These resins are two-component products consisting of an epoxy resin part and a hardener part.
The hardeners contain terminators that can be added to the epoxy rings of the resin during processing, or catalytic functions that trigger the copolymerization of the epoxy system. This reaction takes place without elimination, so the resulting polymer has minimal shrinkage. The perfectly polymerized epoxy resin belongs to the family of thermosetting plastics which, by definition, are infusible and insoluble under the action of heat, solvents and radiation.
The reaction of a bi-functional epoxy resin and a classical tetrafunctional hardener can be represented by (Diagram 1):
