Tune of the helix sense of amino acid-containing poly(N-propargylamides) by temperature and solvent. Control by competition between structurally different units with the same chirality

Homo- and copolymerizations of chiral amino acid-based N-propargylamides, i.e., N-(tert-butoxycarbonyl)-l-alanine N′-propargylamide (LA) and N-(trifluoroacetyl)-l-valine N′-propargylamide (FLV), were conducted with (nbd)Rh+[η6-C6H5B−(C6H5)3] as a catalyst to afford the corresponding copolymers with moderate molecular weights in good yields. The CD and UV-Vis spectra showed that poly(LA) and poly(FLV) take helical structures with predominantly one-handed helices, whose CD signs are opposite. The helices of the homopolymers could be tuned by temperature and solvent. The specific rotation, CD and UV-Vis spectra showed that some of the copolymers underwent temperature- and solvent-induced helix inversion.