Rapid synthesis of functional poly(ester amide)s through thiol-ene chemistry

Poly(ester amide)s (PEAs) bearing various side chains were synthesized by post-polymerization modification of PA-1, a vinylidene containing PEA. The thiols 1-dodecanethiol (1A-SH), 2-phenylethanethiol (1B-SH), 2-mercaptoethanol (1C-SH), thioglycolic acid (1D-SH), furfuryl mercaptan (1E-SH) and sodium-2-mercaptoethanesulfonate (1F-SH) were reacted with PA-1 to form PEAs PA-1A through PA-1F respectively. PEAs containing non-polar thiol side chains (PA-1A, PA-1B, PA-1E), showed little change in solubility compared to PA-1, while PEAs with more polar side chains improved solubility in more polar solvents. PA-1F, functionalized with sodium-2-mercaptoethanesulfonate, became water-soluble. The introduction of pendant functional groups impacted the thermal behaviors of PEAs in a wide range. The PEAs were thermally stable up to 368 °C, with glass transition temperatures (T_g) measured between 117 to 152 °C. Moreover, to demonstrate the versatility of the PEAs, thermal reprocessable networks and polyurethanes were successfully fabricated by reacting with a bismaleimide (1,6-bis(maleimido)hexane, 1,6-BMH) and a diisocyanate (4,4'-diphenylmethane diisocyanate, 4,4'-MDI), respectively. This study paves the way for the facile synthesis of functional poly(ester amide)s with great potential in many fields.

Correction: Making good on a promise: ionic liquids with genuinely high degrees of thermal stability

Correction for 'Making good on a promise: ionic liquids with genuinely high degrees of thermal stability' by Brooks D. Rabideau et al., Chem. Commun., 2018, 54, 5019-5031, https://doi.org/10.1039/C8CC01716F.

Correction: Tuning the melting point of selected ionic liquids through adjustment of the cation's dipole moment

Correction for 'Tuning the melting point of selected ionic liquids through adjustment of the cation's dipole moment' by Brooks D. Rabideau et al., Phys. Chem. Chem. Phys., 2020, 22, 12301-12311, https://doi.org/10.1039/D0CP01214A.

Correction: Understanding liquid-liquid equilibria in binary mixtures of hydrocarbons with a thermally robust perarylphosphonium-based ionic liquid

[This corrects the article DOI: 10.1039/D1RA06268A.].

Cyclopropane as an Unsaturation "Effect Isostere": Lowering the Melting Points in Lipid-like Ionic Liquids

The replacement of unsaturation with a cyclopropane motif as a (bio)isostere is a widespread strategy in bacteria to tune the fluidity of lipid bilayers and protect membranes when exposed to adverse environmental conditions, e.g., high temperature, low pH, etc. Inspired by this phenomenon, we herein address the relative effect of the cyclopropanation, both cis and trans configurations, on melting points, packing efficiency, and order of a series of lipid-like ionic liquids via a combination of thermophysical analysis, X-ray crystallography, and computational modeling. The data indicate there is considerable structural latitude possible when designing highly lipophilic ionic liquids that exhibit low melting points. While cyclopropanation of the lipid-like ionic liquids provides more resistance to aerobic degradation than their olefin analogs, the impact on the melting point decrease is not as pronounced. Our results demonstrate that incorporating one or more cyclopropyl moieties in long aliphatic chains of imidazolium-based ionic liquids is highly effective in lowering the melting points of such materials relative to their counterparts bearing linear, saturated, or thioether side chains. It is shown that the cyclopropane moiety effectively disrupts packing, favoring formation of gauche conformer in the side chains, resulting in enhancement of fluidity. This was irrespective of the configuration of the methylene bridge, although marked differences in the effect of cis- and trans-monocyclopropanated ILs on the melting points were observed.

Understanding liquid–liquid equilibria in binary mixtures of hydrocarbons with a thermally robust perarylphosphonium-based ionic liquid

Binary mixtures of hydrocarbons and a thermally robust ionic liquid (IL) incorporating a perarylphosphonium-based cation are investigated experimentally and computationally. Experimentally, it is seen that excess toluene added to the IL forms two distinct liquid phases, an “ion-rich” phase of fixed composition and a phase that is nearly pure toluene. Conversely, n-heptane is observed to be essentially immiscible in the neat IL. Molecular dynamics simulations capture both of these behaviours. Furthermore, the simulated composition of the toluene-rich IL phase is within 10% of the experimentally determined composition. Additional simulations are performed on the binary mixtures of the IL and ten other small hydrocarbons having mixed aromatic/aliphatic character. It is found that hydrocarbons with a predominant aliphatic character are largely immiscible with the IL, while those with a predominant aromatic character readily mix with the IL. A detailed analysis of the structure and energetic changes that occur on mixing reveals the nature of the ion-rich phase. The simulations show a bicontinuous phase with hydrocarbon uptake akin to absorption and swelling by a porous absorbent. Aromatic hydrocarbons are driven into the neat IL via dispersion forces with the IL cations and, to a lesser extent, the IL anions. The ion–ion network expands to accommodate the hydrocarbons, yet maintains a core connective structure. At a certain loading, this network becomes stretched to its limit. The energetic penalty associated with breaking the core connective network outweighs the gain from new hydrocarbon–IL interactions, leaving additional hydrocarbons in the neat phase. The spatially alternating charge of the expanded IL network is shown to interact favourably with the stacked aromatic subphase, something not possible for aliphatic hydrocarbons.

Binary mixtures of hydrocarbons and a thermally robust ionic liquid (IL) incorporating a perarylphosphonium-based cation are investigated experimentally and computationally.

Tuning the melting point of selected ionic liquids through adjustment of the cation's dipole moment

In previous work with thermally robust salts [Cassity et al., Phys. Chem. Chem. Phys., 2017, 19, 31560] it was noted that an increase in the dipole moment of the cation generally led to a decrease in the melting point. Molecular dynamics simulations of the liquid state revealed that an increased dipole moment reduces cation-cation repulsions through dipole-dipole alignment. This was believed to reduce the liquid phase enthalpy, which would tend to lower the melting point of the IL. In this work we further test this principle by replacing hydrogen atoms with fluorine atoms at selected positions within the cation. This allows us to alter the electrostatics of the cation without substantially affecting the sterics. Furthermore, the strength of the dipole moment can be controlled by choosing different positions within the cation for replacement. We studied variants of four different parent cations paired with bistriflimide and determined their melting points, and enthalpies and entropies of fusion through DSC experiments. The decreases in the melting point were determined to be enthalpically driven. We found that the dipole moment of the cation, as determined by quantum chemical calculations, is inversely correlated with the melting point of the given compound. Molecular dynamics simulations of the crystalline and solid states of two isomers showed differences in their enthalpies of fusion that closely matched those seen experimentally. Moreover, this reduction in the enthalpy of fusion was determined to be caused by an increase in the enthalpy of the crystalline state. We provide evidence that dipole-dipole interactions between cations leads to the formation of cationic domains in the crystalline state. These cationic associations partially block favourable cation-anion interactions, which are recovered upon melting. If, however, the dipole-dipole interactions between cations is too strong they have a tendency to form glasses. This study provides a design rule for lowering the melting point of structurally similar ILs by altering their dipole moment.

The role of urea in the solubility of cellulose in aqueous quaternary ammonium hydroxide

We examine the role of water and urea in cellulose solubility in tetrabutylammonium hydroxide (TBAH). Molecular dynamics simulations were performed for several different solvent compositions with a fixed cellulose fraction. For each composition, two simulations were carried out with cellulose fixed in each of the crystalline and the dissolved states. From the enthalpy and the entropy of the two states, the difference in Gibbs free energy (ΔG) and hence the spontaneity is determined. A comparison with solubility experiments showed a strong correlation between the calculated ΔG and the experimental measurements. A breakdown of the enthalpic and entropic contributions reveals the roles of water and urea in solubility. At high water concentration, a drop in solubility is attributed to both increased enthalpy and decreased entropy of dissolution. Water displaces strong IL–cellulose interactions for weaker water–cellulose interactions, resulting in an overall enthalpy increase. This is accompanied by a strong decrease in entropy, which is primarily attributed to both water and the entropy of mixing. Adding urea to TBAH(aq) increases solubility by an addition to the mixing term and by reducing losses in solvent entropy upon dissolution. In the absence of urea, the flexible [TBA]⁺ ions lose substantial degrees of freedom when they interact with cellulose. When urea is present, it partially replaces [TBA]⁺ and to a lesser extent OH⁻ near cellulose, losing less entropy because of its rigid structure. This suggests that one way to boost the dissolving power of an ionic liquid is to limit the number of degrees of freedom from the outset.

We examine the role of water and urea in cellulose solubility in tetrabutylammonium hydroxide (TBAH).

Making good on a promise: ionic liquids with genuinely high degrees of thermal stability

Thermally robust materials have been of interest since the middle of the past century for use as high temperature structural materials, lubricants, heat transfer fluids and other uses where thermal stability is necessary or desirable. More recently, ionic liquids have been described as 'thermally robust,' with this moniker often originating from their low volatility rather than their innate stability. As many ionic liquids have vanishingly low vapor pressures, the upper limit of their liquid state is commonly considered to be their degradation temperature, frequently reported from TGA measurements. The short duration ramps often used in TGA experiments can significantly overestimate the temperature at which significant degradation begins to occur when the compounds are held isothermal for even a few hours. Here, we review our recent work, and that of colleagues, in developing thermally robust ionic compounds, primarily perarylphosphonium and perarylsulfonium bistriflimide salts, in some of which cation stability exceeds that of the anion. We have used a combination of molecular design, synthesis, and computational modeling to understand the complex tradeoffs involving thermal stability, low melting point and other desirable physicochemical properties.

Thioether-functionalized picolinium ionic liquids: synthesis, physical properties and computational studies

Facile and robust construction of picolinium ionic liquids via thiol–ene reaction bestows materials with low T_g/T_m values along with high hydrophobicity and heat capacity.

An evaluation of anion suitability for use in ionic liquids with long-term, high-temperature thermal stability

The stability of fourteen different PPN⁺ salts has been studied in 96 hour tests, in air, at temperatures of 200 °C, 250 °C, and 300 °C.

Thermally robust: triarylsulfonium ionic liquids stable in air for 90 days at 300 °C

Select triarylsulfonium salts are ionic liquids with outstanding long-term, high-temperature aerobic stability (no mass loss in 90 days at 300 °C in air), making them among the most thermally stable organic materials known.

The effect of structural modifications on the thermal stability, melting points and ion interactions for a series of tetraaryl-phosphonium-based mesothermal ionic liquids

New mesothermal ionic liquids (left).

Solubility of CO2 and N2O in an Imidazolium-Based Lipidic Ionic Liquid

Imidazolium-based ionic liquids have been extensively studied for their ability to dissolve a wide variety of gases and for their potential to be used as separation agents in industrial processes. For many short chain 1-alkyl-3-methylimidazolium bistriflimde salts, CO₂ and N₂O solublities are very similar. In this work, the solubility of CO₂ and N₂O has been measured in the lipidic ionic liquid 1-methyl-3-(Z-octadec-9-enyl)imidazolium bistriflimide ([oleyl-mim][NTf₂]) at 298 K, 310 and 323 K up to ∼2 MPa. N₂O was found to have higher solubility than CO₂ under the same conditions, similar to the behavior observed when olive oil, a natural lipid, was the liquid solvent. However, the solubility of each gas on a mole fraction basis is lower in the ionic liquid than in olive oil. Comparison of the gas solubilities on a mass fraction basis demonstrates that CO₂ solubility is nearly identical in both liquids; N₂O solubility is higher than CO₂ for both liquids, but more so in the olive oil. The difference is attributed to the high mass fraction of the olive oil that is lipid-like in character. The differential solubility of N₂O/CO₂ in this ionic liquid, in contrast to that of shorter chain 1-alkyl-3-methylimidazolium bistriflimide salts, gives physical insight into the solvent properties of this class of ionic liquids and provides further support for their lipid-like character.

Fusion and Thermal Degradation Behavior of Symmetric Sulfur-Containing Quaternary Ammonium Bromides

Quaternary ammonium salts are widely used in consumer products and industrial processes, where their instability at elevated temperatures limits their range of applications. In this work, the thermal behavior of a new class of quaternary ammonium salts was investigated using differential scanning calorimetry. These salts contain a sulfur atom in each chain at the fourth position from the central nitrogen and are thus termed thiaquats. The temperatures at which these salts melt and thermally degrade were determined, and enthalpies and entropies of fusion were evaluated. Their melting points increase with chain lengths, in contrast to the behavior of traditional quaternary ammonium salts. Furthermore, they exhibit enthalpies and entropies of fusion significantly lower than corresponding tetraalkyl analogues. These trends provide physical insight into the molecular-level behavior of these salts, suggesting that they do not fully dissociate upon melting. The thiaquats also exhibit thermal stability to markedly higher temperatures than traditional quaternary ammonium bromides, a phenomenon that can be explained in by strong pairing between the quaternary cation and bromide anion, which inhibits possible decomposition mechanisms. This enhanced thermal stability may enable applications of these salts in processes where traditional salts are not viable, such as phase-transfer-catalyzed systems performed at elevated temperatures.

Liquid–liquid equilibria of binary mixtures of a lipidic ionic liquid with hydrocarbons

A lipidic ionic liquid is described with very high alkane solubility that is virtually immiscible in the alkane phase.

Multi-ion ionic liquids and a direct, reproducible, diversity-oriented way to make them

Multi-ion ionic liquids featuring large numbers of distinct imidazolium cations can be easily and reproducibly prepared in a simple one-pot procedure. The method provides a dramatic improvement in efficiency over the almost universally used approach of mixing pre-existing ILs to make multi-ion systems.

Modification of Fibers with Nanostructures Using Reactive Dye Chemistry

Reactive dyes conventionally used to chemically bind chromophores to fabrics have been used to develop a platform technology that can modify commercially available fibers with nanoscale structures. To illustrate this concept, commercial nylon and cellulose fibers have been modified with gold nanoparticles of three sizes, metal organic framework (MOF) crystals, and quantum dots in five sizes. The gold modified cellulose and nylon samples have colors that vary based on the size of the gold particles, and the particles remained attached to the fibers, even after being washed with solvents, water, and soap. The MOF was grown on the fibers after applying reactive dyes to anchor the metal building unit to the fibers, and the process produced cellulose fibers with surface areas of ~980 m2/g. Both the nylon and cellulose MOF modified fabrics show preferential adsorption of ethylene over ethane and the ability to adsorb ammonia from air. Quantum dot modified nylon and cellulose fibers have fluorescent properties consistent with the unbound particles and remained attached to the fibers after washing with organic solvents, water, and soap. Applications are broad, and this work provides a first step at coupling conventional dyes and nanotechnology.

Use and recovery of a homogeneous catalyst with carbon dioxide as a solubility switchElectronic supplementary information (ESI) available: methods of preparation of fluorous silica and complexes 1 and 2. See http://www.rsc.org/suppdata/cc/b3/b311146f/

A method for fluorous biphasic catalysis is described,in which the fluorous liquid is replaced by fluorinated silica, the fluorous catalyst is induced to dissolve in the organic solvent by the presence of CO2, and the recovery of the catalyst after the reaction is achieved by release of the CO2 pressure.