AN UNUSUAL INTERPLAY BETWEEN MACROMOLECULAR AND SUPRAMOLECULAR HELICITY IN POLYISOCYANATES DISSOLVED IN A CHIRAL LIQUID-CRYSTAL

A cholesteric liquid-crystal phase with a pitch of about 100 microns prepared from an achiral mesogen doped with an optically active molecule can hardly be described as chiral on a molecular scale; the mesogen director rotates only about 0.36-degrees for a displacement along the cholesteric helical axis of 1000 angstrom. Apparently, this is ''chiral enough'' to break the degeneracy of the mirror-image helical senses in a sample of dynamically racemic poly(n-hexyl isocyanate) of 500 angstrom contour length. This can be deduced from the change in the pitch of the cholesteric phase on dissolving small amounts of this polymer and comparing the result with the addition of an optically active polyisocyanate.