Optical properties and conformations of asymmetric polyamides derived from optically active trans-1,2-cyclopropanedicarboxylic acid

Optical properties and conformations, in solution, of optically active polyamides derived from (+)(S)-trans-1,2-cyclopropanedicarboxylic acid with secondary diamines such as trans-2,5-dimethylpiperazine (DMPIP), piperazine (PIP), or N,N′-dimethylethylenediamine (DMED) have been investigated and compared with the corresponding diamide model compounds. The results suggest that the rigid DMPIP and PIP polyamides may exist in ordered conformations in 2,2,2-trifluoroethanol (TFE) and tetramethylene sulfone (TMS), while reversible conformational transitions to highly extended forms may be induced by the addition of methanesulfonic acid (MSA). In MSA/TMS mixtures, a change in the optical properties, and thus possibly in the conformations, can be observed around 0.5 mole fraction of MSA. A study of CD at higher temperature indicates that the conformations of the DMPIP and PIP polymides tend to be randomized on heating in TMS and probably also in MSA. No evidence for salt effects on conformation has been observed. Possible ordered conformations have been proposed.