Difference Between Polymer and Elastomer

Main Difference – Polymer vs Elastomer

Polymers have a molecular structure consisting chiefly or entirely of a large number of similar units bonded together. These units are called repeating units. These repeating units represent the monomers from which the polymer is made. Since there are many varieties of polymers, all these macromolecules can be categorized depending on several different parameters. When polymers are categorized depending on their molecular forces, there are three groups as thermoplastic polymers, thermosetting polymers, and elastomers. The main difference between polymer and elastomer is that a polymer is any large molecule built with small units called monomers whereas an elastomer is a special type of polymer which has elastic property.

Key Areas Covered

1. What is a Polymer
      – Definition, Categories, General Properties
2. What is an Elastomer
      – Definition, Specific Properties with Examples
3. What is the Difference Between Polymer and Elastomer
      – Comparison of Key Differences

Key Terms: Amorphous Polymers, Elastomer, Macromolecules, Monomer, Natural Polymer, Polymer, Synthetic Polymer, Thermoplastic, Thermosetting

What is a Polymer

A polymer is a macromolecule that is composed of a large number of repeating units. These repeating units represent monomers from which the polymer is made. Monomers are small molecules. These monomers have either double bonds or at least two functional groups per molecule. Then they can undergo polymerization in order to form polymer material.

Since polymers are diverse, they can be categorized into several different groups depending on different parameters. The classification is given below.

Classification of Polymers

Based on the Structure:

Based on the Molecular Forces:

Thermoplastic polymers
Thermosetting polymers
Elastomers

Based on the Source:

Based on the Method of Polymerization:

Addition polymers
Condensation polymers

Polymers have different properties depending on the repeating units present in the polymer, microstructure of the polymer material, etc. Some polymers show plasticity, some show elasticity; some polymers are strong and rigid, some are soft and flexible. Likewise, polymers show a wide range of properties.

As general properties of polymers, followings can be given.

Most of the polymers are resistant to chemicals.
Most polymers act as electrical and thermal insulators.
Generally, polymers have a high strength when compared to their light weight.
Some polymers can be obtained from natural sources, but most of the polymers are synthesized from petroleum oil.

Figure 1: Tacticity of Polymers – Examples of Atactic, Isotactic and Syndiotactic Polymers (from top to bottom)

Tacticity of polymers is another important concept regarding polymers. Polymers can be isotactic, syndiotactic or atactic. This tacticity is determined depending on the position of the pendant groups present in the polymer chains. If the pendent groups are on the same side, they are isotactic polymers. If the groups are in an alternating pattern, then they are syndiotactic. But if the pendant groups are positioned in a random manner, they are atactic polymers.

What is an Elastomer

An elastomer is a type of polymer having the specific characteristic feature of elasticity. Elasticity is the ability of an object or a material to resume its normal shape after being stretched or compressed. Elastomers are rubber-like material and are usually amorphous polymers (there is no ordered structure). The elastic property of elastomers arises due to sufficiently weak Van Der Waal forces between polymer chains or sufficiently irregular structure. If the forces between polymer chains are weak, it gives the polymer flexibility. Likewise, if the polymer has an unorganized structure, it allows the polymer to be more flexible. But in order for a polymer to be flexible, it should have some degree of cross-linking.

Difference Between Polymer and Elastomer

Figure 2: Elastomers

Some elastomers are thermoplastics whereas other elastomers are thermosetting polymers. The most common example for elastomers is rubber. Natural rubber is composed mainly of polyisoprene polymer. Therefore, this compound is the reason for the elasticity of rubber. Natural rubber is obtained from the latex of rubber tree. But rubber can be synthesized to obtain synthetic rubber. Here, petroleum oil and natural gases can be used for the production of rubber.

Definition

Polymer: A polymer is a macromolecule that is composed of a large number of repeating units.

Elastomer: An elastomer is a type of polymer having the specific characteristic feature of elasticity.

Physical Properties

Polymer: Polymers have different physical properties depending on their structures.

Elastomer: Elastomers have the unique physical property of elasticity.

Morphology

Polymer: The morphology of polymers may vary from crystalline structures to amorphous structures.

Elastomer: Elastomers are amorphous polymers.

Elasticity

Polymer: Polymers can rupture when a pressure is applied (except for elastomers).

Elastomer: Elastomers can withstand high pressures due to elastic property.

Flexibility

Polymer: Most polymers except elastomers are stiff and rigid.

Elastomer: Elastomers are flexible.

Conclusion

Elastomers are a type of polymers. The groups of elastomers are separated from other polymers depending on the molecular forces that give elastomers their elasticity. The main difference between polymer and elastomer is that a polymer is any large molecule which is built with small units called monomers whereas an elastomer is a special type of polymer which has elastic property.

References:

1. Gent, Alan N. “Elastomer.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 8 Jan. 2016, Available here.
2. “Polymer.” Wikipedia, Wikimedia Foundation, 13 Oct. 2017, Available here.

Image Courtesy:

1.”Polymers Tacticity V.1″ By Jü – Own work (CC0) via Commons Wikimedia
2. “Thermoplastic elastomer TPE” By LaurensvanLieshout – Own work (CC BY-SA 3.0) via Commons Wikimedia