Types of Polymers

1. Thermoplastics (can be melted with the application of heat).

Crystalline
crystallize when cooled
Amorphous
no crystallization when cooled
Semicrystallin
polymers which contain both crystalline and amorphous segments

2. Thermosets (degrade rather than melt with the application of heat)

3. Elastomers (cross-linked)

Plastics are rigid long-chain polymers which are not usually connected or cross-linked. Plastics can either be thermoplastic-meaning they can be heated and cooled without changing propertiesor - thermoset, where an increase in temperature changes the chemical structure and properties. As a class, plastics have low elongation and high elongation set.

Elastomers are flexible long-chain polymers which are capable of cross-linking. Cross-linking chemically bonds polymer chains which can prevent reversion to a non-cross-linked polymer at elevated temperatures. The cross-link is the key to the elastic, or rubbery, properties of these materials. The elasticity provides resiliency in sealing applications.

Thermoplastic elastomers (TPEs) often combine the properties of elastomers with the ease of processability of thermoplastics. They are the result of a physical combination of soft, elastic polymer segments and hard, crystalline segments which are capable of cross-linking. Thermoplastic elastomers are generally classified by their structure rather than their chemical makeup.

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