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 Tm of PA6. When compared to the pure PA6, a significant decrease was observed in the Tm and Tc of the copolymer obtained with MP whereas values much closer to those of PA6 homopolymer were obtained with SSP. It is shown by 13C NMR spectroscopy that a non-random, blocky structure was obtained after SSP while the incorporation of the salt was random after MP.