New structure of diamine curing agent for epoxy resins with self-restoration ability: Synthesis and spectroscopy characterization

The development of smart materials in aeronautical structures consisting of compounds based on epoxy resins having self-repair capability has been hampered by some criticalities. One of the main critical points is related to the impossibility to use primary amines (e.g.: 4,4'-diaminodiphenyl sulfone, DDS) as hardeners, because they can poison the catalyst responsible for the healing mechanisms. In this paper, the synthesis, characterization and some tests of applicability of a new hardener, the tetramethylated diaminodiphenyl sulfone (tm-DDS), are shown. The tm-DDS is able to rapidly react with epoxy resin, giving a composite material having some characteristics significantly better than composites hardened with different tertiary amines. The new hardener is able to increase the glass transition temperature (Tg) of about 90 degrees C with respect to the more common hardener, ancamine K54, already used in self-healing ;epoxy formulations. (C) 2016 Elsevier B.V. All rights reserved.