Elastomer

An elastomer is a polymer that can undergo large reversible deformation and recover its original shape. Its elastic behavior arises from flexible chains that are usually joined by cross-links.

Polymer chain: A molecule composed of repeating units joined into a long chain. Elastomer molecules deform largely by changing the shapes and arrangements of their chains.
Polymer: A substance made of molecules containing many covalently linked repeating units. Elastomers are a class of polymers distinguished by large, recoverable deformation.
Tire: A ring-shaped vehicle component that supports loads and provides traction through contact with a surface. Elastomers give tire tread and carcasses resilience, grip, and resistance to repeated flexing.
Thermoplastic: A polymer that softens when heated and hardens when cooled, repeatedly, without major chemical change. Unlike elastomers, ordinary thermoplastics are not defined by large reversible deformation at use temperatures.
Cross-link: A chemical or physical connection between separate polymer chains or parts of a chain. Cross-links limit chain motion enough to help a stretched elastomer recover its shape.
Thermoplastic elastomer: An elastomeric polymer that can be softened by heat and processed like a thermoplastic. Its reversible physical domains provide elasticity without permanent chemical cross-links.
O-ring: A loop-shaped seal that closes a gap when compressed between surfaces. Elastomers let an O-ring deform against mating surfaces and maintain a seal.
Plastic deformation: A permanent change in shape that remains after an applied force is removed. Elastomer deformation is largely recoverable, whereas plastic deformation leaves lasting shape change.
Rubber elasticity: Elastic behavior in which polymer chains return toward more probable, disordered conformations after deformation. It describes the entropic force that drives many elastomers back toward their unstretched state.
Thermoset polymer: A polymer network whose covalent cross-links prevent it from melting into a flowable liquid. Many conventional elastomers are thermoset networks formed by curing.

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