Relation between ductility and segmental mobility of nylon-6

High-resolution solid-state 15N and 13C NMR and dynamic mechanical measurements were carried out for solution grown crystals of the α- and γ-forms of nylon-6 to understand the relation between segmental mobility including interchain interactions and ductility of polyamides. The ductility, in the temperature range of 100–180 °C, was lower for the α-crystals than for γ-crystals. 15N chemical shift revealed that the hydrogen bonding was stronger for the γ-crystals than for α-crystals. In addition, lower mobility of NH group in the γ-crystals than in α-crystals was shown by 15NT1 results. The results suggest that the ductility of nylon-6 could not be simply related to the strength of hydrogen bonding. Highly crystalline films of aggregates of solution grown α-crystals and γ-crystals showed no crystalline relaxation in the temperature dependence of dynamic mechanical loss factor, suggesting an existence of strong intermolecular interactions in the crystalline regions although 13CT1 data indicated that the mobility of methylene units was higher in the γ-crystals than in α-crystals. Information on the large-scale chain dynamics in the crystalline regions might be necessary to understand the low ductility of polyamides.