Dynamic Mechanical Analysis of Thermosetting Materials

As described in an earlier paper “Thermal Analysis in Thermoset Characterization,” thermosetting polymers are unique. Unlike thermoplastic polymers, chemical reactions are involved in their use. As a result of these reactions the materials cross-link and become “set”, i.e. they can no longer flow or dissolve. In this paper the behavior and characteristics of thermosetting materials are briefly reviewed (see earlier paper for a more detailed discussion), followed by a detailed discription of dynamic mechanical analysis of the cure process, and ending with some comments on properties of cured thermosets. Cure is illustrated schematically in Fig. 1 for a material with co-reactive monomers such as an epoxy-diamine system. For simplicity the reaction of a difunctional monomer with a trifunctional monomer is considered. Reaction in the early stages of cure {(a) to (b)} produces larger and branched molecules and reduces the total number of molecules.