Ionic Liquids: A Versatile Platform for the Design of a Multifunctional Epoxy Networks 2.0 Generation

Due to their outstanding properties such as high optical transparency, high electrical resistance, high thermal insulation, good thermo-mechanical properties, and dimensional stability, epoxy networks play a key role in the world of thermosetting polymers. In fact, they are widely used in Industry as adhesives, paints and coatings, electrical and electronics applications as well as composite matrices for automotive and aerospace applications. Epoxy networks are issued from epoxy prepolymers composed of two to four oxirane rings able to undergo a polyaddition polymerizations with hardeners (amines, phenols, isocyanates, or acids) or a chain homopolymerization reactions in the presence of initiators such as tertiary amines, imidazoles, or ammonium salts. However, the innovations in this area have reached certain technological limits. Very recently, ionic liquids have shown their potential to be used as new initiators or functional building blocks of epoxy prepolymers and as a novel generation of epoxidized ionic liquid monomers. Thus, a new and innovative pathway has emerged producing a new generation of epoxy thermosets issue from ionic liquids by the concept of ‘function through structural design’ leading to unprecedented improvements in their physical properties. In fact, epoxy networks can be tuned with glass transition temperatures included from -40 to 170°C depending of the targeted applications. Thus, the polymer/ionic liquid synergy leads to the design and development of new dedicated (multi)functional thermosetting materials with improved properties such as ionic conductivity, chemical and thermal stability, fire retardancy, water barrier properties and mechanical performances. The aim of this review is to point out the potential of this novel class of ionic thermoset materials in the field of epoxy thermosets.