Synthesis and properties of aliphatic polyacetamidines

A series of aliphatic polyacetamidines (1) with the common structure [-CH 2 ) m -N=C(CH 3 )-NH-] n was synthesized by the phenol-catalyzed melt polycondensation reaction of various aliphatic diamines with triethyl ortho acetate. The resulting polyacetamidines were characterized by 1 H and 13 C NMR spectroscopy. It could be shown that the NMR spectra are strongly influenced by the solvents used. In pyridine and CD 3 OD, prototropic tautomerism of the amidine group was observed. In pyridine this process is mainly caused by intermolecular proton exchange between two amidine groups whereas in CD 3 OD, proton exchange mainly proceeds via the solvent. The methyl residue on the amidine group revealed pronounced CH-acidity, which is apparent in a proton-deuteron exchange when CD 3 OD was used as a solvent. In CF 3 COOD, the respective amidinium salts were formed. It was found the thermal stability of the polymers increased with increasing chain length of the aliphatic diamines. The shorter aliphatic diamines formed cyclic products with a defined structure.