Influence of liquid crystalline ordering on the properties of selected cured nematic epoxy materials

Properties of liquid crystalline polymer networks depend on the structure of the reagents as well as on the density of cross-linking bonds, which - in turn - is affected by the degree of ordering of the molecules during the reaction. Changing external conditions (including temperature, time of curing and various factors enforcing orientation of the monomers, such as preparation of cell surface or magnetic field) one can obtain different products. The influence of these external factors on the properties of cured epoxy monomers is studied in this paper. Liquid crystalline polymer networks were obtained as a result of curing three different epoxy compounds with 4,4'-diaminodiphenylmethane (DDM). All the three monomers have nematic phases in wide range of temperatures. The process of cross-linking, the final product of curing and the pure monomers were examined using polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). Chemical structure of the products was confirmed using spectroscopic methods. The study demonstrates that setting up specific conditions for curing (a temperature corresponding to liquid crystallinity range of pure monomer and an external factor enforcing molecular alignment in liquid crystalline phase) may result in cured products with somewhat better Organisation at the molecular level. (c) 2008 Elsevier B.V. All rights reserved.