Elastomers, also known as rubbers, are special polymers characterized by their remarkable elasticity. They are lightly cross-linked and amorphous, with a glass transition temperature well below room temperature. Elastomers can be seen as large macromolecules where the intermolecular forces between the polymer chains are weak. These crosslinks prevent irreversible flow, making the polymer chains highly flexible at temperatures above the glass transition point. A small force results in significant deformation. Consequently, elastomers exhibit a low Young’s modulus and very high elongation at break compared to other polymers. The term “elastomer” is often used interchangeably with “rubber,” though “rubber” specifically refers to vulcanized elastomers.

Elastomers are classified into three broad categories: diene elastomers, non-diene elastomers, and thermoplastic elastomers.

⦁ Diene elastomers are polymerized from monomers containing two sequential double bonds, such as polyisoprene, polybutadiene, and polychloroprene.

⦁ Non-diene elastomers include butyl rubber (polyisobutylene), polysiloxanes (silicone rubber), polyurethane (spandex), and fluoro-elastomers. These elastomers lack double bonds in their structure, requiring alternative crosslinking methods such as the addition of trifunctional monomers (condensation polymers), divinyl monomers (free radical polymerization), or copolymerization with small amounts of diene monomers like butadiene.

⦁ Thermoplastic elastomers (TPEs) like SIS and SBS block copolymers, and certain urethanes, contain both rigid (hard) and soft (rubbery) repeat units. Upon cooling from the melt state to below the glass transition temperature, the hard blocks phase-separate to form rigid domains that serve as physical crosslinks for the elastomeric blocks.
The manufacturing of elastomeric parts involves three primary processes: injection molding, transfer molding, and compression molding. The selection of the appropriate molding process depends on various factors, including the shape and size of the parts, the required tolerances, and the type and cost of the elastomer and raw materials.
Selecting the right elastomer for an application involves considering numerous factors such as mechanical and physical service requirements, chemical exposure, operating temperature, service life, manufacturability, and cost.