The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
All other sections in this Literature Study Guide are owned and copyrighted by BookRags, Inc.
An elastomer is a cross-linked, non-crystalline polymer above its glass transition temperature (a characteristic transition point at which a material's physical behavior changes from rigid to rubbery). Rubber bands probably provide the most familiar examples of elastomers. When an elastomer is deformed and released (provided the temperature exceeds the material's glass transition temperature), it snaps back with typical rubber-like behavior. The stress required to deform an elastomer depends on the number of linkages (called crosslinks) among the material's constituent macromolecules, the extent of deformation, and the temperature.
Elastomers may fall into any one of four categories: diene elastomers, saturated elastomers, thermoplastic elastomers, or inorganic elastomers. Diene elastomers have structures based on the molecules butadiene, isoprene, and/or their derivatives or copolymers. Natural rubber (polyisoprene), the first known elastomer, is a member of the diene elasomer family. So are polybutadiene, polychloroprene, and styrene-butadiene rubber. Diene elastomers can be recognized by the presence of double bonds in the main chains of the macromolecular molecules.
Saturated elastomers, which include the polyacrylates, have no double bonds in their main chains, which is to say that the chains are saturated. Saturated elastomers are valued for their resistance to oxygen, water, and ultraviolet light.
Unlike diene and saturated elastomers, thermoplastic elastomers are physically, rather than chemically, cross-linked. They behave just like chemically cross-linked polymers at room temperature, but like uncross-linked polymers at higher temperatures. Thus, the elastomeric properties come and go with changes in temperature. This is a relatively new class of elastomer; examples include block copolymers containing at least three blocks (or segments).
Inorganic elastomers, such as silicone rubber, have good thermal properties and typically find use in high temperature applications.