Infrared spectra and crystal structures of polyamides

Abstract Infrared spectra and x‐ray diffractions of 24 nylons were investigated. The positions of the NH stretching and the amide I bands indicate that the amide groups form hydrogen bonds almost completely, irrespective of the number of CH 2 groups. The position of the amide V band has been correlated with the crystal structure. Nylons characterized by a predominant peak at 725 cm. −1 show only one reflection in the x‐ray photograph. Odd‐odd nylons belong to this type (γ form). Even‐odd and odd‐even nylons also take this γ form when prepared from the melt through quenching. When cast from solution, they seem to take a new form. Amino acid nylons with an odd number of CH 2 groups have a tendency to take the γ form. Three bands closely related with the position of the amide V band are found.