segmental motion is possible, making them relatively soft and deformable, with better elongation, compression, and torsional properties than other polymeric materials. Elastomers and rubbers thus come back fairly close to their original size and shape after the stress is released. The primary uses for these materials include tires, hoses, seals, adhesives, and molded flexible parts, among many others. 

L. D. S. Cain and S. S. Stimler, same title. Part 3. Related Polymeric Materials (Elastomers), NRL Report 6503, Naval Research Laboratory, Washington, DC, 1967. AD 649004. 47 spectra. 

An eiegant theoreticai treatise of poiymer physics which conveys an intuitive understanding of the behaviour of macromoiecuies. Charrier J-M 1990 Polymeric Materials and Processing Plastics, Elastomers and Composites (Munich Hanser)... 

Butadiene copolymers are mainly prepared to yield mbbers (see Styrene-butadiene rubber). Many commercially significant latex paints are based on styrene—butadiene copolymers (see Coatings Paint). In latex paint the weight ratio S B is usually 60 40 with high conversion. Most of the block copolymers prepared by anionic catalysts, eg, butyUithium, are also elastomers. However, some of these block copolymers are thermoplastic mbbers, which behave like cross-linked mbbers at room temperature but show regular thermoplastic flow at elevated temperatures (45,46). Diblock (styrene—butadiene (SB)) and triblock (styrene—butadiene—styrene (SBS)) copolymers are commercially available. Typically, they are blended with PS to achieve a desirable property, eg, improved clarity/flexibiHty (see Polymerblends) (46). These block copolymers represent a class of new and interesting polymeric materials (47,48). Of particular interest are their morphologies (49—52), solution properties (53,54), and mechanical behavior (55,56). 

Thermoplastic polyurethane (TPU) is a type of synthetic polymer that has properties between the characteristics of plastics and rubber. It belongs to the thermoplastic elastomer group. The typical procedure of vulcanization in rubber processing generally is not needed for TPU instead, the processing procedure for normal plastics is used. With a similar hardness to other elastomers, TPU has better elasticity, resistance to oil, and resistance to impact at low temperatures. TPU is a rapidly developing polymeric material. 

The changes in properties observed on aging of different elastomers and their vulcanizates, and of many other polymeric materials, are well known. Antiozonants and antioxidants are employed to limit these changes. However, the most effective antioxidant for one material may be ineffective. 

At present the situation in the field of inorganic polymeric materials is dominated by polysiloxanes (silicones) [14, 24-27], whose utilization as low temperature elastomers, thermally stable fluids, biomaterials etc., is definitely well established. 

Controlled/living radical polymerisation (CRP) is currently a fast developing area in polymer synthesis and it allows preparation of many advanced polymeric materials, including thermoplastic elastomers, surfactants, gels, coatings, biomaterials, materials for electronics and many others. 

Organic polymers are sometimes referred to as plastics (although, this should be confined to thermoplastic polymers), macromolecules or resins, though the latter is often used to describe raw polymeric material awaiting fabrication. Many polymers are used in various forms that are not associated with normal plastic materials. These include paints and coatings, elastomers (rubbers), adhesives, sealants (caulks), surfactants and also their use in various industrial applications, e.g., ion-exchange resins, membranes. 

Billions of pounds of polyolefins are produced annually in the world [1], Through simple insertion reactions, inexpensive and abundant olefins are transformed into polymeric materials for a wide range of applications including plastics, fibers, and elastomers. Despite its long history, the polyolefin industry continues to grow steadily and remains technologically driven because of continuous discovery of... 

The use of polymeric materials as basic structural materials is widespread and of ancient origin. These materials include concrete, wood, glass, and a wide variety of plastics and elastomers. In fact, with the exception of steel, most of a house is polymeric. 

Wallace Carothers and coworkers at DuPont synthesized aliphatic polyesters in the 1930s [Furukawa, 1998 Hounshell and Smith, 1988]. These had melting points below 100°C, which made them unsuitable for firber use. Carothers then turned successfully to polyamides, based on the theoretical consideration that amides melt higher than esters. Polyamides were the first synthetic fibers to be produced commercially. The polyester and polyamide research at DuPont had a major impact on all of polymer science. Carothers laid the foundation for much of our understanding of how to synthesize polymeric materials. Out of that work came other discoveries in the late 1930s, including neoprene, an elastomer produced from chloro-prene, and Teflon, produced from tetrafluoroethylene. The initial commercial application for nylon 6/6 was women s hosiery, but this was short-lived with the intrusion of World War II. The entire nylon 6/6 production was allocated to the war effort in applications for parachutes, tire cord, sewing thread, and rope. The civilian applications for nylon products burst forth and expanded rapidly after the war. 

Finally, for practical reasons it is useful to classify polymeric materials according to where and how they are employed. A common subdivision is that into structural polymers and functional polymers. Structural polymers are characterized by - and are used because of - their good mechanical, thermal, and chemical properties. Hence, they are primarily used as construction materials in addition to or in place of metals, ceramics, or wood in applications like plastics, fibers, films, elastomers, foams, paints, and adhesives. Functional polymers, in contrast, have completely different property profiles, for example, special electrical, optical, or biological properties. They can assume specific chemical or physical functions in devices for microelectronic, biomedical applications, analytics, synthesis, cosmetics, or hygiene. 

Most polymers are applied either as elastomers or as solids. Here, their mechanical properties are the predominant characteristics quantities like the elasticity modulus (Young modulus) E, the shear modulus G, and the temperature-and frequency dependences thereof are of special interest when a material is selected for an application. The mechanical properties of polymers sometimes follow rules which are quite different from those of non-polymeric materials. For example, most polymers do not follow a sudden mechanical load immediately but rather yield slowly, i.e., the deformation increases with time ( retardation ). If the shape of a polymeric item is changed suddenly, the initially high internal stress decreases slowly ( relaxation ). Finally, when an external force (an enforced deformation) is applied to a polymeric material which changes over time with constant (sinus-like) frequency, a phase shift is observed between the force (deformation) and the deformation (internal stress). Therefore, mechanic modules of polymers have to be expressed as complex quantities (see Sect. 2.3.5). 

Of all the commercially available organic and inorganic polymeric materials, RTV silicone elastomer has proved to he one of the most effective encapsulants used for mechanical and moisture protection of the Integrated Circuitry (1C) devices. A general overview of the RTV silicone elastomer and its commercial preparation and cure mechanism are described. Improved electrical performance of the RTV silicone encapsulant, by immobilizing the contaminant ions, such as Na, K" , Cl , with the addition of the heterocyclic poly-ethers as the contaminant ion scavengers seems to have a potential application as the contaminant ionic migration preventor in the electronic applications. 

Compression molding A fabrication method in which a polymeric material, mostly a thermoset (a plastic or an elastomer), is compressed in a heated mold for a specific period of time. 

Elastomer A macromolecular (polymeric) material that, at room temperature, is capable of recovering substantially in shape and size after removal of a deforming force. 

Extrusion A process in which heated or unheated polymeric material (plastic or elastomer) is forced through a shaping orifice (die) in one continuous shape, as in film, sheet, slab, profile, pipe, coating, etc. 

Thermoplastic elastomer (TPE) A polymeric material that is elastic at ambient or moderately elevated or lowered temperature that can be... 

Organic polymers are manufactured and used on a massive scale as plastics and elastomers, films and fibres in areas as diverse as clothing, car tyres, compact discs, packaging materials, prostheses and most recently electroluminescent and electronic devices and sensors. The enormous growth in the use of organic polymeric materials since the 1930s can be mainly attributed to their ease of preparation, lightweight nature and unique ease of fabrication. 

The polymeric materials usually used to manufacture rigid closures are practically the same as those seen under plastic containers (Section 6.1.3.2). The same impurities are therefore to be expected in these packaging components. On the other hand, though made of polymeric materials, elastomeric closures present a different structure. In the manufacture of rubber, elastomer, the chief component, is combined with other chemicals to produce a material with specific properties that meet target needs, such as its above-mentioned ability to reseal on repeated use. Table 28 lists the common elastomers used in the pharmaceutical industry and their monomeric structures. 

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