Research
on ionic liquids is constantly providing information on
their new and more advanced applications. Undoubtedly, the use of
latent curing agents for epoxy resins is one of the most interesting
applications of this group of compounds. In this work, a detailed
description of the synthesis and physicochemical studies of DABCO-based
(1,4-diazabicylo[2.2.2]octane) ionic liquids is presented. Their most
valuable feature is that they can be latent curing agents for polymerization
of epoxy resins, which in turn can be used, when combined with fibers,
as composites with special, new properties. The research includes
detailed discussion of synthesis of new DABCO-ILs, focusing on obtaining
pure compounds and expanding current knowledge on the subject. Thermal
(DSC) and chromatographic (IC) properties have been discussed for
all presented salts. Furthermore, ionic liquids with dicyanamide and
triflate anion have demonstrated the ability to initiate polymerization
of epoxy resins. Subsequently, all mixtures were cured into cubical
shape and were subjected to the Shore hardness test (SHT). The main
advantages of the obtained ILs are (i) the ability to store ionic
liquids/epoxy resin mixture for prolonged periods of time without
deterioration of curing properties and (ii) a significantly lower
quantity of ionic liquids used in the process of curing epoxy resins.
The paper presents the preparation of new ionic liquids based on hexamethylenetetramine with bis(trifluoromethanesulfonyl)imide and dicyanamide anion, which were characterized in detail in terms of their purity (Ion Chromatography) and thermal properties (Differential Scanning Calorimetry), as well as stability. The obtained substances were used to develop curing systems with ethylene glycol, which were successfully tested for their application with bisphenol A diglycidyl ether molecule. In addition, the curing process and its relationship to the structure of the ionic liquid are characterized in detail. The research showed that hexamethylenetetramine-based new ionic liquids can be successfully designed using well-known and simple synthetic methods—the Delepine reaction. Moreover, attention was paid to their stability, related limitations, and the application of hexamethylenetetramine-based ionic liquids in epoxy-curing systems.
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