Transformation of helical sense of poly(N-propargylamides) controlled by competition between structurally different enantiomeric amino acids

Copolymerizations of structurally different chiral amino acid-based N-propargylamides, N-(tert-butoxycarbonyl)-D-alanine-N-propargylamide (DA) with either N-(tert-butoxycarbonyl)-L-valine-N-propargylamide (LV) or N-(tert-butoxycarbonyl)-L-phenylalanine-N-propargylamide (LF), were conducted with (nbd)Rh+[eta(6)-C6H5B-(C6H5)(3)] as a catalyst to obtain the corresponding copolymers with moderate molecular weights in good yields. The specific rotation, CD, and UV-vis spectra showed that some of the copolymers underwent a helix-helix transition driven by temperature change. The transition of helix of poly(LV-co-DA) was much more obvious than that of poly(LF-co-DA). Poly(LV50-CO-DA(50)) underwent a solvent-induced helix-helix transition via random coil.