High-performance holographic polymer-dispersed liquid crystals by incorporating hyperbranched polymers



A minute amount (0.01–0.3 wt %) of ally isocyanate functionalized hyperbranched 2,2-bis (hydroxymethyl) propionic acid (bis-MPA) polyester-16-hydroxyl (HBP) was incorporated covalently into polyurethane acrylate-based holographic polymer dispersed liquid crystals (HPDLCs), and its effects on the compound viscosity, grating kinetics, morphology, diffraction efficiency (DE), and electro-optical properties of the HPDLC films were examined. HBP at low concentrations (0.01–0.05%) reduced the compound viscosity and domain size of liquid crystal (LC) significantly and augmented the cure rate and saturation DE by up to threefold compared to the HBP-free compound. At high concentrations (0.10 and 0.30%), HBP increased the compound viscosity and decreased the rate of grating formation, giving rise to distorted LC-polymer interfaces, which caused a significant decrease in the threshold and operating voltages. The rise and decay time showed a minimum and maximum, respectively, when the compound viscosity was a minimum at 0.03% HBP. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013