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

Abstract

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 +[ η 6-C 6H 5B −(C 6H 5) 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.