Polyamide-6,6-based blocky copolyamides obtained by solid-state modification

Copolyamides based on polyamide-6,6 (PA-6,6) were prepared by solid-state modification (SSM). Para- and meta-xylylenediamine (PXDA, MXDA resp.) were successfully incorporated into the aliphatic PA-6,6 backbone at 200 and 230 °C under an inert gas flow. In the initial stage of the SSM below the melting temperature of PA-6,6 a decrease of the molecular weight was observed due to chain scission, followed by a built up of the molecular weight and incorporation of the comonomer by post-condensation during the next stage. When the solid-state copolymerization was continued for a sufficiently long time, the starting PA-6,6 molecular weight was regained. The incorporation of the comonomer into the PA-6,6 main chain was confirmed by size exclusion chromatography (SEC) with UV detection, which showed the presence of aromatic moieties in the final high molecular weight SSM product. The occurrence of the transamidation reaction was also proven by 1H-NMR spectroscopy. Since the transamidation was limited to the amorphous phase, this SSM resulted in a non-random overall structure of the PA copolymer as shown by the degree of randomness determined by using 13C-NMR spectroscopy. The thermal properties of the SSM products were compared with melt-synthesized copolyamides of similar chemical composition. The higher melting and higher crystallization temperatures of the solid state-modified copolyamides confirmed their non-random, block-like chemical microstructure, whereas the melt-synthesized copolyamides were random.