Optical-Dissymmetry Phase Transitions in an Achiral Helical-Spring Polymer through Controlled Noncovalent Interactions

Noncovalent chemistry may offer diversity in the functions and applications for artificial polymers by allowing various ordered–disordered phase transitions in a precisely controlled manner. To verify this notion from a fundamental perspective, we examined an achiral poly­(phenylacetylene) derivative with an α-helical structure as a helical-spring polymer for revealing phase changes through control of intramolecular hydrogen bonding with the chiral solvent and temperature. When an amine capable of hydrogen bonding was used as the chiral solvent, either an irreversible helix–helix or a reversible helix–coil phase change occurred in an optically dissymmetric manner according to the amount of the chiral solvent added and ambient temperature. Considering the hydrogen-bonding strength values of the solvent mixture and the thermodynamic parameters, we could predict if the optical-dissymmetry phase changes would occur and, if so, how they occur. Our results were similar to those see for the denaturation of proteins, induced by solvent and temperature, based on helix–coil phase transition.