Epoxy Resin/Ionic Liquid Systems: The Influence of Imidazolium Cation Size and Anion Type on Reactivity and Thermomechanical Properties

Abstract

The epoxy compositions with ionic liquids (ILs) differing in the alkyl chain length of imidazolium cation (butyl or decyl), anion type [N(CN) 2 ¯, BF 4 ¯, Cl ¯], as well as ILs concentration (1, 3, and 9 phr) have been prepared, and their curing characteristics at ambient and elevated temperatures have been investigated. Rheometric, differential scanning calorimetry, and Fourier transform infrared measurements revealed substantial differences in the curing characteristics dependent mainly on the IL anion type and its concentration. TGA results showed that thermal decomposition of IL influenced the onset temperature of epoxy resins cross-linking reactions during heat treatment. Dynamic mechanical thermal analysis measurements showed that the type of IL anion had an effect on T g and tan δ values as well. For materials cross-linked with ILs containing dicyanamide anion the highest T g (ca. 170 °C) and the lowest tan δ (0.26) values have been found. On the basis of the obtained results and literature data the mechanism of epoxy resin cross-linking in the presence of imidazolium ionic liquids has been proposed.

3-[2-(Oxiran-2-yl)ethyl]-1-{4-[(2-oxiran-2-yl)ethoxy]benzyl}imidazolium bis(Trifluoromethane)sulfonimide

“…According to these additional characteristics, ionic liquids can be used for specific practical applications as surfactants [2], lubricants, plasticizers, reactive (or non-reactive) additives to polymer matrices, or simply as solvents in electrochemistry [3][4][5]. In the wide range of ionic liquids reported in the literature, it should be noted that those based on the imidazolium fragment have received increasing attention in recent years [6][7][8]. These ionic liquids with multifaceted roles can act as initiators in the polymerization of the epoxy prepolymer or directly as liquid monomers to design epoxy networks or polymerized ionic liquids [9,10].…”

Epoxy resin/phosphonium ionic liquid/carbon nanofiller systems: Chemorheology and properties

“…Ionic liquids (ILs) have been applied as sole crosslinkers for epoxy resin [1][2][3][4][5] or admixtures for epoxy systems cured with conventional hardeners that allowed to modify the properties of the final epoxy materials [3,[6][7][8]. ILs have been used together with polyamine or anhydride hardeners in order to modify epoxy curing process as well as materials glass transition temperature [7,8], lubrication [6], or to improve (nano)filler dispersion [9][10][11].…”

“…ILs have been used together with polyamine or anhydride hardeners in order to modify epoxy curing process as well as materials glass transition temperature [7,8], lubrication [6], or to improve (nano)filler dispersion [9][10][11]. The epoxy compositions with the most often used 1-alkyl-3-methylimidazolium ILs exhibited pot life at ambient temperature: 50-60 days where counteranions were chloride or tetrafluoroborate (3 wt parts/ 100 wt parts of epoxy resin, 3 phr) [4,12]. That parameter was shortened to 30 days when 1-butyl-3-methylimidazolium (BMIM) with dicyanamide anion [2] or even to 3 days when BMIM with thiocyanate anion [5] was used (at 3 phr).…”

“…It has been found that aliphatic phosphonium IL [trihexyltetradecylphosphonium bis(2,4,4-trimethylpentyl) phosphinate, IL-f] allowed to obtain epoxy materials with good thermomechanical properties and high thermal stability [13]. Glass transition temperatures of the epoxy materials crosslinked solely with ILs were often above 150°C [2,4,5,13]. The important advantages of applying ILs for liquid epoxy resin catalytic curing are their low loadings (typically 3-9 phr) as well as fast and easy miscibility with other liquid components resulting in technological feasibility [5].…”

Composition as a Means To Control Morphology and Properties of Epoxy Based Dual-Phase Structural Electrolytes

“…34,40 , the performance of the epoxy can be modulated, since many ILs can be used as curing agents. 31,33,[41][42][43][44] In addition, the properties/structure (morphology) of the epoxy/IL blends and resulting cured epoxies can be adjusted, for example to improve wear and scratch resistance, 32, 33 thermal stability 44 or ion conduction. 10,18 In an earlier study, we described a strong effect of the morphology on the properties of electrolytes based on a blend of an epoxy/amine system and a lithium salt doped IL 10 ; the conclusion was that a relatively coarse bicontinuous structure is the most promising for structural electrochemical applications.…”