Ether-functionalized Ionic Liquids Research Articles

The Coiling Effect in Ether Ionic Liquids: Exploiting Acetate as a Probe for Transport Properties and Microenvironment Analysis.

The inherently high viscosity of ionic liquids (ILs) can limit their potential applications. One approach to address this drawback is to modify the cation side chain with ether groups. Herein, we assessed the structure-property relationship by focusing on acetate (OAc), a strongly coordinating anion, with 1,3-dialkylimidazolium cations with different side chains, including alkyl, ether, and hydroxyl functionalized, as well as their combinations. We evaluated their viscosity, thermal stabilities, and microstructure using Raman and infrared (IR) spectroscopies, allied to density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. The viscosity data showed that the ether insertion significantly enhances the fluidity of the ILs, consistent with the coiling effect of the cation chain. Through a combined experimental and theoretical approach, we analyzed how the OAc anion interacts with ether ILs, revealing a characteristic bidentate coordination, particularly in hydroxyl functionalized ILs due to specific hydrogen bonding with the OH group. IR spectroscopy showed subtle shifts in the acidic hydrogens of imidazolium ring C(2)-H and C(4,5)-H, suggesting weaker interactions between OAc and the imidazolium ring in ether-functionalized ILs. Additionally, spatial distribution functions (SDF) and dihedral angle distribution obtained via AIMD confirmed the intramolecular hydrogen bonding due to the coiling effect of the ether side chain.

Combined thermodynamic and theoretical study on ether-functionalized ionic liquid mixture systems of [MOEmim][TFSI] with ACN/GBL

Ether-functionalized ionic liquids (ILs) have a higher fluidity and are widely used in a variety of applications due to the introduction of the ether group. In order to better understand the relationship between properties and internal interactions of ether-based ILs, we prepared two ether-functionalized ILs 1–2-methoxyethyl-3-methylimidazolium bis((trifluoromethyl)sulfonyl)imide ([MOEmim][TFSI]) with acetonitrile (ACN) or γ-butyrolactone (GBL) mixture systems, and investigated the changes of their thermodynamic properties and internal interaction behaviors over the entire concentration range. First, the thermodynamic properties such as dynamic viscosity, density and electrical conductivity of the two mixture systems were measured from 288.15 K to 343.15 K. The excess molar volume (VE), and viscosity deviation (Δη) were calculated by using the measured experimental density and dynamic viscosity data, which can provide microscopic information on the interactions. Further, the intermolecular interactions of the mixture systems were evaluated by density functional theory (DFT) calculations. The sigma–profile (σ–profile) provided insight into the hydrogen bonds (H-bonds) and molecular surfaces interactions. We also used molecular dynamics simulations (MD) to study ILs mixtures in many different solvent concentrations, thereby providing a microscopic and macroscopic characterization of fluid structure, molecular aggregation, and intermolecular forces.

Density, viscosity, and CO2 solubility in ether-functionalized phosphonium-based bis(trifluoromethanesulfonyl)amide ionic liquids

We measured the densities and viscosities of two ionic liquids, triethyl(methoxymethyl)phosphonium bis(trifluoromethanesulfonyl)amide ([P222(1O1)][TFSA]) and triethyl(2-methoxyethyl)phosphonium bis(trifluoromethanesulfonyl)amide ([P222(2O1)][TFSA]), at atmospheric pressure and 273.15–363.15 K. The high-pressure density at the pressures up to 50 MPa was also measured at 298.15–353.15 K. Meanwhile, CO2 solubility in these phosphonium-based ionic liquids was determined using a magnetic suspension balance at 303.15–333.15 K and pressures up to 6 MPa. The experimental density and viscosity at atmospheric pressure were fitted using quadratic and Vogel-Fulcher-Tammann equations, respectively. The high-pressure density was fitted using the Tait equation and Sanchez-Lacombe equation of state. The properties of the two ether-functionalized ionic liquids were compared to those of triethylpentylphosphonium bis(trifluoromethanesulfonyl)amide [P2225][TFSA]. The density at atmospheric pressure increased in the order [P2225][TFSA] < [P222(2O1)][TFSA] < [P222(1O1)][TFSA]. The introduction of the ether group effectively reduced viscosity in the following order: [P222(1O1)][TFSA] < [P222(2O1)][TFSA] < [P2225][TFSA]. The CO2 solubilities in [P222(1O1)][TFSA] and [P222(2O1)][TFSA] were slightly lower than those in [P2225][TFSA]. In contrast, the molality of CO2 (m1) increased in the order [P2225][TFSA] < [P222(2O1)][TFSA] < [P222(1O1)][TFSA]. Ether functionalized phosphonium-based cations are effective in enhancing the physical absorption of CO2, particularly the molality of CO2.

Molecular Dynamics of Ionic Liquids from Fast-Field Cycling NMR and Molecular Dynamics Simulations.

Understanding the connection between the molecular structure of ionic liquids and their properties is of paramount importance for practical applications. However, this connection can only be established if a broad range of physicochemical properties on different length and time scales is already available. Even then, the interpretation of the results often remains ambiguous due to the natural limits of experimental approaches. Here we use fast-field cycling (FFC) to access both translational and rotational dynamics of ionic liquids. These combined with a comprehensive physicochemical characterization and MD simulations provide a toolkit to give insight into the mechanisms of molecular mechanics. The FFC results are consistent with the computer simulation and conventional physicochemical approaches. We show that curling of the side chains around the positively charged cationic core is essential for the properties of ether-functionalized ionic liquids, and we demonstrate that neither geometry nor polarity alone are sufficient to explain the macroscopic properties.

Physicochemical and excess properties of binary system mixtures of ether-functionalized ionic liquids with DMSO

In the full molar fraction range, the density, surface tension and viscosity of 1-(4-methoxybutyl)-3-methylimidazolium glycine ([COC4mim][Gly]), 1-(4-methoxybutyl)-3-methylimidazolium alanine ([COC4mim][Ala]) and 1-(4-methoxybutyl)-3-methylimidazolium threonine ([COC4mim][Thr]) with DMSO binary mixtures were determined. The variation trends of excess molar volume (VE), excess molar surface Gibbs energy (gsE), Gibbs energy of activation for viscous flow of the relative viscosity (ΔG≠r) and x1 of binary system mixture were systematically studied, and the interaction between ether-functionalized ionic liquids (ILs) and solvent molecules in binary system mixtures was studied. According to the molar surface Gibbs energy definition, excess molar surface Gibbs energy definition and Redlich-Kister empirical equation, the correlation between the predicted and experimental surface tension values of ILs + DMSO binary system mixtures was investigated. Furthermore, using the improved Eötvös empirical equation and thermodynamic formula, molar surface entropy and molar surface enthalpy of binary system mixture were calculated. The molar surface enthalpy of binary mixture was independent of temperature. This fact indicated that the process from the bulk to the surface of binary system mixture was an isocoulombic reaction.

Surface tension, viscosity and electrical conductivity characteristics of new ether-functionalized ionic liquids

1-(2-Ethoxyethyl)-3-methylimidazolium acetic acid ([C2OC2mim][OAc]) and 1-(2-ethoxyethyl)-3-methylimidazolium lactic acid ([C2OC2mim][Lac]) ether-functionalized ionic liquids (ILs) were prepared. In terms of the standard addition method, the experimental data of density, surface tension, refractive index, viscosity and electrical conductivity of two pure ILs were obtained. Using the definition of the molar surface Gibbs energy with Lorentz-Lorenz empirical equation, the surface tensions of ether-functionalized ILs were estimated, and their predicted values were in good agreement with the experimental values. According to the Vogel-Fulcher-Tamman (VFT) equation, the variation tendency between viscosity (or electrical conductivity) and temperature of [C2OC2mim][OAc] and [C2OC2mim][Lac] was studied. The variation trend of the viscosity was opposite to electrical conductivity. Namely, the viscosity gradually decreased and electrical conductivity gradually increased with increasing temperature. The results indicated that VFT equation had an enormous application range for fitting the viscosity and electrical conductivity of ether-functionalized ILs. The activation energies of [C2OC2mim][OAc] and [C2OC2mim][Lac] were estimated by Arrhenius empirical equation. The calculated results indicated that [C2OC2mim][Lac] (Eη means the activation energy, Eη = 41.24 kJ·mol−1) was larger than [C2OC2mim][OAc] (Eη = 33.57 kJ·mol−1). This result may be related to physical size or stronger interactions.

Polarity Prediction of New Ether-Functionalized Ionic Liquids─[COC4mim][Cl] and [COC4mim][Asp

Polarity Prediction of New Ether-Functionalized Ionic Liquids─[COC₄mim][Cl] and [COC₄mim][Asp

Viscosity and electrical conductivity of ether-functionalized ionic liquids-[C1OC2mim][OAc], [C1OC2mim][Pro] and [C2OC2mim][Pro

1-(2-Methoxyethyl)-3-methylimidazolium acetic acid ([C1OC2mim][OAc]), 1-(2-methoxyethyl)-3-methylimidazolium propionic acid ([C1OC2mim][Pro]) and 1-(2-ethoxyethyl)-3-methylimidazolium propionic acid ([C2OC2mim][Pro]) were successfully prepared by two-step synthesis method. Based on the standard addition method, the physicochemical parameters of the density, viscosity and electrical conductivity for ether-functionalized ionic liquids (ILs) were measured. The volume properties of three ether-functionalized ILs and their homologues were estimated by semi-empirical methods. According to the Eying viscosity equation, the relationship between viscosity and activation Gibbs energy for viscous flow (ΔG≠) was studied. The activation energy values for three ether-functionalized ILs were calculated by Arrhenius empirical equation. The activation energies of these ether-functionalized ILs are arranged in the following order: [C1OC2mim][Pro] (Eη = 39.17 kJ·mol−1) > [C2OC2mim][Pro] (Eη = 37.26 kJ·mol−1) > [C1OC2mim][OAc] (Eη = 37.23 kJ·mol−1). Futhermore, the Vogel-Fulcher-Tamman (VFT) equation is used to describe the relationship between viscosity (or electrical conductivity or molar electrical conductivity) and temperature, and the experimental results show that VFT equation has good general applicability.

Inter- and Intramolecular Interactions in Ether-Functionalized Ionic Liquids.

The intra- and intermolecular interactions in ether-functionalized ionic liquids (ILs) are studied by means of infrared (IR) spectroscopy measurements of N-ethoxyethyl-N-methylpiperidiniumbis(fluorosulfonyl)imide (P1,2O2-FSI) and N-ethoxyethyl-N-methylmorpholiniumbis(fluorosulfonyl)imide (M1,2O2-FSI). The temperature dependence of the spectra in the medium IR range allows the study of the anion conformer distribution and its variation during phase transitions. In particular, it is found that for both ILs the trans conformer of FSI is more stable than the cis conformer, and the enthalpy differences between them are calculated and are found to decrease upon the addition of a Li salt. The results obtained in the far IR range, combined with ab initio calculation of the ionic couple performed using the B3LYP-D functional and considering both empirical dispersion corrections and the presence of a polar solvent, provide evidence for the occurrence of a hydrogen bonding between the O atom of the anion and its closest H atoms directly linked to a C atom of the cation. The comparison with samples having the same cations but with bis(trifluoromethanesulfonyl)imide (TFSI) as an anion, that is, M1,2O2-TFSI and P1,2O2-TFSI, as well as with samples having cations without the ether-functionalization neither in the ring nor in the side chain, such as N-propyl-N-methylpyrrolidinium-FSI (PYR13-FSI) and 1-butyl-1-methylpyrrolidinium-TFSI (PYR14-TFSI), indicates that the occurrence of such highly directional interaction between anion and cation is better observable in the ether-functionalized samples, in particular in those containing FSI as an anion.

Low-Viscosity Ether-Functionalized Ionic Liquids as Solvents for the Enhancement of Lignocellulosic Biomass Dissolution

Due to the substantial usage of fossil fuels, the utilization of lignocellulosic biomass as renewable sources for fuels and chemical production has been widely explored. The dissolution of lignocellulosic biomass in proper solvents is vital prior to the extraction of its important constituents, and ionic liquids (ILs) have been found to be efficient solvents for biomass dissolution. However, the high viscosity of ILs limits the dissolution process. Therefore, with the aim to enhance the dissolution of lignocellulosic biomass, a series of new ether-functionalized ILs with low viscosity values were synthesized and characterized. Their properties, such as density, viscosity and thermal stability, were analyzed and discussed in comparison with a common commercial IL, namely 1-butyl-3-methylimidazolium chloride (BMIMCl). The presence of the ether group in the new ILs reduces the viscosity of the ILs to some appreciable extent in comparison to BMIMCl. 1-2(methoxyethyl)-3-methylimidazolium chloride (MOE-MImCl), which possesses the lowest viscosity value among the other ether-functionalized ILs, demonstrates an ability to be a powerful solvent in the application of biomass dissolution via the sonication method. In addition, an optimization study employing response surface methodology (RSM) was carried out in order to obtain the optimum conditions for maximum dissolution of biomass in the solvents. Results suggested that the maximum biomass dissolution can be achieved by using 3 weight% of initial biomass loading with 40% amplitude of sonication at 32.23 min of sonication period.

Comparative study of the hydrogen bonding properties between bis(fluorosulfonyl)imide/bis(trifluoromethyl)sulfonylimide-based ether-functionalized ionic liquids and methanol

Bis(fluorosulfonyl)imide ([FSI]−) and bis(trifluoromethyl)sulfonylimide ([TFSI]−)-based ionic liquids have potential applications in electrochemistry. However, some fundamental questions regarding their hydrogen bonding properties remain to be answered. In this work, the hydrogen bonding interactions between two [FSI]− and [TFSI]−-based ionic liquids and methanol (CH3OH) and their microscopic structure were comparatively investigated by infrared spectroscopy, excess spectroscopy and quantum chemical calculations. Some conclusions can be drawn: (1) The hydrogen bonding interactions in the two systems are strengthened with the addition of CH3OH. Moreover, EOMIMFSI ([EOMIM]+, 1-methoxyethyl-3-methylimidazolium) can form stronger hydrogen bonds with CH3OH than EOMIMTFSI. (2) The excess peaks of v(O–H), v(aromatic C–Hs) and vas(S=O) show fixed positive and negative excess peaks, indicating distinct complexes. With combination of the excess spectra and quantum chemical calculations, the newly formed distinct complexes were assigned to the ion cluster-CH3OH, the ion pair-CH3OH, and isolated ion-CH3OH complexes. The microscopic structure of the two systems was also shown with dilution. (3) The C4–H in EOMIMFSI is the main interaction site interacting with CH3OH, while the C2–H in EOMIMTFSI is the main interaction site.

The microscopic structure of 1-Methoxyethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EOMIMTFSI) during dilution with polar solvents

Ether-functionalized ionic liquids (ILs) have attracted increasing attention in the fields of electrochemistry and energy; however, few fundamental studies of the microscopic properties of ether-functionalized ILs have been reported. In this work, the hydrogen bonding interactions between the ether-functionalized IL 1-methoxyethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EOMIMTFSI) and co-solvents, chloroform (CHCl3), acetonitrile (CH3CN) and dimethyl sulfoxide (DMSO), were investigated at the whole concentration range by Fourier transform infrared spectroscopy (FTIR), excess infrared spectroscopy, and quantum chemical calculations. The following conclusions were made: (1) during dilution with co-solvents, the hydrogen bonding interactions in the three systems were strengthened, and the strength of the hydrogen bonds decreased in the following order: EOMIMTFSI−DMSO > EOMIMTFSI−CHCl3 > EOMIMTFSI−CH3CN. (2) DMSO could disrupt the hydrogen bonding interactions between the cations and anions in EOMIMTFSI, and [EOMIM]+−DMSO complexes were observed in the excess infrared spectrums. CHCl3 and CH3CN were unable to disrupt the electrostatic interactions, and only ion cluster–co-solvent and ion pair–co-solvent complexes were observed. (3) The main interaction sites were different in the studied systems. In the systems of EOMIMTFSI−CHCl3 and EOMIMTFSI−DMSO, the main interaction sites between the co-solvent and cations were C2−H, whereas in the EOMIMTFSI−CH3CN system, the corresponding interaction site was C5−H.

Physical Properties and Its Estimation of Binary Mixtures of Ether-Functionalized Ionic Liquids [C22O1IM][NTF2] with Alcohols

The binary mixtures composed of 1-ethyl-3-(2-methoxyethyl)-imidazolium bis(trifluoromethylsulfonyl)imide [C22O1IM][NTF2] and alcohols were prepared, and the density and viscosity were measured firs...

Experimental determination of viscosity for the binary mixtures of the ether-functionalized ionic liquids [C22O1IM][TfO] with monohydric alcohols

In order to apply ionic liquids in various fields, it is necessary to understand their physical and chemical properties. Viscosity, in particular, is an important parameter of multicomponent solutions and plays a decisive role in mass transfer, heat transfer and fluid flow in industrial process. In this work, the ether-functionalized ionic liquid [C22O1IM][TfO] was synthesized and characterized by 1H NMR, 13C NMR, ESI mass spectrometry and elemental analysis. The viscosity of the binary mixture of ionic liquid [C22O1IM][TfO] with ethanol, 1-propanol and 2-propanol in the full concentration range of T = (288.15–318.15) K were measured. The relationships between the viscosity of the binary system and concentration and temperature were investigated. By Vogel–Tamman–Fulcher (VTF) equation and Arrhenius equation, the temperature dependences of the viscosities for the binary system were described and the VTF equation showed better correlation for the binary system. The viscosity deviation that expresses the difference between the actual value and the ideal value of the mixture viscosity, Δη, was calculated. At the same time, the Gibbs energy of activation for viscous flow of the relative viscosity for the mixture, ΔG≠r, was also calculated based on the relative viscosity, ηr, and ΔG≠r is negative that is consistent with the results of, Δη, it means that the interaction between ions becomes weak due to the solvation. The viscosity deviation, Δη, and the Gibbs energy of activation for viscous flow of the relative viscosity for the mixture, ΔG≠r, could be well fitted by the Redlich–Kister equation. In addition, the related entropies and enthalpies were also calculated and discussed.

Effect of temperature on the minimum excess molar volume and the molar surface Gibbs energy of the binary of the ether-functionalized ionic liquids [C22O1IM][SCN] with monohydric alcohols at T = (288.15–318.15) K

Abstract The density and surface tension for the binary system of ionic liquid (ILs) [C22O1IM][SCN] with monohydric alcohols with short chain which includes ethanol, 1-propanol, 2-propanol and 1-butanol are measured across the entire range of mole fraction at T = (288.15–318.15) K. The excess molar volumes of the binary system are calculated based on the density values, and at the same time, the relationship between the minimum excess molar volumes and temperature are further explored firstly. The molar surface Gibbs energy and the excess molar surface Gibbs energy of the binary mixtures system can be calculated by the density and surface tension, and the interaction between the components in both liquid and surface phase of the binary mixture is discussed. In addition, its applications are also explored, including the estimation of the molar surface Gibbs energy and surface tension for the binary system and the improvement of the traditional Eӧtvӧs equation.

Synthesis and characterization of physicochemical properties of new ether-functionalized amino acid ionic liquids

Abstract Since the effect of ether functionalities on physicochemical properties varies strongly, So the experimental study of in properties is still primarily important for ether-functionalized ionic liquids to be properly applied, as well as for providing reference data for more reliable predictions. In this work, two novel ether-functionalized amino acid ionic liquids 1-(2-methoxyethyl)-3-methylimidazolium threonine and 1-(2-ethoxyethyl)-3-methylimidazolium threonine were synthesized and characterized. Physicochemical properties, including density, surface tension, viscosity and refractive index were measured at different temperatures and atmospheric pressure. According to the volumetric properties of ether-functionalized ionic liquids, the contribution of an ether O atom in the alkoxy side chain to molecular volume, standard entropy and lattice energy were estimated to be 0.0102 nm3, 13 J·K−1·mol−1 and 3 kJ·mol−1, respectively. Combined the molar surface Gibbs energy with Lorentz-Lorenz relationship, an equation for predicting surface tensions of ionic liquids was obtained, and the predicted values agree well with the experimental data. Moreover, an equation of the polarity coefficient P was proposed and the polarity of other ionic liquids was estimated. The polarity of the same series of ionic liquids decreases with the length of the alkoxy chain, the hydrophilicity becomes relatively weak, and the hydrophobicity is relatively enhanced. Using Eyring's viscosity equation and thermodynamic formula, an expression for calculating the viscous flow activation energy of ionic liquids was obtained, and the values were in good agreement with the values calculated by the Arrhenius equation.

The effect of introducing an ether group into an imidazolium-based ionic liquid in binary mixtures with DMSO.

Ether-functionalized ionic liquids (ILs) have successfully been employed in diverse applications, but their interactions with other solvents are not understood well. In this work, mixtures of 1-methoxyethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EOMIMFSI) and dimethylsulfoxide (DMSO) are studied in terms of their solution structure and hydrogen bonding interactions. The corresponding alkyl-substituted IL 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIMFSI) is analyzed for comparison. A combination of FTIR spectroscopy, excess spectroscopy, and quantum chemical calculations is employed for this purpose. The datasets allow drawing a number of conclusions as follows: (1) the ether group forms intramolecular hydrogen bonds that compete with anions and DMSO; hence, introducing ether groups into the imidazolium-based IL leads to the weakening of hydrogen bonds in the mixtures. (2) With the help of excess spectra and quantum chemical calculations, some complexes such as ion clusters, ion pairs, and individual ions were identified and assigned in the two systems. The solution structures at different concentrations were examined by analyzing the excess spectra of ν(C2-H) and ν(C-D) in the two IL-DMSO-d6 systems. (3) The introduced ether groups result in changes of the main interaction sites, which were found to be concentration-dependent. In the EOMIMFSI-DMSO system, when isolated ions are the main existing form, the C2-Hs are still the main sites interacting with DMSO. However, when ion pairs or larger ion clusters are the main existing species, the C4-Hs are the main sites interacting with DMSO.

The excess molar volume and the molar surface Gibbs energy of the binary of the ether-functionalized ionic liquids [C22O1IM][TfO] with ethanol and isomeric propanols at T = (288.15–318.15) K

The density and surface tension for the binary mixtures of ionic liquid (ILs) [C22O1IM][TfO] with ethanol, 1-propanol and 2-propanol are measured across the entire range of mole fraction at T = (288.15–318.15) K. The excess molar volumes of the binary mixtures are calculated, the relationship between VE and the mole fraction and temperature are explored. Especially, the term, △VE/△T is proposed to describe the interaction between the solvent and solute quantificationally. The molar surface Gibbs energy of the binary mixtures are obtained based on the density and surface tension, and the interaction between the components in both liquid and surface phase of the binary mixture is discussed. And its applications are also explored, including the estimation of surface tension for the binary mixtures and the improvement of the traditional Eötvös equation. At the same time, the polarity of the binary mixtures of [C22O1IM][TfO] with alcohols is obtained.

The molar surface Gibbs energy and polarity of ether-functionalized ionic liquids

Ether groups are well-known for their unique contribution to low viscosity and high conductivity, hence ether-functionalized ionic liquids (EFILs) have been widely studied and successfully employed in various applications. Three EFILs 1-(2-methoxyethyl)-3-methylimidazolium chloride, 1-(2-ethoxyethyl)-3-methylimidazolium chloride and 1-(2-ethoxyethyl)-3-methylimidazolium bromide were prepared and characterized. Their surface tension, density and refractive index in the range of T = (288.15–328.15) K were measured and the molar surface Gibbs energy, gs, were calculated. Combined gs with Lorentz-Lorenz equation, an expression for predicting surface tensions of ionic liquids was obtained, and the predicted values were in good agreement with the experimental ones. According to the gs, the vaporisation enthalpies were predicted and the association enthalpies of ionic liquids were estimated. A new method for estimating the difference of heat capacities between the vapour phase and the liquid phase of ionic liquids was put forward, and the estimated values were in the same order of magnitude as the Verevkin method. Moreover, the concept of the polarity coefficient P for ionic liquids was proposed and the polarity of many ionic liquids was estimated.

Ether-functionalized ionic liquids for nonaqueous biocatalysis: Effect of different cation cores

Abstract Ether-functionalized ionic liquids (ILs) usually have low viscosities, and can be designed to be compatible with enzymes. However, there is a lack of understanding of the effect of different ether-functionalized structures on the enzyme activity. We systematically evaluated new ether-functionalized ILs carrying different cation cores (pairing with Tf2N− anions) in two Novozym 435-catalyzed reactions: (1) the transesterification of ethyl sorbate with 1-propanol at 50 °C; (2) the ring-opening polymerization (ROP) of e-caprolactone at 70 °C. The lipase showed different activities: in the first reaction, [CH3OCH2CH2-Et3N][Tf2N] and [CH3OCH2CH2-Py][Tf2N] gave the highest reaction rates; in the second reaction, [CH3OCH2CH2-PBu3][Tf2N] produced the highest molecular mass (Mw up to 25,400 Da). The lipase’s thermal stability in [CH3OCH2CH2-Et3N][Tf2N] was found much higher than that in t-butanol. The fluorescence spectra of free lipase (excited at 280 nm) in these ILs reveal that the wavelength of the maximum emission peak occurred at 314 nm for both [CH3OCH2CH2PBu3][Tf2N] and [CH3OCH2CH2PEt3][Tf2N], which matched closely with that (313 nm) in aqueous phosphate buffer (pH 7.5, 20 mM), while other ether-functionalized ILs led to various degrees of red shifts. In summary, the lipase activity is not only dependent on the IL structure, but also on the substrate and other reaction conditions.