Flexible Nanocrystalline-Titania/Polyimide Hybrids with High Refractive Index and Excellent Thermal Dimensional Stability

In this study, a novel synthetic route was developed to prepare polyimide-nanocrystalline-titania hybrid optical films with a relatively high titania content (up to 50 wt %) and thickness (20-30 mu m) from soluble polyimides containing hydroxyl groups. Two series of newly soluble polyimides were synthesized from the hydroxy-substituted diamines with various commercial tetracarboxylic dianhydrides. The hydroxyl groups on the backbone of the polyimides could provide the organic-inorganic bonding and resulted in homogeneous hybrid solutions by controlling the mole ratio of titanium butoxide/hydroxyl group. AFM, SEM, TEM, and XRD results indicated the formation of well-dispersed nanocrystalline-titania. The flexible hybrid films could be successfully obtained and revealed relatively good surface planarity, thermal dimensional stability, tunable refractive index, and high optical transparency. A three-layer antireflection coating based on the hybrid films was prepared and showed a reflectance of less than 0.5% in the visible range indicated its potential optical applications. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48:1433-1440, 2010