| Abstract: | The objective of the research is to investigate epoxy resins where crosslinks formed in curing reactions can be cleaved and reformed without significant sacrifice in resin properties. In this phase of the investigation, experimental disulfide-containing crosslinking agents have been studied, including dihydrazides of dithiodicarboxylic acids(aliphatic and aromatic) and dithio-aromatic diamines. Conditions for curing reactions and for subsequent cleavage of crosslinks by reduction have been determined in model systems and confirmed for a prototype epoxy resin. A preliminary comparative evaluation of cure kinetics and of crosslink density and thermal and mechanical properties has been carried out for this resin cured with aromatic curing agents (4,4′-dithiodianiline and methylene dianiline) and with aliphatic compounds (3,3′-dithiopropionic acid dihydrazide and hexamethylene diamine). It has been shown that in a resin fully cured with disulfide-containing crosslinking agents, crosslinks could be ruptured by reduction, and reestablished by oxidation under mild conditions. |
