A solid state NMR study on crystalline forms of nylon 6

High‐resolution 13C‐NMR spectra were studied for two different crystalline structures of nylon 6 in the solid state by the cross polarization/magic angle spinning (CP/MAS) method. Two crystalline structures, α‐form and γ‐form, gave different chemical shifts for methylene carbons. The results showed that the hydrogen bonds between intermolecular chains are stronger in the γ‐form than in the α‐form. This strongly supports the results of the X‐ray study of nylon 6 by Malta et al. Our results also showed that interamolecular delocalization of positive charges occurs in the γ‐form through hyperconjugation in which the dihedral angle between the π bond and neighboring σ bonds is 30° while no such effect can be expected in the α‐form in which the angle is 0°.