Structure−Property Relations in Cholesteric Networks from Chiral Polyisocyanates

In this work we prepared lyotropic cholesteric phases from new polyisocyanate terpolymers in styrene and were able to “freeze” this supramolecular structureand thereby the associated optical propertiesin a cross-linked polymer blend by photopolymerization. We synthesized the new chiral polyisocyanates (nylon 1) by living polymerization techniques, using a new titanium catalyst of Bruce Novak. In this way it is possible to incorporate methacrylate groups, which are necessary to prevent a demixing during the photo-cross-linking process, and to control the molecular weight, which is necessary to obtain lyotropic phases of low viscosity. Terpolymers with more than 8 mol % of chiral side groups give rise to lyotropic phases with selective reflection in the visible range. Unexpectedly, we observed a minimum in the plot of wavelength of reflection versus polymer concentration. The selective reflection shifts to larger wavelengths (red shift) with increasing temperature. Photo-cross-linking at different temperatures allows a permanent “freezing” of different colors without loss of the optical quality. In this way flexible polymer films with opalescent colors and an angular dependent color are accessible.