Ring Opening to Make Type AB Nylons

We make type AB nylons, such as nylon 6 and nylon 12, by the hydrolytic ring opening of lactams in the presence of water at temperatures of about 260-270 C. 

The polymerization process for nylon 6 consists primarily of the three types of reaction illustrated in Fig. 23.6. Each of the reactions is reversible, vith the equilibrium of the products being controlled primarily by the concentration of water in the reaction vessel. The reaction is initiated by the hydrolytic ring opening of caprolactam to form S-aminohexanoic acid, as shown in Fig. 23.6 a). Chain extension of the type shown in Fig. 23.6 b) dominates when water is abimdant (10 to 20%) in the reaction mixture. At lower water levels (2 to 5%) chains grow primarily by the mechanism shown in Fig. 23.6 c). In order to Emit the average molecular 

A typical commercial reactor consists of a vertical tube, up to 10 m in height, into the top of which the monomer is fed continuously. As polymerization proceeds, the increasingly viscous polymer solution travels do vn the column. Molten polymer is drawn from the bottom of the reaction tube and is subsequently cooled and chopped into pellets. The final manufacturing stage consists of exposing the pellets to a strong vacuum at a slightly elevated temperature to remove residual monomer and vater. 

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