The other group is obtained by condensation or ring-opening polymerization of lactams, whose long-chain molecules have the chemical structure formula H-[NH(CH2)xCO]-OH.
Depending on the number of carbon atoms contained in their unit structure, different varieties can be named. Nylon 6, for example, indicates that it is obtained by the ring-opening polymerisation of a caprolactam containing six carbon atoms.
Nylon 6, Nylon 66 and other aliphatic nylon all consist of linear macromolecules with an amide bond (-NHCO-). The -CO- and -NH- groups in the nylon molecule can form inter- or intra-molecular hydrogen bonds and can also be combined with other molecules, so nylon has a good moisture absorption capacity and can form a good crystalline structure.
The -CH2-(methylene) molecules in nylon can only generate weak van der Waals forces between them, so the -CH2- chain part of the molecular chain is more curly. The number of -CH2- in each nylon molecule varies, so that the hydrogen bonds between molecules are not identical and the probability of molecular curling is also different. In addition, some nylon molecules are also directional. The structural properties of the fibres are not identical depending on the orientation of the molecules.
