Ion‐dipole interactions and chiroptical property changes of an optically active nylon‐type polyamide in CaCl2‐methanol solutions

Abstract

AbstractThe chiroptical properties of poly(‐) 1,2‐diaminopropane sebacamide) (I) and of its model molecule: the N, N'‐didecanoyl (‐) 1,2‐diaminopropane (II) in CaCl2‐methanol solutions have been investigated by ORD (optical rotatory dispersion) and CD (circular dichroism) over a wide range of salt/monomeric units or salt/model molar ratios τ. The origin of the observed CD bands is discussed on the basis of the electronic transitions of isolated amide chromophores. The polymer behaves exactly as if the monomeric units were completely independent. The optical activities of (I) and (II) in CaCl2‐methanol solutions are found to depend on two overlapping phenomena: an ion‐dipole complex which prevails at low τ; a solvent‐like effect of the excess salt on the complexed species. A method for calculating the ion‐dipole association constant Kc from the optical rotatory power changes as a function of τ, is described. It is not necessary to know [ϕms] and [mms], the molar specific rotatory powers of the model and polymeric complexed species, which are subsequently deduced using Kc. The structure of the ion‐dipole complex and the nature of the solvent‐like effect are discussed.