EVOLUTION OF STRUCTURE AND PROPERTIES OF A LIQUID-CRYSTALLINE EPOXY DURING CURING

The evolution of structure, and thermal and dynamic mechanical propert ies of a liquid crystalline epoxy during curing has been studied with differential scanning calorimetry (DSC), polarized optical microscopy, x-ray scattering, and dynamic mechanical analysis. The liquid crystal line epoxy was the diglycidyl ether of 4,4'-dihydroxy-alpha-methylstil bene (DGEDHMS). Two curing agents were used in this study: a difunctio nal amine, the aniline adduct of DGEDHMS, and a tetra-functional sulfo namido amine, sulfanilamide. The effects of curing agent, cure time, a nd cure temperature have been investigated. Isothermal curing of the l iquid crystalline epoxy with the difunctional amine and the tetra-func tional sulfonamido amine causes an increase in the mesophase stability of the liquid crystalline epoxy resin. The curing also leads to vario us liquid crystalline textures, depending on the curing agent and cure temperature. These textures coarsen during the isothermal curing. Mor eover, curing with both curing agents results in a layered structure w ith mesogenic units aligned perpendicular to the layer surfaces. The l ayer thickness decreases with cure temperature for the systems cured w ith the tetra-functional curing agent. The glass transition temperatur e of the cured networks rises with increasing cure temperature due to the increased crosslink density. The shear modulus of the cured networ ks shows a strong temperature dependence. However, it does not change appreciably with cure temperature. (C) 1997 John Wiley & Sons, Inc.