Control of One-Handed Helicity in Polyacetylenes: Impact of an Extremely Small Amount of Chiral Substituents
Tomoyuki Ikai, Yuki Morita, Tsuyoshi Majima, Shoki Takeda, Ryoma Ishidate, Kosuke Oki, Nozomu Suzuki, Hajime Ohtani, Hiromi Aoi, Katsuhiro Maeda, Kento Okoshi, Eiji Yashima
Abstract
Controlling the one-handed helicity in synthetic polymers is crucial for developing helical polymer-based advanced chiral materials. We now report that an extremely small amount of chiral biphenylylacetylene (BPA) monomers (ca. 0.3-0.5 mol %) allows complete control of the one-handed helicity throughout the polymer chains mostly composed of achiral BPAs. Chiral substituents introduced at the 2-position of the biphenyl units of BPA positioned in the vicinity of the polymer backbones contribute to a significant amplification of the helical bias, as interpreted by theoretical modeling and simulation. The helical structures, such as the helical pitch and absolute helical handedness (right- or left-handed helix) of the one-handed helical copolymers, were unambiguously determined by high-resolution atomic force microscopy combined with X-ray diffraction. The exceptionally strong helix-biasing power of the chiral BPA provides a highly durable and practically useful chiral material for the separation of enantiomers in chromatography by copolymerization of an achiral functional BPA with a small amount of the chiral BPA (0.5 mol %) due to the robust helical scaffold of the one-handed helical copolymer.