Thermal and mechanical properties of liquid crystalline epoxy resins as a function of mesogen concentration

Liquid crystalline thermosets are known to exhibit a number of improved characteristics in comparison with traditional plastics. We now describe quantitatively how the thermal and mechanical properties of a number of liquid crystalline epoxy resins vary with polymer mesogen concentration, using biphenyl- and biphenol-based diepoxides with varying spacer lengths and a range of aromatic diamine curing agents. Although macroscopically isotropic, the degree of order at the microdomain level can be related to the network physical properties, and thus increasing mesogen content leads to increased intermolecular interactions between the polymer chains and hence reduced micro-Brownian motion and reduced free volume. These properties are manifested as increased elastic moduli at high temperatures, reduced thermal coefficients of expansion, increased decomposition onset temperatures and reduced solvent absorption. (C) 2000 Elsevier Science Ltd. All rights reserved.