“In-Situ Photopolymerization” of Discotic Liquid Crystalline Acrylates in the Discotic Nematic Phase

Abstract

In order to stabilize the anisotropic properties of films made from discotic liquid crystals (DLCs), we applied the “in-situ photopolymerization” process to reactive DLCs. We synthesized triphenylene benzoate derivatives with 1 to 6 acrylate end groups and studied the influence of the number of acrylates on their discotic nematic (N_D) phase and on their photo-initiated polymerization behavior. The discotic acrylates align spontaneously between substrates in the N_D phase, leading to thin films with a negative birefringence. We used the Haller extrapolation method to evaluate the order parameter of these materials. Oriented thin films of monomer were then “frozen in” using photo-initiated polymerization. We studied the optical properties of the resulting polymer films and in particular the dependence of the birefringence on the polymerization temperature. X-ray diffraction analyses of polymer films made from the diacrylate show a decrease of order with higher polymerization temperatures.