Solution 13C NMR spectroscopy of polyamide homopolymers (nylons 6, 11, 12, 66, 69, 610 and 612) and several commercial copolymers

Abstract

Well-resolved 13C NMR spectra of nylons 6, 11, 12, 66, 69, 610, and 612 dissolved in 4:1 TFE/CDCl3 allowed complete assignment of all major backbone peaks. In addition, several low intensity peaks were identified representing cis amide groups, acid end-groups and amine end-groups. Several peaks associated with the trans amide units in the spectra of each polyamide homopolymer were identified as uniquely characteristic of that polymer. Using these unique peaks, all the polyamides studied could be distinguished from each other as homopolymers and as repeat units in copolymers. For example, three unknown polyamides (supplied by a colleague) were identified as nylon 6, nylon 66 and nylon 610 using only solution 13C NMR spectroscopy. Based on these results, several commercial polymers were examined. Using solution 13C NMR spectroscopy, the copolymer compositions, molecular weights, end-group and cis amide contents, plus the amount of residual ε-caprolactam were all determined. For example, Spiderwire Super Mono® fishing line was found to have a number average molecular weight of 25,333g/mol and to contain 82mol% nylon 6 repeat units and 18mol% nylon 66 repeat units. The residual ε-caprolactam, acid end-group and amine end-group contents were calculated as 1.25, 0.61 and 0.0mol%, respectively. The cis amide contents were calculated to be 1.2mol% for nylon 6 units and 0.61mol% for nylon 66 segments.