Design, Synthesis, And Characterization Of Mesogen-Jacketed Liquid Crystalline Polymers Containing Conjugative Mesogens

This dissertation is focused on the investigation of phase behavior and birefringence of mesogen-jacketed liquid crystalline polymers containing tolane withπ-electron conjugative side chains. Design, synthesis, and characterization of novel liquid crystalline polymers containingπ-electron conjugative mesogenic cores were carried out. Their liquid crystalline (LC) phase behavior was investigated thoroughly. On the basis of phase structure, we investigated the positive birefringence characteristic of the monomers and the polymer films, and the potential application as optical compensators in liquid crystal displays (LCD). Optoelectronic properties of monomers and polymers were also studied.A series of 2,5-bis(5-alkyl-2-butadinylthiophene-yl)styrene monomers [VTCn(n = 2, 3, 4, 6, and 8)] and (2,5-bis[2-(4?-methylphenyl)ethynyl] styrene monomer (VBC1)containing largeπ-electron conjugative groups (thiophene and diacetylenes)were synthesized and characterized. The chemical structures of the monomers were confirmed by 1H NMR, mass spectrometry, and elemental analysis. Differential scanning calorimetry (DSC) and polarized light microscopy (PLM) were used to study the mesomorphic phase behavior of monomers. It was found that the LC phase behavior of the monomers was influenced by the length of the alkoxy tail. Nematic LC phases were observed in most VTCn monomers. The nematic LC phase of VBC1 was only observed during cooling. Free radical polymerization of VTC3 monomer was carried out to obtain the mesogen-jacketed liquid crystalline polymer (MJLCP).A series of new methacrylate monomers 2,5-bis[2-(4'-alkoxyphenyl)ethynyl] benzyl methacrylate (MACn, n = 1, 4, 6, 8, 10, and 12), 2,5-bis[2-(6?-decanoxynaphthyl)ethynyl] benzyl methacrylate (MANC10), and 2,5-bis[2-(4'-decanoxyphenyl)ethynyl] benzyl acrylate (AC10)containing largeπ-electron conjugative groups (acetylenes, phenyl, and naphthalenes)were designed and synthesized. The chemical structures of the monomers were confirmed by 1H NMR, mass spectrometry, and elemental analysis. DSC and PLM were used to study the mesomorphic phase behavior of the monomers. It was found that the LC phase behavior of the monomers was also influenced by the length of the alkoxy tail. Nematic LC phases were observed in all monomers.Free radical polymerization of MACn, MANC10, AC10 monomers was carried out, and to obtain MJLCPs PMACn, PMANC10, and PAC10. DSC, PLM, and wide-angle X-ray diffraction were used to study the phase structures of the polymers. For the polymers PMACn with short linkages, columnar nematic phases formed when the flexible tail was butoxy group (n = 4), and for those with flexible tails longer than butoxy groups, SA phases were observed. Similarly, PMANC10 also formed a well-defined SA phase. Compared with the results of other MJLCPs, the short linkages did not hinder the formation of the SA phase. This implies that the polymer molecules in the LC phase could be more ribbon-like rather than rod-like.The birefringence of the monomers was investigated. The monomers had a relatively high birefringence values, which was consisted with the objective of our molecular design. We also investigated the positive birefringence of polymers MAC4 and PMAC8 films by the prism coupler, and the results showed highly positive birefringence values for the polymers, which suggested that the MJLCP structure was beneficial to obtain films with highly positive birefringence to be used as optical compensators. Moreover, measurements using UV-Vis and fluorescence spectroscopy showed that monomers MACn (n = 1, 4, 6, 8, 10, and 12)had good photoluminescent properties with high quantum efficiency of 89.0-96.2% and the wavelengths were in the range of blue light. Device Performances of polymers PMAC1(ITO/PEDOT:PSS/PMAC1/TPBI(16 nm)/LiF(1 nm)/Al(100 nm)) had a low turn-on voltage.