13C NMR spectra of nylon 6/12 copolymers and related model compounds

The 13C NMR spectra of model mono- to tetra-amides containing CO, (CH2)5 and (CH2)11 groups in varied sequential arrangements have been used to reinterpret assignments previously proposed for signals in the spectra of nylon 6/12 random copolyamides. From the CO signal intensities, the mean nylon 6 and nylon 12 homo-unit block lengths have been determined in copolyamides prepared by rapid (ca. 15 min) activated anionic lactam copolymerisation at 180°C. The results are virtually identical with published data for equilibrium copolymers of similar co-unit ratios made by hydrolytic polymerisation at 260°C in reaction times >144 h. Maximum sequential randomness occurs at ca. 50–60 mol% nylon 6 component, coinciding with minima in the thermal and solid-state properties.