Difference Between Nylon 6 and Nylon 66

Main Difference – Nylon 6 vs Nylon 66

Nylon 6 and nylon 66 are polyamide compounds. A polyamide is a polymer composed of repeating amide linkages (-CO-NH-) that are either synthetic or natural. Nylon 6 and nylon 66 are synthetic polyamides. Nylon 6 is a semi-crystalline polyamide and is not a condensation polymer. Nylon 66 is another form of polyamide. The main difference between nylon 6 and nylon 66 is that nylon 6 is formed via ring opening polymerization whereas nylon 66 is formed via condensation polymerization.  

Key Areas Covered

1. What is Nylon 6
– Definition, Synthesis, Uses
2. What is Nylon 66
– Definition, Synthesis, Uses
3. What is the Difference Between Nylon 6 and Nylon 66
– Comparison of Key Differences

Key Terms: Caprolactam, Condensation Polymerization, Nylon 6, Nylon 66, Polyamide, Ring Opening Polymerization

Difference Between Nylon 6 and Nylon 66 - Comparison Summary

What is Nylon 6

Nylon 6, also known as polycaprolactam, is a polyamide formed via ring opening polymerization. It is a semi-crystalline polyamide. It is sold under different names in different countries. Ex: Perlon (Germany). The chemical formula of nylon 6 can be given as (C6H11NO)n.

Nylon 6 is different from other types of nylon due to the difference in the synthesis process. Nylon 6 is produced from only one type of monomer known as caprolactam. It is synthesized via ring opening polymerization of caprolactam.

Nylon is mainly produced by heating caprolactam to 250oC with about 4% water thrown in. Caprolactam has a carbonyl group. When water molecules are present, the oxygen of the carbonyl group gets a proton from the water molecule. This gives the oxygen atom a positive electrical charge, which is unfavorable. Hence, the compound rearranges, leaving the positive charge on the carbonyl carbon atom. Then this carbon atom can be attacked by a nucleophile, here OH. This results in opening the ring of the caprolactam molecule. This opened segment can cause the opening of another ring, leading to the ring opening polymerization.  

Difference Between Nylon 6 and Nylon 66

Figure 1: Nylon 6 Synthesis

Nylon 6 has applications in material that require a high strength. It is widely used in gears, fittings, bearings, as a material for power tools housings, etc. As a common application, nylon 6 is used as fibers in toothbrushes, surgical structures, as threads, as strings for some musical instruments, etc.

What is Nylon 66

Nylon 66 (precisely nylon 6,6) is a polyamide made via condensation polymerization of a diamine and a dicarboxylic acid. The monomers used in the production of nylon 66 are hexamethylenediamine and adipic acid. Both these compounds consist of 6 carbon molecules, which leads to name the polymer formed from them as nylon 6,6.

Main Difference - Nylon 6 vs Nylon 66

Figure 2: Nylon 66 Structure

The synthesizing of nylon 6,6 is a type of polycondensation reaction. Here, equivalent amounts of hexamethylenediamine and adipic acid are combined with water in a reactor. This polymerization process creates amide bonds between the monomers. Hence, nylon 66 consists of repeating amide linkages.

Nylon 66 is used for applications where high mechanical strength and rigidity are required. Nylon 66 is a very rigid material and is highly resistant to heat and chemicals. The major applications include use as fibers in the textile industry, carpets, etc.

Difference Between Nylon 6 and Nylon 66

Definition

Nylon 6: Nylon 6, also known as polycaprolactam, is a polyamide formed via ring opening polymerization.

Nylon 66: Nylon 66 (precisely nylon 6,6) is a polyamide made via condensation polymerization of a diamine and a dicarboxylic acid.

Number of Monomers

Nylon 6: Nylon 6 requires only one type of monomer for its production.

Nylon 66: Nylon 66 requires two types of monomers for its production.

Monomers

Nylon 6: Nylon 6 is produced from caprolactam.

Nylon 66: Nylon 66 is produced from hexamethylenediamine and adipic acid.

Polymerization Process

Nylon 6: Nylon 6 is produced via ring opening polymerization.

Nylon 66: Nylon 66 is produced via condensation polymerization.

Carbon Atoms

Nylon 6: One repeating unit of nylon 6 contains 6 carbon atoms.

Nylon 66: One repeating unit of nylon 66 contains 12 carbon atoms.

Conclusion

Both nylon 6 and nylon 66 are forms of nylon and are polyamides. These materials have different applications based on their chemical structure. The main difference between nylon 6 and nylon 66 is that nylon 6 is formed via ring opening polymerization whereas nylon 66 is formed via condensation polymerization. 

Reference:

1. “Making Nylon 6.” The Polymer Science Learning Center, Available here.
2. “Nylon 66.” Wikipedia, Wikimedia Foundation, 29 Jan. 2018, Available here.
3. “Nylon 6 and Nylon 66.” Chemical Compounds, Encyclopedia.com, Available here.

Image Courtesy:

1. “Caprolactam polymerization” By Nuklear at English Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “Nylon 6,6″ By D.328 07:44, 13 December 2005 (UTC) – drawn by D.328 (JChemPaint) (CC BY-SA 3.0) via Commons Wikimedia

About the Author: Madhusha

Madhusha is a BSc (Hons) graduate in the field of Biological Sciences and is currently pursuing for her Masters in Industrial and Environmental Chemistry. Her interest areas for writing and research include Biochemistry and Environmental Chemistry.

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