Photopolymerization and Molecular Orientational Order of the Discotic Nematic Phase in 2,3,6,7,10,11-Hexakis(4-(8-acryloyloxyoctyloxy)benzoyloxy)triphenylene

A triphenylene-based discotic liquid crystal, 2,3,6,7,10,11-hexakis(4-(8-acryloyloxyoctyloxy)benzoyloxy)triphenylene (6ABTP) was investigated on the behavior of local order parameters for the discotic nematic (ND) phase from the viewpoint of change of the molecular orientational order by photopolymerization. The local order parameters of the aromatic CC, CH and two CO bonds of the acryloyl and benzoyl CO groups were evaluated by an infrared dichroic method of Vij et al. It was found that 6ABTP tends to show a homeotropic alignment in the ND phase on a polyimide film spin-coated on BaF2 and the triphenylene core shows a large order parameter (ca. 0.4–1.0), while the CO moieties have a quite lower one (< 0.3). In order to investigate the disordering of molecular alignment due to crosslinking by photopolymerization, the behavior of local order parameters in photopolymerization was also evaluated. It was found that the order parameter of the aromatic core in the ND phase remarkably decreases at the early stage of photopolymerization, but only about 20% of decrease in the order parameter could be attained at the end of polymerization. Microscopic view of the texture for the film after photopolymerization at 120 °C.