Characterization of Poly(ethyleneoxyethylene Terephthalate-co-adipate) Using NMR Spectroscopy

Comonomer sequence distribution and (1)H-NMR chemical shifts were determined for poly(ethylencoxyethylene terephthalate-co-adipate) (PEOETA) copolyester. The sequence distribution of terephthalate (T) and adipate (A) residues was found to be random, which is typical for copolyesters synthesized via bulk polycondensation. The inner methylene protons of EOE residues appeared as a pair of doublets due to chemical shift differences among the EOE-centered dyad sequences TT, TA, AT, and AA. The four equivalent phenylene protons of T residues appeared as a triplet due to chemical shift differences among the T-centered triad sequences TTT, TTA (=ATA), and ATA. Higher-order tetrad and pentad sensitivity were also observed for the inner methylene and phenylene protons, respectively, especially for TT- and TTT-centered sequences. The sequence sensitivity of the phenylene protons was attributed to unique spatial interactions between themselves and protons within adjacent adipate and EOE units. These spatial interactions were confirmed using Nuclear Overhauser Enhancement Spectroscopy (NOESY)