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Caprolactam molecule used to synthesize Nylon 6 by ring opening polymerization

Nylon 6 or polycaprolactam is a polymer developed by Paul Schlack at IG Farben to reproduce the properties of nylon 6,6 without violating the patent on its production. Unlike most other nylons, nylon 6 is not a condensation polymer, but instead is formed by ring-opening polymerization. This makes it a special case in the comparison between condensation and addition polymers. Its competition with nylon 6,6 and the example it set have also shaped the economics of the synthetic fiber industry. It was given the trademark Perlon in the year 1952.

Synthesis

Nylon 6 begins as pure caprolactam. As caprolactam has 6 carbon atoms, it got the name Nylon-6.

When caprolactam is heated at about 533 K in an inert atmosphere of nitrogen for about 4-5 hours, the ring breaks and undergoes polymerization. Then the molten mass is passed through spinnerets to form fibres of Nylon 6.

Polymerization of caprolactam to Nylon 6.

During polymerization, the peptide bond within each caprolactam molecule is broken, with the active groups on each side re-forming two new bonds as the monomer becomes part of the polymer backbone. Unlike nylon 6,6, in which the direction of the amide bond reverses at each bond, all nylon 6 amide bonds lie in the same direction (see figure). Nylon 6 therefore resembles natural polypeptides more closely; in fact, caprolactam would become an amino acid if it were hydrolyzed. This difference has little effect on the polymer's mechanical or chemical properties, but is sufficient to create a legal distinction.

Nylon 6 (above) has a structure similar to Nylon 6,6 (below).

Properties

1. Nylon 6 fibres are tough, possessing high tensile strength.
2. Fibres have high elasticity and lustre.
3. Highly resistant to abrasion, chemicals like acids, alkalis, etc.
4. They are wrinkle proof.
5. It has the potential to be used as a technical nutrient
6. Nylon 6 absorb up to 2.4 % of water which results in reduction in tensile strength
7. Nylon 6 is semicrystalline polyamide

Applications

1. Bristles for toothbrushes, sutures for surgery, etc.
2. Manufacture of hosiery, knitted garments, etc.
3. Manufacture of a large variety of threads, ropes, filaments, nets, tire cords, etc.
4. Gun frames, such as those used by Glock, are made with a composite of Nylon 6 and other polymers.¹

External links

• The Promise of Nylon 6: A Case Study in Intelligent Product Design by William McDonough & Michael Braungart

Wikipedia content modification information:

• This page was last modified on 30 October 2008, at 07:25.

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