13C-NMR Sequence Analysis. 23. Synthesis and NMR Spectroscopic Characterization of Polyoxamides with Alternating and Random Sequences of Aliphatic Diamines

Three classes of polyoxamides were prepared: homopolymers derived from α-, ω-diaminoalkanes, and 4,4′-diaminodiphenyl-methane, copolymers with an alternating sequence of two different aliphatic diamines and copolymers with a random sequence of two different diamines. For their syntheses a new class of monomers, the diamine bisoxamide diethyl esters, were prepared from α,ω-diamines and oxalic acid chloride ethyl ester. The 22.63 MHz ¹³C-NMR spectra of the polyoxamide solution in fluorosulfonic acid permitted sequence analysis because the carbonyl signals are sensitive to the nature of the neighboring diamine units. In contrast, 9.12 MHz ¹⁵N-NMR spectra did not give any sequence information. The thermal stability of the polyoxamides was investigated, but differential scanning calorimetry did not give useful information on the crystallinity of the polyoxamides because of their thermal degradation.