Role of curing agent on the nature of the mesophase and the properties of mesogenic epoxy resins

Reaction of poly-functional epoxy with suitable curing agent is a well established practice to produce thermosetting materials with chemical and physical properties strongly depending upon the chemical nature of the reacting molecules as well as on the processing conditions. Among the curing agent most extensively used and investigated are the primary and secondary amines, both aromatic and aliphatic, carboxylic acids and anhydrides. The suitability of epoxy group to react via ring opening mechanism catalyzed by a wide variety of experimental conditions is the primary reason for the wide applications based on epoxy resins. On the other hand the draw back of the ready reactivity is the difficulty to control the crosslinking density and other structural parameters affecting the properties of the materials. This statement holds true especially in the case of liquid crystalline epoxy resins. In fact, the structural features and distribution of crosslinks along the molecular backbone strongly influences the liquid crystalline phase developed during the curing process and the performances and the applicability of the resulting material.