Synthesis, Chiroptical Properties, and pH Responsibility of Aspartic Acid- and Glutamic Acid-Based Helical Polyacetylenes

l -Aspartic and l -glutamic acid-based novel N -propargylamides, ( S )-HC⋮CCH 2 NHCOCH(CH 2 COOcyclohexyl)NHCOO t -Bu ( 1 ) and ( S )-HC⋮CCH 2 NHCOCH(CH 2 CH 2 COOcyclohexyl)NHCOO t -Bu, were synthesized and polymerized using a rhodium catalyst. The corresponding polymers [poly( 1 ) and poly( 2 )] with moderate molecular weights were obtained in good yields. CD and UV−vis spectroscopic analyses revealed that poly( 1 ) and poly( 2 ) took helical structures, whose tightness was different. The presence of intramolecular hydrogen bonding was confirmed by liquid-state IR spectroscopy. Poly( 1a ) and poly( 2a ) carrying free carboxyl groups were obtained by alkaline hydrolysis of poly( 1 ) and poly( 2 ). Poly( 1a ) did not form a helix, while poly( 2a ) formed a helix undergoing inversion of helical sense and change of tightness upon addition of KOH.