Thermodynamics of Tri- and Tetraepoxyimidazolium NTf₂ Amine Polyaddition: A Theoretical Perspective

The thermodynamics of newly designed tri- and tetraepoxyimidazolium NTf2 monomers reacting with several diamines used as curing agents to form epoxy/amine thermosets was studied. The ability of each epoxy/amine combination to induce cross-linking both through the substitution of multiple epoxy groups and through multiple additions to a single amine was investigated. Through an increased understanding of the thermodynamics of epoxy–amine polymerization in complex polyepoxy-ILs, it is possible to more thoroughly understand the factors affecting the reactivity in these complex systems. These calculations showed that while each possible epoxy–amine combination was exergonic to both forms of cross-linking, the degree to which both amines-induced cross-linking and epoxy-induced cross-linking was favored varied between epoxy–amine combinations. Thermodynamic results obtained using density functional theory were experimentally validated through differential scanning calorimetry results, wherein similar trends were noted between theory and experiment. Among the trends noted in amines–epoxy combinations tested, tetraepoxyimidazolium NTf2/PACM (i.e., a cycloaliphatic diamine) was found to be a prime candidate for amine cross-linking, with the addition of a second epoxy to a single amine group being notably the most negative of all epoxy–amine combinations at −77.6 kJ mol–1. While in the case of epoxy cross-linking, the aliphatic polyetheramine denoted Jeffamine-D230-containing systems were found to be the most exergonic, with additions of primary amines to triepoxyimidazolium and tetraepoxyimidazolium NTf2 averaging −86.9 kJ mol–1. Interaction energy analysis indicated that the aromatic amine named sulfanilamide is the most favorable to engage in reactions due to having the most negative interaction energies with already highly substituted epoxy monomers. These results can be used to adjust the cross-linking possibilities of tri- and tetraepoxyimidazolium NTf2/amine polymerization and give insight into the predominant cross-linking reactions in these unique systems

Microencapsulated Diepoxy-Functionalized Ionic Liquids to the Design of Self-Healable Epoxy Networks

An extrinsic self-healing mechanism based on microencapsulated healing agents represents an original way to produce self-healable thermosetting materials without modifying the structural architecture of the co-monomers. In this work, self-healing was achieved through poly­(melamine–formaldehyde) (PMF) microcapsules containing a polymerizable diepoxidized ionic liquid monomer denoted as ILEM. First, a synthetic route to design ILEM@PMF microcapsules via in situ polymerization was developed and optimized through the choice of surfactants, core/shell ratios, and stirring speeds. Then, the obtained microcapsules (10 wt %) were incorporated into three different epoxy–amine networks and their effects on the morphology, thermal behavior, i.e., glass transition temperature (Tg) and degradation temperature (Td), as well as on the mechanical properties were investigated. In addition, a pre-crack was generated with a fresh razor blade into the center groove of the epoxy networks and their self-healing performances were observed by scanning electron microscopy before and after the curing process

Research on the Dynamic Response Properties of Nonlethal Projectiles for Injury Risk Assessment

Based on the models already on the market, we have manufactured six types of nonlethal projectiles. We have made convex heads out of polyurethane foam (PUR) filled with mineral fillers like alumina (Al2O3) and montmorillonite (MMT). We chose a suitable holder for nonlethal projectiles. Also, we made a custom industrial model and used CAD modeling in SolidWorks to simulate the deformation of the nonlethal projectiles. The polymeric nonlethal projectile holders were then 3D-printed. We performed a dynamic mechanical analysis (DMA) and discussed the results. Likewise, we conducted ballistic impact experiments on nonlethal projectiles (XM1006) and nonlethal projectiles manufactured that were evaluated using a rigid wall and a pneumatic launcher. Furthermore, we looked at cell structure, the spread of the mean pore diameter, and the particle size distributions of the mineral fillers using scanning electron microscopy (SEM). We evaluated and discussed injury risks from nonlethal impacts. Data on nonlethal projectile lethality and safe impact speed are collected. This study explains how lab studies and real-world practice coexist through nonlethal projectile properties

Supercritical CO₂–Ionic Liquids: A Successful Wedding To Prepare Biopolymer Foams

In this work, tetraalkylphosphonium and dialkyl imidazolium ionic liquids have been studied as surfactant agents of layered silicates (montmorillonite, MMT). The influence of the chemical nature of the cations as well as the counteranions on the thermal behavior (TGA), on the structural analysis (XRD) and on the surface energies of organically modified montmorillonites has been investigated. Then, poly­(butylene adipate-<i>co</i>-terephthalate) (PBAT)–clay nanocomposites were processed by melt mixing using a twin screw extruder in order to achieve the better dispersion of MMT and were used to prepare cellular foams with supercritical carbon dioxide (ScCO₂). Thus, a small amount (2 wt %) of imidazolium-treated montmorillonite is the relevant candidate to decrease the cell size (600 to 125 μm)

Ionic liquids: A New Route for the Design of Epoxy Networks

A new way to synthesize epoxy networks was reported in this work using phosphonium based ionic liquids combined with phosphinate, carboxylate, and phosphate counteranions. The influence of the chemical nature of the anions was investigated on the polymerization kinetics of epoxy systems as well as the thermal and mechanical properties of epoxy–IL networks. In all cases, ILs displayed a high reactivity toward epoxy prepolymer and led to the formation of poly epoxy networks with high epoxy group conversion, i.e., up to 90%. In addition, epoxy–IL networks have high hydrophobicity and an excellent thermal stability (above 350 °C) under N₂ with the glass transition temperatures (<i>T</i>_g) ranging from 90 to 140 °C depending on the chemical structure of ILs. For the first time, the mechanical properties of epoxy–IL networks were also evaluated in terms of flexural properties and fracture toughness (<i>K</i>_Ic)

Development of Bioresorbable Hydrophilic–Hydrophobic Electrospun Scaffolds for Neural Tissue Engineering

In this study, electrospun fiber scaffolds based on biodegradable and bioabsorbable polymers and showing a similar structure to that of the extracellular matrix (ECM) present in the neural tissues were prepared. The effects of electrospun-based scaffolds processed from poly­(lactic acid) (PLA)/poly­(lactide-b-ethylene glycol-b-lactide) block copolymer (PELA) and PLA/polyethylene glycol (PEG) (50:50 by wt) blends on the morphology, wettability, and mechanical properties, as well as on neural stem cell (NSC) behavior, were investigated. Thus, PLA/PELA and PLA/PEG fiber mats composed of PEG with different chain lengths were evaluated for optimal use as tissue engineering scaffolds. In both cases, the hydrophilic character of the scaffold surface was increased from the introduction of PEG homopolymer or PEG-based block copolymer compared with neat PLA. A microphase separation and a surface erosion of PLA/PEG blend-based electrospun fibers were highlighted, whereas PLA/PELA blend-based fibers displayed a moderate hydrophilic surface and a tunable balance between surface erosion and bulk degradation. Even if the mechanical properties of PLA fibers containing PEG or PELA decreased slightly, an excellent compromise between stiffness and the ability to sustain large deformation was found for PLA/PELA­(2k), which displayed a significant increase in strain at break, that is, up to 500%. Our results suggest that both neat PLA and PLA/PELA blends supplemented with growth factors may mimic neural-like constructs and provide structural stability. Nonetheless, electrospun PLA/PELA blends have a suitable surface property, which may act synergistically in the modulation of biopotential for implantable scaffolding in neural tissue engineering

Theoretical Analysis of Physical and Chemical CO₂ Absorption by Tri- and Tetraepoxidized Imidazolium Ionic Liquids

The efficient capture of CO2 from flue gas or directly from the atmosphere is a key subject to mitigate global warming, with several chemical and physical absorption methods previously reported. Through polarizable molecular dynamics (MD) simulations and high-level quantum chemical (QC) calculations, the physical and chemical absorption of CO2 by ionic liquids based on imidazolium cations bearing oxirane groups was investigated. The ability of the imidazolium group to absorb CO2 was found to be prevalent in both the tri- and tetraepoxidized imidazolium ionic liquids (ILs) with coordination numbers over 2 for CO2 within the first solvation shell in both systems. Thermodynamic analysis of the addition of CO2 to convert epoxy groups to cyclic carbonates also indicated that the overall reaction is exergonic for all systems tested, allowing for chemical absorption of CO2 to also be favored. The rate-determining step of the chemical absorption involved the initial opening of the epoxy ring through addition of the chloride anion and was seen to vary greatly between the epoxy groups tested. Among the groups tested, the less sterically hindered monoepoxy side of the triepoxidized imidazolium was shown to be uniquely capable of undergoing intramolecular hydrogen bonding and thus lowering the barrier required for the intermediate structure to form during the reaction. Overall, this theoretical investigation highlights the potential for epoxidized imidazolium chloride ionic liquids for simultaneous chemical and physical absorption of CO2

From the Design of Novel Tri- and Tetra-Epoxidized Ionic Liquid Monomers to the End-of-Life of Multifunctional Degradable Epoxy Thermosets

The design and development of multifunctional epoxy thermosets have recently stimulated continuous research on new degradable epoxy monomers. Herein, tri- and tetra-epoxidized imidazolium monomers were rationally designed with cleavable ester groups and synthesized on a multigram scale (up to 100 g), yielding room-temperature ionic liquids. These monomers were used as molecular building blocks and cured with three primary amine hardeners having different reactivities, leading to six different network architectures. Overall, the resulting epoxy–amine networks exhibit high thermal stability (>350 °C), excellent mechanical properties combined with a shape memory behavior, glass transition temperatures (Tgs) from 55 to 120 °C, and complete degradability under mild conditions. In addition, nonpolarizable, all-atom molecular dynamics simulations were applied in order to investigate the molecular interactions during the polyaddition reaction-based polymerization and then to predict the thermomechanical and mechanical properties of the resulting networks. Thus, this work employs computational chemistry, organic synthesis, and material science to develop high-performance as well as environmentally friendly networks to meet the requirements of the circular economy

From the Design of Novel Tri- and Tetra-Epoxidized Ionic Liquid Monomers to the End-of-Life of Multifunctional Degradable Epoxy Thermosets

The design and development of multifunctional epoxy thermosets have recently stimulated continuous research on new degradable epoxy monomers. Herein, tri- and tetra-epoxidized imidazolium monomers were rationally designed with cleavable ester groups and synthesized on a multigram scale (up to 100 g), yielding room-temperature ionic liquids. These monomers were used as molecular building blocks and cured with three primary amine hardeners having different reactivities, leading to six different network architectures. Overall, the resulting epoxy–amine networks exhibit high thermal stability (>350 °C), excellent mechanical properties combined with a shape memory behavior, glass transition temperatures (Tgs) from 55 to 120 °C, and complete degradability under mild conditions. In addition, nonpolarizable, all-atom molecular dynamics simulations were applied in order to investigate the molecular interactions during the polyaddition reaction-based polymerization and then to predict the thermomechanical and mechanical properties of the resulting networks. Thus, this work employs computational chemistry, organic synthesis, and material science to develop high-performance as well as environmentally friendly networks to meet the requirements of the circular economy