Transamidation in Melt-Mixed Aliphatic and Aromatic Polyamides. 3. Molecular Characterization Using Gradient Elution Chromatography (GEC)

Melt-mixing of blends of polyamide 46 (PA 46) and polyamide 6I (PA 6I) gives rise to the formation of copolymers on account of the occurrence of transamidation reactions. The degree of transamidation as obtained during the first minutes of melt-mixing is often too low to permit characterization by NMR or FTIR. To solve this problem, gradient elution chromatography (GEC) has been used. It is visualized using this technique to what extent transamidation is occurring during the first 10 min of melt-mixing. Also, the dependence of the reaction rate on the extrusion temperature has been studied using GEC. Melt-blending of PA 46 having varying end-group concentrations and end-group ratios with PA 6I does not seem to alter the elution behavior of the copolyamides formed; this indicates a transamidation mechanism of hydrolysis and recombination. Finally, it has been proved that degradation processes occurring during the residence time of the melt in the extruder do not influence the retention time of the polyamides in the column.