Multiscale structural analysis of polyamide hybrids prepared by in-situ anionic polymerization

The structure of polyamide 6-montmorillonite hybrid (PA6-MMT) composites prepared in-situ by means of activated anionic polymerization (AAP) of caprolactam (CL) was studied by various methods. It was established by WAXS that the predominant PA6 polymorph in the MMT hybrids obtained by AAP is the α-PA6 form, contrary to the conventional hybrids produced by melt intercalation with hydrolytic PA6 where almost pure γ-PA6 was observed. The gradual transition of ε-CL into α-PA6 as the AAP advances, as well as the polymorphic changes of the resulting hybrids as a function of temperature were observed for the first time by in-beam AAP during a WAXS measurement in synchrotron beamline (Figure 1, a). It can be seen that the two crystalline reflections of the α-polymorph are abruptly formed after 10 min of polymerization at 165oC. Until the end of AAP one observes disappearance of CL crystalline reflections whereby amorphous PA6 material is apparently formed. Heating of anionic PA6 to 200oC (below Brill transition) maintains the α-polymorph, whereas melting at 260oC and subsequent recrystallization result in γ-PA6.