Synthesis and characterization of urethane based liquid crystal materials

Liquid crystalline polymers are usually synthesized by covalent linking of rigid mesogens and polymer backbones via flexible spacers. Side chain liquid crystalline polymers (SCLCPs) integrates low-molar mass liquid crystals and polymers' one of a kind characteristics. Since SCLCPs have appealing electrical and optical characteristics, they have been the object of intense researching mostly. Among these features they can be used in microelectronic devices in range of date storage and nonlinear optics. Liquid crystals which are the unique state of matter have a wide application area such as digital displays, sensors and LCD screens. In this thesis, urethane compounds and their hydrogen bonded liquid crystal polymers were synthesized and optoelectronic properties are characterized. First, Polyethylene glycol 500 monomethyl ether (PEG 500) was reacted with butyl isocyanate (BI) and toluene diisocyanate (TDI) separately. Also, diethyleneglycol monomethyl ether (DEGME) was reacted with butyl isocyanate and toluene diisocyanate. Urethane based liquid crystalline polymers were prepared by using intermolecular hydrogen bonding concept. For this aim, hydrogen-bonded crystalline polymer was synthesized reacting urethane compounds with H-bond donors. Synthesis of Hydrogen Bond Donors: 11-(4-Cyanobiphenyl-4'-oxy) undecan-1-ol (LC11) was synthesized as a bond donor. The structure of the LC11 was characterized by FT-IR and 1H-NMR spectroscopy. Preparation of urethane based liquid crystalline polymers: Urethane based polymers were engaged as hydrogen bond acceptors and LC11 was employed as a hydrogen bond donor to yield hydrogen bonded PEG based liquid crystalline mesogen. Intermolecular H-bonding between nitrogen of amine of the polymer and hydroxyl groups of the hydrogen donors formed the structure of the side chain liquid crystalline polymers. In characterization of hydrogen bonded urethane based polymers FT-IR (Fourier Transform Infra Red) spectroscopy, DSC (Differantial Scanning Calorimetry) and POM (Polarized Optic Microscope) methods were used. Hydrogen bonding donors and acceptors are positioned that intramolecular hydrogen bonding is favorable, displaying slightly broadened O-H stretching absorption band in the range of 3200 to 3500 cm-1, according to FT-IR spectra of the polymers. The phase behavior of all the hydrogen bonded liquid crystalline polymers was studied using a combination of DSC and POM methods. DSC thermograms were obtained in second heating cycles. The samples were heated with a 10°C/min scan rate in an N2 atmosphere. POM (X200) analysis also confirmed DSC results along with the results of phase transitions.