An epoxy thermoset that includes a reaction product of a toughening agent prepared from a reaction of a first epoxy resin and a polyether polyamine, a second epoxy resin and a liquid amine hardener for the toughening agent and the second epoxy resin. The toughening agent is an adduct of the second epoxy resin and the polyether polyamine. The polyether polyamine phase of the toughening agent separates to form particles in the epoxy thermoset, where the particles have a volume average diameter in a range from 20 nanometers to 200 nanometers.