Optical activity based on macromolecular asymmetry

Abstract

Optically active isotactic polychloral was prepared in which the optical activity comes exclusively from molecular asymmetry (i.e., helical conformation). Molecular asymmetry requires a high conformational energy barrier for the polymer backbone, and an asymmetric initiator to induce a predominance of one helical screw-sense. Polychloral meets the criteria. Asymmetric initiators used to obtain optically active polychloral include tetramethyl ammonium (+)- or (−)-0-acetylmandelate, tetramethylammonium (+)- or (−)-0-methylmandelate, the lithiumalkoxides of methyl (+)- or (−)-mandelate, lithium cholesten-3β-oxide, lithium cholestan-3β-oxide, and lithium (+)- or (−)-2-octanoxide. Using the above initiators at 0.5 mol %, a maximum specific rotation of [α] D25 = 5000 was obtained for polychloral. Errors in specific rotation were typically ±7%.