''In-situ photopolymerization'' of discotic crystalline acrylates in the discotic nematic phase

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.