Perlon, structure

The nonaromatic PU shown in structure 4.68 is sold under the trade name Perlon U. As in the case with nylons and polyesters, higher melting products are formed when the number of carbon atoms is even since this allows a closer packing of the chains. 

Azepan-2-one (hexano-6-lactam, --caprolactam, 28) is industrially the most important azepine derivative. It is used in the production of perlon and is synthesized by Beckmann rearrangement of cyclohexanone oxime. Structurally related to caprolactam is the CNS stimulant pentetrazole 29 (1,5-pentamethylenetetrazole, see p 217). 

Caprolactam for use as fibers is hydrolytically polymerized in batches as 80%-90% aqueous solutions with 0.2%-0.5% acetic acid and ethylene diamine at 250-280° C. The acetic acid acts as chain stabilizer (see above). The ethylene diamine increases the amine equivalent of PA 6 so that mixed weaves of Perlon and wool can be evenly dyed. The water is removed as steam in the polymerization progresses. Caprolactam is also polymerized continuously by what is known as the VK process (vereinfacht-A ontinuierliche, or simplified continuous, process). This process is carried out without pressure with, for example, 6-amino caproic acid or AH salt as initiator. In contrast to the production of nylon 6,6, this process can proceed continuously the melt can be directly spun from the reactor. Polyamide 6 fibers have good properties but they yellow slowly since pyrrole structures are formed at the chain ends. 

As known, polyamides are grouped into nylon tj es (A, B, C, Table 15) and perlon types (D, E, Table 15). Alkali fusion of the nylon types yields their structural bases of diamine and dicarboxylic add. That of perlon types should lead to aminoadds but these ui ergo secoidary thermal reactions under the temperature conditions obtainiiig here. PolyamMe 6 is a dal case since it unexped lty reforms e-capro-lactam during both thermal and hydrolytic breakdown, whidi enables it to be identified. The experimental conditions for the isothermal alkali fission of polyamides are given in Table 15. 

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