Elena I. Lozinskaya

Ionic Liquids as Novel Reaction Media for the Synthesis of Condensation Polymers

The use of ionic liquids as novel solvent for the synthesis of condensation polymers was investigated. A series of ionic liquids including new ones was synthesized and purified. 1,3-Dialkylimidazolium-based ionic liquids seem to be suitable reaction and activating media for the synthesis of high-molecular-weight aromatic polyimides and polyamides. Inherent viscosities of the polymers obtained in 1,3-dialkylimidazolium bromides ranges from 0.52 to 1.35 dL/g.

IR and X-ray Study of Polymorphism in 1-Alkyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imides

The crystal structure of [C(n)mim]NTf(2) (n = 2, 4, 6) was studied for the first time simultaneously by X-ray diffraction method and IR spectroscopy. The temperature-dependent IR spectrum for crystalline [C(4)mim]NTf(2) was demonstrated to correlate with both the X-ray data and the calorimetric results obtained earlier. Therefore, it was found that IR spectroscopy is able to establish the correspondence between the X-ray and the calorimetric data in this case. The joint use of X-ray diffraction, IR spectroscopy, and quantum-chemical calculations allowed us to determine the structure of all [C(2)mim]NTf(2) crystalline modifications obtained earlier by adiabatic calorimetry measurements. Thus, a new approach for the future identification of ionic liquid crystal structure by use of temperature-dependent infrared spectroscopy is suggested and justified.

Design and synthesis of new anionic “polymeric ionic liquids” with high charge delocalization

Three novel ionic monomers having highly delocalized anions and electrochemically stable mobile cations, namely, 1-butyl-1-methylpyrrolidinium 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethane-sulfonyl)imide, 1-butyl-1-methylpyrrolidinium 1,1-dicyano-1-[(3-(methacryloyloxy)propylsulfonyl)]methanide and 1-butyl-1-methylpyrrolidinium 1-cyano-1-[(3-(methacryloyloxy)propylsulfonyl)]imide were synthesized and characterized. The structure of these monomers was designed to be a mimic of the most highly conductive bis(trifluoromethylsulfonyl)imide, tricyanomethanide and dicyanamide anions. By radical polymerization procedure a series of new anionic “polymeric ionic liquids” (PILs) were prepared. The solubility of these linear PILs, thermal stability, glass transition temperatures, molar masses and ionic conductivities were estimated. An advantage of the novel PILs was demonstrated by the comparison of their ionic conductivity at 25 °C (2.0 × 10−8 ÷ 1.6 × 10−7 S cm−1) with the unmodified poly(1-ethyl-1-methylpyrrolidinium 3-(methacryloyloxy)propane-1-sulfonate) analog. The increase in ionic conductivity is as high as three orders of magnitude and was found to depend on the size of the attached anion. The new ionic monomers were subsequently copolymerized with poly(ethylene glycol) dimethacrylate and poly(ethylene glycol) methyl ether methacrylate. The investigation of the copolymers properties revealed further improvement of the conductivity in approximately two orders of magnitude and the achievement of σ = 4.8 ÷ 6.8 × 10−6 S cm−1) at 40 °C.

Extremely short C–H⋯F contacts in the 1-methyl-3-propyl-imidazolium SiF6—the reason for ionic “liquid” unexpected high melting point

The synthesis and XRD investigation of hexafluorosilicate salt with 1-propyl-3-methyl imidazolium ([Pmim]+) cation is described. Analysis of crystal packing has revealed that an unexpectedly high melting point (mp, 210 °C) of salt resulted from the presence of extremely short interionic C(Im)H⋯F contacts in the crystal (1.94–2.42 A). The absence of strong C–H⋯F interaction for alkyl radicals led to high mobility of substituents and resulted in phase transition of the order–disorder type. The total energy of the CH⋯F interactions in the hypothetical [SiF6(Pmim)6]+4 cluster according to DFT calculation and topological analysis of the electron density distribution attains ca. 33 kcal mol−1.

Turning into poly(ionic liquid)s as a tool for polyimide modification: synthesis, characterization and CO2 separation properties

In an attempt to improve the mechanical and thermal properties of poly(ionic liquid)s (PILs), a new synthetic method for the modification of polyimides is reported here for the first time. The proposed methodology consists of the transformation of polyimides into their ionic forms via subsequent N-alkylation and quaternization of benzimidazole or quinuclidine moieties. Finally, an ion exchange reaction was also carried out in order to prepare polymers bearing the bis(trifluoromethylsulfonyl)imide anion. The elaboration of optimal conditions for the reactions afforded the preparation of high molecular weight (Mn = 2.2–9.7 × 104) cationic polyelectrolytes with a degree of quaternization as high as 96%. Among the unique features of these new PILs are the preservation of excellent mechanical and thermal properties inherent in polyimides, the adjustable surface wettability with variable water contact angles from 70.5 to 94.3°, the enhanced hydrolytic stability (up to 9 h in boiling water) and improved gas transport properties (CO2 permeability up to 28.9 Barrer for a neat film and 85.0 Barrer for a filled membrane at 20 °C and 100 kPa).

Ionic semi-interpenetrating networks as a new approach for highly conductive and stretchable polymer materials

The synthesis and characterization of ionically conductive polymer films with high stretchability and good elasticity based on ionic semi-interpenetrating polymer networks (semi-IPNs) are discussed. Such innovative semi-IPN materials were prepared by radical copolymerization of an ionic monomer, namely, (N-[2-(2-(2-(methacryloyloxy)ethoxy)ethoxy)ethyl]-N-methylpyrrolidinium bis(fluorosulfonyl)imide) with poly(ethylene glycol)(di)methacrylates in the presence of the dissolved nitrile butadiene rubber, ionic liquid and lithium salt, using a simple one-step process. The suggested approach allows for simultaneous imparting of high ionic conductivity (1.3 × 10−4 S cm−1 at 25 °C) and excellent mechanical properties (tensile strength up to 80 kPa, elongation up to 60%) to a single polymer material. Ionic semi-IPNs, possessing unusual “Emmentaler cheese” like structure, exhibit a wide electrochemical stability window (4.9 V) and acceptable time-stable interfacial properties in contact with metallic lithium. Preliminary battery tests have shown that Li/LiFePO4 solid-state cells are capable to deliver a 77 mA h g−1 average specific capacity at 40 °C during 75 charge/discharge cycles.

A New Volume-Based Approach for Predicting Thermophysical Behavior of Ionic Liquids and Ionic Liquid Crystals

Volume-based prediction of melting points and other properties of ionic liquids (ILs) relies on empirical relations with volumes of ions in these low-melting organic salts. Here we report an accurate way to ionic volumes by Baders partitioning of electron densities from X-ray diffraction obtained via a simple database approach. For a series of 1-tetradecyl-3-methylimidazolium salts, the volumes of different anions are found to correlate linearly with melting points; larger anions giving lower-melting ILs. The volume-based concept is transferred to ionic liquid crystals (ILs that adopt liquid crystalline mesophases, ILCs) for predicting the domain of their existence from the knowledge of their constituents. For 1-alkyl-3-methylimidazolium ILCs, linear correlations of ionic volumes with the occurrence of LC mesophase and its stability are revealed, thus paving the way to rational design of ILCs by combining suitably sized ions.

Supramolecular ionic networks with superior thermal and transport properties based on novel delocalized di-anionic compounds

Supramolecular ionic networks based on highly delocalized dianions having (trifluoromethane-sulfonyl)imide, (propylsulfonyl)methanide and (cyano-propylsulfonyl)imide groups were developed and their physical properties were examined in detail. Most of the synthesized compounds were semi-crystalline possessing Tm values close to 100 °C; however, amorphous networks were also obtained using aromatic asymmetric dianions. Rheological measurements in temperature sweep tests at a constant frequency confirmed two different behaviors: a fast melting close to the Tm for semi-crystalline materials and a thermoreversible network for liquid transition for the amorphous supramolecular ionic networks. It was found that the amorphous ionic networks showed significantly higher ionic conductivity (10−3 S cm−1 at 100 °C) than the crystalline ionic networks (10−6 S cm−1) and previously reported amorphous citrate ionic networks (10−5 S cm−1). The supramolecular ionic networks containing hydrophobic (trifluoromethanesulfonyl)imide groups demonstrated improved water stability and higher thermal stability than the previously synthesized carboxylate ones. Noticeably, the obtained amorphous supramolecular ionic networks combine not only high ionic conductivity and thermal stability, but also self-healing properties into the same material.

Long-awaited polymorphic modification of triphenyl phosphite

A new monoclinic polymorph of triphenyl phosphite has been investigated by means of X-ray diffraction analysis; crystallization of the new polymorph was found to be a result of solvent polarity (in our case ionic liquid) and method of cooling.

Poly(ionic liquid)-based polyurethanes having imidazolium, ammonium, morpholinium or pyrrolidinium cations:

The synthesis of cationic polyelectrolytes based on condensation-derived backbone is rarely performed due to the difficulty obtaining of the respective ionic monomers in high purity. Despite such an approach is favorable as it results in ionic polymers with well-defined chemical structure and ionic group distribution. In this work two efficient methods are presented for the synthesis of ionic diols in high purity, namely the technique with pyranyl protection of OH-groups and the direct quaternization of tertiary amine alcohols. Applying these methods five novel ionic diols bearing various cations, namely, 1,1-bis(2-hydroxyethyl)pyrrolidin-1-ium bromide, 4,4-bis(2-hydroxyethyl)morpholin-4-ium bromide, N,N-bis(2-hydroxyethyl)-N-methylethanammonium, 1,1′-(pentane-1,5-diyl)bis(1-(2-hydroxyethyl)pyrrolidin-1-ium) dibromide, and 3-(2-hydroxyethyl)-1-(5-(3-(3-hydroxypropyl)-1H-imidazol-3-ium-1-yl)pentyl)-1H-imidazol-3-ium dibromide, were synthesized in high purity and high yields. The tin(II) mediated solution polycondensation of ionic diols with commercial hexamethylene diisocyanate or 4,4′-methylenebis(cyclohexyl isocyanate) resulted in a series of ionic, high molecular weight (M w = 2.3 × 104 −8.0 × 104) polyurethanes (PUs). The influence of various reaction parameters including reaction temperature and time, catalyst concentration and solvent nature upon PUs molecular weight was investigated. After the exchange of bromide to (CF3SO2)2N- anion the obtained poly(ionic liquid)s exhibit high thermal stability with onset mass loss above 225°C and demonstrate glass transition temperatures in the wide range from −22°C to 76°C depending on the nature of ionic diol used. Ionic PUs present excellent solubility in most organic solvents and are capable to form tough, flexible films with tensile strength up to 29.7 MPa.