Structure and Molecular Dynamics in Metal-Containing Polyamide 6 Microparticles

Polymer microparticles are used in additive manufacturing, separation and purification devices, biocatalysis, or for the recognition of biomolecules. This study reports on the effect of metal fillers on the structure and molecular dynamics of polyamide 6 (PA6) microparticles (MPs) containing up to 19 wt.% of Al, Cu, or Mg. These hybrid MPs are synthesized via reactive microencapsulation by anionic ring-opening polymerization in solution, in the presence of the metal filler. 13C high-resolution solid-state NMR (ssNMR) spectroscopy is employed as the primary characterization method using magic angle spinning (MAS) and cross-polarization (CP)/MAS. Depending on the metal filler, the ssNMR crystallinity index of the MP varies between 39–50%, as determined by deconvolution of the 13C MAS and CP/MAS spectra. These values correlate very well with the crystallinity derived from thermal or X-ray diffraction data. The molecular dynamics study on PA6 and Cu-containing MP shows similar mobility of carbon nuclei in the kHz, but not in the MHz frequency ranges. The paramagnetic Al and Mg have an observable effect on the relaxation; however, conclusions regarding the PA6 carbon motions cannot be unequivocally made. These results are useful in the preparation of hybrid microparticles with customized structures and magneto-electrical properties.