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.