13C‐NMR sequence analysis. 11. Anionic copolymerization of lactams

Using sodium as the catalyst and benzoylchloride as cocatalyst, copolymerizations of γ‐butyrolactam with ε‐caprolactam and ω‐capryllactam were carried out at 100°C. In a similar manner copolymerizations of ε‐cparolactam, ω‐capryllactam, and ε‐laurinlactam were achieved at 150 and 250°C without a cocatalyst. The 90.5‐MHz 13C‐NMR spectra of all random copolyamides in fluorosulfonic acid show three or more CO signals that allow the ratio of homogeneous (AA and BB) to heterogeneous (AB and BA) amide groups to be determined. These results cleárly demonstrate that despite the reaction temperature or reactivity of the lactams the copolyamides do not contain long homogeneous blocks (An and Bn). The CO signals of the random copolyamides were assigned by comparison with the corresponding homopolyamides and alternating copolyamides. Solutions of the alternating copolyamide (‐β‐Ala‐ε‐Aca‐)n, in fluorosulfonic acid were measured to determine whether the 13C chemical shifts and line widths are dependent on concentration.