15N NMR spectroscopy, 10 Investigation on structure/shift relationships of nylon‐6,6 polyamides

Series of polyamides were prepared from p-phenylenediamine, and aliphatic α,ω-diamines on the one hand, and fumaric acid, isophthalic acid, terephthalic acid, and aliphatic α,ω-diacids on the other hand. The natural abundance 15N NMR spectra of these polyamides were measured in trifluoroacetic acid, and relationships between the chemical shifts and the structure of the monomer units are discussed. Increasing chain length of the aliphatic diamines results in increasing downfield shift of the diamines themselves and of the polyamides derived from them. No “γ-effect” or similar deviations from the monotonic shift function are observed; however, the influence of the diacid residues on the chemical shift is less regular. The shifts of the homopolyamides are useful for assigning or predicting the shifts of copolyamides. The 15N NMR spectrum of the copolyamide “Trogamide T” is discussed.