Unexpectedly Strong Chiral Amplification of Chiral/Achiral and Chiral/Chiral Copolymers of Biphenylylacetylenes and Further Enhancement/Inversion and Memory of the Macromolecular Helicity

We report an unexpectedly strong amplification of the macromolecular helicity in dynamic helical copolymers of chi-ral/achiral and chiral/chiral (R/S) biphenylylacetylenes in which the chiral residues are remote from the biphenyl pendants and further from the main chains. The copolymers consisting of 20 mol% chiral monomers and chiral monomers of 20% enanti-omeric excess (ee) showed a full induced circular dichroism (ICD) as intense as that of the chiral homopolymer. In contrast, an analogous poly(phenylacetylene) bearing the identical chiral residue (100% ee) showed no circular dichroism (CD) in the polymer backbone, indicating the critical role of the biphenyl moieties in the observed high chiral amplification. As antici-pated, the helix-sense excesses of the copolymer backbones composed of a small amount of chiral units (< 20 mol%) and chiral units of a low ee (< 20%) were reduced. Interestingly, however, the macromolecular helicity of the copolymers was further drastically enhanced as a greater excess...