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 cha racteristics in comparison with traditional plastics. We now describe quant itatively how the thermal and mechanical properties of a number of liquid c rystalline epoxy resins vary with polymer mesogen concentration, using biph enyl- 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 phy sical properties, and thus increasing mesogen content leads to increased in termolecular interactions between the polymer chains and hence reduced micr o-Brownian motion and reduced free volume. These properties are manifested as increased elastic moduli at high temperatures, reduced thermal coefficie nts of expansion, increased decomposition onset temperatures and reduced so lvent absorption. (C) 2000 Elsevier Science Ltd. All rights reserved.