It is shown that the incorporation of comonomers into polyamide (PA6) is possible below the melting temperature of the polymer. For this purpose, a nylon salt of 1,5-diamino-2-methylpentane (Dytek A) and isophthalic acid (IPA) was used and reactions were carried out via both solid-state polymerization (SSP) of the nylon salt with PA6 and melt copolymerization (MP) of the nylon salt with e-caprolactam for comparison. For the SSP the nylon salt was pre-mixed with the amorphous phase of PA6 by a solution mixing process, followed by evaporation of the solvent, after which transamidation reactions were forced below the T-m of PA6. When compared to the pure PA6, a significant decrease was observed in the T-m, and T-c of the copolymer obtained with MP whereas values much closer to those of PA6 homopolymer were obtained with SSP. It is shown by C-13 NMR spectroscopy that a non-random, blocky structure was obtained after SSP while the incorporation of the salt was random after MP. (c) 2012 Elsevier Ltd. All rights reserved.