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High

Copolyamides based on polyamide-6,6 (PA-6,6) were prepared by solid-state modification (SSM). Para-and meta-xylylenediamine 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 postcondensation 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 ultraviolet 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 1 H nuclear magnetic resonance (NMR) spectroscopy. As the transamidation was limited to the amorphous phase, this SSM resulted in a nonrandom overall structure of the PA copolymer as shown by the degree of randomness determined using 13 C 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 nonrandom, block-like chemical microstructure, whereas the melt-synthesized copolyamides were random.

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