Summary: In this work, a novel method using water as a pre‐dispersant of pristine sodium montmorillonite (Na+‐MMT) and ε‐caprolactam (CL) monomer was developed for the preparation of exfoliated monomer casting polyamide 6 (MCPA6)/MMT nanocomposites via in situ anionic ring opening polymerization. The dispersion effect of MMT in the MCPA6 matrix was investigated by means of X‐ray diffraction (XRD), as well as transmission electronic microscopy (TEM). The results indicated that nanoscale dispersed MMT was successfully achieved in the MCPA6 matrix. Furthermore, the addition of a small amount of MMT dramatically improved the thermal stability of MCAP6. Analysis using differential scanning calorimetry (DSC) and XRD indicated that nanoscale dispersed MMT sheets acted as heterogeneous nucleation agents, which favored the formation of the γ‐crystalline form of the MCPA6 matrix.

Summary: Exfoliated Na+‐MMT/polyamide‐6 and intercalated organic MMT/polyamide‐6 nanocomposites were prepared using sodium montmorillonite with water dispersion and organic MMT with acetone dispersion via anionic ring‐opening polymerization, respectively. The effects of Na+‐MMT and OMMT on the polyamide‐6 were compared. Analysis shows that incorporation of exfoliated Na+‐MMT obviously improved mechanical properties, thermal stability, crystalline rate and favored formation of a γ‐crystalline form of matrix, but intercalated OMMT has no obvious effect on it. Nanoscale dispersing Na+‐MMT dramatically elevated the viscosity of matrix comparing with pure polyamide‐6. FTIR analysis indicates that the exfoliated Na+‐MMT improved the stability of hydrogen bonding comparing with the OMMT treated by alkylammonium salt modifier, which is different from previous studies. It is believed that hydrogen bonding between Na+‐MMT and polyamide‐6 plays a pivotal role.FTIR spectra of the NH stretching region of (a) PA, (b) PAM and (c) PAO.imageFTIR spectra of the NH stretching region of (a) PA, (b) PAM and (c) PAO.