Synthesis and optical properties of asymmetric polyamides derived from cyclopropyl diacids and diamines

Abstract

The polyamides were prepared from the dicarbonyl chloride of (+) (S)- or (−)(R)- trans -1,2-cyclopropanedicarboxylic acid (C3A) with either the dihydrochloride salt of (+)(S)- or (−)(R)- trans -1,2-diaminocyclopropane (C3B) or the dihydrobromide salt of (+)(S)- or (−)(R)- trans -1,2-bis(methylamino)cyclopropane (C3MB) by interfacial polycondensation. Several diamide model compounds composed of these monomers were also synthesized. The polyamides [poly(C3A-C3B)] derived from C3A and C3B have the capability of hydrogen bonding, while the polyamides [poly-(C3A-C3MB)] derived from C3A and C3MB do not. Poly(C3A-C3B) were insoluble in common organic solvents except strong acids. Poly(C3A-C3MB) were soluble in common organic solvents. Poly(C3A-C3B) had melting points higher than 300°C. Poly(C3A-C3MB) melted at 180–235°C. The ORD and CD study has shown that poly(+)C3A(+)C3B in methane sulfonic acid (MSA), 2,2,2-trifluoroethanol (TFE) (5 v % MSA), and tetramethylenesulfone (TMS) (5 v % MSA) exhibits a very strong Cotton effect or CD peak at 212–218 mΜ, attributable to a component of the split Π–Π * transition of the amide chromophores. Poly(+)C3A(+)C3MB in MSA and TFE (5 v % MSA) shows a strong Cotton effect or CD peak at 217–223 mΜ and an intermediate Cotton effect or CD trough at 202–204 mΜ as well as an intermediate Cotton effect or CD trough at 220–222 mΜ and an intermediate Cotton effect or CD peak at 202–204 mΜ in TFE and TMS. These peaks and troughs may be assigned to splitting of the Π–Π * transition. The CD spectra of poly(+)C3A(+)C3MB in nonacidic media are quite different from those in acidic media: they are almost mirror images. The CD spectra in this transition induced by MSA suggests that a transition from a compact helix to another more extended helix with opposite handedness occurs similar to poly-L-proline I ⇄ II. This transition may be explained by electrostatic repulsion between protonated amide groups. Viscosity data have shown that the conformation is changed to a highly extended from in acidic media. The polyamides and diamides derived from enantiomers exhibit mirror image spectra. Poly(+)C3A(+)C3B and poly(+)C3A(+)C3MB in every solvent studied exhibit a marked enhancement of the rotatory strength of ORD and CD with respect to the corresponding diamide models.